Histological alterations in chronically hypoperfused myocardium. Correlation with PET findings

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.

A Prospective Comparative Study between 99mTc MIBI Myocardial Perfusion Single-Photon Emission Computed Tomography and Dobutamine Stress Echocardiography to Detect Viable Myocardium in Patients with Coronary Artery Disease

Introduction

The objective of this study was to compare 99mTc MIBI myocardial perfusion SPECT and Dobutamine Stress Echocardiography (DSE) in detecting viable myocardium in patients with Coronary Artery Disease.

Materials and Methods

Total of 50 patients who with CAD and poor LV function were idenitifed on 2D Echo using 16 segment cardiac model. These patients underwent 99mTc MIBI myocardial perfusion SPECT and Dobutamine Stress Echocardiography and the results were compared with the gold standard 18F-FDG PET-CT findings.

Results

A Total of 550 dysfunctional segments were identified in datasets of 50 patients on 2D echo. No significant difference was noted between the pairwise positive outcome of viable segment between MIBI SPECT and DSE (p=0.875). MIBI SPECT showed a sensitivity of 86.5% and specificity of 90.0% when compared with 18F-FDG PET-CT which was comparable with DSE having a sensitivity of 87.6% and specificity of 90.7%.

Conclusion

99mTc MIBI SPECT is an effective good alternative for evaluation of viable myocardial segments in patients with dysfunctional myocardium and can be considered especially in elderly or obese patients and patients with lung disease having poor echocardiographic imaging window due to lack of an optimal acoustic window.

Metabolic heterogeneous zone assessed by 18 FDG-PET is predictive of postablation mortality in patients with ventricular tachycardia

PURPOSE

We sought to study the predictive value of the metabolic heterogeneous zone (HZ) as determined by ¹⁸ Fluorodeoxyglucose (¹⁸ FDG) positron emission tomography (PET) viability studies in ventricular tachycardia (VT) patients.

METHODS

PET studies utilizing ⁸² Rubidium (⁸² Rb) tracer for perfusion and ¹⁸ FDG tracer for viability were analyzed using PMOD (PMOD Technologies) and further analyzed using 684-segment plots. ¹⁸ FDG uptake was normalized to the area with maximal perfusion on the rest ⁸² Rb study. Metabolic scar, HZ, and healthy segments were defined with perfusion-normalized ¹⁸ FDG uptake between 0%-50%, 50%-70%, and >70%, respectively.

RESULTS

Thirty-four VT patients (age, 63 ± 12 years) were evaluated with ¹⁸ FDG-PET viability study. Most (n = 31) patients underwent VT ablation. Patients were categorized to HZ < median versus HZ ≥ median based on a median HZ area size of 21.0 cm² . HZ size was significantly larger in the deceased group than the alive group (35.2 cm² vs. 18.1 cm² , p = .01). Deaths were significantly higher in HZ ≥ 21 cm² group than HZ < 21 cm² group (58.8% vs. 11.8%, p = .005). Survival analysis showed significantly higher mortality in the HZ ≥ 21 cm² group than the HZ < 21 cm² group (HR = 4.1, 95% CI: 1.3-12.6, p = .016). In a multivariable analysis, HZ was found to be an independent predictor for all-cause mortality (HR = 1.07, 95% CI: 1.02-1.12, p = .01) CONCLUSIONS: Increased HZ size of myocardium was associated with increased mortality. Metabolic HZ quantification may be of value in risk stratification and management of ischemic and nonischemic patients with VT.

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.

Myocardial function in patients with anomalous left coronary artery from the pulmonary artery syndrome: A long-term speckle tracking echocardiographic study

Background

Anomalous origin of the left coronary artery (LCA) from the pulmonary artery (ALCAPA) is a rare congenital heart disease. Retrograde flow from the right coronary artery (RCA) through natural collaterals to the low-pressure main pulmonary artery causes extensive ischemia. Limited data concerning the extent of permanent myocardial damage and functional recovery after surgical repair in the long-term follow-up is available.

Aim

Determination of the incidence of incipient myocardial dysfunction in ALCAPA patients in the long-term observation using tissue Doppler and speckle tracking echocardiography.

Methods and results

Eighteen ALCAPA patients after surgical repair (at median age of 7 months, range 3–167) underwent echocardiographic examination after (median) 17 years. All but 4 patients in NYHA class II presented well at follow-up. No narrowing in proximal LCA was detected in color Doppler. The initial (pre-surgical) left ventricular (LV) ejection fraction of 33±17% almost normalized to 55±6%, but was lower than in the age, sex and body surface area matched control group: 62±5% (p<0.001). At follow-up, LV global longitudinal strain (LS): -15.8±3.3% vs -21.9±1.7%; right ventricular LS: -20.6±3.9% vs -24.9±4.6%; left atrial LS: 27.7±4.3% vs 41.0±11.5%; right atrial LS: 26.8±7.4% vs 44.0±7.9% and early pulsed wave to tissue Doppler mitral filling ratio (E/E’): 8.1±2.6 vs 5.8±1.3 were impaired in the ALCAPA population in comparison to the control group (p<0.01 for all comparisons). LV radial and circumferential strain did not differ between groups. Mean LS in the ALCAPA patients in the RCA region was -19.0±4.4%, while in the LCA region -13.8±7.3% (p<0.00001).

