Profound apoptosis-mediated regional myocyte loss and compensatory hypertrophy in pigs with hibernating myocardium

Subendocardial "ischemic-like" state in patients with severe aortic stenosis: Insights from myocardial histopathology and ultrastructure

BACKGROUND

Myocardial adaptation to severe aortic stenosis (AS) is a complex process that involves myocardial fibrosis (MF) beyond cardiomyocyte hypertrophy. Perfusion impairment is believed to be involved in myocardial remodeling in chronic pressure overload.

AIM

To describe morphological and ultrastructural myocardial changes at endomyocardial tissue sampling, possibly reflecting subendocardial ischemia, in a group of patients with severe AS referred to surgical aortic valve replacement (AVR), with no previous history of ischemic cardiomyopathy.

METHODS

One-hundred-fifty-eight patients (73 [68-77] years, 50% women) referred for surgical AVR because of severe symptomatic AS with preoperative clinical and imaging study and no previous history of ischemic cardiomyopathy. Intra-operative septal endomyocardial sampling was obtained in 129 patients. Tissue sections were stained with Masson´s Trichrome for MF quantification and periodic acid-Schiff (PAS) staining was performed to assess the presence of intracellular glycogen. Ultrastructure was analyzed through Transmission electron microscopy (TEM).

RESULTS

MF totalized a median fraction of 11.90% (6.54-19.97%) of EMB, with highly prevalent perivascular involvement (95.3%). None of the samples had histological evidence of myocardial infarction. In 58 patients (45%) we found subendocardial groups of cardiomyocytes with cytoplasmatic enlargement, vacuolization and myofiber derangement, surrounded by extensive interstitial fibrosis. These cardiomyocytes were PAS positive, PAS-diastase resistant and Alcian Blue/PAS indicative of the presence of neutral intracellular glyco-saccharides. At TEM there were signs of cardiomyocyte degeneration with sarcomere disorganization and reduction, organelle rarefaction but no signs of intracellular specific accumulation.

CONCLUSION

Almost half of the patients with severe AS referred for surgical AVR have histological and ultrastructural signs of subendocardial cardiomyocyte ischemic insult. It might be inferred that local perfusion imbalance contributes to myocardial remodeling and fibrosis in chronic pressure overload.

Myocardial Injury, Troponin Release and Cardiomyocyte Death in Brief Ischemia, Failure and Ventricular Remodeling

Troponin released from irreversibly injured myocytes is the gold standard biomarker for the rapid identification of an acute coronary syndrome. In acute myocardial infarction, necrotic cell death is characterized by sarcolemmal disruption in response to a critical level of energy depletion after more than 15-minutes of ischemia. While troponin I and T are highly specific for cardiomyocyte death, high-sensitivity assays have demonstrated that measurable circulating levels of troponin are present in the majority of normal subjects. In addition, transient as well as chronic elevations have been demonstrated in many disease states not clearly associated with myocardial ischemia. The latter observations have given rise to the clinical concept of myocardial injury. This review will summarize evidence supporting the notion that circulating troponin levels parallel the extent of myocyte apoptosis in normal ventricular remodeling and in pathophysiological conditions not associated with infarction or necrosis. It will review the evidence that myocyte apoptosis can be accelerated by both diastolic strain from elevated ventricular preload as well as systolic strain from dyskinesis after brief episodes of ischemia too short to cause a critical level of myocyte energy depletion. We then show how chronic, low rates of myocyte apoptosis from endogenous myocyte turnover, repetitive ischemia or repetitive elevations in LV diastolic pressure can lead to significant myocyte loss in the absence of neurohormonal stimulation. Finally, we posit that the differential response to strain-induced injury in heart failure may determine whether progressive myocyte loss and HFrEF or interstitial fibrosis and HFpEF become the heart failure phenotype.

Cell Therapy in Patients with Heart Failure: A Comprehensive Review and Emerging Concepts

This review summarizes the results of clinical trials of cell therapy in patients with heart failure (HF). In contrast to acute myocardial infarction (where results have been consistently negative for more than a decade), in the setting of HF the results of Phase I–II trials are encouraging, both in ischaemic and non-ischaemic cardiomyopathy. Several well-designed Phase II studies have met their primary endpoint and demonstrated an efficacy signal, which is remarkable considering that only one dose of cells was used. That an efficacy signal was seen 6–12 months after a single treatment provides a rationale for larger, rigorous trials. Importantly, no safety concerns have emerged. Amongst the various cell types tested, mesenchymal stromal cells derived from bone marrow (BM), umbilical cord, or adipose tissue show the greatest promise. In contrast, embryonic stem cells are not likely to become a clinical therapy. Unfractionated BM cells and cardiosphere-derived cells have been abandoned. The cell products used for HF will most likely be allogeneic. New approaches, such as repeated cell treatment and intravenous delivery, may revolutionize the field. As is the case for most new therapies, the development of cell therapies for HF has been slow, plagued by multifarious problems, and punctuated by many setbacks; at present, the utility of cell therapy in HF remains to be determined. What the field needs is rigorous, well-designed Phase III trials. The most important things to move forward are to keep an open mind, avoid preconceived notions, and let ourselves be guided by the evidence.

Myocardial stunning and hibernation revisited

Unlike acute myocardial infarction with reperfusion, in which infarct size is the end point reflecting irreversible injury, myocardial stunning and hibernation result from reversible myocardial ischaemia-reperfusion injury, and contractile dysfunction is the obvious end point. Stunned myocardium is characterized by a disproportionately long-lasting, yet fully reversible, contractile dysfunction that follows brief bouts of myocardial ischaemia. Reperfusion precipitates a burst of reactive oxygen species formation and alterations in excitation-contraction coupling, which interact and cause the contractile dysfunction. Hibernating myocardium is characterized by reduced regional contractile function and blood flow, which both recover after reperfusion or revascularization. Short-term myocardial hibernation is an adaptation of contractile function to the reduced blood flow such that energy and substrate metabolism recover during the ongoing ischaemia. Chronic myocardial hibernation is characterized by severe morphological alterations and altered expression of metabolic and pro-survival proteins. Myocardial stunning is observed clinically and must be recognized but is rarely haemodynamically compromising and does not require treatment. Myocardial hibernation is clinically identified with the use of imaging techniques, and the myocardium recovers after revascularization. Several trials in the past two decades have challenged the superiority of revascularization over medical therapy for symptomatic relief and prognosis in patients with chronic coronary syndromes. A better understanding of the pathophysiology of myocardial stunning and hibernation is important for a more precise indication of revascularization and its consequences. Therefore, this Review summarizes the current knowledge of the pathophysiology of these characteristic reperfusion phenomena and highlights their clinical implications.

Vulnerability for ventricular arrhythmias in patients with chronic coronary total occlusion

INTRODUCTION

The presence of a chronic total occlusion (CTO) is associated with an increased risk of ventricular arrhythmias.

AREAS COVERED

This review provides an overview of the relationship between CTO and ventricular arrhythmias, arrhythmogenic mechanisms, and the effect of revascularization.

EXPERT OPINION

Studies in recipients of an implantable cardioverter-defibrillator (ICD) have shown that a CTO is an independent predictor of appropriate ICD therapy. The myocardial territory supplied by a CTO is a pro-arrhythmogenic milieu characterized by scar tissue, large scar border zone, hibernating myocardium, residual ischemia despite collaterals, areas of slow conduction, and heterogeneity in repolarization. Restoring coronary flow by revascularization might be associated with electrical homogenization as reflected by a decrease in QT(c) dispersion, decrease in T wave peak-to-end interval, reduction of late potentials, and decrease in scar border zone area. Future research should explore whether CTO revascularization results in a lower burden of ventricular arrhythmias. Furthermore, risk stratification of CTO patients without severe LV dysfunction is interesting to identify potential ICD candidates. Potential tools for risk stratification are the use of electrocardiographic parameters, body surface mapping, electrophysiological study, and close rhythm monitoring using an insertable cardiac monitor.

