Metabolic and functional recovery of ischemic human myocardium after coronary angioplasty

Absolute Resting 13N-Ammonia PET Myocardial Blood Flow for Predicting Myocardial Viability and Recovery of Ventricular Function after Coronary Artery Bypass Grafting

OBJECTIVE

We aimed to evaluate the feasibility of resting myocardial blood flow (rMBF), quantified with dynamic 13 N-Ammonia (NH3) PET, for identifying myocardial viability and predicting improvement of left ventricular ejection fraction (LVEF) after coronary artery bypass grafting (CABG).

METHODS

Ninety-three patients with coronary artery disease (CAD) and chronic LVEF < 45%, scheduled for CABG, had dynamic 13NH3 PET and 18F-FDG PET imaging. The perfusion/metabolism polar maps were categorized in four patterns: normal (N), mismatch (M1), match (M2) and reverse mismatch (RM). The value of rMBF for identifying viable myocardium (M1, RM) and post CABG improvement of LVEF≥8% was analyzed by receiver operating characteristic (ROC) curves. Correlations of rMBF in segments to ΔLVEF post CABG were verified.

RESULTS

Mean rMBFs were significantly different (N=0.60±0.14; M1=0.44±0.07, M2=0.34±0.08, RM=0.53±0.09 ml/min/g, P<0.001). The optimal rMBF cutoff to identify viable myocardium was 0.42 ml/min/g (sensitivity=88.3%, specificity=82.0%) and 0.43 ml/min/g for predicting improvement of LVEF ≥8% (74.6%, 80.0%). The extent and rMBF of combined M1/RM demonstrated a moderate to high correlation to improved LVEF (r=0.78, 0.71, P<0.001).

CONCLUSION

Resting MBF, derived by dynamic 13NH3 PET, may be positioned as a supplement to 18F-FDG PET imaging for assessing the presence of viable myocardium and predicting potential improvement of LVEF after CABG.

Coronary blood flow in heart failure: cause, consequence and bystander

Heart failure is a clinical syndrome where cardiac output is not sufficient to sustain adequate perfusion and normal bodily functions, initially during exercise and in more severe forms also at rest. The two most frequent forms are heart failure of ischemic origin and of non-ischemic origin. In heart failure of ischemic origin, reduced coronary blood flow is causal to cardiac contractile dysfunction, and this is true for stunned and hibernating myocardium, coronary microembolization, myocardial infarction and post-infarct remodeling, possibly also for the takotsubo syndrome. The most frequent form of non-ischemic heart failure is dilated cardiomyopathy, caused by genetic mutations, myocarditis, toxic agents or sustained tachyarrhythmias, where alterations in coronary blood flow result from and contribute to cardiac contractile dysfunction. Hypertrophic cardiomyopathy is caused by genetic mutations but can also result from increased pressure and volume overload (hypertension, valve disease). Heart failure with preserved ejection fraction is characterized by pronounced coronary microvascular dysfunction, the causal contribution of which is however not clear. The present review characterizes the alterations of coronary blood flow which are causes or consequences of heart failure in its different manifestations. Apart from any potentially accompanying coronary atherosclerosis, all heart failure entities share common features of impaired coronary blood flow, but to a different extent: enhanced extravascular compression, impaired nitric oxide-mediated, endothelium-dependent vasodilation and enhanced vasoconstriction to mediators of neurohumoral activation. Impaired coronary blood flow contributes to the progression of heart failure and is thus a valid target for established and novel treatment regimens.

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.

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

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

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

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

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

Chronic ischemic left ventricular dysfunction: from pathophysiology to imaging and its integration into clinical practice

Chronic ischemic left ventricular dysfunction is present in a number of clinical syndromes in which myocardial revascularization results in an improvement of left ventricular function, patients' functional class, and their survival. Early diagnosis of and treatment of viability is essential. Coronary arteriography is of limited value in diagnosis of viability. Noninvasive testing is essential for diagnosis, which can be matched to the pathophysiologic changes that occur in hibernating myocardium. However, no single test has a perfect, or near perfect, sensitivity and specificity, and thus, a combination of tests are usually needed. Algorithms are developed to integrate these tests in clinical decision making.

Serial alterations and prognostic implications of myocardial perfusion and fatty acid metabolism in patients with acute myocardial infarction

BACKGROUND

Impaired fatty acid metabolism the myocardial infarction (MI)-related area has prognostic value, but can alter over time. The aim of this study was to correlate alterations in myocardial fatty acid uptake and perfusion assessed by serial imaging with future outcomes in post-MI patients.

METHODS AND RESULTS

Following 2 imaging procedures using 15-4-iodophenyl-3-(R,S)-methylpentadecanoic acid (BMIPP) and perfusion tracers at an 11-month interval, 97 patients with acute MI were followed up for 33 months with respect to the primary endpoints of death, non-fatal MI and heart failure. Regional tracer uptake was semi-quantified for both the MI-related and remote coronary territories. A large BMIPP defect relative to a perfusion defect appeared on MI-related coronary territories. Thirteen patients with cardiac events had a greater prevalence of large BMIPP and perfusion defect scores for the MI-related areas on the first scan, previous MI, diabetes mellitus, and worsening of perfusion tracer uptake in the MI-related area than those without cardiac events. Multivariate analysis identified worsening perfusion in the MI-related area on the second scan, a large BMIPP defect in the same area on the first scan and previous MI as significant predictors with chi-square values of 3.48, 6.41 and 6.84, respectively. A combination of 3 predictors significantly (p<0.05) increased the global chi-square value to 15.45 compared with each chi-square value.

CONCLUSIONS

The size of the infarct-related risk area assessed by early cardiac BMIPP imaging and deterioration of perfusion tracer uptake in the compromised area for the first 12 months following acute MI are related to future cardiac events, indicating a rationale for identifying metabolically damaged but viable myocardium for further risk stratification of post-MI patients.

A QRS score versus ST-segment changes during exercise testing: which is the most reliable ischaemic marker after myocardial revascularisation?

BACKGROUND

The diagnostic ability of exercise testing based on ST-segment changes is low for the detection of restenosis after percutaneous transluminal coronary angioplasty (PTCA) or ischaemia after bypass surgery (CABG). The aim of this study was to improve the diagnostic accuracy of exercise testing in patients with a history of PTCA or CABG, with the implementation of a QRS score.

METHODS

We studied 128 post-PTCA patients (aged 49 +/- 8 years) and 104 post-CABG patients (aged 54 +/- 8 years), who had either positive exercise tests with or without angina, or negative exercise tests with continuing angina-like symptoms, and underwent cardiac catheterisation.

RESULTS

The univariate risk ratio of exercise-induced ST-segment deviation to detect restenosis was 3.05 (p = 0.005) and 0.83 (p = 0.690) in group A and group B patients, respectively. The univariate risk ratios of abnormal QRS score values to detect restenosis were 32.1 (p < 0.001) and 18.8 (p < 0.001) for group A and group B patients, respectively. The univariate risk ratios of the combination of exercise-induced ST-segment changes and of abnormal QRS score values to detect restenosis was 9.43 (p < 0.001) and 3.77 (p < 0.044) for group A and group B patients, respectively. The value of the area under the ROC curves is higher for the QRS score in group A patients, group B patients and for the whole study population.