Conclusions

Despite good clinical condition and normalized LV ejection fraction in ALCAPA patients after surgical repair in the long-term follow-up, the diastolic and longitudinal systolic function of all cardiac chambers remained impaired, especially in the LCA region. Lifelong surveillance of repaired ALCAPA patients is needed.

[Surgical Treatment of Ischemic Cardiomyopathy: Current State of the Problem]

In this article we present discussion of the current state of the problem of surgical treatment of ischemic cardiomyopathy (ICM). The pathophysiological aspects of left ventricular remodeling in patients with ICM are also covered. A detailed characterization of methods for assessing the myocardial viability is given and their role in patients with ICM is shown. The problem of right ventricular dysfunction in ICM is discussed. Main attention is focused on the methods of surgical treatment of ICM. Limitations of the Surgical Treatment for Ischemic Heart Failure (STICH) study are analyzed. The article is intended for cardiologists, general practitioners and cardiac surgeons.

Basic fibroblast growth factor attenuates left-ventricular remodeling following surgical ventricular restoration in a rat ischemic cardiomyopathy model

OBJECTIVE

Although surgical ventricular restoration for ischemic cardiomyopathy is expected as an alternative or bridge to heart transplantation, post-operative remodeling of left ventricle (LV) needs to be addressed. This study aimed to examine the effect of basic fibroblast growth factor (bFGF), which induces angiogenesis and tissue regeneration in ischemic myocardium, to prevent remodeling after surgical ventricular restoration (SVR) using a rat ischemic cardiomyopathy model.

METHODS

Four weeks after coronary artery ligation, rats were divided into two groups: rats treated with SVR alone (SVR; n = 21), and rats treated with SVR and local sustained release of bFGF using gelatin hydrogel sheet (SVR + bFGF; n = 22). Cardiac function was assessed by serial echocardiography and cardiac catheterization. Cardiac tissue sections were histologically examined for vascular density and fibrosis.

RESULTS

Higher systolic function and lower LV end-diastolic pressure (LVEDP) were observed in rats treated with SVR + bFGF (SVR vs SVR + bFGF; Ees: 0.22 ± 0.11 vs 0.33 ± 0.22 mmHg/μL, p = 0.0328; LVEDP: 12.7 ± 7.0 vs 8.5 ± 4.3 mmHg, p = 0.0230). LV area tended to be lower in rats treated with SVR + bFGF compared to rats treated with SVR alone (left-ventricular end-diastolic area: 0.66 ± 0.07 vs 0.62 ± 0.07 cm², p = 0.071). Vascular density tended to be higher in rats treated with SVR + bFGF than those without bFGF (23.3 ± 8.1 vs 28.8 ± 9.5/mm², p = 0.0509).

CONCLUSIONS

BFGF induced angiogenesis and attenuated remodeling after SVR which secured the efficacy of SVR in a rat ischemic cardiomyopathy model.

Torpor-arousal cycles in Syrian hamster heart are associated with transient activation of the protein quality control system

Hibernation consists of torpor, with marked suppression of metabolism and physiological functions, alternated with arousal periods featuring their full restoration. The heart is particularly challenged, exemplified by its rate reduction from 400 to 5-10 beats per minute during torpor in Syrian hamsters. In addition, during arousals, the heart needs to accommodate the very rapid return to normal function, which lead to our hypothesis that cardiac function during hibernation is supported by maintenance of protein homeostasis through adaptations in the protein quality control (PQC) system. Hereto, we examined autophagy, the endoplasmic reticulum (ER) unfolded protein (UPR_ER) response and the heat shock response (HSR) in Syrian hamster hearts during torpor and arousal. Transition from torpor to arousal (1.5 h) was associated with stimulation of the PQC system during early arousal, demonstrated by induction of autophagosomes, as shown by an increase in LC3B-II protein abundance, likely related to the activation of the UPR_ER during late torpor in response to proteotoxic stress. The HSR was not activated during torpor or arousal. Our results demonstrate activation of the cardiac PQC system - particularly autophagosomal degradation - in early arousal in response to cardiac stress, to clear excess aberrant or damaged proteins, being gradually formed during the torpor bout and/or the rapid increase in heart rate during the transition from torpor to arousal. This mechanism may enable the large gain in cardiac function during the transition from torpor to arousal, which may hold promise to further understand 'hibernation' of cardiomyocytes in human heart disease.

Left Ventricular Mechanics in Patients with Abnormal Origin of the Left Main Coronary Artery from the Pulmonary Trunk Late after Successful Repair

OBJECTIVE

Our aim was to evaluate left ventricular (LV) mechanics by using speckle tracking echocardiography (STE) in asymptomatic patients with abnormal origin of the left main coronary artery from the pulmonary trunk (ALCAPA), late after successful repair, in the presence of LV ejection fraction (EF) >50%.

METHODS

We studied 30 ALCAPA patients (median age 4 years, range 1-25 years, NYHA class I, LVEF >50%) and 16 healthy age- and sex-matched controls (median age 5 years, range 1-25 years). All underwent standard echocardiographic evaluation and STE.