Quantitative proteomic and phosphoproteomic profiling of ischemic myocardial stunning in swine

Despite decades of research on the pathophysiology of myocardial stunning, protein changes and/or phosphorylation status underlying alterations in cardiac function/structure remain inadequately understood. Here, we utilized comprehensive and quantitative proteomic and phosphoproteomic approaches to explore molecular mechanisms of myocardial stunning in swine. The closed-chest swine (n = 5 pigs) were subjected to a 10-min left anterior descending coronary artery (LAD) occlusion producing regional myocardial stunning. Tissues from the ischemic LAD region and a remote nonischemic area of the left ventricle were collected 1 h after reperfusion. Ion current-based proteomics (IonStar) and quantitative phosphoproteomics were employed in parallel to identify alterations in protein level and site-specific phosphorylation changes. A novel swine heart protein database exhibiting high accuracy and low redundancy was developed here to facilitate comprehensive study. Further informatic investigations identified potential protein-protein interactions in stunned myocardium. In total, we quantified 2,099 protein groups and 4,699 phosphorylation sites with only 0.4% missing values. Proteomic analyses revealed downregulation of contractile function and extracellular matrix remodeling. Meanwhile, alterations in phosphorylation linked with contractile dysfunction and apoptotic cell death were uncovered. NetworKIN/STRING analysis predicted regulatory kinases responsible for altered phosphosites, such as protein kinase C-mediated phosphorylation of cardiac troponin I-S199 and CaMKII-mediated phosphorylation of phospholamban-T17. In summary, the ion current-based proteomics and phosphoproteomics reliably identified novel alterations in protein content and phosphorylation contributing to contractile dysfunction, extracellular matrix (ECM) damage, and programmed cell death in stunned myocardium, which corroborate well with our physiological observations. Moreover, this work developed a comprehensive database of the swine heart proteome, a highly valuable resource for future translational research in porcine models with cardiovascular diseases.NEW & NOTEWORTHY We first used ion current-based proteomics and phosphoproteomics to reliably identify novel alterations in protein expression and phosphorylation contributing to contractile dysfunction, extracellular matrix (ECM) damage, and programmed cell death in stunned myocardium and developed a comprehensive swine heart-specific proteome database, which provides a valuable resource for future research in porcine models of cardiovascular diseases.

Transmural variation in microvascular remodeling following percutaneous revascularization of a chronic coronary stenosis in swine

Remodeling of the coronary microcirculation is known to occur distal to a chronic coronary stenosis, but the reversibility of these changes and their functional significance on maximum myocardial perfusion before and after revascularization is unknown. Accordingly, swine instrumented with a chronic silastic stenosis on the left anterior descending coronary artery to produce hibernating myocardium underwent percutaneous coronary intervention (PCI; n = 8) and were compared with animals with a persistent stenosis (n = 8), as well as sham controls (n = 6). Stenotic animals demonstrated an increased subendocardial arteriolar wall thickness-to-lumen ratio (37.8 ± 3.3 vs. 28.3 ± 1.3% in sham, P = 0.04), reduced lumen area per arteriole (597 ± 88 vs. 927 ± 113 μm2, P = 0.04), and a compensatory increase in arteriolar density (9.4 ± 1.0 vs. 5.3 ± 0.4 arterioles/mm2, P < 0.01). As a result, vasodilated flow immediately after PCI was similar to normally perfused remote regions (5.1 ± 1.0 vs. 4.8 ± 0.9 ml·min-1·g-1, P = 0.87). When assessed 1-mo after PCI, increases in wall thickness-to-lumen diameter (42.2 ± 3.3%) and reductions in lumen area per arteriole (638 ± 59 μm2) remained unchanged, but arteriolar density returned to normal (5.2 ± 0.5 arterioles/mm2). As a result, maximum subendocardial flow during adenosine declined and was lower than remote regions (2.6 ± 0.3 vs. 5.9 ± 1.1 ml·min-1·g-1, P = 0.01). There was no microvascular remodeling in subepicardial arterioles, and maximum perfusion remained unchanged. These data demonstrate that subendocardial microvascular remodeling occurs distal to a chronic epicardial stenosis. The regression of arteriolar density without increases in luminal area may precipitate stress-induced subendocardial ischemia in the absence of a physiologically significant stenosis.NEW & NOTEWORTHY Swine with a chronic coronary stenosis exhibit subendocardial microvascular remodeling distal to a critical stenosis characterized by an increase in arteriolar wall thickness and reduction in lumen area with a compensatory increase in arteriolar density. The present study is the first to demonstrate that subendocardial arteriolar density normalizes 1-mo after revascularization, but the lumen area of individual arterioles remains reduced. This leads to a reduction in maximal subendocardial perfusion at this time point despite initial normalization of vasodilator reserve after revascularization. This pattern of chronic microvascular structural remodeling could contribute to recurrent subendocardial ischemia in the absence of coronary restenosis during tachycardia and increases in myocardial oxygen demand.

Adaptive Reductions in Left Ventricular Diastolic Compliance Protect the Heart From Stretch-Induced Stunning

Swine subjected to 2 weeks of repetitive pressure overload (RPO) exhibited significant myocyte loss, but left ventricular (LV) systolic function was preserved, and chamber dilatation did not occur. Instead, myocardial remodeling characterized by myocyte hypertrophy and interstitial fibrosis led to a marked reduction in LV diastolic compliance, which protected the heart from stretch-induced myocyte injury and preserved LV ejection fraction without anatomic LV hypertrophy. These results support a novel paradigm that links cardiac adaptations to RPO with the pathogenesis of reduced LV diastolic compliance and may explain how LV stiffening can occur in the absence of sustained hypertension or anatomic hypertrophy.

Myocardial ischemia: lack of coronary blood flow, myocardial oxygen supply-demand imbalance, or what?

This opinionated article reviews current concepts of myocardial ischemia. Specifically, the historical background is briefly presented. Then, the prevailing paradigm of myocardial oxygen-supply-demand imbalance is criticized since demand is a virtual parameter that cannot be measured and data on measurements of myocardial blood flow and contractile function rather support matching between flow and function. Finally, a concept of myocardial ischemia that focusses on the reduction of coronary blood flow to below 8-10 µl/g per beat with consequences for myocardial electrical, metabolic, contractile and morphological features is advocated.

Effects of different doses of granulocyte colony-stimulating factor mobilization therapy on ischemic cardiomyopathy

G-CSF mobilization might be beneficial to ICM, but the relationship between effect/safety and the dosage of G-CSF remains unclear. In this study, 24 pigs were used to build ICM models and were randomized into four groups. Four weeks later, different dosages of G-CSF were given daily by subcutaneous injection for 5 days. Another 4 weeks later, all the animals were sacrificed. Electrocardiography, coronary arteriography, left ventriculography, transthoracic echocardiography, cardiac MRI, and SPECT, histopathologic analysis, and immunohistochemistry techniques were used to evaluate left ventricular function and myocardial infarct size. Four weeks after G-CSF treatment, pigs in middle-dose G-CSF group exhibited obvious improvements of left ventricular remodeling and function. Moderate G-CSF mobilization ameliorated the regional contractility of ICM, preserved myocardial viability, and reduced myocardial infarct size. More neovascularization and fewer apoptotic myocardial cells were observed in the ischemic region of the heart in middle-dose group. Expression of vWF, VEGF and MCP-1 were up-regulated, and Akt1 was activated in high- and middle-dose groups. Moreover, CRP, TNF-α and S-100 were elevated after high-dose G-CSF mobilization. Middle-dose G-CSF mobilization therapy is an effective and safe treatment for ICM, and probably acts via a mechanism involving promoting neovascularization, inhibiting cardiac fibrosis and anti-apoptosis.