CONCLUSIONS

QRS score values significantly improve the diagnostic ability of ST-segment change-based exercise testing, for the assessment of restenosis after PTCA or ischaemia after CABG.

Characterization of dysfunctional myocardium by positron emission tomography and magnetic resonance: relation to functional outcome after revascularization

BACKGROUND

Metabolic assessment of dysfunctional myocardium by PET allows prediction of functional recovery after revascularization. Contrast-enhanced MR (ce-MR) discriminates transmural distribution of viable and scar tissue with excellent spatial resolution. Both techniques were applied in ischemic chronic left ventricular dysfunction to relate metabolism and tissue composition to changes of contractile function after revascularization.

METHODS AND RESULTS

Nineteen patients with myocardial infarctions (>3 months) were studied by MR and PET, and 10 patients were followed by MR 11+/-2 months after revascularization. In 56 to 64 segments/heart, systolic wall thickening, viable mass, and thickness of viable rim tissue were determined by MR (inversion-recovery MR with 0.25 mmol/kg Gd-chelate). [18F]Fluorodeoxyglucose (FDG) uptake and resting perfusion (13N-ammonia) were determined by PET. Viable tissue per segment on ce-MR correlated with FDG uptake per segment (r=0.62 and 0.82 for segments with and without flow metabolism mismatch, P<0.0001). FDG uptake > or =50% (a predictor of functional recovery) corresponded to a viable rim thickness of 4.5 mm on ce-MR. Thick (>4.5 mm) and metabolically viable segments (> or =50% FDG uptake) showed functional recovery in 85%, whereas thin metabolically nonviable segments improved function in 13% (P<0.0005). Metabolically viable segments with a thin viable rim and thick segments with reduced FDG uptake improved function in only 36% and 23% of segments, respectively (NS versus thin metabolically nonviable). In these 2 classes of segments, scar per segment was higher than in thick viable segments (P<0.0001).

CONCLUSIONS

Metabolism and tissue composition discriminate various classes of dysfunctional myocardium. Most metabolically viable segments with a thick viable rim on ce-MR recover function after revascularization, whereas all other classes showed low recovery rates of contractile function.

Low-dose adenosine stress echocardiography: detection of myocardial viability

OBJECTIVE

The aim of this study was to evaluate the diagnostic potential of low-dose adenosine stress echocardiography in detection of myocardial viability.

BACKGROUND

Vasodilation through low dose dipyridamole infusion may recruit contractile reserve by increasing coronary flow or by increasing levels of endogenous adenosine.

METHODS

Forty-three patients with resting dyssynergy, due to previous myocardial infarction, underwent low-dose adenosine (80, 100, 110 mcg/kg/min in 3 minutes intervals) echocardiography test. Gold standard for myocardial viability was improvement in systolic thickening of dyssinergic segments of >or= 1 grade at follow-up. Coronary angiography was done in 41 pts. Twenty-seven patients were revascularized and 16 were medically treated. Echocardiographic follow up data (12 +/- 2 months) were available in 24 revascularized patients.

RESULTS

Wall motion score index improved from rest 1.55 +/- 0.30 to 1.33 +/- 0.26 at low-dose adenosine (p < 0.001). Of the 257 segments with baseline dyssynergy, adenosine echocardiography identified 122 segments as positive for viability, and 135 as necrotic since no improvement of systolic thickening was observed. Follow-up wall motion score index was 1.31 +/- 0.30 (p < 0.001 vs. rest). The sensitivity of adenosine echo test for identification of viable segments was 87%, while specificity was 95%, and diagnostic accuracy 90%. Positive and negative predictive values were 97% and 80%, respectively.

CONCLUSION

Low-dose adenosine stress echocardiography test has high diagnostic potential for detection of myocardial viability in the group of patients with left ventricle dysfunction due to previous myocardial infarction. Low dose adenosine stress echocardiography may be adequate alternative to low-dose dobutamine test for evaluation of myocardial viability.

Use of pharmaceuticals in noninvasive cardiovascular diagnosis

A number of pharmaceuticals are employed as diagnostic agents for cardiovascular diseases. Four groups of agents are reviewed here: 1) vasoactive substances employed as adjuncts to physical maneuvers in diagnosis of structural heart disease; 2) vasodilators used to produce heterogeneity of coronary flow; 3) sympathomimetic agents simulating the effects of exercise on the heart for the purpose of detection of coronary artery stenosis; and 4) ultrasonic contrast agents used to enhance myocardial imaging for the assessment of segmental wall motion. In the first group are amyl nitrate, a vasodilator, and methoxamine and phenylephrine, both vasopressors. The vasodilators of the second group are dipyridamole and adenosine. When combined with scintigraphic perfusion imaging or with echocardiographic assessment of segmental wall motion, these agents can detect single- or multiple-vessel coronary artery disease with sensitivity and specificity comparable to submaximal exercise. They are especially useful for preoperative risk assessment before noncardiac surgery. The sympathomimetic agents of the third group, dobutamine and arbutamine, increase myocardial contractility and heart rate, and dilate the peripheral vasculature. As with the vasodilators, when combined with nuclear or echocardiographic techniques they are equivalent to exercise in detection of coronary disease. They are especially useful in patients with bronchospastic disease and for assessment of myocardial viability. Agents from groups 2 and 3 have acceptable side-effect and safety profiles. The last group reviewed includes echocardiographic contrast agents that, in this investigative setting, are employed to enhance detection of segmental wall motion when used with agents from groups 2 and 3.

Myocardial viability assessment with gated SPECT Tc-99m tetrofosmin % wall thickening: comparison with F-18 FDG-PET

OBJECT

This study was designed to assess the value of gated SPECT Tc-99m-tetrofosmin (TF) wall thickening (WT) in addition to TF exercise (Ex)/rest myocardial SPECT, in comparison with F-18 fluorodeoxyglucose (FDG)-PET.

METHODS

The study population consisted of 33 patients with old myocardial infarction (27 men and 6 women; mean age, 62 +/- 8 years old). All patients underwent Ex/rest TF SPECT and glucose loading FDG-PET. Polar map images of Ex/rest TF were generated and divided into 24 segments for further analysis. We classified LV segments according to the exercise-rest perfusion scintigraphy. LV segments with less than 70% of the maximum TF activity on the exercise image were defined as stress-induced defects. Among these, the segments whose TF activity increased by 10% from exercise to rest images or exceeded 70% of the maximum uptake were defined as reversible (viable) defects. The remaining defects on the rest image were irreversible (non-viable) defect segments, and were considered for viability study on the basis of %WT. %WT was calculated according to the standard method: [(counts ES - counts ED)/counts ED] x 100. A viable segment on gated SPECT was defined as a segment whose %WT exceeded the lower limit of the normal value (mean - SD). PET viability was defined as FDG uptake exceeding 50% of the maximum count.

RESULTS

Among the 792 segments evaluated in the 33 patients studied, there were 689 PET viable segments. Of the 689 segments analyzed, 198 (29%) were identified as having defects on Ex images. Among these defects, 55 (8%) were reversible or partially reversible, as evidenced by rest images, and 143 (21%) were irreversible. Of the irreversible segments on Ex/rest images, 106 (15%) demonstrated no apparent WT by gated TF SPECT, whereas 37 (6%) segments with irreversible defects did have apparent WT. Overall, the sensitivity of Ex/rest TF perfusion imaging was 79%. Sensitivity was improved from 79% to 85% by combining %WT and perfusion data, but specificity was reduced from 70% to 56%.