RESULTS

LV dimensions and LVEF (63.6 ± 8.2% vs. 64.1 ± 5.1%, p = 0.826) were not different between patients and controls. Diastolic parameters were significantly abnormal in our patients versus controls (E/e' average: 11.9 ± 5.8 vs. 6.6 ± 3.0, p = 0.0014). Global LV longitudinal strain was significantly lower in ALCAPA patients versus controls (-17.6 ± 3.5% vs. -23.4 ± 3.1%, p < 0.0001). LV torsion (9.1 ± 4.9° vs. 11.9 ± 3.3°, p = 0.046) was significantly impaired in ALCAPA patients.

CONCLUSIONS

After successful repair in asymptomatic ALCAPA patients, despite an LVEF >50%, diastolic function, LV longitudinal deformation and LV torsion remain impaired. We suggest including a detailed study of the diastolic function and cardiac mechanics in the clinical follow-up of these patients to identify the subgroup of patients at higher risk.

Principles and techniques of imaging in identifying the substrate of ventricular arrhythmia

Life-threatening ventricular arrhythmias (VA) are a major cause of death in patients with cardiomyopathy. To date, impaired left ventricular ejection fraction remains the primary criterion for implantable cardioverter-defibrillator therapy to prevent sudden cardiac death. In recent years, however, advanced imaging techniques such as nuclear imaging, cardiac magnetic resonance imaging, and computed tomography have allowed for a more detailed evaluation of the underlying substrate of VA. These imaging modalities have emerged as a promising approach to assess the risk of sudden cardiac death. In addition, non-invasive identification of the critical sites of arrhythmias may guide ablation therapy. Typical anatomical substrates that can be evaluated by multiple advanced imaging techniques include perfusion abnormalities, scar and its border zone, and sympathetic denervation. Understanding the principles and techniques of different imaging modalities is essential to gain more insight in their role in identifying the arrhythmic substrate. The current review describes the principles of currently available imaging techniques to identify the substrate of VA.

Cardiomyocyte proliferation in cardiac development and regeneration: a guide to methodologies and interpretations

The newt and the zebrafish have the ability to regenerate many of their tissues and organs including the heart. Thus, a major goal in experimental medicine is to elucidate the molecular mechanisms underlying the regenerative capacity of these species. A wide variety of experiments have demonstrated that naturally occurring heart regeneration relies on cardiomyocyte proliferation. Thus, major efforts have been invested to induce proliferation of mammalian cardiomyocytes in order to improve cardiac function after injury or to protect the heart from further functional deterioration. In this review, we describe and analyze methods currently used to evaluate cardiomyocyte proliferation. In addition, we summarize the literature on naturally occurring heart regeneration. Our analysis highlights that newt and zebrafish heart regeneration relies on factors that are also utilized in cardiomyocyte proliferation during mammalian fetal development. Most of these factors have, however, failed to induce adult mammalian cardiomyocyte proliferation. Finally, our analysis of mammalian neonatal heart regeneration indicates experiments that could resolve conflicting results in the literature, such as binucleation assays and clonal analysis. Collectively, cardiac regeneration based on cardiomyocyte proliferation is a promising approach for improving adult human cardiac function after injury, but it is important to elucidate the mechanisms arresting mammalian cardiomyocyte proliferation after birth and to utilize better assays to determine formation of new muscle mass.

Chronic ischemic viable myocardium in man: Aspects of dedifferentiation

Histologic analysis of biopsies derived from patients with chronic dysfunctional but viable (hibernating) myocardium showed characteristic cell alterations. These changes consisted of a partial to complete loss of sarcomeres, accumulation of glycogen, and disorganization and loss of sarcoplasmic reticulum. Most of the adaptive changes that these affected cells undergo are suggestive of dedifferentiation. In the present study the expression and organizational pattern of contractile and cytoskeletal proteins such as titin, cardiotin, and α-smooth muscle actin were assessed in hibernating and normal myocardium because the expression and organization of these constituents have been related to certain stages of cardiomyocyte differentiation. In normal cells titin shows a cross-striated staining pattern, whereas cardiotin displays a fibrillar array, parallel to the sarcomeres. α-Smooth muscle actin is not expressed in adult cardiomyocytes. The expression of titin in a punctated pattern and the marked decrease to virtual absence of cardiotin in hibernating cardiomyocytes speak in favor of an embryonic phenotype of these cells. The re-expression of α-smooth muscle actin in hibernating cells strongly supports this hypothesis. The observations on three different structural proteins of heart muscle suggest that hibernating myocardium acquired aspects of muscle cell dedifferentiation.