Guidelines for experimental models of myocardial ischemia and infarction

Myocardial infarction is a prevalent major cardiovascular event that arises from myocardial ischemia with or without reperfusion, and basic and translational research is needed to better understand its underlying mechanisms and consequences for cardiac structure and function. Ischemia underlies a broad range of clinical scenarios ranging from angina to hibernation to permanent occlusion, and while reperfusion is mandatory for salvage from ischemic injury, reperfusion also inflicts injury on its own. In this consensus statement, we present recommendations for animal models of myocardial ischemia and infarction. With increasing awareness of the need for rigor and reproducibility in designing and performing scientific research to ensure validation of results, the goal of this review is to provide best practice information regarding myocardial ischemia-reperfusion and infarction models.

Listen to this article’s corresponding podcast at ajpheart.podbean.com/e/guidelines-for-experimental-models-of-myocardial-ischemia-and-infarction/.

Brief Myocardial Ischemia Produces Cardiac Troponin I Release and Focal Myocyte Apoptosis in the Absence of Pathological Infarction in Swine

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High-sensitivity cTnI assays have increasingly identified a rise and fall in situations not typically thought to be associated with infarction, such as exercise stress in patients with coronary disease and prolonged exercise in apparently healthy marathon runners.

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Using a porcine model of brief ischemia leading to myocardial stunning following a 10-min coronary occlusion, the authors demonstrate a delayed release of cTnI after what had previously been felt to be completely reversible ischemia.

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Although tissue necrosis, sarcolemmal disruption, and infarction are absent after brief ischemia, TUNEL staining demonstrates rare single myocytes undergoing irreversible injury from apoptosis.

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These studies demonstrate that significant cTnI release can occur after a brief duration of ischemia that could be compatible with angina.

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In the absence of an acute coronary syndrome or a prolonged myocardial supply/demand imbalance, it may be more appropriate to ascribe significant cTnI elevations after brief ischemia to myocardial injury rather than infarction.

In a porcine model of brief ischemia leading to reversible stunning in the absence of tissue necrosis, we demonstrated delayed release of cardiac troponin I (cTnI) that exceeded the 99th percentile for normal animals 60 min after reperfusion and rose to readily detectable levels 24 h later. Although tissue analysis at 60 min showed no evidence of infarction, TUNEL staining demonstrated isolated myocytes undergoing apoptosis, which was absent after 24 h. These results demonstrate that cTnI elevations occur after ischemia of a duration that is insufficient to produce myocyte necrosis and reflect myocyte injury associated with apoptosis in the absence of pathological evidence of infarction.

Inhibiting Extracellular Vesicle Release from Human Cardiosphere Derived Cells with Lentiviral Knockdown of nSMase2 Differentially Effects Proliferation and Apoptosis in Cardiomyocytes, Fibroblasts and Endothelial Cells In Vitro

Numerous studies have shown a beneficial effect of cardiosphere-derived cell (CDC) therapy on regeneration of injured myocardium. Paracrine signaling by CDC secreted exosomes may contribute to improved cardiac function. However, it has not yet been demonstrated by a genetic approach that exosome release contributes to the therapeutic effect of transplanted CDCs. By employing a lentiviral knockdown (KD) strategy against neutral spingomyelinase 2 (nSMase2), a crucial gene in exosome secretion, we have defined the role of physiologically secreted human CDC-derived exosomes on cardiac fibroblast, endothelial cell and primary cardiomyocyte proliferation, cell death, migration and angiogenesis using a series of in vitro coculture assays. We found that secretion of hCDC-derived exosomes was effectively inhibited by nSMase2 lentiviral KD and shRNAi expression was stable and constitutive. hCDC exosome release contributed to the angiogenic and pro-migratory effects of hCDCs on HUVECs, decreased proliferation of fibroblasts, and decreased apoptosis of cardiomyocytes. These in vitro reactions support a role for exosome secretion as a paracrine mechanism of stem cell-mediated cardiac repair in vivo. Importantly, we have established a novel tool to test constitutive inhibition of exosome secretion in stem cell populations in animal models of cardiac disease.

Heart-Derived Stem Cells in Miniature Swine with Coronary Microembolization: Novel Ischemic Cardiomyopathy Model to Assess the Efficacy of Cell-Based Therapy

A major problem in translating stem cell therapeutics is the difficulty of producing stable, long-term severe left ventricular (LV) dysfunction in a large animal model. For that purpose, extensive infarction was created in sinclair miniswine by injecting microspheres (1.5 × 10⁶ microspheres, 45 μm diameter) in LAD. At 2 months after embolization, animals (n = 11) were randomized to receive allogeneic cardiosphere-derived cells derived from atrium (CDCs: 20 × 10⁶, n = 5) or saline (untreated, n = 6). Four weeks after therapy myocardial function, myocyte proliferation (Ki67), mitosis (phosphor-Histone H3; pHH3), apoptosis, infarct size (TTC), myocyte nuclear density, and cell size were evaluated. CDCs injected into infarcted and remodeled remote myocardium (global infusion) increased regional function and global function contrasting no change in untreated animals. CDCs reduced infarct volume and stimulated Ki67 and pHH3 positive myocytes in infarct and remote regions. As a result, myocyte number (nuclear density) increased and myocyte cell diameter decreased in both infarct and remote regions. Coronary microembolization produces stable long-term ischemic cardiomyopathy. Global infusion of CDCs stimulates myocyte regeneration and improves left ventricular ejection fraction. Thus, global infusion of CDCs could become a new therapy to reverse LV dysfunction in patients with asymptomatic heart failure.

Carvedilol Improves Myocardial Contractility Compared With Metoprolol in Patients With Chronic Hibernating Myocardium After Revascularization

Background: We tested the hypothesis of whether carvedilol delays morphologic degeneration and improves functional outcome compared with metoprolol tartrate in patients with hibernating myocardium undergoing surgical revascularization. We have previously shown that patients with chronic hibernating myocardium undergo progressive cellular degeneration and fibrosis.

Methods: Twenty patients with multivessel coronary artery disease revascularization and hibernating myocardium as assessed by technetium-99m perfusion scintigraphy and fluorine-18-fluorodeoxyglucose positron emission tomography were randomized to receive either carvedilol or metoprolol tartrate for at least 2 months before surgery, and this was continued for 7 months postoperatively. Left ventricular ejection fraction and regional wall motion abnormalities were assessed by left ventriculography at baseline and 7 months postoperatively. Intraoperative transmural needle biopsy samples were obtained for microscopic analysis.

