Hibernating myocardium: clinical and functional response to revascularisation

Myocardial viability as integral part of the diagnostic and therapeutic approach to ischemic heart failure

Chronic heart failure is a major public-health problem with a high prevalence, complex treatment, and high mortality. A careful and comprehensive analysis is needed to provide optimal (and personalized) therapy to heart failure patients. The main 4 non-invasive imaging techniques (echocardiography, magnetic resonance imaging, multi-detector-computed tomography, and nuclear imaging) provide information on cardiovascular anatomy and function, which form the basis of the assessment of the pathophysiology underlying heart failure. The selection of imaging modalities depends on the information that is needed for the clinical management of the patients: (1) underlying etiology (ischemic vs non-ischemic); (2) in ischemic patients, need for revascularization should be evaluated (myocardial ischemia/viability?); (3) left ventricular function and shape assessment; (4) presence of significant secondary mitral regurgitation; (5) device therapy with cardiac resynchronization therapy and/or implantable cardiac defibrillator (risk of sudden cardiac death). This review is dedicated to assessment of myocardial viability, however "isolated assessment of myocardial viability" may be clinically not meaningful and should be considered among all those different variables. This complete information will enable personalized treatment of the patient with ischemic heart failure.

Intravascular cell delivery device for therapeutic VEGF-induced angiogenesis in chronic vascular occlusion

Site specific targeting remains elusive for gene and stem cell therapies in the cardiovascular field. One promising option involves use of devices that deliver larger and more sustained cell/gene payloads to specific disease sites using the versatility of percutaneous vascular access technology. Smooth muscle cells (SMCs) engineered to deliver high local concentrations of an angiogenic molecule (VEGF) were placed in an intravascular cell delivery device (ICDD) in a porcine model of chronic total occlusion (CTO) involving ameroid placement on the proximal left circumflex (LCx) artery. Implanted SMC were retained within the ICDD and were competent for VEGF production in vitro and in vivo. Following implantation, micro-CT analyses revealed that ICDD-VEGF significantly enhanced vasa vasora microvessel density with a concomitant increase in tissue VEGF protein levels and formation of endothelial cell colonies suggesting increased angiogenic potential. ICDD-VEGF markedly enhanced regional blood flow determined by microsphere and contrast CT analysis translating to a functional improvement in regional wall motion and global left ventricular (LV) systolic and diastolic function. Our data indicate robust, clinically relevant angiogenesis can be achieved in a human scale porcine chronic vascular occlusion model following ICDD-VEGF-based delivery of angiogenic cells. This may have implications for percutaneous delivery of numerous therapeutic factors promoting creation of microvascular bypass networks in chronic vaso-occlusive diseases.

Effectiveness of the fixed-dose combination therapy with perindopril and amlodipine in coronary heart disease patients after coronary artery bypass graft surgery

Aim.To study the effectiveness of the fixed-dose combination therapy with perindopril and amlodipine (Prestance 5/5 mg/d) in coronary heart disease (CHD) patients after coronary artery bypass graft (CABG) surgery.Material and methods.The clinical trial included 65 patients (37 men, 28 women aged 45-68 years; mean age 56,3±3,5 years) after CABG. All patients were randomised into two groups: the control group (CG; n=35) and the main group (MG; n=30). Both groups received antiplatelet agents and statins, while the MG patients additionally received Prestance (5/5 mg/d). Prestance therapy started three-four weeks after CABG and lasted for four months. All participants underwent 24-hour monitoring of ECG and blood pressure (BP), Doppler echocardiography, and Doppler ultrasound of brachial and common carotid arteries.Results.Compared to the CG, the MG demonstrated decreased incidence of pain and painless ischemia episodes, reduced maximal ST segment depression and its total duration, and increased rate threshold of myocardial ischemia. In addition, Prestance therapy was associated with improved systolic and diastolic heart function and significantly improved endothelium-dependent vasodilatation. In patients with normal BP, Prestance (5/5 mg/d) did not cause hypotension, but reduced excessive BP variability. In the MG, acute coronary syndrome (ACS) was registered in 1 individual (3,3 %), while in the CG, it was registered in 4 patients (11.4 %), and in 3 cases, coronary artery stenting was performed.Conclusion.In patients with normal BP, Prestance (5/5 mg/d) therapy in the early post-CABG period had a pronounced anti-ischemic, cardio- and vasoprotective effects, and also prevented excessive BP variability.

