Pathophysiological mechanisms of chronic reversible left ventricular dysfunction due to coronary artery disease (hibernating myocardium)

Clinical impact of multimodality assessment of myocardial viability

Coronary artery disease (CAD) is a prevalent cause of left ventricular dysfunction. Nevertheless, effective elective revascularization, particularly surgical revascularization, can enhance long-term outcomes and, in selected cases, global left ventricular contractility. The assessment of myocardial viability and scars is still relevant in guiding treatment decisions and selecting patients who are likely to benefit most from blood flow restoration. Although the most recent randomized studies challenge the notion of "hibernating myocardium" and the clinical usefulness of assessing myocardial viability, the advancement of imaging techniques still renders this assessment valuable in specific situations. According to the guidelines of the European Society of Cardiology, non-invasive stress imaging may be employed to define myocardial ischemia and viability in patients with CAD and heart failure before revascularization. Currently, several non-invasive imaging techniques are available to evaluate the presence and extent of viable myocardium. The selection of the most suitable technique should be based on the patient, clinical context, and resource availability. This narrative review evaluates the characteristics of available imaging modalities for assessing myocardial viability to determine the most appropriate therapeutic strategy.

Coronary Chronic Total Occlusion Revascularization: When, Who and How?

Coronary chronic total occlusions (CTO) are an increasingly frequent entity in clinical practice and represent a challenging percutaneous coronary intervention (PCI) scenario. Despite data from randomized trials that have not yet demonstrated a clear benefit of CTO recanalization, the widespread of CTO-PCI has substantially increased. The improvement in operators' techniques, equipment, and training programs has led to an improvement in the success rate and safety of these procedures, which will represent an important field of future development of PCI. The present review will summarize clinical outcomes and technical and safety issues of CTO revascularization with the aim to guide clinical daily cath-lab practice.

Evaluation and management of patients with coronary chronic total occlusions considered for revascularisation. A clinical consensus statement of the European Association of Percutaneous Cardiovascular Interventions (EAPCI) of the ESC, the European Association of Cardiovascular Imaging (EACVI) of the ESC, and the ESC Working Group on Cardiovascular Surgery

Chronic total occlusions (CTOs) of coronary arteries can be found in the context of chronic or acute coronary syndromes; sometimes they are an incidental finding in those apparently healthy individuals undergoing imaging for preoperative risk assessment. Recently, the invasive management of CTOs has made impressive progress due to sophisticated preinterventional assessment, including advanced non-invasive imaging, the availability of novel and dedicated tools for CTO percutaneous coronary intervention (PCI), and experienced interventionalists working in specialised centres. Thus, it is crucial that referring physicians who see patients with CTO be aware of recent developments and of the initial evaluation requirements for such patients. Besides a careful history and clinical examination, electrocardiograms, exercise tests, and non-invasive imaging modalities are important for selecting the patients most suitable for CTO PCI, while others may be referred to coronary artery bypass graft or optimal medical therapy only. While CTO PCI improves angina and reduces the use of antianginal drugs in patients with symptoms and proven ischaemia, hibernation and/or wall motion abnormalities at baseline or during stress, the effect of CTO PCI on major cardiovascular events is still controversial. This clinical consensus statement specifically focuses on referring physicians, providing a comprehensive algorithm for the preinterventional evaluation of patients with CTO and the current evidence for the clinical effectiveness of the procedure. The proposed care track has been developed by members and with the support of the European Association of Percutaneous Cardiovascular Interventions (EAPCI), the European Association of Cardiovascular Imaging (EACVI), and the European Society of Cardiology (ESC) Working Group on Cardiovascular Surgery.

Procedures for chronic total occlusion: when are they recommended and when not

Coronary chronic total occlusion (CTO) produces an important clinical problem, often treated with medical therapy or coronary artery bypass grafting. Recent clinical studies, both registries and randomized trials, demonstrated that percutaneous coronary interventions (PCI), could provide a valid therapeutic option. Nonetheless, significant reduction in all-cause mortality, cardiac mortality, myocardial infarction, MACE, and MACCE has not been demonstrated in the subgroups analysis of randomized trials. These analyses suggest that PCI for CTO should be reserved for patients with angina or with large areas of the myocardium with reversible ischaemia. Large randomized studies should search for a personalized approach, considering the risks and complexity of PCI in CTO, which should mainly consider the extension of the ischaemia and the viability of the myocardium.

Rationale and design of the SYNTAX II trial evaluating the short to long-term outcomes of state-of-the-art percutaneous coronary revascularisation in patients with de novo three-vessel disease

AIMS

The applicability of the results of the SYNTAX trial comparing percutaneous coronary intervention (PCI) using first-generation drug-eluting stents (DES) with coronary artery bypass graft (CABG) surgery for the treatment of patients with complex coronary artery disease (CAD) has been challenged by recent major technical and procedural developments in coronary revascularisation. Functional assessment of coronary lesions has contributed to marked improvements in both safety and efficacy of DES implantation. In addition, the recent development of the SYNTAX score II, a clinical tool based on anatomical and clinical factors, allows individualised objective decision making regarding the optimal revascularisation modality in patients with complex CAD. The ongoing SYNTAX II trial is currently evaluating the effectiveness of the clinical and technological advances in the treatment of patients with complex (de novo three-vessel) CAD.

METHODS AND RESULTS

The SYNTAX II trial is a multicentre, all-comers, open-label, single-arm trial aiming to recruit 450 patients with de novo three-vessel CAD in approximately 25 European interventional cardiology centres. All patients will be selected and treated following the SYNTAX II strategy, which includes: a) establishing the appropriateness of revascularisation utilising the SYNTAX score II as a clinical tool to allow objective decision making by the Heart Team, b) ischaemia-driven revascularisation based on functional intracoronary assessment, c) implantation of the new-generation everolimus-eluting platinum chromium coronary stent with thin struts and abluminal bioabsorbable polymer coating to promote rapid vessel healing, d) intravascular ultrasound-guided DES implantation, and e) treatment at centres with expertise in CTO recanalisation. The primary endpoint is a composite of the major adverse cardiac and cerebral events (MACCE) rate at one-year follow-up compared to the historical PCI arm of the SYNTAX trial. An exploratory endpoint will be MACCE at five-year follow-up compared to the historical surgical arm of the SYNTAX trial.

CONCLUSIONS

The SYNTAX II trial will provide valuable information on outcomes of state-of-the-art PCI for the contemporary management of complex (de novo three-vessel) CAD. SYNTAX II will be of critical value in the design of future trials in this arena.

