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Three-Dimensional Fibroblast Matrix Improves Left Ventricular Function post MI
Curators: Larry H. Bernstein, MD. FCAP and Aviva Lev-Ari, PhD, RN
Implantation of a Three-Dimensional Fibroblast Matrix Improves Left Ventricular Function and Blood Flow After Acute Myocardial Infarction
Hoang M. Thai*, Elizabeth Juneman*, Jordan Lancaster*, Tracy Hagerty*, Rose Do*, Lisa Castellano*, Robert Kellar†, Stuart Williams†, Gulshan Sethi*, Monika Schmelz*, Mohamed Gaballa*,†, and Steven Goldman* *Section of Cardiology, Department of Medicine and Pathology, Southern Arizona VA Health Care System, Sarver Heart Center, University of Arizona, Tucson, AZ, †Theregen Inc., San Francisco, CA
This study was designed to determine if a viable biodegradable three-dimensional fibroblast construct (3DFC) patch implanted on the left ventricle after myocardial infarction (MI) improves left ventricular (LV) function and blood flow. We ligated the left coronary artery of adult male Sprague-Dawley rats and implanted the 3DFC at the time of the infarct. Three weeks after MI, the 3DFC improved LV systolic function by increasing (p < 0.05) ejection fraction (37 ± 3% to 62 ± 5%), increasing regional systolic displacement of the infarcted wall (0.04 ± 0.02 to 0.11 ± 0.03 cm), and shifting the passive LV diastolic pressure volume relationship toward the pressure axis. The 3FDC improved LV remodeling by decreasing (p < 0.05) LV end-systolic and end-diastolic diameters with no change in LV systolic pressure. The 3DFC did not change LV end-diastolic pressure (LV EDP; 25 ± 2 vs. 23 ± 2 mmHg) but the addition of captopril (2mg/L drinking water) lowered (p < 0.05) LV EDP to 12.9 ± 2.5 mmHg and shifted the pressure–volume relationship toward the pressure axis and decreased (p < 0.05) the LV operating end-diastolic volume from 0.49 ± 0.02 to 0.34 ± 0.03 ml. The 3DFC increased myocardial blood flow to the infarcted anterior wall after MI over threefold (p < 0.05). This biodegradable 3DFC patch improves LV function and myocardial blood flow 3 weeks after MI. This is a potentially new approach to cell-based therapy for heart failure after MI.
Three-Dimensional Fibroblast Patch
Our hypothesis is that the lack of survival of new cells directly injected into the heart is related, in part, to an inadequate blood supply and inadequate matrix support for the new cells. The injected cells are fragile, resulting in cell aggregation due to lack of physical support for the cells to attach to the tissue extracellular matrix. This three-dimensional scaffold offers a potential solution to the problem of an inadequate support structure. While injection of passive materials has been proposed to improve EF potentially by decreasing wall stress (11,35), the 3DFC provides a viable cell matrix that supports new blood vessel growth (15,16). This viable cellular matrix is important because in addition to providing a new support structure for the damaged heart, we also need to create a mature blood supply such that new viable cardiac muscle can be organized in parallel forming physical and neural connections that will conduct electrical signals and create synchronized contractions. Investigators have proposed that the ideal scaffold structure for the heart would consist mainly of highly interconnected pores with a diameter of at least 200 µm, the average size of a capillary, to permit blood vessel penetration and cell interactions (5).
The 3DFC is a viable construct composed of a matrix embedded with human newborn dermal fibroblasts cultured in vitro onto a bioabsorbable mesh to produce living, metabolically active tissue (15,16) (see Fig. 1 and Fig 2). As the fibroblasts proliferate across the mesh, they secrete human dermal collagen, fibronectin, and glycosaminoglycans (GAGs), embedding themselves in a self-produced dermal matrix. The fibroblast cells produce angiogenic growth factors: vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), basic fibroblast growth factor (bFGF), and angiopoietin-1. The construct is grown in medium supplemented with serum and ascorbate; at harvest, the medium is replaced with a 10% DMSO-based cryoprotectant, the tissue is frozen and stored at −70°C. This cryopreservation and rewarming technique has been extensively studied to ensure viability of the patch. Although the mechanisms of action of the 3DFC are not completely understood, new blood vessel growth has been documented previously in SCID mice (15).
Previous work using the 3DFC as a patch for the infarcted heart in SCID mice showed histological evidence of new blood vessel growth and improvements in global LV function using a conductance catheter (16). Our data show increases in myocardial blood flow in the infarcted heart, confirming that these blood vessels are functional and that they connect to the native myocardium. We used echocardiography to document improvements in global and regional LV function. The improvements in regional LV function are important because recent work suggests that the injection of passive materials alone may be enough to reduce wall stress and increase global EF (35). In order to prove that cell-based therapy is affecting more than a passive response, the point has been made that it is necessary to be able to define regional changes in the area of the infarcted myocardium (11). We have done this using echocardiography to document that the 3DFC increases systolic displacement of the infarcted regional anterior wall (Fig. 5). Although the mechanism of action of the 3DFC has not been completely delineated, the viable fibroblasts secrete a number of growth factors, thus providing a paracrine effect to stimulate new blood vessel growth. The vicryl mesh is biodegradable such that, with dissolution, the new blood vessel growth is in the previously damaged myocardium. The most likely explanation for the improvements in regional systolic displacement of the anterior wall is that the increases in myocardial blood flow in the border zone results in recruitment of hibernating or stunned cardiac myocytes.
The fact that the 3DFC is viable with fibroblasts implanted on a mesh is important. There are data showing that inert biodegradable patches are beneficial in treating heart failure. In our laboratory we have shown that an inert biodegradable collagen patch placed on the rat heart after a nontransmural MI improves LV function and prevents adverse LV remodeling (10). There are clinical trials with a collagen type 1 matrix seeded with autologous bone marrow cells in patients undergoing coronary artery bypass surgery (4). The best known implanted mechanical constraint device is the Acorn Corp Cap device; it decreases LV size but does not cause constrictive physiology (22). There are no blood flow studies with the Acorn device. There is a recent report using an inert biodegradable polyester urethane cardiac patch applied to rats 2 weeks after coronary ligation where the LV cavity size does not change but fractional area change increases and compliance improves; there are no blood flow data in this report (6).
Application of a Patch as an Alternative to Direct Cell Injection
The use of a biodegradable patch that provides a support structure allowing new cells to attach and grow in a damaged heart is a possible alternative to the current approach of direct cell injection for cell-based therapy. Not only are the results from current clinical trials of cell-based therapy disappointing, the approach used in these trials is cumbersome, requiring harvesting bone marrow and a repeat cardiac catheterization with infarct artery reocclusion to reinject purified autologous mononuclear cells into the coronary arteries. Another problem is the recent report that intracoronary delivery of bone marrow cells results in damage to the coronary artery with luminal loss in the infarct related artery (20). These data suggest that we need new options for cell-based therapy for heart failure.
The translational aspect of this work is important; there is potential for clinical application of this 3DFC patch. At present there are two ongoing phase I clinical trials using the 3DFC; the first is a pilot trial in patients applying the 3DFC patch at the time of coronary artery bypass surgery when the surgeon cannot place a graft to a area of viable myocardium. This trial is designed to determine if the 3DFC increases myocardial perfusion to an area that the surgeon could not graft. While in this clinical study the 3DFC patch is placed with the chest open, two cases have been done with a minimally invasive approach using a modified video-assisted thorascopic surgery VATS procedure. The second trial is in patients getting a left ventricular assist device (LVAD). The 3DFC is applied at the time of LVAD placement and, upon LVAD removal, histology is done on the area of 3DFC placement in order to examine for evidence of angiogenesis.
Summary
We report improvements in myocardial blood flow, regional and global LV function, and partial reversal of LV remodeling using a viable three-dimensional fibroblast patch implanted in rats at the time of an acute MI. This patch provides a support structure that allows cells to grow into the damaged heart and creates new blood vessel growth, resulting in improved blood flow. With the limited success of direct cell injection into the heart, the 3DFC represents a new approach to cell-based therapy for heart failure.