Analysis of Myocardial (18)F-FDG Uptake by PET/CT in the Patients with Different Dialectically Classified Coronary Heart Diseases (CHD)

To quantify myocardial glucose metabolism by (18)F-FDG PET/CT in patients that have coronary heart disease (CHD) according to traditional Chinese medicine classification. Ninety patients with CHD were enrolled and were categorized into three groups. All patients underwent PET-CT examination for (18)F-FDG uptake quantification. In group A, the radioactive signals were weak in multiple segments in 27 cases (90 %). One case had no visualization and two had normal visualization (mean SUV = 4 ± 0.6). In group B, the radioactive signals were in some local areas in eight cases (26.7 %). Twenty cases had an overall increase in signal density (SUV ≥ 8) (66.7 %). One case had no visualization, and one case had normal visualization (mean SUV 4 ± 0.6). In group C, 23 cases had no visual or a weak visual (SUV ≤ 2 ± 0.3) (76.7 %). Seven cases had segmental weak signals or signal defects. Different types of CHD demonstrate different metabolisms of myocardium glucose. It is necessary to dialectically classify CHD and apply differential treatment.

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.

Cardiac MR for the assessment of myocardial viability

This article focuses on delayed contrast enhanced MRI (DE-MRI) to assess myocardial viability. We start by discussing previous literature that evaluated the potential importance of myocardial viability testing and follow up with the more recent Surgical Treatment for Heart Disease Trial (STICH) trial results. We then provide an overview of the basic concepts and technical aspects of the current DE-MRI technique and review the initial studies demonstrating that DE-MRI before coronary revascularization can predict functional improvement. Finally, we use DE-MRI as a paradigm to discuss physiological insights into viability assessment and examine common assumptions in the metrics used to evaluate viability techniques.

Hibernating myocardium in heart failure

Ischemic left ventricular systolic dysfunction may result from myocardial necrosis or from hypocontractile areas of viable myocardium. In some cases, recovery of contractility may occur on revascularization--this reversibly dysfunctional tissue is commonly referred to as hibernating myocardium. Observational data suggest that revascularization of patients with ischemic left ventricular systolic dysfunction and known viable myocardium provides a survival benefit over medical therapy. Identification of viable, dysfunctional myocardium may be especially worthwhile in deciding which patients with ischemic left ventricular systolic dysfunction will benefit from revascularization procedures. Randomized, prospective trials evaluating this are currently ongoing. This review will provide an overview of the complex pathophysiology of viable, dysfunctional myocardium, and will discuss outcomes after revascularization. Of the techniques used to determine the presence of hibernating myocardium, functional methods such as stress echocardiography and cardiac magnetic resonance appear more specific, but less sensitive, than the nuclear modalities, which assess perfusion and metabolic activity. Currently, the availability of all methods is variable.

Revascularization in patients with chronic ischaemic myocardial dysfunction: insights from cardiovascular magnetic resonance imaging

In patients with chronic ischaemic left ventricular dysfunction, revascularization may lead to symptomatic and prognostic improvement. Cardiovascular magnetic resonance (CMR) imaging with its high spatial resolution provides the qualitative and quantitative, global and regional information on myocardial anatomy and function. In combination with a gadolinium-based contrast agent, CMR allows an accurate quantification of the myocardial scar and predicts the likelihood of functional recovery after revascularization. The aim of this review is to summarize our current understanding of the detection of myocardial viability using CMR, and why it may be the preferred technique in the assessment of patients with ischaemic cardiomyopathy.

Myocardial viability: what we knew and what is new

Some patients with chronic ischemic left ventricular dysfunction have shown significant improvements of contractility with favorable long-term prognosis after revascularization. Several imaging techniques are available for the assessment of viable myocardium, based on the detection of preserved perfusion, preserved glucose metabolism, intact cell membrane and mitochondria, and presence of contractile reserve. Nuclear cardiology techniques, dobutamine echocardiography and positron emission tomography are used to assess myocardial viability. In recent years, new advances have improved methods of detecting myocardial viability. This paper summarizes the pathophysiology, methods, and impact of detection of myocardial viability, concentrating on recent advances in such methods. We reviewed the literature using search engines MIDLINE, SCOUPS, and EMBASE from 1988 to February 2012. We used key words: myocardial viability, hibernation, stunning, and ischemic cardiomyopathy. Recent studies showed that the presence of viable myocardium was associated with a greater likelihood of survival in patients with coronary artery disease and LV dysfunction, but the assessment of myocardial viability did not identify patients with survival benefit from revascularization, as compared with medical therapy alone. This topic is still debatable and needs more evidence.

Potential of delayed gadolinium enhancement magnetic resonance imaging for quantification of reverse remodeling of the peri-infarct zone in patients with ischemic cardiomyopathy treated with chronic vasodilator therapy: initial experience

PURPOSE

The peri-infarct zone represents the morphologic substrate for reentry ventricular tachycardia after myocardial infarction, and its extent is a strong predictor of major cardiac events. Although delayed gadolinium enhancement magnetic resonance imaging (DGE-MRI) was shown to allow for detailed characterization of myocardial infarction by quantifying infarct core zone and peri-infarct zone volume, potentials of DGE-MRI for measuring changes in peri-infarct zone volume are unknown. Therefore, we aimed to assess changes in volume of the peri-infarct zone among patients with ischemic cardiomyopathy treated with chronic vasodilator therapy.

MATERIALS AND METHODS

Core and peri-infarct zone volumes as assessed with DGE-MRI were measured in 5 patients at baseline and after 6 months treatment with sustained-release dipyridamole.