The Role of Ivabradine in the Management of Angina Pectoris

Stable angina pectoris affects 2–4 % of the population in Western countries and entails an annual risk of death and nonfatal myocardial infarction of 1–2 % and 3 %, respectively. Heart rate (HR) is linearly related to myocardial oxygen consumption and coronary blood flow, both at rest and during stress. HR reduction is a key target for the prevention of ischemia/angina and is an important mechanism of action of drugs which are recommended as first line therapy for the treatment of angina in clinical guidelines. However, many patients are often unable to tolerate the doses of beta blocker or non-dihydropyridine calcium antagonists required to achieve the desired symptom control. The selective pacemaker current inhibitor ivabradine was developed as a drug for the management of patients with angina pectoris, through its ability to reduce HR specifically. The available data suggest that ivabradine is a well-tolerated and effective anti-anginal agent and it is recommended as a second-line agent for relief of angina in guidelines. However, recent clinical trials of ivabradine have failed to show prognostic benefit and have raised potential concerns about safety. This article will review the available evidence base for the current role of ivabradine in the management of patients with symptomatic angina pectoris in the context of stable coronary artery disease.

Reperfusion Damage - A Story of Success, Failure, and Hope

Tissue salvage of severely ischemic myocardium requires timely reperfusion by thrombolysis, angioplasty, or bypass. However, recovery of left ventricular function is rare. It may be absent or, even worse, reperfusion can induce further damage. Laboratory studies have shown convincingly that reperfusion can increase injury over and above that attributable to the pre-existing ischemia, precipitating arrhythmias, suppressing the recovery of contractile function ("stunning") and possibly even causing cell death in potentially salvable ischemic tissue. The mechanisms of reperfusion injury have been widely studied and, in the laboratory, it can be attenuated or prevented. Disappointingly, this is not the case in the clinic, particularly after thrombolysis or primary angioplasty. In contrast, excellent results have been achieved by surgeons by means of cardioplegia and hypothermia. For the interventionist, the issue is more complex as, contrary to cardiac surgery where the cardioplegia can be applied before ischemia and the heart can be stopped, during an angioplasty the heart still has to beat to support the circulation. We analyze in detail all these issues.

Altered right ventricular function in the long-term follow-up evaluation of patients after delayed aortic reimplantation of the anomalous left coronary artery from the pulmonary artery

This study aimed to evaluate regional and global ventricular functions in the long term after aortic reimplantation of the anomalous left coronary artery from the pulmonary artery (ALCAPA) and to assess whether the time of surgical repair influences ventricular performance.The study examined 20 patients with a median age of 15 years (range 3-37 years) who had a corrected ALCAPA and 20 age-matched control subjects using echocardiography and tissue Doppler imaging (TDI). The median follow-up period after corrective surgery was 6 years (range 2.6-15 years). Seven patients underwent surgery before the age of 3 years (early-surgery group), whereas 13 patients had surgery after that age (late-surgery group). The TDI-derived myocardial strain of the interventricular septum (IVS), lateral wall of the left ventricle (LV), and lateral wall of the right ventricle (RV) in the basal and mid regions were examined, and a mean was calculated. The pulsed Doppler-derived Tei index was used to assess global left ventricular function. No significant differences were found between the early-surgery group and the control group regarding the regional myocardial strain or the Tei index. Compared with the early-surgery group, the late-surgery group had a significantly higher Tei index (mean 0.37; range 0.31-0.42 vs. mean 0.52; range 0.39-0.69; p < 0.005), a lower strain percentage of the lateral wall of the LV (mean 29; range 17-30 vs. mean 9; range 7-23), IVS (mean 23; range 21-31 vs. mean 19; range 13-25), and lateral wall of the RV (mean 23; range 21-31 vs. mean 19; range 13-25). The age at operation correlated significantly with the Tei index (r = 0.84, p < 0.001) and inversely with the mean strain of the lateral wall of the LV (r = -0.53, p = 0.028), IVS (r = -0.68, p = 0.003), and lateral wall of the RV (r = -0.68, p = 0.003). At the midterm follow-up evaluation after corrective surgery of ALCAPA, not only the left but also the right ventricular function seemed to be affected in patients with delayed diagnosis and late surgical repair but preserved among the younger patients with early diagnosis and corrective surgery.

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.

Anti-inflammatory and pro-angiogenic effects of beta blockers in a canine model of chronic ischemic cardiomyopathy: comparison between carvedilol and metoprolol

There is controversy regarding the superiority of carvedilol (C) over metoprolol (M) in congestive heart failure. We hypothesized that C is superior to M in chronic ischemic cardiomyopathy because of its better anti-inflammatory and pro-angiogenic effects. In order to test our hypothesis we used a chronic canine model of multivessel ischemic cardiomyopathy where myocardial microcatheters were placed from which interstitial fluid was collected over time to measure leukocyte count and cytokine levels. After development of left ventricular dysfunction, the animals were randomized into four groups: sham (n = 7), placebo (n = 8), M (n = 11), and C (n = 10), and followed for 3 months after treatment initiation. Tissue was examined for immunohistochemistry, oxidative stress, and capillary density. At 3 months both rest and stress wall thickening were better in C compared to the other groups. At the end of 3 months of treatment end-systolic wall stress also decreased the most in C. Similarly resting myocardial blood flow (MBF) improved the most in C as did the stress endocardial/epicardial MBF. Myocardial interstitial fluid showed greater attenuation of leukocytosis with C compared to M, which was associated with less fibrosis and oxidative stress. C also had higher IL-10 level and capillary density. In conclusion, in a chronic canine model of multivessel ischemic cardiomyopathy we found 3 months of C treatment resulted in better resting global and regional function as well as better regional function at stress compared to M. These changes were associated with higher myocardial levels of the anti-inflammatory cytokine IL-10 and less myocardial oxidative stress, leukocytosis, and fibrosis. Capillary density and MBF were almost normalized. Thus in the doses used in this study, C appears to be superior to M in a chronic canine model of ischemic cardiomyopathy from beneficial effects on inflammation and angiogenesis. Further studies are required for comparing additional doses of these drugs.

Metabolomic analysis of two different models of delayed preconditioning

Recently we described an ischemic preconditioning induced by repetitive coronary stenosis, which is induced by 6 episodes of non-lethal ischemia over 3 days, and which also resembles the hibernating myocardium phenotype. When compared with traditional second window of ischemic preconditioning using cDNA microarrays, many genes which differed in the repetitive coronary stenosis appeared targeted to metabolism. Accordingly, the goal of this study was to provide a more in depth analysis of changes in metabolism in the different models of delayed preconditioning, i.e., second window and repetitive coronary stenosis. This was accomplished using a metabolomic approach based on liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) techniques. Myocardial samples from the ischemic section of porcine hearts subjected to both models of late preconditioning were compared against sham controls. Interestingly, although both models involve delayed preconditioning, their metabolic signatures were radically different; of the total number of metabolites that changed in both models (135 metabolites) only 7 changed in both models, and significantly more, p<0.01, were altered in the repetitive coronary stenosis (40%) than in the second window (8.1%). The most significant changes observed were in energy metabolism, e.g., phosphocreatine was increased 4 fold and creatine kinase activity increased by 27.2%, a pattern opposite from heart failure, suggesting that the repetitive coronary stenosis and potentially hibernating myocardium have enhanced stress resistance capabilities. The improved energy metabolism could also be a key mechanism contributing to the cardioprotection observed in the repetitive coronary stenosis and in hibernating myocardium. This article is part of a Special Issue entitled "Focus on Cardiac Metabolism".