Results: Postoperatively, the ejection fraction increased from 31% ± 5% to 44% ± 4% ( P < .005) in the carvedilol group (n = 10), and from 30% ± 6% to 40% ± 6% in the metoprolol tartrate group ( P < .05 vs preoperatively and vs carvedilol). Wall motion abnormalities in the carvedilol group improved from -2.1 ± 0.4 to -0.6 ± 0.5 ( P < .05) and from -2.3 ± 0.5 to -1.6 ± 0.6 in the metoprolol tartrate group ( P < .05 vs preoperatively and vs carvedilol). Microscopic analysis after 72 ± 18 days of either treatment showed mild cardiomyocyte degeneration and moderate-to-severe fibrosis (28% ± 7%) in the carvedilol group compared with moderate cardiomyocyte degeneration and moderate-to-severe fibrosis (33% ± 6%) in the metoprolol tartrate group. Apoptosis, as assessed by the terminal deoxynucleotidyl transferase nick end labeling method, was observed in only 1 patient in each group.

Conclusions: Carvedilol treatment of hibernating myocardium results in improved functional recovery after revascularization compared with metoprolol tartrate, and this might partially be related to reduced cardiomyocyte degeneration.

Long-Term Preservation of Left Ventricular Systolic Function in Patients With Refractory Angina Pectoris and Inducible Myocardial Ischemia on Optimal Medical Therapy

Refractory angina pectoris (RAP) represents a clinical condition characterized by frequent episodes of chest pain despite therapy optimization. According to myocardial stunning and myocardial hibernation definitions, RAP should represent the ideal condition for systolic dysfunction development. We aim to investigate the evolution of left ventricular (LV) function in patients with RAP. A retrospective study which encompasses 144 patients with RAP referred to our institution from 1999 to December 2014 was performed. Of them, 88 met the inclusion criteria, and LV function was assessed by echocardiography. All of them had persistent angina episodes on top of optimal medical therapy and evidence of significant inducible myocardial ischemia and no further revascularization options. Nitrates consumption rate, time of angina duration, and the number of angina attacks were evaluated. In the whole population, ejection fraction (EF) was 44% ± 2. EF was significantly lower in patients with previous myocardial infarction (41% ± 1.5 vs 51% ± 1.8, p <0.0001). The duration time and the number of angina attacks did not correlate with EF in the whole population and in patients without previous myocardial infarction. In patients with previous myocardial infarction, the number of anginal attacks did not correlate with EF, but EF appeared higher in patients with angina duration >5 years (<5 years EF 37% ± 1 [n = 26]; >5 years 44% ± 2 [n = 44]; p 0.02). Long-term LV function in patients with RAP is generally preserved. A previous history of myocardial infarction is the only determinant in the development of systolic dysfunction. In conclusion, frequent angina attacks and a long-term history of angina are not apparently associated to worse LV function.

Comparative Efficacy of Intracoronary Allogeneic Mesenchymal Stem Cells and Cardiosphere-Derived Cells in Swine with Hibernating Myocardium

RATIONALE

Allogeneic bone marrow-derived mesenchymal stem cells (MSCs) and cardiosphere-derived cells (CDCs) have each entered clinical trials, but a direct comparison of these cell types has not been performed in a large animal model of hibernating myocardium.

OBJECTIVE

Using completely blinded methodology, we compared the efficacy of global intracoronary allogeneic MSCs (icMSCs, ≈35×10(6)) and CDCs (icCDCs, ≈35×10(6)) versus vehicle in cyclosporine-immunosuppressed swine with a chronic left anterior descending coronary artery stenosis (n=26).

METHODS AND RESULTS

Studies began 3 months after instrumentation when wall thickening was reduced (left anterior descending coronary artery % wall thickening [mean±SD], 38±11% versus 83±26% in remote; P<0.01) and similar among groups. Four weeks after treatment, left anterior descending coronary artery % wall thickening increased similarly after icCDCs and icMSCs, whereas it remained depressed in vehicle-treated controls (icMSCs, 51±13%; icCDCs, 51±17%; vehicle, 34±3%, treatments P<0.05 versus vehicle). There was no change in myocardial perfusion. Both icMSCs and icCDCs increased left anterior descending coronary artery myocyte nuclear density (icMSCs, 1601±279 nuclei/mm(2); icCDCs, 1569±294 nuclei/mm(2); vehicle, 973±181 nuclei/mm(2); treatments P<0.05 versus vehicle) and reduced myocyte diameter (icMSCs, 16.4±1.5 μm; icCDCs, 16.8±1.2 μm; vehicle, 20.2±3.7 μm; treatments P<0.05 versus vehicle) to the same extent. Similar changes in myocyte nuclear density and diameter were observed in the remote region of cell-treated animals. Cell fate analysis using Y-chromosome fluorescent in situ hybridization demonstrated rare cells from sex-mismatched donors.

CONCLUSIONS

Allogeneic icMSCs and icCDCs exhibit comparable therapeutic efficacy in a large animal model of hibernating myocardium. Both cell types produced equivalent increases in regional function and stimulated myocyte regeneration in ischemic and remote myocardium. The activation of endogenous myocyte proliferation and regression of myocyte cellular hypertrophy support a common mechanism of cardiac repair.

Cardiomyocyte Remodeling in Atrial Fibrillation and Hibernating Myocardium: Shared Pathophysiologic Traits Identify Novel Treatment Strategies?

Atrial fibrillation (AF) is the most common arrhythmia and is associated with a high risk of morbidity and mortality. However, there are limited treatment strategies for prevention of disease onset and progression. Development of novel therapies for primary and secondary prevention of AF is critical and requires improved understanding of the cellular and molecular mechanisms underlying the AF disease process. Translational and clinical studies conducted over the past twenty years have revealed that atrial remodeling in AF shares several important pathophysiologic traits with the remodeling processes exhibited by hibernating myocardium that develop in response to chronic ischemia. These shared features, which include an array of structural, metabolic, and electrophysiologic changes, appear to represent a conserved adaptive myocyte response to chronic stress that involves dedifferentiation towards a fetal phenotype to promote survival. In this review, we discuss the pathophysiology of AF, summarize studies supporting a common remodeling program in AF and hibernating myocardium, and propose future therapeutic implications of this emerging paradigm. Ultimately, better understanding of the molecular mechanisms of atrial myocyte remodeling during the onset of AF and the transition from paroxysmal to persistent stages of the disease may facilitate discovery of new therapeutic targets.

Revascularization of chronic hibernating myocardium stimulates myocyte proliferation and partially reverses chronic adaptations to ischemia

BACKGROUND

The time course and extent of recovery after revascularization of viable dysfunctional myocardium are variable. Although fibrosis is a major determinant, myocyte structural and molecular remodeling may also play important roles.

OBJECTIVES

This study sought to determine whether persistent myocyte loss and/or irreversibility of protein changes that develop in hibernating myocardium have an impact on functional recovery in the absence of infarction.

METHODS

Swine implanted with a chronic left anterior descending artery (LAD) stenosis to produce hibernating myocardium underwent percutaneous revascularization, with serial functional recovery evaluated for 1 month (n = 12). Myocardial tissue was evaluated to assess myocyte size, nuclear density, and proliferation indexes in comparison with those of normal animals and nonrevascularized controls. Proteomic analysis by 2-dimensional differential in-gel electrophoresis was used to determine the reversibility of molecular adaptations of hibernating myocytes.

RESULTS

At 3 months, physiological features of hibernating myocardium were confirmed, with depressed LAD wall thickening and no significant infarction. Revascularization normalized LAD flow reserve, with no immediate change in LAD wall thickening. Regional LAD wall thickening slowly improved but remained depressed 1 month post-percutaneous coronary intervention. Surprisingly, revascularization was associated with histological evidence of myocytes re-entering the growth phase of the cell cycle and increases in the number of c-Kit(+) cells. Myocyte nuclear density returned to normal, whereas regional myocyte hypertrophy regressed. Proteomic analysis demonstrated heterogeneous effects of revascularization. Up-regulated stress and cytoskeletal proteins normalized, whereas reduced contractile and metabolic proteins persisted.