RESULTS

Core zone volume remained stable during follow-up [median (range), 19 mL (9 to 42) vs. 16 mL (11 to 46); P=0.785]. The ratio between the peri-infarct zone and the core zone volume decreased significantly at 6 months compared with baseline [median (range), 0.22 (0.19 to 0.42) vs. 0.18 (0.09 to 0.32); P=0.043], and a trend toward reduction in peri-infarct zone volume was found [median (range), 5 mL (2 to 8) vs. 3 mL (2 to 6); P=0.059]. The peri-infarct zone volume decreased in all but 1 patient over the follow-up.

CONCLUSIONS

This initial experience suggests that reverse remodeling of the peri-infarct zone with reduction in peri-infarct zone volume may take place in patients with ischemic cardiomyopathy. Quantification of this process may be feasible with DGE-MRI, but further studies are needed to confirm this hypothesis and to further clarify the role of DGE-MRI for the assessment of changes in peri-infarct zone volume in patients with ischemic cardiomyopathy.

Myocardial infarction induces early increased remote ADAM8 expression of rat hearts after cardiac arrest

BACKGROUND

A disintegrin and metalloproteinase-8 (ADAM8) is a potential surrogate of inflammation which has recently been associated with myocardial infarction. We evaluated in a rat cardiac transplantation model whether ischemia-reperfusion injury alone (IRI) or with early regional myocardial infarction (MI) would suffice to induce inflammatory myocardial remodeling and ADAM8 expression.

MATERIAL AND METHODS

Isogenic heterotopic cardiac transplantation after cardiac arrest was performed to 48 Fischer 344 rats to induce ischemia-reperfusion injury (IRI), of which 27 rats also underwent ligation of the left anterior coronary artery (LAD) of the heart to yield MI. Histology was performed at 0.5, 24 and 48 h after transplantation. ADAM8 was evaluated by qRT-PCR after graft harvesting.

RESULTS

After 0.5 and 48 h respectively, edematous intramyocardial artery nuclei and periadventitial inflammation were more prominent in MI after transplantation, as compared with IRI alone and Controls (57.0 vs 40.0 and 5.0; 1.9 vs 1.1 and 0.9, point score units, p < 0.05, respectively). The expression of ADAM-8 was increased in MI as compared with Controls (1.9 vs 1.0, 1.9 fold increase) at 48 h. In grafts with MI, ADAM8 was localized using immunohistochemistry to the vicinity of the area corresponding to the developing infarction as well as in intramyocardial arteries remote to the infarction area.

CONCLUSIONS

Remote histopathological changes of ischemic cardiac grafts are associated with increased expression of ADAM8 thus emphasizing a global myocardial impact of MI.

Regional myocardial blood flow measured by stress multidetector computed tomography as a predictor of recovery of left ventricular function after coronary artery bypass grafting

BACKGROUND

Multidetector-row computed tomography (MDCT) applications have expanded to evaluation of myocardial blood flow (MBF) and viability. We quantified regional MBF pre- and post-coronary artery bypass grafting (CABG) using adenosine stress and cardiac 64-MDCT, and investigated whether the results predict MBF and left ventricular (LV) function recovery after CABG.

METHODS

We studied 321 regions in 19 CABG patients who underwent adenosine stress 64-row MDCT perfusion imaging and cine magnetic resonance imaging pre- and post-CABG. Myocardial blood flow was estimated from linear regression equation slopes using Patlak plot analyses and compared with LV function by measuring wall thickening (%WT) using cine magnetic resonance imaging.

RESULTS

Overall mean MBFs were 1.39 +/- 0.49 and 1.95 +/- 0.49 mL/(g min) pre- and post-CABG (P < .0001). Myocardial blood flow in revascularized areas increased significantly (pre-CABG 1.18 +/- 0.45, post-CABG 1.99 +/- 0.66 mL/[g min], P < .001), whereas nonischemic areas showed no difference (1.79 +/- 0.70 and 1.97 +/- 0.46 mL/[g min], P = .14). Revascularized areas with preoperative MBF > or = 0.9 mL/(g min) showed significantly greater MBF improvement than those with preoperative MBF <0.9 mL/(g min) (P = .04). In patients with preoperative LV dysfunction (ejection fraction <40%), %WT in revascularized areas with pre-CABG MBF > or = 0.9 mL/(g min) improved significantly after CABG (pre-%WT 40.9 +/- 22.9, post-%WT 52.8 +/- 20.6, P = .03) versus those with pre-CABG MBF <0.9 mL/(g min) (pre-%WT 53.2 +/- 35.5, post-%WT 42.5 +/- 17.0, P = .40).

CONCLUSIONS

Our results demonstrated more significantly increased MBF post-CABG than pre-CABG, particularly in revascularized areas. Regional MBF before CABG may predict MBF and LV function recovery, in the short term, after CABG.

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.

Chronic non-transmural infarction has a delayed recovery of function following revascularization

BACKGROUND

The time course of regional functional recovery following revascularization with regards to the presence or absence of infarction is poorly known. We studied the effect of the presence of chronic non-transmural infarction on the time course of recovery of myocardial perfusion and function after elective revascularization.