CONCLUSION

%WT evaluated from gated TF imaging enhanced myocardial viability assessment in comparison with FDG-PET.

18F-deoxyglucose and the assessment of myocardial viability

The glucose analogue 18F-deoxyglucose allowed for the first time the ability to noninvasively probe and characterize the regional metabolism of glucose as a major fuel substrate of the human heart. Used with positron emission tomography, it became the tool for demonstrating the operation of metabolic processes, long before established in invasive or destructive experiments in animals, directly in the human myocardium. Clinical investigations with 18F-deoxy-glucose, combined with other radiotracers of the myocardium's substrate metabolism, showed the dependency of the heart's substrate selection on circulating levels of glucose, free fatty acid and insulin, and the operation of Randle's cycle in the human myocardium. Regional responses in substrate metabolism to the myocardial ischemia were now visualized entirely noninvasively as, for example, decreases in fatty acid usage and oxidation and oxygen consumption, but foremost as an increase in glucose use. Regional 18F-deoxyglucose uptake markedly in excess of myocardial blood flow in dysfunctional myocardium of patients after a myocardial infarction, with chronic coronary artery disease or with ischemic cardiomyopathy, soon became recognized as a hallmark of myocardial viability or potentially reversible contractile dysfunction. Defined as blood flow metabolism mismatch, this particular regional glucose uptake pattern identifies patients to be at high risk for cardiac events and, at the same time, to benefit most from surgical revascularization. The patterns predict a postrevascularization improvement in global left ventricular function and, even more important, in symptoms related to congestive heart failure and in long-term survival. 18F-deoxyglucose is now widely used with positron emission tomography and, more recently, with single photon emission computed tomography and radiotracers of myocardial perfursion for stratifying ischemic cardiomyopathy patients to the most efficacious treatment.

Electromechanical assessment of left ventricular function following successful percutaneous coronary revascularization

Percutaneous electromechanical mapping was applied to evaluate the impact of coronary revascularization on electrical and mechanical parameters in patients with prior myocardial infarction. In 15 patients with prior (> or = 4 weeks) myocardial Q-wave infarction and regional wall motion abnormalities, left ventricular endocardial mapping was performed immediately prior to percutaneous coronary revascularization. Patients underwent repetitive mapping during 6-month follow-up angiography with good revascularization results in all patients. Mean regional unipolar electrogram (UP) amplitude of all regions remained unchanged (10.4 +/- 4.2 mV prerevascularization vs. 10.2 +/- 4.4 mV postrevascularization), whereas mean local shortening (LS) of all regions increased from 6.0% +/- 5.8% to 9.7% +/- 5.3% (P < 0.001). The percentage of electromechanical match regions (LS < 6% and UP < 9 mV) remained unchanged after revascularization (15% vs. 10%; NS), whereas the percentage of mismatch regions (LS < 6% and UP > 9 mV) declined from 38% to 10% (P < 0.0001). We conclude that electromechanical mapping allows the sensitive detection of improved mechanical function after successful revascularization. Electrical activity remains unchanged 6 months after revascularization and the number of regions with an electromechanical mismatch decrease.

Ischemically compromised myocardium displays different time-courses of functional recovery: correlation with morphological alterations?

OBJECTIVE

It has been demonstrated that positron emission tomography (PET) predicts the functional recovery of viable but ischemically compromised myocardium. Reversible contractile dysfunction after revascularization has been reported for 'hibernating myocardium' and stunned myocardium, however, there are little data concerning the time-course and the extent of improvement of the two different pathophysiological conditions.

METHODS

Twenty-nine patients with advanced coronary artery disease and severely reduced left ventricular function (EF 18--35%) who were referred for isolated coronary artery bypass grafting underwent preoperative PET viability assessment and were functionally assessed by two-dimensional echocardiography preoperatively at 11 days, 14 weeks, and more than 12 months after surgical revascularization. Intraoperative biopsies were taken from dysfunctional areas defined by PET as segments of normal perfusion and normal metabolism (stunned myocardium) and from areas with a 'mismatch' between perfusion and metabolism (hibernating myocardium). The degree of morphological alterations was evaluated by electron microscopy.

RESULTS

In 70% of the 240 dysfunctional segments, 'stunned myocardium' was present whereas 'hibernating myocardium' could be detected in only 24% (P < 0.01). Hibernating myocardium was associated with more severe preoperative wall motion abnormalities and incomplete postoperative recovery. After 1 year, 31% of 'stunned' segments vs. only 18% of 'hibernating' segments showed complete functional restoration (P < 0.05). This incomplete improvement was associated with more severe morphological alterations including depletion of sarcomeres, accumulation of glycogen, loss of sarcoplasmatic reticulum, and cellular sequestration.

CONCLUSIONS

These data indicate that in patients with severe ischemic left ventricular dysfunction 'stunned myocardium' is more prevalent than 'hibernation'. Functional normalization is more frequent in 'stunned' segments, whereas areas of 'hibernation' showed more severe tissue injury and protracted recovery. Different degrees of myocardial injury coexist in most patients, which determines the time-course and the extent of improvement after revascularization.

Cardiac nuclear medicine in monitoring patients with coronary heart disease

Patient monitoring is a major indication for cardiac nuclear medicine procedures. Stress myocardial perfusion scintigraphy was initially used for diagnosis, but monitoring patients with coronary artery disease has become more common. Stress myocardial perfusion scintigraphy has been shown to provide a considerable amount of incremental prognostic information, which may be useful in selecting patients for therapy. In patients being considered for revascularization, fluorodeoxyglucose can be used to identify regions of dysfunctional but viable myocardium, even within regions that show fixed defects on stress perfusion imaging. It can be used to select a group of patients who will improve function with revascularization and who may have an improved outcome. Thus, cardiac nuclear medicine plays a pivotal role in monitoring patients with coronary artery disease.

Early assessment of regional myocardial blood flow and metabolism in thrombolysis in myocardial infarction flow grade 3 reperfused myocardial infarction using carbon-11-acetate

OBJECTIVES

The aim of this study was to investigate the prognostic value of carbon-11-acetate (acetate) positron emission tomography (PET) after successful reperfusion of myocardial infarction (MI).

BACKGROUND

Acetate PET allows the measurement of both myocardial flow and oxidative metabolism. The prognostic value of acetate measurements performed early (within 24 h) after Thrombolysis In Myocardial Infarction (TIMI) flow grade 3 reperfused MI is unknown.

METHODS

In 18 patients with TIMI flow grade 3 reperfusion of their first MI, a dynamic acetate study was performed within 24 h of the acute event. At five days, nitrogen-13-NH3 (NH3) and fluorine-18-labeled fluorodeoxyglucose (FDG) PET studies were performed. Infarct-related areas were classified as "PET viable" or "PET nonviable," as assessed with NH3 and FDG, according to previously established criteria. At five days and three months, radionuclide angiography was performed for evaluation of left ventricular (LV) function.