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.

Radionuclide imaging in stage B heart failure

This article discusses currently available radionuclide techniques in the diagnostic and prognostic evaluation of patients with chronic heart failure, with a focus on stage B/asymptomatic left ventricular dysfunction. Radionuclide imaging is promising for such patients because it can simultaneously determine left ventricular function, evaluate for the presence of obstructive coronary disease, determine the extent of viable myocardium, and evaluate dyssynchronous left ventricular contraction. Radionuclide imaging can thus provide important noninvasive insights into the pathophysiology, prognosis, and management of patients with asymptomatic left ventricular dysfunction as well as more advanced heat failure.

Prevalence of scarred and dysfunctional myocardium in patients with heart failure of ischaemic origin: a cardiovascular magnetic resonance study

BACKGROUND

Cardiovascular magnetic resonance (CMR) with late gadolinium enhancement (LGE) can provide unique data on the transmural extent of scar/viability. We assessed the prevalence of dysfunctional myocardium, including partial thickness scar, which could contribute to left ventricular contractile dysfunction in patients with heart failure and ischaemic heart disease who denied angina symptoms.

METHODS

We invited patients with ischaemic heart disease and a left ventricular ejection fraction < 50% by echocardiography to have LGE CMR. Myocardial contractility and transmural extent of scar were assessed using a 17-segment model.

RESULTS

The median age of the 193 patients enrolled was 70 (interquartile range: 63-76) years and 167 (87%) were men. Of 3281 myocardial segments assessed, 1759 (54%) were dysfunctional, of which 581 (33%) showed no scar, 623 (35%) had scar affecting ≤50% of wall thickness and 555 (32%) had scar affecting > 50% of wall thickness. Of 1522 segments with normal contractile function, only 98 (6%) had evidence of scar on CMR. Overall, 182 (94%) patients had ≥1 and 107 (55%) patients had ≥5 segments with contractile dysfunction that had no scar or ≤50% transmural scar suggesting viability.

CONCLUSIONS

In this cohort of patients with left ventricular systolic dysfunction and ischaemic heart disease, about half of all segments had contractile dysfunction but only one third of these had > 50% of the wall thickness affected by scar, suggesting that most dysfunctional segments could improve in response to an appropriate intervention.

Use of an intracoronary Doppler guidewire for evaluation of coronary hemodynamics in the porcine model of acute hibernating myocardium during dobutamine stress tests

PURPOSE

To determine the coronary hemodynamic characteristics of acute hibernating myocardium (AHM), evaluate the changes in coronary hemodynamics during dobutamine infusion, and investigate the mechanisms by which dobutamine stress echocardiography (DSE) detects AHM.

METHODS

The porcine model of acute hibernating myocardium was created in 10 animals, all of which underwent DSE with doses of 0-40 μg/kg/min. Myocardial segments abnormality was used as a DSE criterion for evaluating AHM. An intracoronary Doppler guidewire was used to measure the coronary hemodynamics; electrocardiography and systemic hemodynamics were recorded simultaneously. The ischemic regions of myocardium were reperfused, and all variables were recorded. Finally, the animals were euthanized and pathologic changes in the heart tissue were documented.

RESULTS

There was no myocardium necrosis. There were 55 myocardial segments with abnormal DSE responses after stenosis, among which 41 segments were judged as AHM because of a biphasic response. Average peak velocity (APV) and coronary flow velocity reserve were improved during DSE. Coronary and systemic hemodynamics were increased during dobutamine infusion. There were significant differences for APV at all evaluated doses and for heart rate blood pressure product at higher doses. The difference between APV resting values and the values for peak dosage (ΔAPV) correlated with the amount of AHM during DSE. Coronary volume blood flow and coronary flow velocity reserve decreased after stenosis.

CONCLUSIONS

ΔAPV may reflect the number of hibernating segments. The relative imbalance between blood supply and oxygen consumption in regional myocardium may be one of the mechanisms by which DSE detects AHM.

Radionuclide Imaging of Viable Myocardium: Is it Underutilized?

Coronary artery disease is the major cause of heart failure in North America. Viability assessment is important as it aims to identify patients who stand to benefit from coronary revascularization. Radionuclide modalities currently used in the assessment of viability include (201)Tl SPECT, (99m)Tc-based SPECT imaging, and (18)F-fluorodexoyglucose ((18)F-FDG)-PET imaging. Different advances have been made in the last year to improve the sensitivity and specificity of these modalities. In addition, the optimum amount of viable (yet dysfunctional) myocardium is important to identify in patients, as a risk-benefit ratio must be considered. Patients with predominantly viable/hibernating myocardium can benefit from revascularization from a mortality and morbidity standpoint. However, in patients with minimal viability (predominantly scarred myocardium), revascularization risk may certainly be too high to justify revascularization without expected benefit. Understanding different radionuclide modalities and new developments in the assessment of viability in ischemic heart failure patients is the focus of this discussion.

Tracing cardiac metabolism in vivo: one substrate at a time

In the myocardial cell, a series of enzyme-catalyzed reactions results in the efficient transfer of chemical energy into mechanical energy. The goals of this article are to emphasize the ability of noninvasive imaging techniques using isotopic tracers to detect the metabolic footprints of heart disease and to propose that cardiac metabolic imaging is more than a useful adjunct to current myocardial perfusion imaging studies. A strength of metabolic imaging is in the assessment of regional myocardial differences in metabolic activity, probing for 1 substrate at a time. We hope that new and developing methods of cardiac imaging will lead to the earlier detection of heart disease and improve the management and quality of life for patients afflicted with ischemic and nonischemic heart muscle disorders.

The assessment of myocardial viability and hibernation using resting thallium imaging

Rest-redistribution thallium-201 imaging is widely used to assess recovery of regional systolic dysfunction in patients with chronic coronary artery disease. In several studies, this technique has demonstrated very high sensitivity but reduced specificity, as reported in general for radionuclide imaging. In clinical terms, this implicates that many dysfunctional territories will not recover after revascularization despite a substantial amount of tracer uptake. Yet, the amount of tracer uptake in a given myocardial segment, although not perfect, remains the best indicator for predicting reversible dysfunction. In fact, the occurrence of redistribution after rest injection is not very common and it does not substantially contribute to the accuracy of the test. However, it is still undetermined whether the presence of redistribution is relevant for prognostic implications.

Radionuclide imaging in ischaemic heart failure

INTRODUCTION OR BACKGROUND

Many tests are available for the investigation of patients with heart failure. The identification of the underlying aetiology of ventricular dysfunction is crucial as early treatment may limit or even reverse myocardial abnormalities.