Figures
Figure 1. Scanning electron micrograph of the 3DFC patch.
The vicryl fibers are “tube-like” structures. The fibroblasts look like irregular structures with long appendages that span from one vicryl fiber to another.
Figure 2.
(A) Three-dimensional fibroblast culture (3DFC) prior to implantation; the suture in the middle of the patch is used to attach the 3DFC to the left ventricle. (B) 3DFC at the time of implantation on the infarcted left ventricle. (C) 3DFC at 3 weeks after myocardial infarction. Note that the 3DFC is well integrated and attached to the infarcted wall. (D) 3DFC in a perfused heart preparation at 3 weeks after myocardial infarction. As note above, the 3DFC is well integrated into the infarcted wall and the suture is easily visible.
Figure 3.
Echocardiographic measured ejection fraction (EF) in sham, myocardial infarction (MI), MI + 3DFC, MI + 3DFC/Cap (captopril), and MI + 3DFC/NV (nonviable). Note that the viable 3DFC increased the EF. The EF remained increased with the addition of captopril to the viable 3DFC; the nonviable 3DFC did not improve EF. Values are mean ± SE. Sham (N = 5); MI (N = 8); MI + 3DFC/cap (N = 10); MI + 3DFC (N = 14); MI + 3DFC (nonviable) (N = 5). *p < 0.05 sham versus all groups; **p < 0.05 MI and MI + 3DFC/NV versus MI + 3DFC/cap and MI + 3DFC.
Figure 4.
Echocardiographic measured systolic displacement of the infarcted anterior wall in sham, myocardial infarction (MI), and MI + 3DFC. Note that the 3DFC improved EF back toward the normal value. Values are mean ± SE. Sham (N = 6); MI (N = 12); MI + 3DFC (N = 15); MI + NV 3DFC (N = 12). *p < 0.05 versus MI; **p < 0.05 versus MI.
Figure 5.
Echocardiographic measured LV end-diastolic and end-systolic diameters in sham, myocardial infarction (MI), and MI + 3DFC. Note that both the LV end-diastolic diameter and end-systolic diameters decrease with the 3 DFC. Values are mean ± SE. Sham (N=6); MI (N=12); MI + 3DFC (N=15); MI + NV 3DFC, (N=12). *p < 0.05 versus sham; **p < 0.05 versus MI.
Figure 6.
Pressure–volume (PV) loops in sham, myocardial infarction (MI), MI + 3DFC, and MI + 3DFC/ captopril. Note that the major shift in the PV loop was with the addition of captopril where the operating LV end-diastolic volume decreased.
Figure 7.
Anterior wall myocardial blood flow in sham (N = 11), at the time of acute myocardial infarction (MI, N = 7), MI at 3 weeks (N = 4), and MI at 3 weeks with 3DFC (N = 4). Note that the 3DFC improved blood flow in the infarcted wall. Values are mean ± SE; *p < 0.05 versus baseline and MI (3w) + 3DFC.
Figure 8
Vessel density defined by Factor VIII staining. Note the increase in vessel density in the area with the 3DFC compared to the untreated myocardial infarction (MI). MI (N = 9), MI + 3DFC (N = 8). Values are mean ± SE. *p < 0.05 versus MI.
Figure 9.
Histopathology sections of Factor VIII staining in MI + 3DFC (A–C) and MI alone (4× and 40×). Note the increased in Factor VIII staining and vessel density with the 3DFC.
State of Cardiology on Wall Stress, Ventricular Workload and Myocardial Contractile Reserve: Aspects of Translational Medicine (TM)
Updated on 2/17/2023
The training statement was developed in collaboration with and endorsed by the American Association for Thoracic Surgery, American Society of Echocardiography, Heart Failure Society of America, Heart Rhythm Society, Society of Cardiovascular Anesthesiologists, Society of Cardiovascular Computed Tomography, Society for Cardiovascular Magnetic Resonance, Society of Thoracic Surgeons, and Society for Vascular Medicine.
Bass TA, et al “2023 ACC/AHA/SCAI advanced training statement on interventional cardiology (coronary, peripheral vascular, and structural heart interventions): A report of the ACC Competency Management Committee”J Am Coll Cardiol 2023; DOI: 10.1016/j.jacc.2022.11.002.
Dong H, Mosca H, Gao E, Akins RE, Gidding SS and Tsuda T
Journal of Translational Medicine 2013, 11:183 (7 August 2013)
In this article we expose the e-Reader to
A. The State of Cardiology on
wall stress
ventricular workload and
myocardial contractile reserve
B. Innovations in a Case Study in Cardiology Physiological Research on above subjects
C. Prevailing Models in Translational Medicine
D. Mapping of One Case Study in Cardiology Physiological Research onto Weber’s Triangle of Biomedicine.
The mapping facilitate e-Reader’s effort to capture the complexity of aspects of Translational Medicine and visualization of the distance on this Triangle between where the results of this case study are and the Human Corner — the Roadmap of the “bench-to-bedside” research, or the “translation” of physiological and basic science research into practical clinical applications.
This article has the following sections:
Introduction
Author: Justin Pearlman, MD, PhD, FACC
Translational medicine aims to fast track the pathway from scientific discovery to clinical applications and assessment of benefits. Cardiovascular examples include novel biomarkers of disease, new heart assist devices, new technologies for catheter intervention, and new medications. The Institute of Medicine’s Clinical Research Roundtable describes translation medicine in two fundamental blocks: “…the transfer of new understandings of disease mechanisms gained in the laboratory into the development of new methods for diagnosis, therapy, and prevention [with] first testing in humans…”, and “…the translation of results from clinical studies into everyday clinical practice and health decision making…” [2].
Identifying where contributions are achieving translation has been addressed by the biometric tool called the triangle of biomedine [3].
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This article has the following EIGHT Sections:
I. Key Explanation Models for the Translational Process in BioMedicine, aka Translational Medicine (TM)
II. TM Model selection in this article, for mapping the fit of a Case Study in Cardiology Physiological Research, within the TM Model selected
III. Limitations of the TM Model to explain the Translational Process in BioMedicine
IV. Mapping the fit of a Case Study in Cardiology Physiological Research, within the TM Model selected
V. Clinical Implications of the Case Study in Cardiology Physiological Research
VI. Limitations of the Case Study in Cardiology Physiological Research
VII. The State of Cardiology on
wall stress
ventricular workload and
myocardial contractile reserve
VIII. What are the Innovations of the Case Study in Cardiology Physiological Research
I. Key Explanation Models for the Translational Process in BioMedicine, aka Translational Medicine (TM)
The National Institutes of Health (NIH) Roadmap places special emphasis on “bench-to-bedside” research, or the “translation” of basic science research into practical clinical applications. The Clinical and Translational Science Awards (CTSA) Consortium is one example of the large investments being made to develop a national infrastructure to support translational science, which involves reducing regulatory burdens, launching new educational initiatives, and forming partnerships between academia and industry. However, while numerous definitions have been suggested for translational science, including the qualitative T1-T4 classification, a consensus has not yet been reached. This makes it challenging to measure the impact of these major policy changes.
BASIC DISCOVERY -T1-> CLINICAL INSIGHTS -T2-> IMPLICATIONS FOR PRACTICE -T3-> IMPLICATIONS FOR POPULATION HEALTH -T4-> IMPLICATIONS FOR GLOBAL HEALTH
Model A: QUALTITATIVE T1-T4 CLASSIFICATION [(7) & (8-10) in Weber’s list of Reference, below]
In biomedicine, translational science is research that has gone from “bench” to “bedside”, resulting in applications such as drug discoverythat can benefit human health [1–6]. However, this is an imprecise description. Numerous definitions have been suggested, including the qualitative T1-T4 classification [7].
Several bibliometric techniques have been developed to quantitatively place publications in the translational spectrum. Narin assigned journals to fields, and then grouped these fields into either “Basic Research” or “Clinical Medicine” [8-10]. Narin also developed another classification called research levels, in which journals are assigned to “Clinical Observation” (Level 1), “Clinical Mix” (Level 2), “Clinical Investigation” (Level 3), or “Basic Research” (Level 4) [8]. He combines Levels 1 and 2 into “Clinical Medicine” and Levels 3 and 4 to “Biomedical Research”.