CONCLUSIONS

Delayed recovery of hibernating myocardium in the absence of scar may reflect persistent reductions in the amounts of contractile and metabolic proteins. Although revascularization appeared to stimulate myocyte proliferation, the persistence of small immature myocytes may have contributed to delayed functional recovery.

Global intracoronary infusion of allogeneic cardiosphere-derived cells improves ventricular function and stimulates endogenous myocyte regeneration throughout the heart in swine with hibernating myocardium

Background

Cardiosphere-derived cells (CDCs) improve ventricular function and reduce fibrotic volume when administered via an infarct-related artery using the “stop-flow” technique. Unfortunately, myocyte loss and dysfunction occur globally in many patients with ischemic and non-ischemic cardiomyopathy, necessitating an approach to distribute CDCs throughout the entire heart. We therefore determined whether global intracoronary infusion of CDCs under continuous flow improves contractile function and stimulates new myocyte formation.

Methods and Results

Swine with hibernating myocardium from a chronic LAD occlusion were studied 3-months after instrumentation (n = 25). CDCs isolated from myocardial biopsies were infused into each major coronary artery (∼33×10⁶ icCDCs). Global icCDC infusion was safe and while ∼3% of injected CDCs were retained, they did not affect ventricular function or myocyte proliferation in normal animals. In contrast, four-weeks after icCDCs were administered to animals with hibernating myocardium, %LADWT increased from 23±6 to 51±5% (p<0.01). In diseased hearts, myocyte proliferation (phospho-histone-H3) increased in hibernating and remote regions with a concomitant increase in myocyte nuclear density. These effects were accompanied by reductions in myocyte diameter consistent with new myocyte formation. Only rare myocytes arose from sex-mismatched donor CDCs.

Conclusions

Global icCDC infusion under continuous flow is feasible and improves contractile function, regresses myocyte cellular hypertrophy and increases myocyte proliferation in diseased but not normal hearts. New myocytes arising via differentiation of injected cells are rare, implicating stimulation of endogenous myocyte regeneration as the primary mechanism of repair.

New vessel formation in the context of cardiomyocyte regeneration--the role and importance of an adequate perfusing vasculature

The history of revascularization for cardiac ischemia dates back to the early 1960's when the first coronary artery bypass graft procedures were performed in humans. With this 50 year history of providing a new vasculature to ischemic and hibernating myocardium, a profound depth of experience has been amassed in clinical cardiovascular medicine as to what does, and does not work in the context of cardiac revascularization, alleviating ischemia and adequacy of myocardial perfusion. These issues are of central relevance to contemporary cell-based cardiac regenerative approaches. While the cardiovascular cell therapy field is surging forward on many exciting fronts, several well accepted clinical axioms related to the cardiac arterial supply appear to be almost overlooked by some of our current basic conceptual and experimental cell therapy paradigms. We present here information drawn from five decades of the clinical revascularization experience, review relevant new data on vascular formation via cell therapy, and put forward the case that for optimal cell-based cardiac regeneration due attention must be paid to providing an adequate vascular supply.

Reproducible ion-current-based approach for 24-plex comparison of the tissue proteomes of hibernating versus normal myocardium in swine models

Hibernating myocardium is an adaptive response to repetitive myocardial ischemia that is clinically common, but the mechanism of adaptation is poorly understood. Here we compared the proteomes of hibernating versus normal myocardium in a porcine model with 24 biological replicates. Using the ion-current-based proteomic strategy optimized in this study to expand upon previous proteomic work, we identified differentially expressed proteins in new molecular pathways of cardiovascular interest. The methodological strategy includes efficient extraction with detergent cocktail; precipitation/digestion procedure with high, quantitative peptide recovery; reproducible nano-LC/MS analysis on a long, heated column packed with small particles; and quantification based on ion-current peak areas. Under the optimized conditions, high efficiency and reproducibility were achieved for each step, which enabled a reliable comparison of 24 the myocardial samples. To achieve confident discovery of differentially regulated proteins in hibernating myocardium, we used highly stringent criteria to define “quantifiable proteins”. These included the filtering criteria of low peptide FDR and S/N > 10 for peptide ion currents, and each protein was quantified independently from ≥2 distinct peptides. For a broad methodological validation, the quantitative results were compared with a parallel, well-validated 2D-DIGE analysis of the same model. Excellent agreement between the two orthogonal methods was observed (R = 0.74), and the ion-current-based method quantified almost one order of magnitude more proteins. In hibernating myocardium, 225 significantly altered proteins were discovered with a low false-discovery rate (∼3%). These proteins are involved in biological processes including metabolism, apoptosis, stress response, contraction, cytoskeleton, transcription, and translation. This provides compelling evidence that hibernating myocardium adapts to chronic ischemia. The major metabolic mechanisms include a down-regulation of mitochondrial respiration and an increase in glycolysis. Meanwhile, cardioprotective and cytoskeletal proteins are increased, while cardiomyocyte contractile proteins are reduced. These intrinsic adaptations to regional ischemia maintain long-term cardiomyocyte viability at the expense of contractile function.

Impaired coronary flow reserve is the most important marker of viable myocardium in the myocardial segment-based analysis of dual-isotope gated myocardial perfusion single-photon emission computed tomography

OBJECTIVE

The aim of this study was to investigate the most robust predictor of myocardial viability among stress/rest reversibility (coronary flow reserve [CFR] impairment), (201)Tl perfusion status at rest, (201)Tl 24 hours redistribution and systolic wall thickening of (99m)Tc-methoxyisobutylisonitrile using a dual isotope gated myocardial perfusion single-photon emission computed tomography (SPECT) in patients with coronary artery disease (CAD) who were re-vascularized with a coronary artery bypass graft (CABG) surgery.

MATERIALS AND METHODS

A total of 39 patients with CAD was enrolled (34 men and 5 women), aged between 36 and 72 years (mean 58 ± 8 standard in years) who underwent both pre- and 3 months post-CABG myocardial SPECT. We analyzed 17 myocardial segments per patient. Perfusion status and wall motion were semi-quantitatively evaluated using a 4-point grading system. Viable myocardium was defined as dysfunctional myocardium which showed wall motion improvement after CABG.

RESULTS

The left ventricular ejection fraction (LVEF) significantly increased from 37.8 ± 9.0% to 45.5 ± 12.3% (p < 0.001) in 22 patients who had a pre-CABG LVEF lower than 50%. Among 590 myocardial segments in the re-vascularized area, 115 showed abnormal wall motion before CABG and 73.9% (85 of 115) had wall motion improvement after CABG. In the univariate analysis (n = 115 segments), stress/rest reversibility (p < 0.001) and (201)Tl rest perfusion status (p = 0.024) were significant predictors of wall motion improvement. However, in multiple logistic regression analysis, stress/rest reversibility alone was a significant predictor for post-CABG wall motion improvement (p < 0.001).

CONCLUSION

Stress/rest reversibility (impaired CFR) during dual-isotope gated myocardial perfusion SPECT was the single most important predictor of wall motion improvement after CABG.

Chronic hibernating myocardium in sheep can occur without degenerating events and is reversed after revascularization

INTRODUCTION

Our goal was to show that blunting of myocardial flow reserve is mainly involved in adaptive chronic myocardial hibernation without apparent cardiomyocyte degeneration.