RESULTS

In infarct-related regions, myocardial blood flow, FDG uptake and oxygen consumption were decreased, compared with remote regions. However, oxygen consumption values, as measured with acetate in both PET-viable and PET-nonviable areas, as assessed with NH3 and FDG, were not significantly different (p = NS). A significant linear correlation was observed between global LV ejection fraction at three months and oxidative metabolism in the infarct-related area (r = 0.8, p < 0.0001). Multivariate analysis revealed that oxidative metabolism measurements in reperfused myocardium was the only significant predictor for recovery of LV function at three months (p < 0.05).

CONCLUSIONS

Measurement of oxidative metabolism early after TIMI flow grade 3 reperfusion of MI offers important prognostic value concerning LV function at follow-up.

The beating open heart for rebuilding ventricular geometry during surgical anterior restoration

Heart failure is an increasing problem because of successful therapies in younger age groups and an overall increase in age in the general population. Ischemic cardiomyopathy secondary to myocardial infarction is the most prevalent entity among the several causes for cardiac failure. Among the surgical options for these patients, neither transplantation nor current ventricular assist devices are able to treat a sufficient number of patients. Ventricular restoration, however, may evolve as a surgical option to treat myocardial failure secondary to postinfarction ventricular dilatation. This procedure must be undertaken in high-risk coronary artery bypass graft (CABG) patients in heart failure. We describe the techniques for both the conventional procedure (CABG +/- mitral valve [MV] repair) using cardioplegic methods, and the beating open heart for surgical anterior ventricular restoration (SAVR) for dyskinetic and akinetic areas in ischemic cardiomyopathies. This combined approach allows safe restoration of the ventricular geometry with minimal use of mechanical support (ie, intra-aortic balloon pump [IABP]) in 195 consecutive patients undergoing this procedure by members of an international team called the RESTORE group.

Prognostic value of impaired myocardial fatty acid uptake in patients with acute myocardial infarction

Impaired cardiac fatty acid uptake, assessed by the radiolabelled fatty acid analogue beta-methyl-p-iodophenyl pentadecanoic acid (I-123-BMIPP), is observed in the myocardium following acute ischaemic events, but the long-term prognostic implication has not been established. This study aimed to determine the prognostic value of cardiac BMIPP uptake in patients with acute myocardial infarction. Following the assessment of thallium-201 and I-123-BMIPP uptake, 101 post-infarct patients were prospectively followed up with primary end points of cardiac death, heart failure and non-fatal infarction. During a mean follow-up of 28 months, three cardiac deaths, three non-fatal infarctions, 23 revascularizations and four recurrences of angina pectoris were observed. Multivariate analysis identified reduced uptake of BMIPP and perfusion, no beta-blocking treatment and greater thallium-BMIPP mismatch (i.e. larger BMIPP defect than thallium defect) as significant predictors for overall cardiac events. Prior myocardial infarction, reduced left ventricular ejection fraction and greater thallium-BMIPP mismatch were selected as independent predictors of harder cardiac events. Female patients, those with greater BMIPP defect or greater thallium-BMIPP mismatch showed worse clinical outcomes. The inclusion of BMIPP data improved the prognostic values of conventional significant predictors. In conclusion, impaired myocardial I-123-BMIPP uptake and perfusion-BMIPP mismatch are related to a high probability of fatal and non-fatal cardiac events, suggesting the aetiological relevance and prognostic value of impaired cardiac fatty acid metabolism in viable, but jeopardized, myocardium following acute myocardial infarction.

Time course of functional recovery after coronary artery bypass graft surgery in patients with chronic left ventricular ischemic dysfunction

Chronic left ventricular (LV) ischemic dysfunction, a condition often referred to as myocardial hibernation, is associated in humans with ultrastructural alterations of the myocytes, including the loss of myofilaments and the accumulation of glycogen. Given the severity of these structural changes, contractile function is unlikely to resume immediately upon revascularization. Therefore, the aim of the present study was to assess the time course of functional improvement after successful revascularization as well as its potential structural correlates. We studied 32 patients with coronary disease and chronic LV ischemic dysfunction who underwent bypass surgery. Dynamic positron emission tomography with N-13 ammonia and F-18 deoxyglucose to assess myocardial perfusion and glucose metabolism was performed in 29 patients. In all patients, a transmural biopsy was harvested from the center of the dysfunctional area, to quantify the increase in extracellular matrix and the presence of structurally altered cardiomyocytes. LV function was serially measured by digitized 2-dimensional echocardiography before and at 10 days, 2 months, and 6 months after revascularization. The time course of recovery of regional function was estimated from the monoexponential decrease in dysfunctional wall motion score. At follow-up, 19 patients had improved LV function, whereas 13 patients showed persistent dysfunction. Before revascularization, reversibly dysfunctional segments had higher myocardial blood flow (82 +/- 29 vs 53 +/- 21 ml. (min. 100 g)(-1), p = 0.044), higher glucose uptake (40 +/- 16 vs 21 +/- 9 micromol. (min. 100 g)(-1), p = 0.001), and less increase in extracellular matrix (25 +/- 15% vs 46 +/- 17%, p = 0.0008) than segments with persistent dysfunction. The extent to which function recovered was positively correlated with myocardial blood flow and negatively correlated with the increase in the extracellular matrix. In patients with reversible dysfunction, the return of segmental function was progressive and followed a monoexponential time course with a median time constant of 23 days (range 6 to 78). The rate of recovery correlated best with the proportion of altered cardiomyocytes in the biopsy. The present study thus indicates that the recovery of regional and global LV function after successful revascularization is progressive and follows a monoexponential time course that is influenced by the extent of the structural changes affecting cardiomyocytes.

Positron emission tomography is a useful tool in differentiating idiopathic from ischemic dilated cardiomyopathy

We evaluated the utility of positron emission tomography in differentiating patients with idiopathic dilated cardiomyopathy from those with ischemic cardiomyopathy. Twenty consecutive non-diabetic patients with dilatation (end-diastolic volume > or = 120 cc/m2) and reduced systolic function (ejection fraction < or = 40%) of the left ventricle on cineangiography, underwent coronary angiography, F18 fluorodeoxyglucose (F18-FDG) (glucose load technique) and N13-ammonia (N13-NH3) positron emission tomography. A semiquantitative score based on the extension and the severity of the uptake defects was calculated. Endomyocardial biopsy was performed in patients with normal coronary arteries. Ten patients (group A) had normal coronary arteries and histologic features of the endomyocardium fitting with the diagnosis of idiopathic dilated cardiomyopathy. Cineangiography showed critical stenosis of at least one major coronary artery in the other 10 patients (group B). The two groups were similar in age. left ventricular end-diastolic volume and ejection fraction. Both N13-NH3, positron emission tomography and F18-FDG positron emission tomography scores were lower in group A than in group B: 0.1 +/- 0.3 vs. 10.6 +/- 5.1 (P<0.0001) and 2.4 +/- 4.4 vs. 9.9 +/- 4.1 (P<0.0001) respectively. but only N13-NH3 positron emission tomography allowed a complete separation of the two groups (score range 0-1 group A vs. 4-12 group B). The F18-FDG score value showed some overlapping between the two groups (score range 0-12 in the group A vs. 2-17 in the group B). All three idiopathic dilated cardiomyopathy patients with a F18-FDG score value >2 had left bundle branch block on standard ECG. Positron emission tomography imaging with N13-NH3 and F18-FDG provided a complete differentiation between idiopathic dilated cardiomyopathy and ischemic cardiomyopathy patients. However patients with left bundle branch block on ECG could present defects in FDG uptake even if affected by idiopathic dilated cardiomyopathy.