Model B: Average research level of a collection of articles as the mean of the research levels of those articles
Lewison developed methods to score the translational research level of individual articles from keywords within the articles’ titles and addresses. He defines the average research level of a collection of articles as the mean of the research levels of those articles [11–13] . For validity, one must assume that the keywords reflect content fairly and without bias. If the government adapts such a scoring system to influence funding in order to promote translational research, that will create a bias.
Model C: “Translatability” of drug development projects
A multidimensional scoring system has been developed to assess the “translatability” of drug development projects [29,30]. This requires manual review of the literature which poses difficulties for scalability and consistency across reviewers and over time.
Model D: Fontelo’s 59 words and phrases suggesting that the article is Translational
Fontelo identified 59 words and phrases, which when present in the titles or abstracts of articles, suggest that the article is translational [31]. It is an interesting sampling method, but it may present a bias to particular styles of presentation.
Model E: The triangle of biomedicine by Griffin M Weber – This Model is the main focus of this article
The Triangle of Biomedicine uses a bibliometric approach to map PubMed articles onto a graph. The corners of the triangle represent research related to animals, to cells and molecules. The position of a publication on the graph is based on its topics, as determined by its Medical Subject Headings (MeSH). Translation is defined as movement of a collection of articles, or the articles that cite those articles, towards the human corner.
Results
The Triangle of Biomedicine provides a quantitative way of determining if an individual scientist, research organization, funding agency, or scientific field is producing results that are relevant to clinical medicine. Validation of the method examined examples that have been previously described in the literature, comparing it to other methods of measuring translational science.
Conclusions
The Triangle of Biomedicine is a novel way to identify translational science and track changes over time. This is important to policy makers in evaluating the impact of the large investments being made to accelerate translation. The Triangle of Biomedicine also provides a simple visual way of depicting this impact, which can be far more powerful than numbers alone. As with any metric, its limitations and potential biases should always be kept in mind. As a result, it should be used to supplement rather than replace alternative methods of measuring or defining translational science. What is unique, though, to the Triangle of Biomedicine, is its simple visual way of depicting translation, which can be far more powerful to policy makers than numbers alone.
Keywords:
Translational science; Bibliometric analysis; Medical subject headings; Data visualization; Citation analysis
II. TM Model selection in this article, for mapping the fit of a Case Study in Cardiology Physiological Research, within the TM Model selected
Model E: The triangle of biomedicine by Griffin M Weber
In this study, we analyze the 20 million publications in the National Library of Medicine’s PubMed database by extending these bibliometric approaches in three ways: (1) We divide basic science into two subcategories, research done on animals or other complex organisms and research done on the cellular or molecular level. We believe it is important to make this distinction due to the rapid increase in “-omics” research and related fields in recent years. (2) We classify articles using their Medical Subject Headings (MeSH), which are assigned based on the content of the articles. Journal fields, title keywords, and addresses only approximate an article’s content. (3) We map the classification scheme onto a graphical diagram, which we call the Triangle of Biomedicine, which makes it possible to visualize patterns and identify trends over time.
Article classification technique
Using a simple algorithm based on an article’s MeSH descriptors, we determined whether each article in PubMed contained research related to three broad topic areas—animals and other complex organisms (A), cells and molecules (C), or humans (H). An article can have more than one topic area. Articles about both animals and cells are classified as AC, articles about both animals and humans are AH, articles about cells and humans are CH, and articles about all three are ACH. Articles that have none of these topic areas are unclassified by this method.
In order to identify translational research, we constructed a trilinear graph [21], where the three topic areas are placed at the corners of an equilateral triangle, with A on the lower-left, C on the top, and H on the lower-right. The midpoints of the edges correspond to AC, AH, and CH articles, and the center of the triangle corresponds to ACH articles.
An article can be plotted on the Triangle of Biomedicine according to the MeSH descriptors that have been assigned to it. For example, if only human descriptors, and no animal or cell descriptors have been assigned to an article, then it is classified as an H article and placed at the H corner. An article with both animal and cell descriptors, and no human descriptors, is classified as an AC article and placed at the AC point. A collection of articles is represented by the average position of its articles. Although an individual article can only be mapped to one of seven points, a collection of articles can be plotted anywhere in the triangle.
An imaginary line, the Translational Axis, can be drawn from the AC point to the H corner. The position of one or more articles when projected onto this axis is the Translational Index (TI). By distorting the Triangle of Biomedicine by bringing the A and C corners together at the AC point, the entire triangle can be collapsed down along the Translational Axis to the more traditional depiction of translational science being a linear path from basic to clinical research. In other words, the Triangle of Biomedicine does not replace the traditional linear view, but rather provides additional clarity into the path research takes towards translation.
Summary of categories
Mapping A-C-H categories to Narin’s basic-clinical classification scheme
The National Library of Medicine (NLM) classifies journals into different disciplines, such as microbiology, pharmacology, or neurology, with the use of Broad Journal Headings. We used Narin’s mappings to group these disciplines into basic research or clinical medicine. Individual articles were given a “basic research” score of 1 if they were in a basic research journal and 0 if they were in a “clinical medicine” journal. For each A-C-H category, a weighted average of its articles’ scores was calculated, with the weights being the inverse of the total number of basic research (4,316,495) and clinical medicine (11,689,341) articles in PubMed. That gives a numeric value for the fraction of articles within a category that are basic research, which is corrected for the fact that PubMed as a whole has a greater number of clinical medicine articles.
Mapping A-C-H categories to Narin’s four-level classification scheme
For each of his four research levels, Narin selected a prototype journal to conduct his analyses:The Journal of the American Medical Association (JAMA, Level 1), The New England Journal of Medicine (NEJM, Level 2), The Journal of Clinical Investigation (JCI, Level 3), and The Journal of Biological Chemistry (JBC, Level 4). Each is widely considered a leading journal and has over 25,000 articles spanning more than 50 years. For each A-C-H category, we determined the number of articles from each of these four journals and calculated a weighted average of their research levels, with the weights being the inverse of the total number of articles each journal has in PubMed.
III. Limitations of the TM Model to explain the Translational Process in BioMedicine: The triangle of biomedicine by Griffin M Weber
This work is limited in several ways. It takes at least a year for most articles to be assigned MeSH descriptors. During that time the articles cannot be classified using the method described in this paper. Also, our classification method is based on a somewhat arbitrary set of MeSH descriptors—different descriptors could have been used to map articles to A-C-H categories. However, the ones we used seemed intuitive and they produced results that were consistent with Narin’s classification schemes. Finally, any metric based on citation analysis is dependent on the particular citation database used, and there are significant differences among the leading databases [22]. In this study, we used citations in PubMed that are derived from PubMed Central because they are freely available in their entirety, and therefore our method can be used without subscriptions to commercial citation databases, such as Scopus and Web of Science, which are cost-prohibitive to most people. However, because these commercial databases have a greater number of citations and index different journals than PubMed, they might show shorter or alternative paths towards translation (i.e., fewer citation generations or less time). Though, as described in our Methods, there is evidence that suggests these differences might be relatively small. Selecting the best citation database for identifying translational research is a topic for future research.
Another area of future research could attempt to identify a subset of H articles that truly reflect changes in health practice and create a separate category P for these articles. This might be possible, for example, by using Khoury’s approach of using PubMed’s “publication type” categorization of each article to select for those that are clinical trials or practice guidelines [7]. This could be visualized in the Triangle of Biomedicine by moving H articles to the center of the triangle and placing P articles in the lower-right corner, thereby highlighting research that has translated beyond H into health practice.
IV. Mapping the fit of a Case Study in Cardiology Physiological Research, within the TM Model selected
The triangle of biomedicine by Griffin M Weber
Figure 1.Disciplines mapped onto the Triangle of Biomedicine.The corners of the triangle correspond to animal (A), cellular or molecular (C), and human (H) research. The dashed blue line indicates the Translational Axis from basic research to clinical medicine. The position of each circle represents the average location of the articles in a discipline. The size of the circle is proportional to the number of articles in that discipline. The color of the circle indicates the Translational Distance (TD)—the average number of citation generations needed to reach an H article. The position of the light blue box connected to each discipline represents the average location of articles citing publications in that discipline. To provide clarity, not all disciplines are shown. Note however, that if authors knew this measurement would be applied and could affect their funding, then they might increase human study citation of basic research to game the “translational distance.”