SOURCES OF DATA

This article describes cardiac radionuclide imaging techniques and their applications in ischaemic ventricular dysfunction. Evidence for the role of these techniques is summarized with particular reference to current guidelines.

AREAS OF AGREEMENT

Both positron emission tomography (PET) and single photon emission computed tomography (SPECT) techniques are widely validated for the detection of myocardial viability and their use is recommended in both national and international guidelines.

AREAS OF CONTROVERSY

Although assessments of ventricular phase and myocardial innervation hold promise for the stratification of patients to cardiac resynchronization therapy, the poor performance of echocardiographic predictors of response in the recently published PROSPECT trial suggest that these techniques face a tough challenge.

GROWING POINTS

The use of integrated multimodality imaging techniques such as PET/computed tomography to assess for ischaemic causes of left ventricular dysfunction is an area that is currently under investigation, as is the role of nuclear techniques in the assessment of stem cell retention, distribution and function when used in patients with heart failure.

AREAS TIMELY FOR DEVELOPING RESEARCH

Ongoing developments in radionuclide molecular imaging for assessment of angiogenesis, apoptosis and interstitial alterations during cardiac remodeling may have important implications for the prognosis and treatment of patients with heart failure.

Sickness behaviour pushed too far--the basis of the syndrome seen in severe protozoal, bacterial and viral diseases and post-trauma

Certain distinctive components of the severe systemic inflammatory syndrome are now well-recognized to be common to malaria, sepsis, viral infections, and post-trauma illness. While their connection with cytokines has been appreciated for some time, the constellation of changes that comprise the syndrome has simply been accepted as an empirical observation, with no theory to explain why they should coexist. New data on the effects of the main pro-inflammatory cytokines on the genetic control of sickness behaviour can be extended to provide a rationale for why this syndrome contains many of its accustomed components, such as reversible encephalopathy, gene silencing, dyserythropoiesis, seizures, coagulopathy, hypoalbuminaemia and hypertriglyceridaemia. It is thus proposed that the pattern of pathology that comprises much of the systemic inflammatory syndrome occurs when one of the usually advantageous roles of pro-inflammatory cytokines – generating sickness behaviour by moderately repressing genes (Dbp, Tef, Hlf, Per1, Per2 and Per3, and the nuclear receptor Rev-erbα) that control circadian rhythm – becomes excessive. Although reversible encephalopathy and gene silencing are severe events with potentially fatal consequences, they can be viewed as having survival advantages through lowering energy demand. In contrast, dyserythropoiesis, seizures, coagulopathy, hypoalbuminaemia and hypertriglyceridaemia may best be viewed as unfortunate consequences of extreme repression of these same genetic controls when the pro-inflammatory cytokines that cause sickness behaviour are produced excessively. As well as casting a new light on the previously unrationalized coexistence of these aspects of systemic inflammatory diseases, this concept is consistent with the case for a primary role for inflammatory cytokines in their pathogenesis across this range of diseases.

Cardioprotection in stunned and hibernating myocardium

Although myocardial ischemia was once thought to result in irreversible cellular damage, it is now demonstrated that in cardiac tissue, submitted to the stress of oxygen and substrate deprivation, endogenous mechanisms of cell survival may be activated. These molecular mechanisms result in physiological conditions of adaptation to ischemia, known as myocardial stunning and hibernation. These conditions result from a switch in gene and protein expression, which sustains cardiac cell survival in a context of oxygen deprivation and during the stress of reperfusion. The pattern of cell survival elicited by ischemia in myocardial stunning or hibernation results in the activation of cytoprotective mechanisms that will protect the heart against further ischemic damage, a condition referred to as ischemic preconditioning. The basic mechanisms underlying stunning and hibernation are still a matter of intense research, which includes the discovery and characterization of novel survival genes not described in the heart before, or the unraveling of new cellular processes, such as autophagy. Understanding how the molecular adaptation of the cardiac myocyte during stress sustains its survival in these conditions therefore might help defining novel mechanisms of endogenous myocardial salvage, in order to expand the conditions of maintained cellular viability and functional salvage of the ischemic myocardium.

Role of nuclear cardiology in advancing cardiac surgery

Cardiac surgeons are commonly faced with issues regarding the balance between the potential risk and the potential benefit of a surgical procedure. Nuclear cardiology procedures [myocardial perfusion SPECT (MPS) and positron emission tomography (PET)] provide the surgeon with objective information that augments standard clinical and angiographic assessments with respect to diagnosis, prognosis, and potential benefit from intervention. Development of the technology and methodology of gated MPS acquisition and interpretation allows assessment of the extent and severity of hypoperfused but viable myocardium, as well as global LVEF and LV volume measurements, diastolic function, and LV geometry. With PET, myocardial metabolism and blood flow reserve can also be measured. This chapter provides insight into the current evidence regarding settings in which nuclear cardiology procedures are helpful to the surgeon in assessment of patients having or being considered for cardiac surgery in the setting of coronary artery disease (CAD). Overall, a risk-benefit approach to MPS results is proposed, with principal focus on identifying patients at risk for major cardiac events who may benefit from a surgical procedure.

Principal strain orientation in the normal human left ventricle

BACKGROUND

Methods that can improve the accuracy of application of directed intervention in the treatment of coronary artery disease deserve investigation. Magnetic resonance imaging with tissue tagging allows for noninvasive, quantitative determination of regionally varying minimum principal strain. Because the directional vector of minimum principal strain has been shown to be sensitive to ischemic involvement, my colleagues and I sought to fully characterize the normal range of vector direction in the in vivo human left ventricle at rest and during inotropic stimulation.

METHODS

Tagged magnetic resonance imaging image sets were acquired in 20 healthy volunteers at rest and during dobutamine infusion. Strain was computed from the measured displacement data by using finite element software. Orientation of minimum principal strain was characterized by measuring the angle (principal strain angle) between the minimum principal strain vector and the local circumferential-longitudinal plane. Values of this angle were computed in 6 ventricular regions and globally.

RESULTS

Resting values of the principal strain angle were small in every region, confirming that maximal normal myocardial contraction occurs primarily in the circumferential-longitudinal plane. Angles were similar during dobutamine infusion. Comparisons between ventricular walls, both at rest and with dobutamine, revealed no marked regional differences in the principal strain angle.

CONCLUSIONS

The direction of maximal myocardial contraction is known to change with ischemic injury to the myocardium and can be a sensitive, regionally varying index of myocardial ischemia. The critical first step in the clinical application of this technology is to accurately characterize normal ranges of principal strain angles.

Dobutamine Stress Echocardiography Is Highly Accurate for the Prediction of Contractile Reserve in the Early Postoperative Period, but May Underestimate Late Recovery in Contractile Reserve After Revascularization of the Hibernating Myocardium

OBJECTIVE

We sought to investigate the accuracy of dobutamine stress echocardiography to predict the degree and timing of recovery in resting function and contractile reserve (CR) after revascularization of the hibernating myocardium.