Use of echocardiography for predicting myocardial viability in patients with reperfused anterior wall myocardial infarction

Dobutamine stress echocardiography (DSE), myocardial contrast echocardiography (MCE), and ultrasonic tissue characterization with integrated backscatter are useful methods for assessing myocardial viability in acute myocardial infarction. In this study, we compared the potential of 3 methods for predicting myocardial viability in 38 patients with reperfused anterior wall acute myocardial infarction. We performed MCE shortly after coronary reperfusion with an intracoronary injection of microbubbles. We recorded 2-dimensional integrated backscatter images at rest and, then, performed low-dose (10 microg/kg/min) DSE 3 days later. In integrated backscatter images, we placed the region of interest in the midwall of the myocardial segment to reconstruct the cyclic variation of myocardial integrated backscatter. The myocardial segment was judged viable when it showed active contraction 3 months later. Among 74 segments analyzed, 34 were judged viable. Presence of contractile response during DSE predicted segmental viability with 91% sensitivity and 78% specificity. Intense and homogenous contrast enhancement with MCE predicted viability with 82% sensitivity and 73% specificity. The presence of synchronous contraction of cyclic variation predicted myocardial viability with 79% sensitivity and 83% specificity. There were no differences in sensitivity and specificity among the 3 methods. Thus, MCE and ultrasonic tissue characterization can predict myocardial viability as accurately as DSE in patients with acute myocardial infarction. The logistics of the methods may determine clinical application.

Physiologic response to gain and loss in coronary minimal luminal diameter in patients treated with coronary angioplasty: prediction of restenosis on the basis of exercise capacity

BACKGROUND

The effect of percutaneous transluminal coronary angioplasty (PTCA) on physiologic measurements has previously been shown, but the relation between physiologic response and degree of change in coronary luminal diameter is not known. We studied the relation between exercise capacity and minimal luminal diameter before and after PTCA. We also explored the usefulness of measurement of attenuation in exercise capacity after PTCA to predict the likelihood of restenosis.

METHODS

Bicycle exercise testing was performed 2 weeks before and 2 and 20 weeks after PTCA in 395 consecutively enrolled patients. Angiograms obtained before and after PTCA and 20 weeks afterward were analyzed by quantitative coronary angiography. Restenosis was defined as both angiographic (>/=50% diameter stenosis at follow-up angiography) and clinical (target-vessel revascularization), after successful PTCA. Exercise capacity was defined as the cumulative work performed divided by body weight (watt x minutes x kilograms(-1)).

RESULTS

Exercise capacity increased 43% (P <.0001) from before PTCA to 2 weeks after PTCA (early increase) and decreased 4% (P =.01) from 2 to 20 weeks after PTCA (late decrease). The gain in minimal luminal diameter (Minimal luminal diameter after - Minimal luminal diameter before) was 0.92 +/- 0.46 mm. The loss in minimal luminal diameter (Minimal luminal diameter after PTCA - Minimal luminal diameter at follow-up examination) was 0.27 +/- 0.42 mm. Exercise capacity and minimal luminal diameter measured before PTCA were positively correlated (coefficient 3.3; R = 0.12; P =.01). Gain in minimal luminal diameter correlated with the early increase in exercise capacity (coefficient -3.8; R = 0.23; P <.0001). Loss in minimal luminal diameter correlated with the late decrease in exercise capacity (coefficient 3.3; R = 0.20; P <.0001). Multivariate logistic regression analysis revealed that the late decrease in exercise capacity was independently predictive of both angiographically (odds ratio 1.13; P <.0001) and clinically (odds ratio 1.12; P <.0001) defined restenosis.

CONCLUSIONS

The results demonstrated a linear relation between the severity of coronary stenosis and exercise capacity measured before PTCA. The degree of coronary luminal enlargement achieved with angioplasty and the luminal reduction that occurred between PTCA and follow-up evaluation correlated with increases and decreases in exercise capacity. Attenuation in exercise capacity was found to be a strong predictor of restenosis.

[Nuclear cardiology: technical bases and clinical applications]

Although the role of nuclear cardiology is currently well consolidated, the addition of new radiotracers and modern techniques makes it necessary to continuously update the requirements, equipment and clinical applications of these isotopic tests. The characteristics of the radioisotopic drugs and examinations presently used are explained in the first part of this text. In the second, the indications of them in diagnostic and prognostic evaluation of the different coronary diseases are presented.

Do the presence and amount of dysfunctional but viable myocardium affect the perioperative outcome of coronary artery bypass graft surgery?

The aim of our study was to assess the influence of the presence and amount of dysfunctional but viable myocardium on the perioperative outcomes in patients with coronary artery disease and moderate-to-severe left ventricular systolic dysfunction, who underwent coronary artery bypass graft surgery. Viability evaluation with low-dose dobutamine echocardiography was performed in 302 consecutive patients with coronary artery disease and left ventricular ejection fraction < or =40%, who were referred for coronary angiography and potential coronary revascularization. To quantify the amount of dysfunctional but viable myocardium, wall motion was scored using a 16-segment model. The dysfunctional segments were defined as viable if they exhibited improvement in their thickening by at least one grade. One hundred and twenty-seven patients underwent coronary artery bypass graft surgery. The perioperative outcomes were evaluated in 122 of them. Five patients were excluded because of inability to revascularize all vessels supplying dysfunctional but viable myocardial segments. Twenty-five patients exhibited a large amount of dysfunctional but viable myocardium (> or =6 segments, group A), 59 patients had a small amount of such myocardium (2-5 segments, group B), and 38 patients were found to have their dysfunctional myocardium irreversibly damaged (group C). The perioperative mortality in groups A, B, and C was 4, 10, and 11% (all P = NS), respectively. The rate of perioperative Q-wave myocardial infarction was 8, 10, and 3% (all P = NS), respectively. Similarly, there were no significant differences among the groups with respect to perioperative outcome variables including ventricular arrhythmias, duration and magnitude of catecholamine support, renal failure, pulmonary edema, and need for mechanical ventricular support or artificial ventilation. In patients with coronary artery disease and moderate-to-severe left ventricular dysfunction who underwent coronary artery bypass graft surgery, the presence and amount of dysfunctional but viable myocardium did not influence the perioperative outcome.

PET as a cardiovascular and metabolic research tool

Positron emission tomography (PET) represents the most advanced scintigraphic imaging technology. It can be employed for cardiovascular research as well as for clinical applications in patients with various cardiovascular diseases. PET allows the noninvasive functional assessment of myocardial perfusion, substrate metabolism and cardiac innervation as well as the study of skeletal muscle metabolism and perfusion in vivo. The large number of existing tracers and the flexibility of the PET technique that allows it to be combined with many other methods, such as the insulin clamp technique, increase its potential as a research tool. In the detection of myocardial viability PET is regarded as the golden standard, and it is the only method available for the quantitative assessment of myocardial blood flow.