METHODS AND RESULTS

Sheep chronically instrumented with critical multivessel stenosis and/or percutaneous transluminal coronary angioplasty (PTCA)-induced revascularization were allowed to run and feed in the open for 2 and 5 months, respectively. Regional myocardial blood flow (MBF) with colored microspheres, regional and global left ventricular function and dimensions (2D echocardiography), and myocardial structure were studied. In sheep with a critical stenosis, a progressive increase in left ventricular end-diastolic and end-systolic cavity area and a decrease in fractional area change were found. Fraction of wall thickness decreased in all left ventricular wall segments. MBF was slightly but not significantly decreased at rest at 2 months. Morphological quantification revealed a rather small but significant increase in diffusely distributed connective tissue, cardiomyocyte hypertrophy, and presence of viable myocardium of which almost 30 % of the myocytes showed depletion of sarcomeres and accumulation of glycogen. The extent of myolysis in the transmural layer correlated with the degree of left ventricular dilation. Structural degeneration of cardiomyocytes was not observed. Balloon dilatation (PTCA) of one of the coronary artery stenoses at 10 weeks revealed recovery of fraction of wall thickness and near normalization of global subcellular structure at 20 weeks.

CONCLUSION

These data indicate that chronic reduction of coronary reserve by itself can induce ischemic cardiomyopathy characterized by left ventricular dilatation, depressed regional and global function, adaptive chronic myocardial hibernation, reactive fibrosis and cardiomyocyte hypertrophy in the absence of obvious degenerative phenomena.

SUMMARY

Reduction of myocardial flow reserve due to chronic coronary artery stenosis in sheep induces adaptive myocardial hibernation without involvement of degenerative phenomena.

Stem cell stimulation of endogenous myocyte regeneration

Cell-based therapy has emerged as a promising approach to combat the myocyte loss and cardiac remodelling that characterize the progression of left ventricular dysfunction to heart failure. Several clinical trials conducted over the past decade have shown that a variety of autologous bone-marrow- and peripheral-blood-derived stem and progenitor cell populations can be safely administered to patients with ischaemic heart disease and yield modest improvements in cardiac function. Concurrently, rapid progress has been made at the pre-clinical level to identify novel therapeutic cell populations, delineate the mechanisms underlying cell-mediated cardiac repair and optimize cell-based approaches for clinical use. The following review summarizes the progress that has been made in this rapidly evolving field over the past decade and examines how our current understanding of the mechanisms involved in successful cardiac regeneration should direct future investigation in this area. Particular emphasis is placed on discussion of the general hypothesis that the benefits of cell therapy primarily result from stimulation of endogenous cardiac repair processes that have only recently been identified in the adult mammalian heart, rather than direct differentiation of exogenous cells. Continued scientific investigation in this area will guide the optimization of cell-based approaches for myocardial regeneration, with the ultimate goal of clinical implementation and substantial improvement in our ability to restore cardiac function in ischaemic heart disease patients.

The physiological significance of a coronary stenosis differentially affects contractility and mitochondrial function in viable chronically dysfunctional myocardium

The reversibility of viable dysfunctional myocardium after revascularization is variable and the reasons for this are unknown. Using 2D-DIGE, we tested the hypothesis that this could reflect the extent of molecular remodeling of myocardial tissue in the absence of infarction. Swine with a progressive left anterior descending (LAD) stenosis were studied 2 months (n = 18) or 3 months (n = 22) post-instrumentation. Coronary flow reserve (vasodilated/rest) was severely reduced at 2 months (LAD 2.6 ± 0.4 versus 5.1 ± 0.4 in normal, p < 0.05) and became critically impaired after 3 months (LAD 1.1 ± 0.2, p < 0.05 vs. 2 months). Despite progression in stenosis severity, reductions in wall thickening at 2 months (LAD 37 ± 4% vs. remote 86 ± 9%, p < 0.05) were unchanged at 3 months (LAD 32 ± 3%, p = ns). Contractile dysfunction was primarily related to reductions (LAD/normal) in contractile proteins which were not affected by stenosis severity (e.g., troponin T, 2 months 0.82 ± 0.03 vs. 0.74 ± 0.03 at 3 months, p-ns). In contrast, mitochondrial function and proteins were normal at 2 months but declined with progression to a critical stenosis (state 3 respiration at 3 months 145 ± 13 vs. 216 ± 5 ng-atoms O2 mg(-1) min(-1) at 2 months, p < 0.05). In a similar fashion, increases in stress (e.g., αB-crystalline 2.13 ± 0.2 vs. 1.17 ± 0.13 at 2 months, p < 0.05) and cytoskeletal proteins (e.g., desmin 1.63 ± 0.12 vs. 1.24 ± 0.10 at 2 months, p < 0.05) only developed with more advanced remodeling from a critical stenosis. We conclude that similar degrees of chronic contractile dysfunction can have diverse intrinsic molecular adaptations to ischemia. This spectrum of adaptations may underlie variability in the time course and extent of reversibility in viable chronically dysfunctional myocardium after revascularization.

Dissociation of hemodynamic and electrocardiographic indexes of myocardial ischemia in pigs with hibernating myocardium and sudden cardiac death

Many survivors of sudden cardiac death (SCD) have normal global ventricular function and severe coronary artery disease but no evidence of symptomatic ischemia or infarction before the development of lethal ventricular arrhythmias, and the trigger for ventricular tachycardia (VT)/ventricular fibrillation (VF) remains unclear. We sought to identify the role of spontaneous ischemia and temporal hemodynamic factors preceding SCD using continuous telemetry of left ventricular (LV) pressure and the ECG for periods up to 5 mo in swine (n = 37) with hibernating myocardium who experience spontaneous VT/VF in the absence of heart failure or infarction. Hemodynamics and ST deviation at the time of VT/VF were compared with survivors with hibernating myocardium as well as sham controls. All episodes of VT/VF occurred during sympathetic activation and were initiated by single premature ventricular contractions, and the VT degenerated into VF in ∼ 30 s. ECG evidence of ischemia was infrequent and no different from those that survived. Baseline hemodynamics were no different among groups, but LV end-diastolic pressure during sympathetic activation was higher at the time of SCD (37 ± 4 vs. 26 ± 4 mmHg, P < 0.05) and the ECG demonstrated QT shortening (155 ± 4 vs. 173 ± 5 ms, P < 0.05). The week before SCD, both parameters were no different from survivors. These data indicate that there are no differences in the degree of sympathetic activation or hemodynamic stress when VT/VF develops in swine with hibernating myocardium. The transiently elevated LV end-diastolic pressure and QT shortening preceding VT/VF raises the possibility that electrocardiographically silent subendocardial ischemia and/or mechanoelectrical feedback serve as a trigger for the development of SCD in chronic ischemic heart disease.

Beneficial effects of ginsenoside-Rg1 on ischemia-induced angiogenesis in diabetic mice

Neovascularization and the formation of collateral vessels are often impaired in diabetes mellitus (DM) population compared with non-diabetics. Alterations in vascular endothelial growth factor (VEGF) signaling and endothelial nitric oxide synthase (eNOS) dysfunction have been confirmed to play a crucial role in impaired neovascularization in diabetic mice. Accumulating data have suggested that Rg1, a main component of Panax ginseng, has the ability to promote tubulogenesis of human umbilical vein endothelial cells (HUVECs) in vitro, and that the mechanism involves increased expression level of VEGF as well as increased eNOS activation. Thus, we speculated that Rg1 might also have therapeutic effects on the impairment of neovascularization in diabetic individuals. The aim of the present study was to investigate whether Rg1 could improve angiogenesis in ischemic hindlimb of diabetic mice in vivo. Our data demonstrated that Rg1 treatment resulted in improved angiogenesis in the diabetic ischemic hindlimb, and the potential mechanism might involve increased eNOS activation, upregulated VEGF expression, and inhibited apoptosis. Our results suggest that Rg1 may be used as a novel and useful adjunctive drug for the therapy of peripheral arterial disease in DM.