METHODS

In all, 24 patients with ischemic cardiomyopathy (ejection fraction < 40%) underwent dobutamine stress echocardiography 1 week before and 6 weeks, 3 months, and 6 months after coronary artery bypass grafting.

RESULTS

Recovery rates at 6 weeks, 3 months, and 6 months postoperation were 21%, 33%, and 45% (P < .01) for resting function and 55%, 65%, and 74% (P < .01) for CR. Positive and negative predictive values for recovery of resting function and CR at 6 months postrevascularization were 66% vs 97% (P < .001) and 78% vs 48% (P < .001), respectively. Positive and negative predictive values were both high for recovery of CR at 6 weeks postrevascularization (89% and 78%).

CONCLUSIONS

Dobutamine stress echocardiography can predict early recovery in CR postrevascularization with an excellent accuracy but may underestimate the degree of late recovery in CR.

Autophagy in chronically ischemic myocardium

We tested the hypothesis that chronically ischemic (IS) myocardium induces autophagy, a cellular degradation process responsible for the turnover of unnecessary or dysfunctional organelles and cytoplasmic proteins, which could protect against the consequences of further ischemia. Chronically instrumented pigs were studied with repetitive myocardial ischemia produced by one, three, or six episodes of 90 min of coronary stenosis (30% reduction in baseline coronary flow followed by reperfusion every 12 h) with the non-IS region as control. In this model, wall thickening in the IS region was chronically depressed by approximately 37%. Using a nonbiased proteomic approach combining 2D gel electrophoresis with in-gel proteolysis, peptide mapping by MS, and sequence database searches for protein identification, we demonstrated increased expression of cathepsin D, a protein known to mediate autophagy. Additional autophagic proteins, cathepsin B, heat shock cognate protein Hsc73 (a key protein marker for chaperone-mediated autophagy), beclin 1 (a mammalian autophagy gene), and the processed form of microtubule-associated protein 1 light chain 3 (a marker for autophagosomes), were also increased. These changes, not evident after one episode, began to appear after two or three episodes and were most marked after six episodes of ischemia, when EM demonstrated autophagic vacuoles in chronically IS myocytes. Conversely, apoptosis, which was most marked after three episodes, decreased strikingly after six episodes, when autophagy had increased. Immunohistochemistry staining for cathepsin B was more intense in areas where apoptosis was absent. Thus, autophagy, triggered by ischemia, could be a homeostatic mechanism, by which apoptosis is inhibited and the deleterious effects of chronic ischemia are limited.

Impaired resting perfusion in viable myocardium distal to chronic coronary stenosis in rats

Chronic coronary artery stenosis results in patchy necrosis in the dependent myocardium and impairs global and regional left ventricular (LV) function in rats in vivo. The aim of the present study was to compare regional myocardial blood flow (RMBF) and function (F) in poststenotic myocardium by using magnetic resonance imaging (MRI) and to compare MRI blood flow changes to histological alterations to assess whether RMBF in the viable poststenotic tissue remains normal. MRI was performed in 11 anesthetized Wistar rats with 2-wk stenosis of the left coronary artery. Postmortem, the extent of fibrotic tissue was quantified. Poststenotic RMBF was significantly reduced to 2.21 ± 0.30 ml·g−1·min−1 compared with RMBF in the remote myocardium (4.05 ± 0.50 ml·g−1·min−1). A significant relationship between the poststenotic RMBF (%remote area) and the poststenotic F (%remote myocardium) was calculated ( r = 0.61, P < 0.05). Assuming perfusion in scar tissue to be 32 ± 5% of perfusion of remote myocardium, as measured in five additional rats, and that in remote myocardium to be 114 ± 25% of that in normal myocardium, as assessed in five sham rats, the calculated perfusion in partially fibrotic tissue samples (35.7 ± 5.2% of analyzed area) was 2.88 ± 0.18 ml·g−1·min−1, whereas measured MRI perfusion was only 1.86 ± 0.24 ml·g−1·min−1 ( P < 0.05). These results indicate that resting perfusion in viable poststenotic myocardium is moderately reduced. Alterations in global and regional LV function are therefore secondary to both patchy fibrosis and reduced resting perfusion.

Comparison of 99mTc-sestamibi/18FDG DISA SPECT with PET for the detection of viability in patients with coronary artery disease and left ventricular dysfunction

PURPOSE

Dual-isotope simultaneous acquisition (DISA) single-photon emission computed tomography (SPECT) is an attractive technique as it permits assessment of both myocardial glucose metabolism and perfusion within a single session, but few data on its accuracy for the assessment of viability are available as yet. In the present study, DISA SPECT was compared with positron emission tomography (PET) for the detection of myocardial viability in normal and dysfunctional left ventricular (LV) myocardium.

METHODS

Fifty-eight patients with chronic coronary artery disease and LV dysfunction (LV ejection fraction 33+/-12%) were studied. Patients underwent a 1-day dipyridamole stress 99mTc-sestamibi/18F-fluorodeoxyglucose (18FDG) DISA SPECT and 13N-ammonia/18FDG PET protocol. Within 1 week, resting MRI was performed to assess contractile function. Comparison of PET and SPECT data was performed using both visual and quantitative analysis.

RESULTS

The correlation of normalised activities of the flow tracers 99mTc-sestamibi and 13N-ammonia was good (r = 0.82; p < 0.001). The correlation between the two 18FDG studies was also good (r = 0.83; p < 0.001). The agreement for the assessment of viability for all segments between DISA SPECT and PET was 82%, with a kappa-statistic of 0.59 (95% CI 0.53-0.64), without a significant difference; in dysfunctional segments only, the agreement was 82%, with a kappa-statistic of 0.63 (95% CI 0.56-0.70), without a significant difference. When the DISA SPECT data were analysed visually, the agreement between DISA SPECT and PET was 83%, with a kappa-statistic of 0.58 (95% CI 0.52-0.63), without a significant difference. Moreover, there was no significant difference between visual and quantitative DISA SPECT analysis for the detection of viability.

CONCLUSION

This study shows an overall good agreement between 99mTc-sestamibi/18FDG DISA SPECT and PET for the assessment of myocardial viability in patients with severe LV dysfunction. Quantitative or visual analysis of the SPECT data did not influence the agreement with PET, suggesting that visual assessment may be sufficient for clinical purposes.