METHODS

Eighteen patients (mean age 69, range 52-84, 17 men) prospectively underwent cine magnetic resonance imaging (MRI), delayed contrast enhanced MRI and rest/stress 99m-Tc-tetrofosmin single photon emission computed tomography (SPECT) before, one and six months after elective coronary artery bypass grafting (CABG) or percutaneous coronary intervention (PCI).

RESULTS

Dysfunctional myocardial segments (n = 337/864, 39%) were classified according to the presence (n = 164) or absence (n = 173) of infarction. Infarct transmurality in dysfunctional segments was largely non-transmural (transmurality = 31 +/- 22%). Quantitative stress perfusion and wall thickening increased at one month in dysfunctional segments without infarction (p < 0.001), with no further improvement at six months. Despite improvements in stress perfusion at one month (p < 0.001), non-transmural infarction displayed a slower and lesser improvement in wall thickening at one (p < 0.05) and six months (p < 0.001).

CONCLUSIONS

Dysfunctional segments without infarction represent repetitively stunned or hibernating myocardium, and these segments improved both perfusion and function within one month after revascularization with no improvement thereafter. Although dysfunctional segments with non-transmural infarction improved in perfusion at one month, functional recovery was mostly seen between one and six months, possibly reflecting a more severe ischemic burden. These findings may be of value in the clinical assessment of regional functional recovery in the time period after revascularization.

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.

Early exercise training after myocardial infarction prevents contractile but not electrical remodelling or hypertrophy

AIMS

Exercise started early after myocardial infarction (MI) improves in vivo cardiac function and myofilament responsiveness to Ca(2+). We investigated whether this represents partial or complete reversal of cellular remodelling.

METHODS AND RESULTS

Mice with MI following left coronary ligation were given free access to a running wheel (MI(EXE), N = 22) or housed sedentary (MI(SED), N = 18) for 8 weeks and compared with sedentary sham-operated animals (SHAM, N = 11). Myocytes were enzymatically isolated from the non-infarcted left ventricle. Myocytes in MI were significantly longer and even more so with exercise (165 +/- 3 microm in MI(EXE) vs. 148 +/- 3 microm in MI(SED) and 136 +/- 2 microm in SHAM; P < 0.05, mean +/- SEM); cell width was not different. Contraction was measured during electrical field stimulation at 1, 2, and 4 Hz. Unloaded cell shortening was significantly reduced in MI(SED) (at 1 Hz, L/L(0)=4.4 +/- 0.3% vs. 6.7 +/- 0.4% in SHAM; P < 0.05, also at 2 and 4 Hz). Exercise restored cell shortening to SHAM values (MI(EXE), L/L(0)=6.4 +/- 0.5%). Membrane currents and [Ca(2+)](i) were measured via whole-cell patch clamping, with Fluo-3 as Ca(2+) indicator, all at 30 degrees C. Ca(2+) transient amplitude, I(CaL) and sarcoplasmic reticulum Ca(2+) content were not different between the three groups. Diastolic Ca(2+) levels at 4 Hz were significantly elevated in MI(SED) only, with a trend to increased spontaneous Ca(2+) release events (sparks). Action potential duration was increased and transient outward K(+) currents significantly reduced after MI; this was unaffected by exercise.

CONCLUSIONS

Early voluntary exercise training after MI restores cell contraction to normal values predominantly because of changes in the myofilament Ca(2+) response and has a beneficial effect on diastolic Ca(2+) handling. However, the beneficial effect is not a complete reversal of remodelling as hypertrophy and loss of repolarizing K(+) currents are not affected.

Re-expression of alpha skeletal actin as a marker for dedifferentiation in cardiac pathologies

Differentiation of foetal cardiomyocytes is accompanied by sequential actin isoform expression, i.e. down-regulation of the ‘embryonic’ alpha smooth muscle actin, followed by an up-regulation of alpha skeletal actin (αSKA) and a final predominant expression of alpha cardiac actin (αCA). Our objective was to detect whether re-expression of αSKA occurred during cardiomyocyte dedifferentiation, a phenomenon that has been observed in different pathologies characterized by myocardial dysfunction. Immunohistochemistry of αCA, αSKA and cardiotin was performed on left ventricle biopsies from human patients after coronary bypass surgery. Furthermore, actin isoform expression was investigated in left ventricle samples of rabbit hearts suffering from pressure- and volume-overload and in adult rabbit ventricular cardiomyocytes during dedifferentiation in vitro. Atrial goat samples up to 16 weeks of sustained atrial fibrillation (AF) were studied ultrastructurally and were immunostained for αCA and αSKA. Up-regulation of αSKA was observed in human ventricular cardiomyocytes showing down-regulation of αCA and cardiotin. A patchy re-expression pattern of αSKA was observed in rabbit left ventricular tissue subjected to pressure- and volume-overload. Dedifferentiating cardiomyocytes in vitro revealed a degradation of the contractile apparatus and local re-expression of αSKA. Comparable αSKA staining patterns were found in several areas of atrial goat tissue during 16 weeks of AF together with a progressive glycogen accumulation at the same time intervals. The expression of αSKA in adult dedifferentiating cardiomyocytes, in combination with PAS-positive glycogen and decreased cardiotin expression, offers an additional tool in the evaluation of myocardial dysfunction and indicates major changes in the contractile properties of these cells.