Value of segmental myocardial strain by 2-dimensional strain echocardiography for assessment of scar area induced in a rat model of myocardial infarction

OBJECTIVES

Two-dimensional strain echocardiography (2DSE) technique has enabled accurate quantification of regional myocardial function. This experimental study was aimed to investigate the value of 2DSE in detection of segmental regional myocardial dysfunction induced by fibrosis following myocardial infarction in a small animal (rat) model.

METHODS

A rat model of myocardial infarction was established by ligation of the proximal left anterior descending coronary artery in 17 SD rats. Regional myocardial function was detected by 2DSE at baseline and 4-weeks post-infarction, including end-systolic radial strain and strain rate (SR and SrR) and end-systolic circumferential strain and strain rate (SC and SrC) of each of six segments at papillary level. According to the size of scar found by histologic Masson staining, the optimal cutoff points of parameters for detecting scar area were analyzed and the sensitivity and specificity of every parameter to detect myocardial scar were obtained using ROC.

RESULTS

(1) Comparing with parameters measured at baseline, there were significant decreases in SR, SrR, SC and SrC of each segment at 4 weeks post-infarction, with the worst in the infarct area (32.90 ± 8.79 vs 11.18 ± 3.89, 6.28 ± 1.35 vs 3.18 ± 0.47, -14.46 ± 2.21 vs -6.30 ± 2.17 and 4.93 ± 0.95 vs 2.59 ± 1.16, respectively) (all P < 0.05). (2)By 4 weeks, the myocardium of infarct area (anteroseptum, anterior and anterolateral) had fibrosis (31.33 ± 9.89, 73.42 ± 13.21 and 13.99 ± 3.24%, respectively) with minimal fibrosis in inferoseptal segment (0.32 ± 0.19%), no fibrosis was found in the inferior and inferolateral segments. (3)Significant negative correlations were found between the size of segmental scar and 2DSE parameters (r-value -0.61 ~ -0.80, all P < 0.01) with the strongest correlation in SR. SR less than 10% has 84% sensitivity and 98% specificity for detecting segments of scar area greater than 30% with AUC = 0.97.

CONCLUSIONS

2DSE is able to assess regional myocardial dysfunction in a rat model of myocardial infarction and has high accuracy in detecting infarct segments with scar area greater than 30%.

Myocardial perfusion and contraction in acute ischemia and chronic ischemic heart disease

A large body of evidence has demonstrated that there is a close coupling between regional myocardial perfusion and contractile function. When ischemia is mild, this can result in the development of a new balance between supply and energy utilization that allows the heart to adapt for a period of hours over which myocardial viability can be maintained, a phenomenon known as "short-term hibernation". Upon reperfusion after reversible ischemia, regional myocardial function remains depressed. The "stunned myocardium" recovers spontaneously over a period of hours to days. The situation in myocardium subjected to chronic repetitive ischemia is more complex. Chronic dysfunction can initially reflect repetitive stunning with insufficient time for the heart to recover between episodes of spontaneous ischemia. As the frequency and/or severity of ischemia increases, the heart undergoes a series of adaptations which downregulate metabolism to maintain myocyte viability at the expense of contractile function. The resulting "hibernating myocardium" develops regional myocyte cellular hypertrophy as a compensatory response to ischemia-induced apoptosis along with a series of molecular adaptations that while regional, are similar to global changes found in advanced heart failure. As a result, flow-function relations become independently affected by tissue remodeling and interventions that stimulate myocyte regeneration. Similarly, chronic vascular remodeling may alter flow regulation in a fashion that increases myocardial vulnerability to ischemia. Here we review our current understanding of myocardial flow-function relations during acute ischemia in normal myocardium and highlight newly identified complexities in their interpretation in viable chronically dysfunctional myocardium with myocyte cellular and molecular remodeling. This article is part of a Special Issue entitled "Coronary Blood Flow".

Development of a preclinical model of ischemic cardiomyopathy in swine

A number of promising therapies for ischemic cardiomyopathy are emerging, and the role of translational research in testing the efficacy and safety of these agents in relevant clinical models has become important. The goal of this study was to develop a chronic model of ischemic cardiomyopathy in a large animal model. In this study, 40 consecutive pigs were initially enrolled. To induce progressive stenosis, a plastic occluder with a fixed diameter of 1.0 mm fitted with an 18-gauge copper wire was placed around the proximal left anterior descending (LAD) coronary artery. Coronary angiography, hemodynamic measurements, and echocardiography were performed at 2 wk and 1, 2, and 3 mo. Overall mortality was 26% at 3 mo, and up to 80% of the pigs showed total occlusion of LAD at 1 mo. A significant depression of peak LV pressure rate of rise (+dP/dt(max)) was observed in the animals showing total artery occlusion throughout the study. Left ventricular ejection fraction was also impaired, and the left ventricular volumes tended to be larger in the pigs with occlusion. Approximately 10% of scar tissue was found in the LAD occluded pigs, whereas the coronary flow pattern in the rest of the area took the pattern of hibernating myocardium. At the same time, histological and protein analysis established the presence of fibrosis and ongoing apoptosis in the ischemic area. In this model, the timing and incidence of total occlusion and low mortality offer significant advantages over other ischemic cardiomyopathy models in conducting preclinical studies.

Non-uniform recovery of left ventricular transmural mechanics in ST-segment elevation myocardial infarction

BACKGROUND

After a transient ischemic episode, the subendocardial region is more severely injured than outer subepicardial layers and may regain a proportionately greater degree of mechanical function in the longitudinal direction. We sought to explore left ventricular (LV) transmural mechanics in patients with ST-segment elevation myocardial infarction (STEMI) for determining the mechanism underlying recovery of global LV function after primary percutaneous coronary intervention (PCI).

METHODS

A total of 42 patients (62 +/- 11 years old, 71% male) with a first STEMI underwent serial assessments of LV longitudinal, circumferential and radial strains (LS, CS and RS) by selective tracking of subendocardial and subepicardial regions within 48 hours and a median of 5 months after PCI. LV mechanical parameters were compared with sixteen age and gender matched normal controls.

RESULTS

In comparison with controls, endocardial and epicardial LS were markedly attenuated at 48 hours following PCI (P < 0.001). An improvement in LV ejection fraction (EF > 5%) following PCI was seen in 24 (57%) patients and was associated with improvement in endocardial and epicardial LS (P < 0.001 and P = 0.003, respectively) and endocardial CS (P = 0.01). Radial strain and wall motion score index, however, remained persistently abnormal. The change in endocardial LS (OR 1.2, 95% CI 1.03 to 1.42, P = 0.01) and the change in epicardial LS (OR 1.2, 95% 1.03 to 1.46, P = 0.02) were significantly associated with the improvement in LVEF, independent of the location of STEMI and the presence of underlying multivessel disease.

CONCLUSIONS

In patients with STEMI treated by PCI, the recovery of LV subendocardial shortening strain seen in the longitudinal direction underlies the improvement in LV global function despite persistent abnormalities in radial mechanics and wall motion score index.

Is detection of hibernating myocardium necessary in deciding revascularization in systolic heart failure?