Chronic total coronary occlusion in patients with intermediate viability: value of low-dose dobutamine and contrast-enhanced 3-T MRI in predicting functional recovery in patients undergoing percutaneous revascularisation with drug-eluting stent

PURPOSE

Myocardial viability was evaluated by magnetic resonance imaging (MRI) in patients with chronic total coronary occlusion (CTO) treated with a drug-eluting stent. Change in left ventricular ejection fraction (LVEF) was analysed.

MATERIALS AND METHODS

Twenty-three patients with CTO underwent delayed-enhancement (DE) and low-dose dobutamine MRI (LD). Diastolic wall thickness (DWT), dobutamine-induced systolic wall thickening (SWT) and DE transmural extension were quantitatively assessed in vessel-related segments, calculating the contribution of viable tissue to SWT, expressed as viability index (VI)=[SWTx(100 - DE)]/100. Patients with transmural enhancement were excluded from revascularisation. At 6 months follow-up, patients underwent coronary angiography (CA) and MRI. Functional recovery was defined as a 2-mm increase in SWT.

RESULTS

Transmural enhancement (mean DE 62.88+/-37.18] was present in three patients. Mean DWT, SWT, VI and DE of recanalised patients were 8.03+/-2.35, 2.64+/-1.56, 1.77+/-1.48 mm and 41.97+/-30.32. Revascularisation was successful in 14/16. Follow-up CA showed patency of treated vessels. Functional recovery was achieved in 13 patients. Functional recovery showed significant correlation with SWT (beta 1,779, p=0.015), and even higher correlation with VI (beta 2.032, p=0.011). LVEF improved significantly [Delta 95% confidence interval (CI) -4.47, p=0.0203).

CONCLUSIONS

Invasive CTO treatment has beneficial effects on myocardial contractility that can be predicted by VI, and on LVEF.

Long-term results of coronary artery bypass grafting in patients with left ventricular dysfunction

BACKGROUND

In this prospective study, we investigated the determinants of long-term outcome, symptoms, and left ventricular function after coronary artery bypass grafting in patients with a moderate to severely decreased left ventricular ejection fraction.

METHODS

Between 1997 and 1998, 75 consecutive patients with moderate to severe left ventricular dysfunction underwent coronary artery bypass grafting procedures. The operative mortality rate was 4.0%, and the 72 survivors were monitored for 8 years. The end points were mortality, symptomatic status (New York Heart Association [NYHA] functional class), and left ventricular function.

RESULTS

The total survival rate after 8 years was 89.3%. During follow-up, 8 patients died. Death was attributed to a cardiac cause in 5 patients and to a noncardiac cause in 3. There was no statistically significant difference between preoperative and late postoperative NYHA functional class, despite a statistically significant improvement that persisted for up to 4 years after CABG. The results of echocardiography showed a statistically significant improvement in the left ventricular ejection fraction (from 0.322 +/- 0.06 preoperatively to 0.463 +/- 0.02 at follow-up, p < 0.001). Multivariate analysis revealed that the left ventricular end-systolic volume index, the presence of angina pectoris, and absence of symptoms of congestive heart failure were preoperative indicators of freedom from heart failure after coronary operations (p < 0.05).

CONCLUSIONS

Coronary artery bypass grafting for patients with moderate-to-severe left ventricular dysfunction is associated with acceptable long-term results. The left ventricular end-systolic volume index is a simple noninvasive method to aid in the preoperative decision making in such patients.

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.

Direct epicardial mapping can differentiate hibernating from scarred myocardium: a validation study with 18F-FDG-PET

AIM

This study investigated the value of epicardial mapping immediately before CABG in the differentiation of hibernating from scarred myocardium in correlation to the noninvasive gold standard (18)F-FDG PET.

METHODS AND RESULTS

In 35 patients with CAD, myocardial perfusion ((99m)Tc-Tetrofosmin-SPECT), viability ((18)F-FDG-PET), and function (LVangiography) were assessed before CABG. 102 bipolar epicardial electrograms per patient (n = 3570 electrograms) were recorded simultaneously with a ventricular jacket array. Based on the scintigraphic and LV angiographic data at the site of each electrode with good myocardial contact (n = 1963), segments (n = 492, 14.1 +/- 5.6 per patient; mean +/- SD) were classified into three groups: hibernating (n = 139), scarred (n = 104), and control (n = 249). Regional mean bipolar voltage values were calculated for Receiver Operating Characteristic (ROC) analysis. Mean bipolar voltage was significantly lower in scarred when compared to hibernating myocardium. ROC curve analysis (area under the curve of 0.92 +/- 0.47, mean +/- SE) for mean bipolar voltage to discriminate between hibernating and scarred myocardium revealed a sensitivity of 94% with a specificity of 83% at a cut-off value of 8.75 mV.