Hypoxic Hypoperfusion Fails to Induce Myocardial Hibernation in Anesthetized Swine

BACKGROUND: Congenital origin of the left coronary artery from the pulmonary artery (ALCAPA) results in chronically dysfunctional myocardium with the partial ability to recover after revascularization. We attempted to establish an ALCAPA syndrome in anesthetized pigs for 24 hours and to compare it with stunned and infarcted myocardium. METHODS AND RESULTS: In group 1 (n = 12), a bypass graft was interposed between the pulmonary artery and the left anterior descending coronary artery (LAD). Reduction of flow in the LAD with gradual increases in flow from the pulmonary artery resulted in an incremental reduction of segment shortening (8.9 +/- 5.3% at 24 hours vs 26.6 +/- 10% at baseline, P <.005). In group 3 (n = 5), 2 cycles of 10-minute LAD occlusion resulted in decreased segment shortening with slow recovery (at 24 hours 18.7 +/- 1.3% vs 24.2 +/- 4% at baseline, segment shortening with slow recovery (at 24 hours 18.7 +/- 1.3% vs 24.2 +/- 4% at baseline, P <.05). In group 3 (n = 6), 1-hour LAD occlusion reduced segment shortening at 24 hours to 4.7 +/- 5.2% (P <.005 vs baseline). Histological analysis of the LAD territory revealed severe degeneration, myolysis, and alteration of the chromatin structure in group 1 comparable to ischemic cell death in group 3, whereas control areas and the LAD area in group 2 showed only minor structural alterations. Infarct size/risk area, as measured by tetrazolium staining, was 49.8 +/- 11.2% in group 1, 9.3 +/- 8.1% in group 2 (P <.005), and 60.3 +/- 9% in group 3. CONCLUSION: Hypoxic myocardial hypoperfusion from the pulmonary artery results in myocardial necrosis in anesthetized pigs. These findings are in contrast to the concept of myocardial hibernation in the ALCAPA syndrome because in this model, hypoxic hypoperfusion failed to induce adaptation to preserve myocardial structure.

Efficacy of coronary angioplasty for the treatment of hibernating myocardium

OBJECTIVES

To determine the efficacy of coronary angioplasty as the sole method of revascularisation in patients with coronary artery disease and chronically dysfunctional but viable myocardium (hibernating myocardium), and to assess the effect of restenosis on functional outcome.

DESIGN AND PATIENTS

24 consecutive patients with hibernating myocardium were studied. Positron emission tomography was used to assess myocardial viability, blood flow, and flow reserve. One patient refused angioplasty, one had bypass surgery, and one died while waiting for an elective procedure. The procedure failed in three patients. The remaining 18 patients had repeat echocardiography, 15 had repeat coronary angiography, and nine had repeat assessments of blood flow and flow reserve at mean (SD) 17 (2) weeks after angioplasty. In three patients restenosis was documented.

RESULTS

The wall motion score index in the revascularised territories improved from 1.71 (0.37) to 1.34 (0.47) (p = 0.008). Thirty of 51 dysfunctional segments improved in territories without restenosis compared with three of 14 in restenosed territories (p = 0.001). Hibernating and normal segments had comparable flows (0.82 (0.26) v 0.89 (0.24) ml/min/g; NS) while flow reserve was lower in hibernating segments (1.55 (0.68) v 2.07 (1.08); p = 0.03). In segments without restenosis flow reserve improved from 2.03 (1.25) to 2.33 (1.4) (p = 0.03). Sensitivity, specificity, and positive and negative predictive accuracy of the viability study were 97%, 77%, 82%, and 96%, respectively. After excluding patients with restenosis, specificity and positive predictive accuracy improved to 90% and 93%.

CONCLUSIONS

Angioplasty improves function in hibernating myocardium, and restenosis prevents recovery; hibernating myocardium is characterised by an impairment of flow reserve; restenosis affects the diagnostic accuracy of viability studies.

Functional evaluation of myocardial viability by 99mTc tetrofosmin gated SPECT--a quantitative comparison with 18F fluorodeoxyglucose positron emission CT (18F FDG PET)

To validate functional analysis of gated SPECT in detecting myocardial viability, seventeen patients (male 15, female 2, mean age 58) with angiographically proven chronic ischemic heart disease (RCA 6, LAD 10, LCX 1) and eight normal volunteers (all male) were studied. All patients underwent 18F FDG PET and 99mTc tetrofosmin (TF) gated SPECT within a week. After being displayed in a polar map, myocardial perfusion was regionally determined by the mean count in 9 segments at end diastole (ED) and end systole (ES) in gated SPECT. Systolic function was determined by the count increase ratio from ED to ES (WTI: ES - ED/ED). Glucose metabolism was assessed by 18F FDG PET in the segments correspondent to those defined for SPECT. TF %uptake of < 60% was defined as hypoperfusion, and FDG %uptake of < 50% was defined as reduced glucose metabolism.

RESULTS

The myocardial segments were classified into 3 categories: "normal" perfusion (n = 85), "mismatch" (reduced perfusion with reserved FDG uptake, n = 25) and "matched" reduced perfusion and metabolic reduction (n = 26). Mean WTI in "mismatch" segment was 0.38 +/- 0.21, and was significantly greater than that in "matched reduced" segments, 0.15 +/- 0.20 (p < 0.001). It was also greater than that in "normal" segments, 0.27 +/- 0.16. Regression analysis showed that association between WTI and FDG %uptake was significant (r = 0.57, p < 0.0005) for the ischemic segments ("mismatch" + "matched", n = 51), but the association was weak for the entire segments although it was statistically significant (r = 0.26, p = 0.02, n = 136).

CONCLUSION

For the segments determined as infarct by perfusion image, systolic functional analysis by gated SPECT is helpful in differentiation of a viable myocardial region or artifact from a scar. Nevertheless, further clinical and technical assessment is required for ECG gating to eliminate overestimation of viability and to warrant clinical use.

Blood flow-metabolism imaging with positron emission tomography in patients with diabetes mellitus for the assessment of reversible left ventricular contractile dysfunction

OBJECTIVES

The purpose of this study was to evaluate the predictive accuracy of positron emission tomography (PET) blood flow-F-18 fluorodeoxyglucose (FDG) imaging in coronary artery disease (CAD) patients with diabetes mellitus (DM).

BACKGROUND

Positron emission tomography accurately predicts the postrevascularization improvement in left ventricular dysfunction in unselected patients with CAD. In diabetic patients, however, poor myocardial glucose utilization may limit the accuracy of the approach.

METHODS

Forty patients (64+/-10 years old; 19 with DM = group I; 21 without DM = group II) with reduced left ventricular ejection fraction (LVEF = 29+/-6%) were studied with N-13 ammonia and FDG PET before coronary revascularization. Studies were performed after intravenous injection of regular insulin (group I) or oral glucose administration (group II). Blood flow-FDG mismatches and matches were identified by polar map analysis in the three vascular territories of the left anterior descending, left circumflex and right coronary artery. Wall motion and LVEF were assessed by two-dimensional echocardiography before and 158+/-123 days after revascularization.

RESULTS

Of 107 vascular territories analyzed, 46 were classified as mismatch, 29 as match and 32 as normal. The FDG image quality, assessed by F-18 myocardium to blood pool activity ratios, and the predictive accuracy were similar in both groups; presence of a blood flow/FDG mismatch had a sensitivity of 92% (group I) and 94% (group II) and a specificity of 85% (group I) and 79% (group II) for an improvement in regional left ventricular function. A postrevascularization improvement in global left ventricular function was related to the extent of blood flow/FDG mismatch; LVEF increased from 30+/-7% to 35+/-7% (p = 0.017) in patients with one mismatch and from 27+/-4% to 41+/-7% (p < 0.001) in those with two mismatches.