Hibernating myocardium: pathophysiology, diagnosis, and treatment

Comprehensive management of patients with chronic ischemic disease is a critically important component of clinical practice. Cardiac myocytes have the potential to adapt to limited flow conditions by adjusting contractile function, reducing metabolism, conserving resources, and preserving myocardial integrity to cope with an oxygen and (or) nutrition shortage. A prime metabolic feature of cardiac myocytes affected by chronic ischemia is the return to a fetal gene pattern with predominance of carbohydrates as the substrate for energy. Structural adaptation with multiple intracellular changes is part of the remodeling process in hibernating myocardium. Transmural heterogeneity, which defines the pattern of injury in ventricular cardiomyocytes and the response to chronic ischemia, is a multifactorial process originating from functional, metabolic, and flow differences in subendocardial and subepicardial regions. Autophagy is typically activated in hibernating myocardium and has been identified as a prosurvival mechanism. Chronic ischemia is associated with changes in the number, size, and distribution of gap junctions and may give rise to conduction disturbances and arrhythmogenesis. Differentiation between viable and nonviable myocardium by assessing sensitivity of inotropic reserve is a crucial diagnostic tool that is correlated with the prognosis and outcome for improved contractility after restoration of blood perfusion in afflicted myocardium.Reliable and accurate diagnosis of ischemic, scar, and viable tissues is critical for recover strategies. Although early surgical reinstitution of blood flow is most effective in restoring physiologic function of the hibernating myocardium, several new approaches offer promising alternatives. Among others, vascular endothelial growth factor and fibroblast growth factor-2 (FGF-2), especially its lo-FGF-2 isoform, have been shown to be effective in rapid neovascularization. Substances such as statins, resveratrol, some hormones, and omega-3 fatty acids can improve recovery effect in chronically underperfused hearts. For patients with drug-refractory ischemia, intramyocardial transplantation of stem cells into predefined areas of the heart can enhance vascularization and have beneficial effects on cardiac function. This review of ischemic injury, its heterogeneity, accurate diagnosis, and newer methods of treatment, shows there is much information and tremendous hope for better management of patients with coronary heart disease.

Influence of coronary artery stenosis severity and coronary collateralization on extent of chronic myocardial scar: insights from quantitative coronary angiography and delayed-enhancement MRI

Objectives:

In patients with chronic ischemic heart disease, the relationship between coronary artery lesion severity and myocardial scarring is unknown.The purpose of this study was to examine the relationship between proximal coronary artery stenosis severity, the amount of coronary collateralization, and myocardial scar extent in the distal distribution of the affected coronary artery based on both quantitative coronary angiography (QCA) and delayed-enhancement magnetic resonance imaging (DE–MRI).

Methods:

Thirty-four patients (26 males, 8 females; age range: 35-86 years) with a coronary artery containing a single, proximal stenosis ≥30% by quantitative coronary angiography (QCA) underwent DE-MRI. The relationship between stenosis severity, collateralization, and myocardial scar morphology (area, transmurality and patchiness) was examined using linear mixed-model ANCOVA.

Results:

There was a statistically significant correlation between stenosis severity and scar extent (r=0.53, p<0.01). Patients with hemodynamically significant stenoses (≥70%) exhibited significantly greater collateralization (p<0.05) and scar extent (p<0.01) than patients with <70% stenosis. However, scarring was often found in patients with stenoses <70%. Also, greater stenosis severity (93±14%) and mean scar extent (41±35%) were found in patients with collaterals than in patients without collaterals (diameter stenosis 48±10%, p<0.01) (scar extent 19±29%, p=0.01).

Conclusions:

Using QCA and DE-MRI, we demonstrate a significant relationship between coronary artery stenosis severity and myocardial scar extent, in the absence of a documented history of acute infarction. The relationship likely reflects increasing ischemia leading to scar formation in the range of angiographically significant stenosis. However, in the absence of collateralization, scar was observed without significant stenosis, especially in females.

Cardiotin localization in mitochondria of cardiomyocytes in vivo and in vitro and its down-regulation during dedifferentiation

BACKGROUND

Cardiotin expression is observed in adult cardiac tissue. In the present study, we provide evidence for the specific localization of cardiotin in cardiac mitochondria and for its down-regulation during adaptive remodeling (dedifferentiation) of cardiomyocytes.

METHODS

Immunocytochemistry was used to study cardiotin localization in adult rabbit papillary muscle, in late-stage embryonic rabbit left ventricular tissue, and in left ventricle samples of rabbits suffering from pressure and volume overload. Western blot analysis of cardiotin was performed in purified pig heart mitochondrial fractions. Cardiotin expression was monitored in vitro in isolated adult rat and rabbit left ventricular cardiomyocytes.

RESULTS

Western blot analysis revealed the presence of cardiotin in the mitochondrial fractions of pig heart. Immunoelectron microscopy confirmed the presence of cardiotin in cardiac mitochondria of normal adult rabbits both in vivo and in vitro. Quantification of the localization of immunogold particles suggests an association of cardiotin with the mitochondrial inner membrane. Cardiotin expression is initiated in late-stage embryonic rabbit heart, whereas in adult ventricular tissue cardiotin clearly stained longitudinal arrays of mitochondria. Pressure- and volume-overloaded myocardium showed a reduction in cardiotin expression in dispersed local myocardial areas. Cell cultures of adult cardiomyocytes showed a gradual loss in cardiotin expression in parallel with a sarcomeric remodeling.