Mechanisms of Cell Survival in Myocardial Hibernation

Myocardial hibernation represents a condition of regional ventricular dysfunction in patients with chronic coronary artery disease, which reverses gradually after revascularization. The precise mechanism mediating the regional dysfunction is still debated. One hypothesis suggests that chronic hypoperfusion results in a self-protecting downregulation in myocardial function and metabolism to match the decreased oxygen supply. An alternative hypothesis suggests that the myocardium is subject to repetitive episodes of ischemic dysfunction resulting from an imbalance between myocardial metabolic demand and supply that eventually creates a sustained depression of contractility. It is generally agreed that hibernating myocardium is submitted repeatedly to ischemic stress, and therefore one question persists: how do myocytes survive in the setting of chronic ischemia? The hallmark of hibernating myocardium is a maintained viability of the dysfunctional myocardium which relies on an increased uptake of glucose. We propose that, in addition to this metabolic adjustment, there must be molecular switches that confer resistance to ischemia in hibernating myocardium. Such mechanisms include the activation of a genomic program of cell survival as well as autophagy. These protective mechanisms are induced by ischemia and remain activated chronically as long as either sustained or intermittent ischemia persists.

Characterization of hibernating myocardium with NOGA electroanatomic endocardial mapping

Because the terms "hibernation" and "viability" are not interchangeable, the recognition of hibernating myocardium within viable segments remained elusive for NOGA electroanatomic endocardial mapping. The aim of the present study was to determine the characteristics of hibernating myocardium in NOGA mapping. Baseline and follow-up endocardial mapping, thallium-201 myocardial perfusion scintigraphy at rest, and contrast ventriculography were performed in 28 patients who had proved viable myocardium before and 7.3 +/- 2.5 months after percutaneous coronary intervention. Significantly improved regional wall motion in the revascularized territory (region of interest) was confirmed in 9 patients (group 1) at follow-up (from -2.11 +/- 0.87 to -1.48 +/- 0.43 SD/chord, p <0.05), whereas no change in regional wall motion was observed in 19 patients (group 2; from -2.56 +/- 0.88 to -2.79 +/- 0.91 SD/chord). Average normalized thallium uptake at rest increased significantly in groups 1 and 2 after revascularization. A trend toward increased unipolar voltages in the region of interest was observed in group 1 at follow-up (from 10.6 +/- 3.5 to 11.7 +/- 4.0 mV, p = 0.073), whereas no change was observed in group 2 (from 8.7 +/- 4.4 to 8.9 +/- 3.8 mV). A significant increase in local linear shortening was measured only in group 1 (from 7.5 +/- 5.2% to 10.3 +/- 3.9%, p <0.05). Hibernating myocardial segments exhibited significantly higher unipolar voltages and late thallium uptake at rest at baseline. Receiver-operator characteristic analysis showed a mean unipolar voltage of 9.0 mV (predictive accuracy 0.708, common sensitivity and specificity 72%) in the region of interest for prediction of functional recovery. In conclusion, for characterizing the hibernating myocardium within viable segments, NOGA endocardial mapping offers on-line guidance for percutaneous coronary and noncoronary myocardial revascularization.

Viable Myocardium: How Much Is Enough? A Comparison of Viability by Comparative Imaging Techniques to Assess the Quantity and Functionality of Ischemic Myocardium

Left ventricular systolic dysfunction is mainly a result of coronary artery disease (CAD). Decrease in myocardial contractility results as a response to a chronic hypoperfusion state that produces a change in cardiac myocyte metabolism, resulting in a perfusion-contraction mismatch in which function is sacrificed for survival. If revascularization is performed in a timely fashion, metabolism can be restored leading to recovery of function. Through the use of noninvasive imaging modalities, assessing myocardial viability can be easily performed and will aid in selecting those patients who will benefit from revascularization. Viable myocardium can be identified by nuclear modalities that have a high sensitivity but a lower specificity, such as thallium-201 single photon emission computed tomography and positron emission tomography (PET); or by the use of dobutamine stress echocardiogram (DSE), which has a decreased sensitivity but a better specificity. A modality that is increasingly being used with an overall good sensitivity and specificity is contrast-enhanced magnetic resonance imaging. The purpose of this review is to explore the amount of myocardial viability that is relevant to pursue revascularization, since as myocardial function improves there is a decrease in morbidity and mortality from heart failure and arrhythmias.

Reversible myocardial dysfunction: basics and evaluation

Large areas of non-functional but viable myocardium with reversible dysfunction are commonly seen in patients with acute myocardial infarction. Both reperfusion of acutely ischemic myocardium and chronic myocardial ischemia may produce a reversible forms of ventricular dysfunction. The two main conditions that lead to reversible myocardial dysfunction are stunned myocardium and hibernating myocardium. Myocardial stunning represents post-ischemic myocardial dysfunction that persists despite restoration of normal flow, with gradual return of contractile function. Hibernating myocardium is a state of persistently impaired myocardial function at rest due to reduced coronary blood flow owing to residual stenosis that can be restored toward normal by revascularization. The success of the revascularization procedures depends on the presence of amount of dysfunctional but viable myocardium. The basics and evaluation of reversible myocardial dysfunction are reviewed.

Coronary blood flow, metabolism, and function in dysfunctional viable myocardium before and early after surgical revascularisation

OBJECTIVES

To assess the link between perfusion, metabolism, and function in viable myocardium before and early after surgical revascularisation.

DESIGN

Myocardial blood flow (MBF, thermodilution technique), metabolism (lactate, glucose, and free fatty acid extraction and fluxes), and function (transoesophageal echocardiography) were assessed in patients with critical stenosis of the left anterior descending coronary artery (LAD) before and 30 minutes after surgical revascularisation.

SETTING

Tertiary cardiac centre.

PATIENTS

23 patients (mean (SEM) age 57 (1.7) years with LAD stenosis: 17 had dysfunctional viable myocardium in the LAD territory, as shown by thallium-201 rest redistribution and dobutamine stress echocardiography (group 1), and six had normally contracting myocardium (group 2).

RESULTS

LAD MBF was lower in group 1 than in group 2 (58 (7) v 113 (21) ml/min, p < 0.001) before revascularisation and improved postoperatively in group 1 (129 (133) ml/min, p < 0.001) but not in group 2 (105 (20) ml/min, p = 0.26). Group 1 also had functional improvement in the LAD territory at intraoperative echocardiography (mean regional wall motion score from 2.6 (0.85) to 1.5 (0.98), p < 0.01). Oxidative metabolism, with lactate and free fatty acid extraction, was found preoperatively and postoperatively in both groups; however, lactate and free fatty acid uptake increased after revascularisation only in group 1.

CONCLUSIONS

MBF is reduced and oxidative metabolism is preserved at rest in dysfunctional but viable myocardium. Surgical revascularisation yields immediate perfusion and functional improvement, and increases the uptake of lactate and free fatty acids.

Time course of functional recovery after coronary artery bypass grafting surgery according to the preoperative reversibility of perfusion impairment on myocardial SPECT

PURPOSE

Ischaemic myocardial dysfunction shows different time courses of functional recovery according to the pathophysiological characteristics of the dysfunction. In this study, we investigated the time course of functional recovery according to the preoperative reversibility of perfusion impairment on myocardial single-photon emission computed tomography (SPECT) after revascularisation surgery.