CONCLUSION

Hibernating myocardium can be differentiated correctly from scarred myocardium by direct epicardial mapping. In the future, hibernating myocardium may be detectable by body surface mapping techniques using inverse solutions.

Clinical assessment in ischaemic cardiomyopathy

Despite the trend of decreasing death rates attributable to ischaemic heart disease and stroke, the prevalence of heart failure and the resultant death rates in the United States have almost tripled between 1974 and 1994 [1]. Coronary artery disease is the commonest cause of heart failure in developed countries, accounting for up to 60% of cases. Advances in medical therapy, particularly the use of angiotensin-converting enzyme inhibitors and beta-blockers, have served to reduce morbidity and mortality in patients with left ventricular (LV) dysfunction due to coronary artery disease [2-5]. However, these improvements have been modest, and despite these therapies, patients with severe ischaemic cardiomyopathy continue to have a high mortality when treated medically. It is increasingly clear that the impaired LV function in these patients is not always an irreversible process. Traditionally, these observations have been made following demonstrable improvements in systolic function after coronary revascularization procedures. Diagnostic testing to evaluate the presence and extent of viable myocardium has therefore become an important component of the clinical assessment of patients with chronic coronary artery disease and LV dysfunction.

Coronary artery surgery for ischemic heart failure: risks, benefits, and the importance of assessment of myocardial viability

Heart failure and left ventricular dysfunction are common and are most often caused by myocardial ischemia/infarction secondary to occlusive coronary artery disease. Although recent refinements in medical therapy have resulted in improved survival, morbidity and mortality remain high in patients with advanced heart failure. Heart transplantation remains an option for selected patients, and implantable left ventricular assist devices may soon provide another treatment strategy for such patients. However, patients with established postischemic heart failure, significant myocardial viability, and coronary artery anatomy amenable to surgical revascularization can derive significant functional and survival benefit after coronary artery surgery, albeit with an increased perioperative risk. We discuss the role of coronary artery surgery in ischemic heart failure and review the evidence for such an approach.

Dobutamine magnetic resonance imaging as a predictor of myocardial functional recovery after revascularisation

OBJECTIVE

To assess the use of dobutamine magnetic resonance imaging (MRI) as a preoperative predictor of myocardial functional recovery after revascularisation, comparing wall motion and radial wall thickening analyses by observer and semi-automated edge detection.

PATIENTS

25 men with multivessel coronary disease and resting wall motion abnormalities were studied with preoperative rest and stress MRI.

MAIN OUTCOME MEASURES

Observer analysis for radial wall thickening was compared with a normal range, while wall motion analysis used a standard four point scale. Semi-automated analysis was performed using an edge detection algorithm. Segments displaying either improved or worsened thickening or motion with dobutamine were considered viable. Postoperative rest images were performed 3-6 months after coronary artery bypass grafting (CABG) for comparison.

RESULTS

For observer analysis the values for sensitivity and specificity were 50% and 72% for wall motion, with respective values of 50% and 68% for thickening. With semi-automated edge detection the figures for motion were 60% and 73%, with corresponding values of 79% and 58% for thickening. Combining thickening and motion for the semi-automated method to describe any change in segmental function yielded a sensitivity of 71% and specificity of 70%.

CONCLUSIONS

Dobutamine MRI is a reasonably good predictor of myocardial functional recovery after CABG. The use of semi-automated edge detection analysis improved results.

Radionuclide imaging of the heart

Nuclear cardiology is an established part of diagnosis and assessment of patients with possible heart disease, the two most common tests being myocardial perfusion imaging and radionuclide ventriculography. Myocardial perfusion imaging comprises approximately 75% of nuclear cardiology studies in the UK, and is used in diagnosis and management of coronary artery disease.