CONCLUSIONS

Our results demonstrate the specific localization of cardiotin in adult cardiomyocyte mitochondria and propose its use as an early marker for cardiomyocyte adaptive remodeling and dedifferentiation.

Hibernating myocardium: diagnosis and patient outcomes

Approximately 50% of the patients with chronic obstructive coronary artery disease resulting in chronic contractile dysfunction have hibernating myocardium and may benefit from revascularization. This pooled analysis describes the relative merits of dobutamine echocardiography, thallium-201 and technetium-99m scintigraphy, positron emission tomography, and magnetic resonance imaging, for the diagnosis of hibernating myocardium and prediction of patient outcomes.

Structural remodelling of cardiomyocytes in the border zone of infarcted rabbit heart

Cardiomyocyte dedifferentiation, as detected in hibernating myocardium of chronic ischemic patients, is one of the characteristics seen at the border of myocardial infarcts in small and large animals. Our objectives were to study in detail the morphological changes occurring at the border zone of a rabbit myocardial infarction and its use as model for hibernating myocardium. Ligation of the left coronary artery (LAD) was performed on rabbit hearts and animals were sacrificed at 2, 4, 8 and 12 weeks post-infarction. These hearts together with a non-infarcted control heart were perfusion-fixed and tissue samples were embedded in epoxy resin. Hibernating cardiomyocytes were mainly distributed in the non-infarcted region adjacent to the border zone of infarcted myocardium but only in a limited number. In the border zone itself vacuolated cardiomyocytes surrounded by fibrotic tissue were frequently observed. Ultrastructural analysis of these vacuolated cells revealed the presence of a basal lamina inside the vacuoles adjacent to the surrounding membrane, the presence of pinocytotic vesicles and an association with cisternae of the sarcoplasmatic reticulum. Myocyte quantitative analyses revealed a gradual increase in vacuolar area/total cell area ratio and in collagen fibril deposition inside the vacuoles from 2 to 12 weeks post-infarction. Related to the remote zone, the increase in cell width of myocytes located in and adjacent to the border zone demonstrated cellular hypertrophy. These results indicate the occurrence of cardiomyocyte remodelling mechanisms in the border zone and adjacent regions of infarcted myocardium. It is suggested that the vacuoles represent plasma membrane invaginations and/or dilatations of T-tubular structures.

Relevance of apoptosis in influencing recovery of hibernating myocardium

BACKGROUND

Hibernating myocardium (HM) is viable but dysfunctional myocardium which can recover following revascularization. Myocyte necrosis is virtually absent in HM; however, cellular loss may take place by apoptosis, although this is controversial.

AIM

To assess the presence of apoptosis and its relevance in HM.

METHODS

During coronary artery by-pass surgery (CABG), 21 patients underwent transmural biopsy in the dysfunctional left anterior descending artery tributary area of the left ventricle (LV), with kinetic recovery at follow-up, thus fulfilling the HM criteria. All patients underwent echocardiographic follow-up at 12 months. All biopsies were evaluated by light microscopy, electron microscopy (EM), and molecular analysis.

RESULTS

All biopsies were structurally altered, showing increased fibrosis and myocytes with variable size. Myocyte dedifferentiation was not detected by immunohistochemistry or EM. On stepwise linear regression, 1 year LVEF was predicted by the apoptotic index (beta=-0.973, p=0.002), the normotrophic cell percentage (beta=0.449, p=0.038), and mean fibrosis (beta=-0.412, p=0.51).

CONCLUSIONS

Our biopsy study detected a wide range of morphological substrate heterogeneity in HM with degenerative features. We have demonstrated for the first time in humans that myocyte apoptosis is an important phenomenon in HM, negatively influencing LV functional recovery after CABG.

Assessment of myocardial viability by radionuclide and echocardiographic techniques: is it simply a sensitivity and specificity issue?

PURPOSE OF REVIEW

The assessment of myocardial viability provides important information that may guide therapeutic decisions in patients with coronary artery disease and left ventricular dysfunction. This review describes methods for assessing myocardial viability using single-photon emission computed tomography, with an emphasis on how to optimize the detection of viable myocardium using current techniques. Relevant comparisons of radionuclide techniques with echocardiographic methods are also discussed.

RECENT FINDINGS

The basis for the assessment of myocardial viability using radionuclides is reviewed briefly. Radionuclide techniques provide important prognostic information that may affect the decision on if patients with coronary artery disease should be revascularized or treated medically. Data suggest that dobutamine stress echocardiography may underestimate viability in certain patients. Radionuclide techniques that assess both radiotracer uptake and ventricular function can provide a comprehensive approach to detect viable myocardium in most patients.

SUMMARY

The methods for assessing myocardial viability using single-photon emission computed tomography are accurate, reproducible, and widely available. Viability testing should be considered in patients with known coronary artery disease and left ventricular dysfunction. Further studies are warranted to assess the affect of viability assessment on clinical outcomes.