METHODS

Forty-eight patients (42 men and 6 women; mean age 59+/-9 years) who underwent revascularisation surgery were included in the study. 201Tl rest/dipyridamole stress (99m)Tc-sestamibi gated SPECT was performed 10+/-8 days before (preoperative), 105+/-13 days after (early follow-up) and 497+/-66 days after (late follow-up) surgery. Using a 20-segment model, segmental perfusion and thickening were quantified with automatic software. As an indicator of the reversibility of perfusion impairment, a reversibility score (RevS) was defined as a measure of rest minus stress perfusion values. Segmental dysfunction and functional recovery were defined from quantified thickening values. Function-recovered segments were divided into early recovery and late recovery groups, and preoperative perfusion status was compared in these groups. Function-recovered segments were also re-classified into high-RevS and low-RevS groups according to the preoperative RevS, and the time courses of functional recovery were investigated in each group.

RESULTS

A total of 502 segments were included in the analysis and 263 were finally classified as function-recovered segments. Of these, 172 were in the early recovery and 91 in the late recovery group. In terms of preoperative perfusion status, RevS was 8.9+/-10.8 in the early recovery group and 5.4+/-11.0 in the late recovery group (P=0.01). When all 502 segments were classified by RevS, no difference in the proportion of final function recovery was observed between the high-RevS and the low-RevS group (54% vs 51%). However, the proportion of early recovery was higher in the high-RevS group (73%) than in the low-RevS group (57%) (P=0.01).

CONCLUSION

Ischaemic dysfunctional myocardium with reversible perfusion impairment tends to recover function earlier after revascularisation surgery than myocardium with a persistent decrease in perfusion.

Human hibernating myocardium is jeopardized by apoptotic and autophagic cell death

OBJECTIVES

The aim of the present study was to objectify the loss of myocytes and the mechanism by which myocytes die in human hibernating myocardium (HHM).

BACKGROUND

Intracellular degeneration, reduced cellular protein synthesis, and the replacement fibrosis contribute to structural disintegration of HHM.

METHODS

In 14 patients, HHM was diagnosed by dobutamine echocardiography, radionuclide ventriculography, and thallium-201 scintigraphy. Functional recovery was documented by repeating the preoperative clinical investigations three months after successful coronary artery bypass graft surgery (CABG). During CABG, transmural biopsies were taken from the center of HHM regions and studied by electron microscopy, immunohistochemistry, the terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL) method, reverse transcription-polymerase chain reaction, and Western blotting. Control samples were taken from nondiseased human myocardium.

RESULTS

All patients showed significant improvement or normalization of the regional function of HHM. Ubiquitin-related autophagic cell death was evident ultrastructurally by the occurrence of autophagic vacuoles, cellular degeneration, and nuclear disassembly. Ubiquitin-protein complexes were found in 0.03 +/- 0.008% (control: 0%, p < 0.005) of all myocytes. The proteasome 20S subunit/total myocytes were reduced from 63.3 +/- 9.6% in control myocardium to 36.9 +/- 8.4% in HHM. Complement-9, indicating oncosis, was found in only one of 14 biopsies. TUNEL-positive myocytes were 0.002 +/- 0.0003%. Electron microscopy showed apoptotic cells in 3 of 14 samples. However, the bcl-2/bax ratio was significantly reduced. Moreover, caspase-3 messenger ribonucleic acid was 8.5 times upregulated, and caspase-3 was activated. Cell death was absent in controls.

CONCLUSIONS

In HHM, ubiquitin-related autophagic cell death and apoptosis cause a loss of myocytes. This plays an important role in progressive tissue damage and causes a reduction of the extent of functional recovery of HHM.

Comparison of functional recovery of mildly hypokinetic versus severely dysfunctional left ventricular segments after revascularization in patients with ischemic cardiomyopathy

Dysfunctional left ventricular (LV) segments showing contractile reserve during dobutamine stress echocardiography (DSE) are considered viable myocardium; functional recovery is expected after revascularization. Many segments, however, particularly mildly hypokinetic segments, do not recover. The reason for this failure is unknown. Two-dimensional echocardiography at rest and low-high-dose DSE were performed before revascularization in 114 consecutive patients with ischemic cardiomyopathy. Two-dimensional echocardiography at rest was repeated after 9 to 12 months. Segmental function was scored by a 5-point grading score. Functional recovery after revascularization was assessed in mildly hypokinetic (score 2, group I) and severely dysfunctional segments (score 3 to 5, group II). For each segment, functional recovery was defined as an improvement in functional score of > or =1 grade compared with the baseline score at rest. During low-dose DSE (up to 10 microg/kg/min), 183 group I segments (68%) and 438 group II (39%) segments had contractile reserve (p <0.0001). However, functional recovery was observed less frequently in group I segments (41%) than in group II segments (55%) with contractile reserve (p <0.005). During high-dose DSE (up to 40 microg/kg/min), in the group I segments with contractile reserve at the low dose, the sustained improvement pattern (indicating subendocardial scar) was prevalent (73%). After revascularization, 73% of segments with sustained improvement did not recover. Conversely, the biphasic response (indicating ischemically jeopardized myocardium) was observed only in 27% of group I segments. Functional recovery occurred in 39 of these segments (78%) (p <0.001 vs sustained improvement). Hence, mildly hypokinetic segments probably indicate the presence of subendocardial scars, and may explain the failure in functional recovery after revascularization.

Pathophysiology and diagnosis of hibernating myocardium in patients with post-ischemic heart failure: the contribution of PET

Identification and treatment of hibernating myocardium (HM) lead to improvement in LV function and prognosis in patients with post-ischemic heart failure. Different techniques are used to diagnose HM: echocardiography, MRI, SPECT and PET and, in patients with moderate LV impairment, their predictive values are similar. There are few data on patients with severe LV dysfunction and heart failure in whom the greatest benefits are apparent after revascularization. Quantification of FDG uptake with PET during hyperinsulinemic euglycemic clamp is accurate in these patients with the greatest mortality risk in whom other techniques may give high false negative rates. The debate on whether resting myocardial blood flow to HM is reduced or not has stimulated new research on heart failure in patients with coronary artery disease. PET with H2(15)O or 13NH3 has been used for the absolute quantification of regional blood flow in human HM. When HM is properly identified, resting blood flow is not different from that in healthy volunteers although a reduction of approximately 20% can be demonstrated in a minority of cases. PET studies have shown that the main feature of HM is a severe impairment of coronary vasodilator reserve that improves after revascularization in parallel with LV function. Thus, the pathophysiology of HM is more complex than initially postulated. The recent evidence that repetitive ischemia in patients can be cumulative and lead to more severe and prolonged stunning, lends further support to the hypothesis that, at least initially, stunning and HM are two facets of the same coin.