For this article we selected A Case Study in Cardiology Physiological Research
Integrated wall stress: a new methodological approach to assess ventricular workload and myocardial contractile reserve
Hailong Dong124, Heather Mosca1, Erhe Gao3, Robert E Akins1, Samuel S Gidding2and Takeshi Tsuda12*
This study appeared in 2013 in the Journal of Translational Medicine. It studied mice, creating heart attacks in order to evaluate the physiologic significance of “integrated wall stress” (IWS) as a marker of total ventricular workload. The measure IWS was obtained by integrating continuous wall stress curve by accumulating wall stress values at millisecond sampling intervals over one minute, in order to include in wall stress effects of heart rate and contractility (inotropic status of the myocardium). As an example of translational medicine, it raises numerous issues. As a mouse study, it qualifies as basic science. It examines the impact of heart attack on changes inducible by the inotropic agent dobutamine. If the concept were to influence clinical care and outcomes, it would qualify as translational. All of the tools applied to the mice are applicable to patients: heart attacks (albeit not purposefully induced), the echocardiography measurements, and the dobutamine impact. That enables citation of human studies in the references, and ready application to human studies in the future. Mice however have much faster heart rates, so the choice of one minute for the integral may have different significance for humans. Gene expression was also measured. The authors conclude IWS represents a balance between external ventricular workload and intrinsic myocardial contractile reserve. The fact that the Journal has the word “translational” may represent a bias. Many of the links between animal and human focused references occur electively in the discussion section. The authors propose the measurement might help identify pre-clinical borderline failing of contractility. If so, the full axis of translational value will require that IWS can improve outcomes. Currently, blood levels of brain naturetic peptide are used as a marker of myocardial strain that may help identify early failing contractility. Presumably, early recognition could identify a population that might benefit from early intervention to forestall progression. Evidence based medicine will have difficulties. First, it is biased by the “Will Roger’s Effect” whereby early recognition of a disease subdivides the lowest class, inherently shifting the apparent status of each half of the subdivision (Will Roger’s made a joke that when Oklahoma residents moved to California for the gold rush, they improved the average intelligence of both groups, an observation adapted to explain a redefinition bias). Second, the actual basis for a change in clinical application will be complex, with political as well as scientific influences. Third, it will be even more difficult to discern its impact on outcomes, even if targeted therapy for patients with distinctive IWS is associated with an apparent improvement in outcomes. Convincing documentation would require extensive comparisons and controlled studies, but once a method is clinically adapted, it is commonly considered unethical to perform a controlled study in which the “preferred method” is not applied to a group.
V. Clinical Implications of the Case Study in Cardiology Physiological Research
Background
Wall stress is a useful concept to understand the progression of ventricular remodeling. We measured cumulative LV wall stress throughout the cardiac cycle over unit time and tested whether this “integrated wall stress (IWS)” would provide a reliable marker of total ventricular workload.
Methods and results
We applied IWS to mice after experimental myocardial infarction (MI) and sham-operated mice, both at rest and under dobutamine stimulation. Small infarcts were created so as not to cause subsequent overt hemodynamic decompensation. IWS was calculated over one minute through simultaneous measurement of LV internal diameter and wall thickness by echocardiography and LV pressure by LV catheterization. At rest, the MI group showed concentric LV hypertrophy pattern with preserved LV cavity size, LV systolic function, and IWS comparable with the sham group. Dobutamine stimulation induced a dose-dependent increase in IWS in MI mice, but not in sham mice; MI mice mainly increased heart rate, whereas sham mice increased LV systolic and diastolic function. IWS showed good correlation with a product of peak-systolic wall stress and heart rate. We postulate that this increase in IWS in post–MI mice represents limited myocardial contractile reserve.
Conclusion
We hereby propose that IWS provides a useful estimate of total ventricular workload in the mouse model and that increased IWS indicates limited LV myocardial contractile reserve.
IWS can be estimated by obtaining IWS index, which is calculated non-invasively by simultaneous M-mode echocardiogram and cuff blood pressure measurement, i.e., PS-WS instead of ES-WS and heart rate. This will provide a sensitive way to detect subclinical borderline failing myocardium in which the decline in LV myocardial contractile reserve precedes apparent LV dysfunction. This method may be clinically useful to address LV myocardial reserve in those patients who are not amenable to perform on exercise stress test, such as immediate post-operative patients under mechanical ventilation, critically ill patients with questionable LV dysfunction, and patients with primary muscular disorders and general muscular weakness (i.e., Duchenne muscular dystrophy).
VI. Limitations of the Case Study in Cardiology Physiological Research
There are certain limitations in this study.
First, wall stress measurement is reliable when there is an equal wall thickness with symmetrical structure. Obviously, with the creation of small MI, there is an asymmetry of LV myocardium in both structure and consistency (myocardium vs. scar tissue). However, the scar tissue is small and restricted to the LV apex (approximately 14% of entire LV myocardium [5]). In fact, most of LV wall was thickened after induction of this small experimental MI. Nevertheless, we acknowledge that this is our major limitation.
Secondly, there is an individual variability in response to dobutamine stimulation even in sham mice. Although the average sham mice (n = 5) showed only a modest increase in HR, PS-WS, and IWS during dobutamine stimulation, one mouse presented in Figure 1 showed a notable increase in HR and PS-WS in response to dobutamine. Nevertheless, even with increased HR and PS-WS, the calculated IWS remained relatively unchanged in the sham-operated mice.
Lastly, the reliability of IWS index is based upon the stipulation that ED-WS is significantly low compared with the systolic wall stress. Thus, IWS index may not be accurate in obvious volume overload cases and/or dilated hearts with LV dysfunction where ED-WS is significantly higher than that in normal condition. Of note, ED-WS in human is higher than that in mice in relation to PS-WS, probably around 15 to 20% of PS-WS [12].
VII. State of Cardiology on
wall stress
ventricular workload and
myocardial contractile reserve
Ventricular remodeling is a chronic progressive pathological process that results in heart failure after myocardial infarction (MI) or persistent unrelieved biomechanical overload [1,2]. Persistent and unrelieved biomechanical overload in combination with activation of inflammatory mediators and neurohormones is thought to be responsible for progressive ventricular remodeling after MI [3,4], but studies to investigate specific mechanisms in animals are hampered by the difficulty involved in quantifying biomechanical workload in vivo. The magnitude of ventricular remodeling advances in line with progressive ventricular geometric changes including myocardial hypertrophy and chamber dilatation with accompanying functional deterioration [1,2]. Previously, we proposed that post-ischemic ventricular remodeling is a pathological spectrum ranging from benign myocardial hypertrophy to progressive heart failure in the mouse model in which the prognosis is primarily determined by the magnitude of residual hemodynamic effects [5]. However, there has been no optimum quantitative measurement of ventricular workload as a contributory indicator of ventricular remodeling other than wall stress theory to explain how ventricular dilatation and hypertrophy develop after loss of viable working myocardium [6,7].
The concept of ventricular wall stress was introduced by Strauer et al. as a primary determinant of myocardial oxygen demand [8]. They indicated that overall myocardial energy demand depends upon intramyocardial wall tension, inotropic state of the myocardium, and heart rate. Wall stress theory is commonly introduced to explain development of concentric hypertrophy in chronic pressure overload and progressive ventricular dilatation in the failing heart. One study argued that peak-systolic wall stress increased as LV function worsened in a chronic volume overloaded status [9], and another suggested that peak-systolic wall stress closely reflected LV functional reserve during exercise [10]. However, the effect of heart rate or myocardial contractility was not considered in either study. Heart rate has been shown to be one of several important factors contributing to myocardial oxygen consumption [11].