CONCLUSIONS

The predictive accuracy of blood flow/FDG imaging is maintained in patients with DM when a clinically acceptable study protocol, which guarantees good FDG image quality, is used. The extent of a blood flow/metabolism mismatch is correlated with the magnitude of the postrevascularization improvement in global left ventricular function.

Prevalence of hibernating myocardium in patients with severely impaired ischaemic left ventricles

OBJECTIVE

Severe impairment of left ventricular (LV) contraction is associated with an adverse prognosis in patients with ischaemic heart disease. Revascularisation may improve the impaired LV contraction if hibernating myocardium is present. The proportion of patients likely to benefit from this intervention is unknown. Therefore, the prevalence of hibernating myocardium in patients with ischaemic heart disease and severe impairment of LV contraction was assessed.

DESIGN

From a consecutive series of patients undergoing coronary angiography for the investigation of chest pain or LV impairment, all patients with ischaemic heart disease and an LV ejection fraction (LVEF) < or = 30% were identified. These patients underwent positron emission tomography (PET) to detect hibernating myocardium, identified by perfusion metabolism mismatch.

SETTING

A teaching hospital directly serving 500,000 people.

RESULTS

Of a total of 301 patients, 36 had ischaemic heart disease and an LVEF < or = 30%. Twenty-seven patients had PET images, while nine patients were not imaged because of emergency revascularisation (three), loss to follow up (one), inability to give consent (four), and age < 50 years (one, ethics committee guidelines). Imaged and non-imaged groups were similar in LV impairment, demographic characteristics, and risk factor profile. Fourteen patients (52% of the imaged or 39% of all patients with ischaemic heart disease and LVEF < or = 30%) had significant areas of hibernating myocardium on PET.

CONCLUSION

It is possible that up to 50% of patients with ischaemic heart disease and severely impaired left ventricles have hibernating myocardium.

Restoration of contractile function in the enlarged left ventricle by exclusion of remodeled akinetic anterior segment: surgical strategy, myocardial protection, and angiographic results

A variant of the Dor cardioprotective approach for reducing ventricular volume was applied to 12 consecutive postinfarction patients with akinetic anterior segments. Cardioplegia was avoided for restoration, but used for revascularization and valve replacement. The continually perfused beating open heart was used for protection during surgical anterior ventricular restoration (SAVR). These ischemic cardiomyopathy patients (age 77 +/- 6 years) preoperatively had high LVEDVI (170 vs 75 mL/m2, normal) and LVESVI (132 vs 25 mL/m2, normal) and 20 +/- 8% ejection fraction (mean +/- S.D.). An oval patch with outer flange for hemostasis was used. Patients also underwent revascularization (10/12), reoperation (6/12), and valve procedures (6/12). Continuous perfusion of the beating open heart was used for cardiac protection during restoration. Blood cardioplegia was used for revascularization and valvular procedures. Transesophageal echocardiogram (TEE) estimated intraventricular contractility in all patients, and biplane ventriculograms were used in 8 patients to measure cardioreduction. Immediate hemodynamic performance was excellent in all patients, despite 178 +/- 34 minutes of bypass. Extracorporeal circulation was stopped 10 minutes after closing the ventriculotomy. No intraaortic balloon pump or LV assist devices were needed. Ejection fraction estimated by TEE increased from 20% to 45%; and biplane ventriculograms showed 28% reduction of LVEDVI, 39% reduction of LVESVI, and raised ejection fraction from 20% to 35%. The spherical ventricular shape after akinetic infarction was made into a more normal elliptical contour by this procedure. Subsequently, restoration may become as important as revascularization in treating akinetic segments after anterior infarction.

Myocardial viability during dobutamine echocardiography predicts survival in patients with coronary artery disease and severe left ventricular systolic dysfunction

OBJECTIVES

The purpose of this study was to assess whether the presence or absence of myocardial viability during dobutamine echocardiography (DE) predicts survival in patients with coronary artery disease (CAD) and severe left ventricular (LV) dysfunction.

BACKGROUND

In patients with CAD, the presence of myocardial viability during DE identifies viable myocardium and predicts recovery of LV systolic function after revascularization. However, there is little data on the relation between myocardial viability and clinical outcome in patients with CAD and severe LV dysfunction.

METHODS

We studied 318 patients with CAD and a LV ejection fraction (EF) < or =35% who underwent DE and were followed for 18+/-10 months. Patients were classified into four groups. Group I (n=85) consisted of patients who had evidence of myocardial viability and subsequently underwent revascularization. Group II (n=119) consisted of patients with myocardial viability who did not undergo revascularization. Group III (n=30) consisted of patients who did not have myocardial viability and underwent revascularization. Finally, group IV (n=84) patients lacked myocardial viability and did not undergo revascularization.

RESULTS

The four groups had similar baseline characteristics and rest LVEF. During follow-up there were 51 deaths (16%). The mortality rate was 6% in group I, 20% in group II, 17% in group III and 20% in group TV (p=0.01, group I vs. other groups).

CONCLUSIONS

In patients with CAD and severe LV dysfunction who demonstrated myocardial viability during DE, revascularization improved survival compared with medical therapy.

Coronary revascularization in the treatment of moderate and severe postischemic left ventricular dysfunction

Chronic postischemic left ventricular (LV) dysfunction can improve following coronary revascularization (hibernating myocardium). However, it is not clear whether the severity of LV dysfunction determines functional outcome after revascularization and the accuracy of tests to predict myocardial viability. We studied 47 patients with coronary artery disease and chronic LV dysfunction. Before coronary bypass, patients underwent (18F)2-fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) during euglycemic hyperinsulinemic clamp to assess viability. Global and regional LV function were assessed before and 4 to 6 months after surgery. Patients were arbitrarily divided into 2 groups with moderate and severe LV dysfunction. Group 1 (n = 26) had an ejection fraction (EF) of < or = 30% and group 2 (n = 21) > 30%. After bypass, the EF (22+/-6% vs 31+/-10%; p <0.0001) and global wall motion score (WMS) (2.05+/-0.39 vs 1.56+/-0.34; p <0.001) improved in group 1, whereas the EF (43+/-9% vs 43+/-12%; p = NS) was unchanged in group 2, although WMS tended to improve (1.42+/-0.38 vs 1.32+/-0.39; p = 0.09). The proportion of dysfunctional segments (72% vs 32%; p <0.0001) and FDG uptake in these segments (0.44+/-0.15 vs 0.34+/-0.15 micromol/g/min, p <0.0001) were greater in group 1 than in group 2. The baseline EF influenced the predictive accuracy of PET, with highest positive predictive accuracy in group 2 and highest negative predictive accuracy in group 1. Thus, coronary revascularization has the potential for greatest benefit in patients with the most severe dysfunction, but with evidence of viability, and the entity of LV dysfunction affects the predictive accuracy of viability studies.

Clinical usefulness of iodine 123-labeled fatty acid imaging in patients with acute myocardial infarction

BACKGROUND

Iodine 123-labeled 15-(p-iodophenyl)-3R,S-methylpentadecanoic acid (BMIPP) has recently been developed, since normal myocardium metabolizes free fatty acids. This study investigated the clinical usefulness of BMIPP imaging in patients with acute myocardial infarction (MI), particularly in the detection of stunned myocardium in patients who underwent acute coronary revascularization.