Individual prediction of functional recovery after coronary revascularization in patients with ischemic cardiomyopathy: the scar-to-biphasic model

Currently, the prediction of improvement of left ventricular (LV) ejection fraction (EF) after revascularization in patients with ischemic cardiomyopathy relies only on viable myocardium extent, whereas both the amount of viable and scar tissue may be important. A model was developed, based on the amount of viable and nonviable myocardium, to predict functional recovery. Viable and scarred myocardium was defined by dobutamine stress echocardiography (DSE) in 108 consecutive patients. LVEF before and 9 to 12 months after revascularization was assessed by radionuclide ventriculography; an improvement of > or =5% was considered significant. In the 1,089 dysfunctional segments (63%), DSE elicited biphasic response in 216 segments (20%), sustained improvement in 205 (19%), worsening in 43 (4%), and no change in 625 (57%). LVEF improved in 39 patients (36%). Only the numbers of biphasic and scar segments were predictors of improvement or no improvement of LVEF (odds ratio 1.5, 95% confidence interval 1.2 to 1.7, p <0.0001 for biphasic segments; odds ratio 0.8, 95% confidence interval 0.7 to 0.9, p <0.0005 for scarred segments). The sustained improvement and worsening pattern were not predictive of improvement or no improvement. A regression function, based on the number of scar and biphasic segments, showed that the likelihood of recovery was 85% in patients with extensive biphasic tissue and no scars and 11% in patients with extensive scars and no biphasic myocardium. Patients with a mixture of scar and biphasic tissue had an intermediate likelihood of improvement (50%). In patients with ischemic cardiomyopathy and a mixture of viable and nonviable tissue, both numbers of viable and nonviable segments should be considered to accurately predict functional recovery after revascularization.

Radionuclide viability testing: should it affect treatment strategy in patients with cardiomyopathy and significant coronary artery disease?

BACKGROUND

Ischemic heart failure is a significant source of morbidity and mortality, yet it has an unclear treatment strategy. The assessment of viable myocardium by nuclear imaging studies has shown promise in predicting improvements in ejection fraction and symptoms. However, the relationship of viability to long-term mortality has not been fully established.

METHODS

A number of studies have addressed long-term mortality with nuclear viability imaging in patients with impaired left ventricular function and significant coronary artery disease. These studies were analyzed to determine differences in design, results, trends, and limitations. They were then evaluated by use of qualitative criteria established for prognostic studies.

RESULTS

Fourteen studies met our criteria. Although the conclusions differed, it appears that patients with viability who undergo revascularization have the highest survival rate, whereas patients with viability who are treated medically have a much lower survival rate. Patients without viability have an intermediate survival rate, regardless of treatment. Several limitations were identified, including a lack of randomization, small sample size, inadequate follow-up, and extensive study protocol and design differences.

CONCLUSIONS

The use of viability testing in patients with heart failure and significant coronary artery disease has shown promise in predicting the long-term mortality rate with treatment allocation. However, there is a need for further study involving larger cohorts with a randomized design, longer periods of follow-up, improved study designs, and identification of referral bias and viability prevalence.

Determinants of mid- and long-term results in patients after surgical revascularization for ischemic cardiomyopathy

BACKGROUND

The revascularization of patients suffering from ischemic cardiomyopathy is possible with acceptable perioperative mortality and morbidity. Many publications have discussed the problem of predicting myocardial viability, whereas the quality of the peripheral coronary vessels has been focused on less frequently.

METHODS

We studied 908 consecutive patients with ischemic cardiomyopathy revascularized between January 1, 1988 and April 30, 2000. Death, recurrent heart failure, hospitalization due to cardiac causes, ventricular assist device implantation, heart transplantation, and ventricular arrhythmias were defined as adverse events. To analyze the importance of pre- and perioperative variables (state of the coronary arteries, myocardial viability, complete vs incomplete revascularization, urgency of the operation, previous operations, gender, diabetes, preoperative New York Heart Association class, age, number of grafts, and ischemic time), a proportional hazards model was used.

RESULTS

The most important predictors of short- and long-term event-free survival were the quality of the coronary arteries, followed by myocardial viability, complete revascularization, number of bypass grafts, and an elective operation.

CONCLUSIONS

The coronary vascular system can be described by means of a simple scoring system. A good or at least moderate coronary artery perfusing an area of dysfunctional yet viable myocardium is the main predictor of a successful perioperative course and an event-free survival. Patients with a poor coronary vasculature regardless of myocardial viability should not be considered suitable for revascularization.

Effects of brief ischemia and reperfusion on the myocardium and the role of nitric oxide

Brief myocardial ischemia/reperfusion has complex effects on the myocardium. In the short term the myocardium may be stunned with temporarily reduced contractile function, though this may also be accompanied by the modification and de novo synthesis of proteins that protect the heart against subsequent early or delayed insults. Repeated episodes of non-lethal ischemia, which are common in the clinical setting, combine all of these phenomena and may ultimately result in chronic contractile dysfunction. Nitric oxide is intimately linked to many of these alterations in cellular function and defense. This article examines data predominantly from in vivo large animal studies that relate to these ischemia-induced changes, the evidence for the proposed mechanisms behind both myocardial stunning and preconditioning while concentrating on the role of nitric oxide in these conditions.

Coronary flow: clinical considerations

In the measurement of coronary blood flow to determine the success of percutaneous coronary intervention, invasive techniques, coupled with plaque characterisation and other intracoronary imaging modalities, may prove invaluable.

Novel mechanisms mediating stunned myocardium

Myocardial stunning is defined as the prolonged contractile dysfunction following an ischemic episode that does not result in necrosis, which also occurs in patients with coronary artery disease. There is also evidence to consider myocardial stunning as a fundamental component of hibernating myocardium. Various experimental approaches (from a brief episode to prolonged partial ischemia) and animal models (from rodents to large mammals) have been developed to investigate the pathogenesis of myocardial stunning. Three hypotheses to explain the mechanism, i.e. oxygen radical, Troponin I degradation, and Ca(2+), have been proposed. The first was tested primarily using large mammalian models, whereas the others were tested primarily using rodent models. Recently, the Ca(2+) handling hyothesis has been tested in a large mammalian swine model of myocardial stunning, in which both Ca(2+) and transients and L-type Ca(2+) current density were decreased. Relaxation function and phospholamban phosphorylation are also radically different in large mammalian and rodent models. In addition, troponin I degradation, which was identified as the mechanism of stunning in rodent models, was not found in stunned swine myocardium. Interestingly, the large mammalian model demonstrates that stunning elicits broad changes in gene and protein regulation, some of which have not been observed in the heart previously. The overall genomic adaptation upregulates the expression of survival genes that prevent irreversible damage. Pursuing these new concepts derived from large mammalian models of ischemia/reperfusion will provide more comprehensive mechanistic information underlying myocardial stunning and will serve to devise new therapeutic modalities for patients.