Herein, we introduce a novel concept of “integrated wall stress (IWS)” to assess its significance as a marker of total ventricular workload and to validate its physiological relevance in the mouse model. The concept of continuous LV wall stress measurement was reported previously, but authors did not address the overall effects of changing wall stress during the cardiac cycle on the working myocardium [12]. We have defined IWS as cumulative wall stress over unit time: IWS was obtained by integrating continuous wall stress curve by accumulating wall stress values at millisecond sampling intervals over 1 min. By calculating IWS, we were able to incorporate the effects of not only systolic wall stress, but also of heart rate and inotropic status of the myocardium. These data were analyzed against conventional hemodynamic parameters in animals with and without MI in conjunction with incremental dobutamine stress. We hypothesize that unchanged IWS represents stable ventricular myocardial contractile reserve and that increase in IWS implies an early sign of mismatch between myocardial reserve and workload imposed on ventricular myocardium.
VIII. What are the Innovations of the Case Study in Cardiology Physiological Research
IWS measures total wall stress throughout the cardiac cycle over a unit time (= 1 min) including the effect of heart rate and inotropic state of the ventricular myocardium, whereas one-spot measurement of PS-WS and ED-WS only reflects maximum and minimum wall stress during a cardiac cycle, respectively. We hypothesized that increase in IWS indicates failure of myocardium to counteract increased ventricular workload. We have measured IWS in the mouse model in various physiological and pathological conditions to validate this hypothesis. Unchanged IWS observed in sham operated mice may imply that the contractile reserve of ventricular myocardium can absorb the increased cardiac output, whereas increased IWS after MI suggests that ventricular workloads exceeds intrinsic myocardial contractile reserve. Thus, we postulate that IWS is a reliable physiological marker in indicating a balance between external ventricular workload and intrinsic myocardial contractile reserve.
#1
IWS and myocardial reserve
“Wall stress theory” is an important concept in understanding the process of cardiac hypertrophy in response to increased hemodynamic loading [16]. When the LV myocardium encounters biomechanical overload, either pressure overload or volume overload, cardiac hypertrophy is naturally induced to normalize the wall stress so that myocardium can minimize the increase in myocardial oxygen demand; myocardial oxygen consumption depends mainly on systolic wall stress, heart rate, and contractility [8,17]. A question arises whether this hypertrophic response is a compensatory physiological adaptation to stabilize the wall stress or a pathological process leading to ventricular remodeling and heart failure. Physiological hypertrophy as seen in trained athletes reveals increased contractile reserve, whereas pathological hypertrophy shows a decrease in contractile reserve in addition to molecular expression of ventricular remodeling [18–20]. However, what regulates the transition from compensatory adaptation to maladaptive process is not well understood.
Systolic wall stress has been studied extensively as a clinical marker for myocardial reserve. Systolic wall stress reflects the major determinants of the degree of LV hypertrophy and plays a predominant role in LV function and myocardial energy balance [17]. It has been shown that increased systolic wall stress inversely correlates with systolic function and myocardial reserve in patients with chronic volume overload [9,10,21], chronic pressure overload [22,23], and dilated cardiomyopathy [24]. However, one-point measurement of systolic wall stress does not encompass the effect of heart rate and contractile status, the other critical factors that affect myocardial oxygen demand [11]. The idea of IWS has been proposed to incorporate wall stress throughout the cardiac cycle and reflects the effects of heart rate and contractile status.
Myocardial oxygen consumption is determined mainly by ventricular wall stress, heart rate and contractility [17], which are all incorporated in IWS measurement. Continuous measurement of LV wall stress was previously reported in humans [12,15] and dogs [11] with a similar method, but not in mice. By integrating the continuous WS over one minute, we estimated the balance between myocardial contractile reserve and total external ventricular workload and examined its trend in relation to inotropic stimulation in the mouse heart in vivo. In this study, we have proposed unchanged IWS as a marker of sufficient myocardial contractile reserve, since increased wall stress demands higher myocardial oxygen consumption. Indeed, systolic wall stress does not increase with strenuous isometric exercise in healthy young athletes [25]. Thus, we propose that increase in IWS indicates diminished myocardial contractile reserve.
#2
Small MI model as a unique model to study early phase of progressive ventricular remodeling
A complex series of protective and damaging events takes place after MI, resulting in increased ventricular workload [26]. Initial ventricular geometric change is considered as a primary compensatory response to counteract an abrupt loss of contractile tissue. In classical theories of wall stress, which rely on the law of Laplace, the mechanisms of progressive ventricular dilatation and functional deterioration of the LV are attributed to the increased wall stress that is not compensated by the intrinsic compensatory mechanisms [2,16]. Although this theory is obvious in advanced stage of heart failure, the subclinical ventricular remodeling following borderline cases such as following small MI with initial full compensatory response is not well explained.
Study shown that our small MI model induced concentric hypertrophy without LV dilatation as if initial myocardial damage was completely compensated (Figure 2) [5]. Although LV hypertrophy is induced initially to normalize the wall stress and to prevent ventricular dilatation, this hypertrophy is not altogether a physiological one because of decreased inotrophic and lusitropic reserve when stimulated with dobutamine (Figure 4) and because of simultaneous molecular and histological evidence of remodeling in the remote nonischemic LV myocardium (Figure 3). IWS and PS-WS become normalized in small MI at rest under anesthesia as a result of reactive hypertrophy accompanied by increased ANP and BNP mRNA level. Borderline maladaptive LVH is characterized by maintained LV performance at the expense of limited myocardial contractile reserve, and this abnormality can be unmasked by inotropic stimulation [18]. The trend of IWS at rest and with dobutamine stimulation suggests that MI mice were likely exposed to higher IWS during usual awake and active condition than sham-operated mice. In contrast, systolic wall stress in the pressure overload-induced LV hypertrophy showed a level comparable to that of sham both at rest and under stimulation by β1 adrenergic agonist, prenalterol, with comparable heart rate changes [27]. For this reason, IWS assessment by measuring cumulative WS in a unit time with and without inotropic stimuation should serve as a sensitive marker to assess whether induced LV hypertrophy is a compensatory physiological adaptation process or a pathological maladaptation process. Increased IWS that indicates imposed workload surpassing myocardial contractile reserve is likely to become a major driving factor in inducing progressive ventricular remodeling or initiating deleterious maladaptive processes after MI.
#3
IWS represents myocardial oxygen demand that can be estimated non-invasively
Study demonstrated a very good correlation between IWS and the product of PS-WS and HR (“IWS index”) in both MI and sham-operated hearts (Figure 6). This formula appears physiologically acceptable provided that ED-WS is sufficiently low compared with the PS-WS (approximately 10%, as is shown in Figures 4B and C). ES-WS was previously introduced as a useful tool for assessing myocardial loading status and myocardial oxygen consumption, but its measurement requires complicated preparation [28,29]. Because there is an excellent correlation between PS-WS and ES-WS, it has been demonstrated that ES-WS can be substituted by PS-WS [28], which can be easily obtained non-invasively [30]. ES-WS was previously determined as a useful marker to quantify LV afterload and contractility that can be simply and accurately measured non-invasively [15]. As myocardial oxygen consumption is mainly dependent upon systolic wall stress, contractility, and heart rate, it seems reasonable to propose that IWS and IWS index represent the status of myocardial contractile reserve.
Conclusions & Next Phases in Translational Medicine and Cardiology Physiological Research
Author: Justin Pearlman, MD, PhD, FACC
Visual and numeric scores that assess the commitment to translation of basic discoveries to measured impact on human outcomes followed by increased prevalence of the benefits is of course desirable, but fraught with challenges. Metrics of translational medicine may lead to rewards that can “game” the system by promoting choices of MeSH codes that augment the score for individual articles and/or clusters of work from a center of research without correlation to the actual impact of the body of work. The fairness of a metric also must account for division of labor whereby one group of researchers achieves major basic discoveries that ferment useful applications to improved outcomes in patient care, while others focus on applications or application assessments that may have widely disparate degrees of impact on the reduction to practice, validation and dissemination of improved care.