Myocardial revascularization for the treatment of post-ischemic heart failure

Heart failure due to coronary artery disease is a major public health problem. Medical treatment ameliorates symptoms and prognosis, although mortality remains high. Heart failure occurs when a sizeable number of myocytes do not contract. This may be due to irreversible myocyte loss (infarct) and/or dysfunctional but viable myocytes (hibernating), which can resume function following coronary artery bypass surgery. The presence of hibernating myocardium can be predicted by noninvasive nuclear imaging using both single photon (SPECT) and positron emission tomography, and also by stress echocardiography. A number of uncontrolled studies have demonstrated a promising role for coronary artery bypass surgery in patients with heart failure in whom a substantial amount of hibernating myocardium is present. These findings, particularly the magnitude of the benefits reported, justify the need for a randomized trial in this patient population.

Sequential changes in heart rate variability after coronary artery bypass grafting

Heart rate variability (HRV) decreased soon after coronary artery bypass grafting and returned to the preoperative level within 2 months; however, HRV did not exceed the preoperative level, even 6 months after coronary artery bypass grafting. Although myocardial ischemia can be improved by coronary artery bypass grafting, HRV did not benefit from coronary artery bypass grafting within 6 months.

Comparison of 201Tl, 99mTc-tetrofosmin, and dobutamine magnetic resonance imaging for identifying hibernating myocardium

BACKGROUND

Both radionuclide perfusion tracers and contractile response to dobutamine have been used to identify hibernating myocardium. The aim was to compare 201Tl (thallium) single photon emission CT (SPECT), 99mTc-tetrofosmin (tetrofosmin) SPECT, and dobutamine cine MRI for identifying regions of reversible myocardial dysfunction.

METHODS AND RESULTS

Thirty patients with 3-vessel coronary artery disease and impaired left ventricular function (mean LVEF, 24.0%; SD, 8.3%) scheduled for coronary bypass grafting were recruited. All underwent rest/dobutamine stress (5 to 10 microg . kg-1 . min-1) cine MRI, stress/rest tetrofosmin SPECT, and stress/redistribution and separate-day rest/redistribution thallium SPECT before surgery. Stress/redistribution thallium SPECT and resting MRI were repeated after surgery. In a 9-segment model, SPECT images were scored visually for tracer uptake, which was also measured from a polar plot of myocardial counts. MRI was scored visually for endocardial motion, myocardial thickening, and thickness. Five patients died before follow-up, and 2 declined postoperative investigation. In the remaining 23 patients, mean LVEF increased from 24.0% (SD, 8.3%) to 29.7% (SD, 11.1%) (P<0.05). Of 207 segments analyzed, 145 had significantly abnormal wall motion before surgery, and 82 of these improved function after revascularization. The criteria for predicting recovery of severely hypokinetic segments on preoperative imaging were tracer uptake graded "moderately reduced" or better, or positive inotropic response on dobutamine MRI. Late-rest thallium images showed the highest sensitivity (76%), compared with stress-redistribution thallium (68%) and rest tetrofosmin (66%) (P<0.05). All 3 tracer techniques were nonspecific (44%, 51%, and 49%, respectively). Redistribution of thallium after the resting injection was insensitive (18%) but highly specific (83%). Inotropic response to dobutamine was also insensitive (50%) but specific (81%).

CONCLUSIONS

Radionuclide uptake is a sensitive but nonspecific predictor of myocardial functional recovery, whereas dobutamine MRI is specific but insensitive.

Hibernating myocardium

Decreased myocardial contraction occurs as a consequence of a reduction in blood flow. The concept of hibernation implies a downregulation of contractile function as an adaptation to a reduction in myocardial blood flow that serves to maintain myocardial integrity and viability during persistent ischemia. Unequivocal evidence for this concept exists in scenarios of myocardial ischemia that lasts for several hours, and sustained perfusion-contraction matching, recovery of energy and substrate metabolism, the potential for recruitment of inotropic reserve at the expense of metabolic recovery, and lack of necrosis are established criteria of short-term hibernation. The mechanisms of short-term hibernation, apart from reduced calcium responsiveness, are not clear at present. Experimental studies with chronic coronary stenosis lasting more than several hours have failed to continuously monitor flow and function. Nevertheless, a number of studies in chronic animal models and patients have demonstrated regional myocardial dysfunction at reduced resting blood flow that recovered upon reperfusion, consistent with chronic hibernation. Further studies are required to distinguish chronic hibernation from cumulative stunning. With a better understanding of the mechanisms underlying short-term hibernation, it is hoped that these adaptive responses can be recruited and reinforced to minimize the consequences of acute myocardial ischemia and delay impending infarction. Patients with chronic hibernation must be identified and undergo adequate reperfusion therapy.