Although the prognosis of systolic heart failure, also called heart failure with reduced ejection fraction, has improved with advances in therapy, the prognosis remains poor in patients who become refractory to such therapies. That cardiac transplantation improves the quality of life and survival of such patients has been established, but it is available to a very small number of patients. Thus, newer pharmacologic and nonpharmacologic therapies for patients with refractory systolic heart failure are being explored. Because chronic ischemic heart disease is the most common cause of systolic heart failure, potential exists for revascularization therapy. Although revascularization can be performed with low procedural mortality, improvement in left ventricular function, relief of symptoms, and long-term prognosis appear to be related to the presence and extent of viable ischemic hibernating myocardium. In conclusion, the detection of hibernating myocardium is highly desirable before revascularization treatment is undertaken.

11C-meta-hydroxyephedrine defects persist despite functional improvement in hibernating myocardium

BACKGROUND

Regional cardiac sympathetic nerve dysfunction develops in hibernating myocardium and may play a role in its association with sudden cardiac death. Interventions to improve cardiac function (i.e., revascularization) improve survival, but the potential reversibility of sympathetic nerve dysfunction remains unclear.

METHODS AND RESULTS

Pigs (n = 11) were chronically instrumented with a proximal left anterior descending coronary artery (LAD) stenosis to produce hibernating myocardium. Prior to therapeutic interventions, there was LAD occlusion with collateral-dependent myocardium, reduced regional function (echocardiographic LAD wall-thickening 23% +/- 4% vs 83% +/- 6% in Remote, P < .001), and large defects in (11)C-meta-hydroxyephedrine (HED) PET (48% +/- 4% of LV area, 26% +/- 2% integrated reduction). Successful PCI or pravastatin therapy improved regional (LAD wall-thickening 23% +/- 4% to 42% +/- 6%, P < .05) and global LV function (fractional shortening 24% +/- 2% to 31% +/- 2%, P < .01), but did not alter regional HED uptake, retention, defect size, or defect severity.

CONCLUSIONS

Despite significant functional improvement of hibernating myocardium as a result of PCI or pravastatin therapy, there were no changes in HED defect size or severity. Thus, inhomogeneity in myocardial sympathetic innervation persisted, and the lack of plasticity suggests that even in the absence of significant infarction, structural rather than functional defects are responsible for reduced myocardial norepinephrine uptake in chronic ischemic heart disease.

Pravastatin improves function in hibernating myocardium by mobilizing CD133+ and cKit+ bone marrow progenitor cells and promoting myocytes to reenter the growth phase of the cardiac cell cycle

3-hydroxy-3-methyl glutaryl coenzyme A reductase inhibitors have been reported to increase circulating bone marrow progenitor cells and variably improve global function in heart failure. The potential role of improved perfusion versus direct effects of statins on cardiac myocytes has not been established. We chronically instrumented swine with a left anterior descending artery (LAD) stenosis to produce chronic hibernating myocardium with regional contractile dysfunction in the absence of heart failure. Hemodynamics, function, perfusion, and histopathology were assessed in pigs treated for 5 weeks with pravastatin (n=12) versus untreated controls (n=10). Regional LAD wall thickening was depressed under baseline conditions (LAD 3.7+/-0.3 versus 6.6+/-0.3 in remote regions, P<0.01). It remained unchanged in untreated animals but increased from 3.8+/-0.6 to 5.2+/-0.5 mm after pravastatin (P<0.01). There was no increase in myocardial perfusion at rest or during vasodilation. Pravastatin mobilized circulating CD133(+)/cKit(+) bone marrow progenitor cells and increased myocardial tissue levels (LAD CD133(+) cells from 140+/-33 to 884+/-167 cells/10(6) myocyte nuclei and cKit(+) cells from 223+/-49 to 953+/-123 cells/10(6) myocyte nuclei). Pravastatin increased myocytes in mitosis (phospho-histone-H3; 9+/-5 to 43+/-7 nuclei/10(6) myocyte nuclei, P<0.05) and the growth phase of the cell cycle (Ki67; 410+/-82 to 1261+/-235 nuclei/10(6) myocyte nuclei, P<0.05) in diseased but not normal hearts. As a result, pravastatin increased LAD myocyte nuclear density from 830+/-41 to 1027+/-55 nuclei/mm(2) (P<0.05). These data indicate that, in the absence of impaired endothelial function and heart failure, dysfunctional hibernating myocardium improves after pravastatin. This effect is independent of myocardial perfusion and related to mobilization of CD133(+)/cKit(+) bone marrow progenitor cells which stimulate myocyte proliferation resulting in quantitative increases in myocyte nuclear density.

Intramyocardial transplantation of bone marrow-derived stem cells: ultrasonic strain rate imaging in a model of hibernating myocardium

BACKGROUND

The aim of this study was to evaluate potential cardioprotective effects of bone marrow-derived stem cells in chronic ischemic myocardium regarding strain rate parameters during dobutamine stress echocardiography.

METHODS

An ameroid constrictor was placed around the circumflex artery in 23 pigs to induce hibernating myocardium. Pigs received autologous mesenchymal stem cells (auto MSCs), allogeneic MSC (allo MSC), autologous mononuclear cells (auto MNCs), or placebo injections into the ischemic region. During dobutamine stress echocardiography, peak systolic strain rates (SR(sys)) and systolic and postsystolic strain values (epsilon(sys), epsilon(ps)) were determined. The animals were evaluated regarding myocardial fibrosis, neovascularization, apoptosis, and myocardial beta-adrenergic receptor density.

RESULTS

The median ejection fraction was reduced in the control group compared with the auto MSC-, allo MSC-, and auto MNC-treated pigs (36.5% vs 46.0% vs 46.0% vs 41.5%; P = .001, respectively). Histopathology revealed a decreased myocardial fibrosis in auto MSC- (16.3%), allo MSC- (11.3%), and auto MNC- (16.7%) treated pigs compared with controls (31.0%; P = .004). The fibrosis and echocardiographic deformation data correlated in the posterior walls: rest peak SR(sys)r = -0.92; epsilon(sys)r = -0.86; 10 microg dobutamine stimulation peak SR(sys)r = -0.88, epsilon(sys), r = -0.87 (P = .0001).

CONCLUSION

Endocardial injection of stem cells may induce cardioprotective effects in chronic ischemic myocardium and helps to keep the ischemic myocardium viable.

Tissue-specific pyruvate dehydrogenase complex deficiency causes cardiac hypertrophy and sudden death of weaned male mice

Pyruvate dehydrogenase complex (PDC) plays an important role in energy homeostasis in the heart by catalyzing the oxidative decarboxylation of pyruvate derived primarily from glucose and lactate. Because various pathophysiological states can markedly alter cardiac glucose metabolism and PDC has been shown to be altered in response to chronic ischemia, cardiac physiology of a mouse model with knockout of the alpha-subunit of the pyruvate dehydrogenase component of PDC in heart/skeletal muscle (H/SM-PDCKO) was investigated. H/SM-PDCKO mice did not show embryonic lethality and grew normally during the preweaning period. Heart and skeletal muscle of homozygous male mice had very low PDC activity (approximately 5% of wild-type), and PDC activity in these tissues from heterozygous females was approximately 50%. Male mice did not survive for >7 days after weaning on a rodent chow diet. However, they survived on a high-fat diet and developed left ventricular hypertrophy and reduced left ventricular systolic function compared with wild-type male mice. The changes in the heterozygote female mice were of lesser severity. The deficiency of PDC in H/SM-PDCKO male mice greatly compromises the ability of the heart to oxidize glucose for the generation of energy (and hence cardiac function) and results in cardiac pathological changes. This mouse model demonstrates the importance of glucose oxidation in cardiac energetics and function under basal conditions.