Thus in order to promote useful metrics of translational medicine progress, we propose a set of metrics on the metrics:
1. impact of reviewer skill/bias
2. impact of author coding/bias
3. ability to assess an impact factor independent of author word choices
4. ability to credit basic research for its downstream impact on other researchers culminating in clinical applications, validation, and dissemination of human benefits
5. ability to discern pioneering advances from “me too” duplications of effort and minor variations on work of the same group or others
6. ability to assess cost effectiveness, including the occurrences of subsequent re-investigations to clarify issues that could have been addressed in the instance study
7. ability to compute contribution to quality life year gain per dollar of added care
Journal of Translational Medicine 2013, 11:126 (24 May 2013)
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Doctors at the Cleveland Clinic began to suspect in 2012 that something might be wrong with a high-tech implant used to treat patients with advanced heart failure like former Vice President Dick Cheney.
Thoratec Corportation
The HeartMate II is a left ventricular assist device, which contains a pump that continuously pushes blood through the heart.
The number of patients developing potentially fatal blood clots soon after getting the implant seemed to be rising. Then early this year, researchers completed a check of hospital records and their concern turned to alarm.
The data showed that the incidence of blood clots among patients who got the device, called the HeartMate II, after March 2011 was nearly four times that of patients who had gotten the same device in previous years. Patients who developed pump-related clots died or needed emergency steps like heart transplants or device replacements to save them.
“When we got the data, we said, ‘Wow,’ ” said Dr. Randall C. Starling, a cardiologist at Cleveland Clinic.
On Wednesday, The New England Journal of Medicineposted a study on its website detailing the findings from the Cleveland Clinic and two other hospitals about the device. The HeartMate II belongs to a category of products known as a left ventricular assist device and it contains a pump that continuously pushes blood through the heart.
The abrupt increase in pump-related blood clots reported in the study is likely to raise questions about whether its manufacturer, Thoratec Corporation, modified the device, either intentionally or accidentally. By March, the Cleveland Clinic had informed both Thoratec and the Food and Drug Administration about the problems seen there, Dr. Starling said.
Officials at Thoratec declined to be interviewed. But in a statement, the company, which is based in Pleasanton, Calif., said that the HeartMate II had been intensively studied and used in more 16,000 patients worldwide with excellent results. It added that the six-month survival rate of patients who received the device had remained consistently high.
“Individual center experience with thrombosis varies significantly, and Thoratec actively partners with clinicians at all centers to minimize this risk,” the company said in a statement.
Thoratec and other cardiologists also pointed to a federally funded registry that shows a smaller rise in the rate of blood clots, or thrombosis, among patients getting a HeartMate II than the one reported Wednesday by the three hospitals. In the registry, which is known as Intermacs, the rate of pump-related blood clot associated with the HeartMate II rose to about 5 percent in devices implanted after May 2011 compared with about 2 percent in previous years.
The data reported on Wednesday in The New England Journal of Medicine found rates of clot formation two months after a device’s implant had risen to 8.4 percent after March 2011 from 2.2 percent in earlier years. Researchers also suggested in the study that the Intermacs registry might not capture all cases of pump-related blood clots, such as when patients gets emergency heart transplants after a clot forms.
Not only did the rate of blood clots increase, but the clots also occurred much sooner than in the past, according to the study. After March 2011, the median time before a clot was 2.7 months, compared with 18.6 months in previous years. In addition to the Cleveland Clinic, the report on Wednesday included data from Duke University and Washington University in St. Louis.
All mechanical heart implants are prone to producing blood clots that can form on a device’s surface. And experts say that the rate of blood clot formation can be affected by a variety of factors like changes in the use of blood-thinning drugs or the health of a patient.
In a telephone interview, Dr. Starling described the Thoratec officials as cooperative, adding that they have been looking into the problem since March to understand its cause. He said that he could only speculate about the reason for the rapid rise in early blood clots but believed it was probably device-related.
“My belief is that it is something as subtle as a change in software that affects pump flow or heat dissipation near a bearing,” said Dr. Starling, who is a consultant to Thoratec.
Asked about his comments, Thoratec responded that it had yet to determine the reason for even the smaller rise in blood clots seen in the federally funded database. “We have performed extensive analysis on HeartMate II and have not identified any change that would cause the increase observed in the Intermacs registry,” the company said.
In a statement, the F.D.A. said that it was reviewing the findings of the study. “The agency shares the authors concerns about the possibility of increased pump thrombosis,” the F.D.A. said in a statement.
The fortunes of Thoratec, which has been a favorite of Wall Street investors, may depend on its ability to find an answer to the apparent jump in pump-related blood clots. Over the last two years, the company’s stock has climbed from about $30 a share to over $43 a share. In trading Wednesday, Thoratec stock closed at $42.12 a share, up 61 cents. (The New England Journal of Medicine article was released after the stock market closed.)
The HeartMate II has been a lifesaver for many patients like Mr. Cheney in the final stages of heart failure, who got his device in 2010, sustaining them until they get a heart transplant or permanently assisting their heart. Dr. Starling said that he planned to keep using the HeartMate II in appropriate patients at the Cleveland Clinic because those facing death from heart failure had few options.
But the company has also been pushing to expand the device’s use beyond patients who face imminent death from heart failure. For example, the F.D.A. approved a clinical trial for patients with significant, but less severe, heart failure to receive a HeartMate II to compare their outcomes with patients who take drugs for the same condition. Researchers at the University of Michigan Medical Center who are leading the trial said on Wednesday that, based on the lower rates of blood clots seen in the Intermacs registry, they are planning to move forward with the trial.
Dr. Starling and researchers at the Cleveland Clinic tried this spring to get The New England Journal of Medicine to publish a report about the findings at that hospital, but the publication declined, saying the data might simply represent the experience of one facility. As a result, Dr. Starling contacted Duke University and Washington University for their data. When analyzed, it mirrored events at the Cleveland Clinic, he said.
The problems seen with the HeartMate II at the three hospitals were continuing as recently as this summer, when researchers paused the collection of data to prepare Wednesday’s study. The study also noted that a preliminary analysis of data provided by a fourth hospital, the University of Pennsylvania, showed the same pattern of blood clot formation, but that the data had been submitted too late for full analysis.
This account is a vital piece of recognition of very rapid advances in cardiothoracic interventions to support cardiac function mechanically by pump in the situation of loss of contractile function and circulatory output sufficient to sustain life, as can occur with the development of cardiogenic shock. This has been mentioned and its use has been documented in other portions of this series. On the one hand, PCI has a long and steady history in the development of interventional cardiology. This necessitated the availability of thoracic-surgical operative support. The situation is changed, and is more properly, conditional.
I. Impella LD – ABIOMED, Inc.
This micro-axial blood pump can be inserted into the left ventricle via open chest procedures. The Impella LD device has a 9 Fr catheter-based platform and a 21 Fr micro-axial pump and is inserted through the ascending aorta, across the aortic and mitralvalves and into the left ventricle. It requires minimal bedside support and a 9 Fr single-access point requires no priming outside the body.
Impella Recover LD/LP 5.0
The Impella Recover miniaturized impeller pump located within a catheter. The Impella Recover LD/LP 5.0 Support System has been developed to address the need for ventricular support in patients who develop heart failure after heart surgery (called cardiogenic shock) and who have not responded to standard medical therapy. The system is designed to provide immediate support and restore hemodynamic stability for a period of up to 7 days. Used as a bridge to therapy, it allows time for developing a definitive treatment strategy.
The Impella Recover LD 5.0 showing implantation via direct placement into the left ventricle.
Insert B – location in LV
The Impella Recover system is a miniaturized impeller pump located within a catheter. The device can provide support for the left side of the heart using either the
Recover LD 5.0 (implanted via direct placement into the left ventricle) or the
Recover LP 5.0 LV (placed percutaneously through the groin and positioned in the left ventricle).
The microaxial pump of the Recover LP/LD 5.0 can pump up to 4.5 liters per minute at a speed of 33,000 rpm. The pump is located at the distal end of a 9 Fr catheter.
II. IABP VS. Percutaneous LVADS
An intra-aortic balloon pump (IABP) remains the method of choice for mechanical assistance1 in patients experiencing LV failure because of its
proven hemodynamic capabilities,
prompt time to therapy, and
low complication rates.
Percutaneous left ventricular assist devices (pLVADs), such as described above, represent an emerging option for partial or total circulatory support2 and several studies have compared the and efficacy of these devices with intra-aortic balloon pump (IABP) (IABP.)
Despite some randomized controlled trials demonstrating better hemodynamic profiles for pLVADs compared with IABP, there is no difference in 30-day survival or trend toward a reduced 30-day mortality rate associated with pLVADs. Patients treated with pLVADs tended to have a
higher incidence of leg ischemia and
device related bleeding.3
Further, no differences have been detected in the overall use of
positive inotropic drugs or
vasopressors in patients with pLVADs.4,5
However, pLVADs may increase their use for patients not responding to
PCI,
fluids,
inotropes, and
IABP
Therefore, the decision making process on how to treat requires an integrated stepwise approach. A pLVAD might be considered on the basis of
anticipated individual risk,
success rates, and for
postprocedural events.6
Potential Algorithm for Device Selection during High-Risk PCI
Until an alternative modality, characterized by improved efficacy and safety features compared with IABP, is developed, IABP remains the cornerstone of temporary circulatory support.2
Device Comparison for Treatment of Cardiogenic Shock: traditional intra-aortic balloon therapy with Impella 2.5 percutaneous ventricular assist device
1. Percutaneous LVADs in AMI complicated by cardiogenic shock. H Thiele, et al. EHJ 2007;28:2057-2063
2. Cardiogenic shock current concepts and improving outcomes. H R Reynolds et al. Circulation 2008 ;117 :686-697
3. Percutaneous left ventricular assist devices vs. IABP counterpulsation for treatment of cardiogenic shock. J M Cheng, et al. EHJ doi:10.1093/eurheart/ehp292
4. A randomized clinical trial to evaluate the safety and efficacy of a pLVAD vs. IABP for treatment of cardiogenic shock caused by MI. M Seyfarth, et al. JACC 2008;52:1584-8
5. A randomized multicenter clinical study to evaluate the safety and efficacy of the tandem heart pLVAD vs. conventional therapy with IABP for treatment of cardiogenic shock.
6. Percutaneous LVADs in AMI complicated by cardiogenic shock. H Thiele, et al. EHJ 2007;28:2057-2063
The Impella 2.5 is a percutaneously placed partial circulatory assist device that is increasingly being used in high-risk coronary interventional procedures to provide hemodynamic support. The Impella 2.5 is able to unload the left ventricle rapidly and effectively and increase cardiac output more than an intra-aortic balloon catheter can. Potential complications include bleeding, limb ischemia, hemolysis, and infection. One community hospital’s approach to establishing a multidisciplinary program for use of the Impella 2.5 is described.
Patients who undergo high-risk percutaneous coronary intervention (PCI), such as procedures on friable saphenous vein grafts or the left main coronary artery, may have an intra-aortic balloon catheter placed if they require hemodynamic support during the procedure. Currently, the intra-aortic balloon pump (IABP) is the most commonly used device for circulatory support. A newer option that is now available for select patients is the Impella 2.5, a short-term partial circulatory support device or percutaneous ventricular assist device (VAD).
In this article, I discuss the Impella 2.5, review indications and contraindications for its use, delineate potential complications of the Impella 2.5, and discuss implications for nursing care for patients receiving extended support from an Impella 2.5. Additionally, I share our experiences as we developed our Impella program at our community hospital. Routine management of patients after PCI is not addressed.
IABP Therapy: Background
decreases after-load,
decreases myocardial oxygen consumption,
increases coronary artery perfusion, and
modestly enhances cardiac output.1,2
The IABP cannot provide total circulatory support. Patients must have some level of left ventricular function for an IABP to be effective.
Optimal hemodynamic effect from the IABP is dependent on:
the balloon’s position in the aorta,
the blood displacement volume,
the balloon diameter in relation to aortic diameter,
the timing of balloon inflation in diastole and deflation in systole, and
the patient’s own blood pressure and vascular resistance.3,4
Impella 2.5 Catheter – ABIOMED, Inc.
Effect
reduces myocardial oxygen consumption,
improves mean arterial pressure, and
reduces pulmonary capillary wedge pressure.2
The Impella 2.5 has been used for
hemodynamic support during high-risk PCI and for
hemodynamic support of patients with
myocardial infarction complicated by cardiogenic shock or ventricular septal defect,
cardiomyopathy with acute decompensation,
postcardiotomy shock,
off-pump coronary artery bypass grafting surgery, or
heart transplant rejection and
as a bridge to the next decision.9
The Impella provides a greater increase in cardiac output than the other IABP provides. In one trial5 in which an IABP was compared with an Impella in cardiogenic shock patients, after 30 minutes of therapy, the cardiac index (calculated as cardiac output in liters per minute divided by body surface area in square meters) increased by 0.5 in the patients with the Impella compared with 0.1 in the patients with an IABP.
Unlike the IABP, the Impella does not require timing, nor is a trigger from an electrocardiographic rhythm or arterial pressure needed (Table 1). The device received 510(k) clearance from the Food and Drug Administration in June 2008 for providing up to 6 hours of partial circulatory support. In Europe, the Impella 2.5 is approved for use up to 5 days. Reports of longer duration of therapy in both the United States and Europe have been published.8,9
Clinical Research and Registry Findings
Abiomed has sponsored several trials, including PROTECT I, PROTECT II, RECOVER I, RECOVER II, and ISAR-SHOCK.
The PROTECT I study was done to assess the safety and efficacy of device placement in patients undergoing high-risk PCI.10
Twenty patients who had
poor ventricular function (ejection fraction =35%) and had
PCI on an unprotected left main coronary artery or the
last remaining patent coronary artery or graft.
The device was successfully placed in all patients, and the duration of support ranged from 0.4 to 2.5 hours. Following this trial, the Impella 2.5 device received its 510(k) approval from the Food and Drug Administration.
The ISAR-SHOCK trial was done to evaluate the safety and efficacy of the Impella 2.5 versus the IAPB in patients with cardiogenic shock due to acute myocardial infarction.5 Patients were randomized to support from an IABP (n=13) or an Impella (n=12).
The trial’s primary end point of hemodynamic improvement was defined as improved cardiac index at 30 minutes after implantation.
Improvements in cardiac index were greater with the Impella (P=.02).
The diastolic pressure increased more with Impella (P=.002).
There was a nonsignificant difference in the MAP (P=.09), as was the use of inotropic agents and vasopressors similar in both groups of patients.
Device Design: Impella 2.5 Catheter
The Impella 2.5 catheter contains a nonpulsatile microaxial continuous flow blood pump that pulls blood from the left ventricle to the ascending aorta, creating increased forward flow and increased cardiac output. An axial pump is one that is made up of impellar blades, or rotors, that spin around a central shaft; the spinning of these blades is what moves blood through the device.13
The Impella 2.5 catheter has 2 lumens. A tubing system called the Quick Set-Up has been developed for use in the catheterization laboratory. It is a single tubing system that bifurcates and connects to each port of the catheter. This arrangement allows rapid initial setup of the console so that support can be initiated quickly. When the Quick Set-Up is used, the 10% to 20% dextrose solution used to purge the motor is not heparinized. One lumen carries fluid to the impellar blades and continuously purges the motor to prevent the formation of thrombus. The proximal port of this lumen is yellow. The second lumen ends near the motor above the level of the aortic valve and is used to monitor aortic pressure.
The components required to run the device are assembled on a rolling cart and include the power source, the Braun Vista infusion pump, and the Impella console. The Impella console powers the microaxial blood pump and monitors the functioning of the device, including the purge pressure and several other parameters. The console can run on a fully charged battery for up to 1 hour.
Placement of the Device
The Impella 2.5 catheter is placed percutaneously through the common femoral artery and advanced retrograde to the left ventricle over a guidewire. Fluoroscopic guidance in the catheterization laboratory or operating room is required. After the device is properly positioned, it is activated and blood is rapidly withdrawn by the microaxial blood pump from the inlet valve in the left ventricle and moved to the aorta via the outlet area, which sits above the aortic valve in the aorta.
If the patient tolerates the PCI procedure and hemodynamic instability does not develop, the Impella 2.5 may be removed at the end of the case, or it can be withdrawn, leaving the arterial sheath in place, which can be removed when the patient’s activated clotting time or partial thromboplastin time has returned to near normal levels. For patients who become hemodynamically unstable or who have complications during the PCI (eg, no reflow, hypotension, or lethal arrhythmias), the device can remain in place for continued partial circulatory support, and the patient is transported to the critical care setting.
Potential Complications of Impella Therapy
The most commonly reported complications of Impella 2.5 placement and support include
limb ischemia,
vascular injury, and
bleeding requiring blood transfusion.6,9
Hemolysis is an inherent risk of the axial construction, and results in transfusions.5,10
Hemolysis can be mechanically induced when red blood cells are damaged as they pass through the microaxial pump. Other potential complications include
aortic valve damage,
displacement of the distal tip of the device into the aorta,
infection, and
sepsis.
Device failure, although not often reported, can occur.
Patients on Impella 2.5 support who may require
interrogation of a permanent pacemaker or
implantable cardioverter defibrillator
present an interesting situation. In order for the interrogator to connect with the permanent pacemaker or implantable cardioverter defibrillator, the Impella console must be turned off for a few seconds while the signal is established. As soon as the signal has been established, Impella support is immediately restarted.
Impella 2.5 Console Management
The recommended maximum performance level for continuous use is P8. At P8, the flow rate is 1.9 to 2.6 L/min and the motor is turning at 50000 revolutions per minute. When activated, the console is silent. No sound other than alarms is audible during Impella support, unlike the sound heard with an IABP. Ten different performance levels ranging from P0 to P9 are available. As the performance level increases, the flow rate and number of revolutions per minute increase. At maximum performance (P9), the pump rotates at 50000 revolutions per minute and delivers a flow rate of 2.1 to 2.6 L/min. P9 can be activated only for 5-minute intervals when the Impella 2.5 is in use.
IV. PROTECT II Study – Experts Discussion
the use of the Impella support device and the intraortic balloon pump for high-risk percutaneous coronary intervention
DR. SMALLING: Well, the idea about the PROTECT trial is that it would show that using the Impella device to support high-risk angioplasty was not inferior to utilizing the balloon pump for the same patient subset. Ejection fraction’s were in the 30%–35% range. Supposedly last remaining vessel or left main disease or left-main plus three-vessel disease and low EF; so I think that was the screening for entry into the trial.
major adverse cardiac event endpoints
Acute myocardial infarction,
mortality,
bleeding,
mortality was the same. Their endpoints really didn’t show that much difference. In subgroup analysis, they felt that they Impella may have had a little advantage over balloon pump.
DR. KERN: So do you think this study would tip the interventionalist to move in one direction or the other for high-risk angioplasty?
DR. SMALLING: That’s an interesting concept, you know? One has to get to: What is really a high-risk angioplasty. I think you and I are both old enough to remember that back in the mid-’80s, we determined that high-risk angioplasty was a patient with an ejection fraction of 25% or less, with a jeopardy score over 6. The EFs were a little higher. And, I guess, based on our prior experience with other support devices — like, for instance, CPS and then, later on, the Tandem Heart — there really was not an advantage of so-called more vigorous support systems. And so, the balloon pump served as well.
DR. SMALLING:
Those of us that have looked carefully at what it can really do, I think it may get one liter a minute at most, maybe more.1-6 But I think, for all intents and purposes, it doesn’t support at a very vigorous level. So I think personally, if I had someone I was really worried about, I would opt for something more substantial like, for instance, a Tandem Heart device.
DR. KERN: I think this is a really good summary of the study and the. Are there any final thoughts for those of us who want to read the PROTECT II study when it comes out?
DR. SMALLING: We have to consider a $20,000, $25,000 device. Is that really necessary to do something that we could often do without any support at all, or perhaps with a less costly device like a balloon pump.
DR. KERN: We’re going to talk for a few minutes about the PROTECT II study results that were presented here in their form. And Ron, I know you’ve been involved with following the work of the PROTECT II investigators. Were you a trial site for this study?
DR. WAKSMAN: No, actually, we were not, but we have a lot of interest in high-risk PCI and using devices to make this safe — mainly safe — and also effective. We were not investigators, but we did try to look, based on the inclusion/exclusion criteria, on our own accord with the balloon pump. If you recall, this study actually was comparing balloon time to the Impella device for patients who are high-risk PCI.
The composite endpoint was very complicated. They added like probably nine variables there, which is unusual for a study design. … They basically estimated that the event rate on the balloon pump would be higher than what we thought it should be. So we looked at our own data, and we found out that the actual — if you go by the inclusion/exclusion criteria and their endpoints — the overall event rate in the balloon pump would be much lower than they predicted and built in their sample size.
DR. KERN: And, so, the presentation of the PROTECT II trial, was it presented as a positive study or a negative study.
DR. WAKSMAN: Overall the study did not meet the endpoint. So the bottom line, you can call it the neutral study, which is a nice way to say it.
if you go and do all those analyses, you may find some areas that you can tease a P value, but I don’t think that this has any scientific value, and people should be very careful. We’re not playing now with numbers or with statistics, this is about patient care. You’re doing a study — the study, I think, has some flaws in the design to begin with — and we actually pointed that out when we were asked to participate in the study. But if the study did not meet the endpoint, then I think all those subanalyses, subgroups, you extract from here, you add to there, and you get a P value, that means nothing. So we have to be careful when we interpret this, other than as a neutral study that you basically cannot adopt any of the … it did not meet the hypothesis, that’s the bottom line.
A first-in-man study of the Reitan catheter pump for circulatory support in patients undergoing high-risk percutaneous coronary intervention.
Smith EJ, Reitan O, Keeble T, Dixon K, Rothman MT.
Department of Cardiology, London Chest Hospital, United Kingdom.
Catheter Cardiovasc Interv. 2009 Jun 1;73(7):859-65. http://dx.doi.org/10.1002/ccd.21865.
To investigate the safety of a novel percutaneous circulatory support device during high-risk percutaneous coronary intervention (PCI).
BACKGROUND:
The Reitan catheter pump (RCP) consists of a catheter-mounted pump-head with a foldable propeller and surrounding cage. Positioned in the descending aorta the pump creates a pressure gradient, reducing afterload and enhancing organ perfusion.
METHODS:
Ten consecutive patients requiring circulatory support underwent PCI; mean age 71 +/- 9; LVEF 34% +/- 11%; jeopardy score 8 +/- 2.3. The RCP was inserted via the femoral artery. Hemostasis was achieved using Perclose sutures. PCI was performed via the radial artery. Outcomes included in-hospital death, MI, stroke, and vascular injury. Hemoglobin (Hb), free plasma Hb (fHb), platelets, and creatinine (cre) were measured pre PCI and post RCP removal.
RESULTS:
The pump was inserted and operated successfully in 9/10 cases (median 79 min). Propeller rotation at 10,444 +/- 1,424 rpm maintained an aortic gradient of 9.8 +/- 2 mm Hg. Although fHb increased,
there was no significant hemolysis (4.7 +/- 2.4 mg/dl pre vs. 11.9 +/- 10.5 post, P = 0.04, reference 20 mg/dl).
Platelets were unchanged (pre 257 +/- 74 x 10(9) vs. 245 +/- 63, P = NS).
Renal function improved (cre pre 110 +/- 27 micromol/l vs. 99 +/- 28, P = 0.004).
All PCI procedures were successful with no deaths or strokes, one MI, and no vascular complications following pump removal.
CONCLUSIONS:
The RCP can be used safely in high-risk PCI patients.
A coronary angiogram that shows the LMCA, LAD and LCX. (Photo credit: Wikipedia)
English: Simulation of a wave pump human ventricular assist device (Photo credit: Wikipedia)
English: Figure A shows the structure and blood flow in the interior of a normal heart. Figure B shows two common locations for a ventricular septal defect. The defect allows oxygen-rich blood from the left ventricle to mix with oxygen-poor blood in the right ventricle. (Photo credit: Wikipedia)
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