METHODS

The subjects were 41 patients with acute MI who had undergone emergency coronary revascularization. Both BMIPP and thallium-201 images at rest were obtained during the subacute phase. The myocardial distribution of radiotracers was quantified by generating circumferential count-distribution profile analysis. Initial 201Tl imaging, delayed 201Tl imaging, and BMIPP imaging were performed, and the mean count densities in the infarct region (initial 201Tl images [TL1], delayed 201Tl images [TL2], and BMIPP images in the infarct region [BM], respectively) were obtained. The differences between mean count densities (TL1-BM: BM subtracted from TL1; TL2-BM: BM subtracted from TL2) were also calculated.

RESULTS

BM showed a higher correlation with wall motion data by echocardiography (WM) in the acute phase than other nuclear imaging tests, whereas TL2 showed the highest correlation with WM in the chronic phase. Acute to chronic WM improvement showed a good correlation with TL2-BM.

CONCLUSION

Single photon emission computed tomography imaging with BMIPP is a candidate for providing the "memory image" of ischemic damage, whereas TL2 reflects all viable tissue. The mismatch between the tracers can serve as an indicator of myocardial stunning.

Basic and clinical aspects of myocardial stunning

Although the pathogenesis of myocardial stunning has not been definitively established, the two major hypotheses are that it is caused by the generation of oxygen-derived free radicals on reperfusion and by a loss of sensitivity of contractile filaments to calcium. These hypotheses are not mutually exclusive and are likely to represent different facets of the same pathophysiological cascade. For example, a burst of free radical generation after reperfusion could alter contractile filaments in a manner that renders them less responsive to calcium. Increased free radical formation could also cause cellular calcium overload, which would damage the contractile apparatus of the myocytes. There is now considerable evidence that myocardial stunning occurs clinically in various situations in which the heart is exposed to transient ischemia, such as unstable angina, acute myocardial infarction with early reperfusion, exercise-induced ischemia, cardiac surgery, and cardiac transplantation. Recognition of myocardial stunning is clinically important and may impact patient treatment. Although no ideal diagnostic technique for myocardial stunning has yet been developed, thallium-201 scintigraphy or dobutamine echocardiography are available and can be useful to identify viable myocardium with reversible wall motion abnormalities. An intriguing possibility is that so-called chronic hibernation may in fact be the result of repetitive episodes of stunning, which have a cumulative effect and cause protracted postischemic left ventricular dysfunction. A better understanding of myocardial stunning will expand our knowledge of the pathophysiology of myocardial ischemia and provide a rationale for developing new therapeutic strategies designed to prevent postischemic dysfunction.

Low dose dobutamine echocardiography predicts improvement in functional capacity after exercise training in patients with ischemic cardiomyopathy: prognostic implication

OBJECTIVES

This study sought to investigate whether the identification of hibernating myocardium by low dose dobutamine stress echocardiography (LDSE) may predict an improvement in functional capacity after moderate exercise training in patients with ischemic cardiomyopathy. Another objective was to assess whether exercise training may affect the outcome.

BACKGROUND

There is evidence that exercise training improves left ventricular (LV) function as well as functional capacity in patients with a previous myocardial infarction and LV dysfunction. We hypothesized that the magnitude of these improvements might be related to the extent of hibernating myocardium.

METHODS

We studied 71 consecutive patients 56+/-9 years old (mean +/- SD) with chronic heart failure secondary to ischemic cardiomyopathy (LV ejection fraction [LVEF] <40%). All patients were in sinus rhythm and were clinically stable during the previous 3 months. Patients were randomized into two matched groups. Group T (n = 36) underwent exercise training at 60% of peak oxygen uptake (Vo2) three times a week for 10 weeks. Group C (n = 35) did not exercise. At study entry and end, all patients underwent an exercise test with gas exchange analysis and LDSE (5 to 20 microg/kg body weight per min).

RESULTS

At baseline, a positive contractile response (CS+) to LDSE was observed in 317 of 576 segments in group T and 291 of 560 segments in group C. After 10 weeks, peak Vo2 and peak work rate increased only in trained patients (peak Vo2: from 16.2+/-3 to 20.8+/-4 ml/kg per min; work capacity: from 108+/-20 to 131+/-25 W, p < 0.001 vs. group C for both). The presence of CS+ at baseline was associated with a sensitivity of 70% and a specificity of 77% for predicting an increase in the functional capacity after exercise training. Positive and negative predictive values of LDSE were 84% and 59%, respectively. Independent predictors of cardiac events were a pre-to-posttraining difference in LVEF at peak dobutamine infusion and the presence of a viable response at baseline (p = 0.004 and 0.008, respectively). The log-rank test demonstrated that trained patients had a significantly lower probability of cardiac events during follow-up than sedentary control patients (p < 0.001).

CONCLUSIONS

The presence of hibernating myocardium as assessed by LDSE predicts the magnitude of improvement in functional capacity after moderate exercise training in patients with chronic heart failure. A significant increase in functional capacity after exercise training is associated with a lower incidence of cardiac events during follow-up.

Prolonged myocardial hibernation exacerbates cardiomyocyte degeneration and impairs recovery of function after revascularization

OBJECTIVES

We sought to define the effects of time on contractile function, morphology and functional recovery after coronary revascularization in patients with dysfunctional but viable (hibernating) myocardium.

BACKGROUND

Functional recovery after coronary artery bypass graft surgery in patients with chronic myocardial hibernation is incomplete or delayed. The proposed cause is a progressive temporal degeneration of cardiomyocytes.

METHODS

In 32 patients with multivessel coronary disease, regional wall motion analysis was performed in hypoperfused but metabolically active areas before and 6 months after bypass surgery. During bypass surgery, transmural biopsy samples were obtained from the center of the hypokinetic zone for light and electron microscopic analyses. The proposed duration of myocardial hibernation was retrospectively assessed.

RESULTS

Patients with a subacute hibernating condition (<50 days) demonstrated a higher preoperative ejection fraction (EF, 50+/-8%), and a better preserved wall motion (WM) in the supraapical wall (-1.4+/-0.4) than did patients with intermediate-term (>50 days, EF 37+/-9%, p < 0.05; WM -2.4+/-1.5, p = 0.08) or chronic (>6 months, EF 40+/-14%, WM -2.7+/-0.9, p < 0.005) ischemia. Structural degeneration correlated with the duration of ischemia (r = 0.56, p < 0.05). Postoperative recovery of function was enhanced in patients with a short history of hibernation compared with patients with an intermediate-term or chronic condition (EF 60+/-10% vs. 40+/-10%, p < 0.001, and vs. 47+/-14%, p < 0.05).

CONCLUSIONS

Hibernating myocardium exhibits time-dependent deterioration due to progressive structural degeneration with enhanced fibrosis. Early revascularization should be attempted to salvage the jeopardized tissue and improve postoperative outcome.

Reliability of the exercise-induced ST-segment changes to detect restenosis three months after coronary angioplasty: significance of the appearance in other leads

BACKGROUND

Exercise-induced ST-segment changes 3 months after angioplasty may sometimes show a false-positive result.

METHODS

We therefore analyzed the ST changes observed during the exercise tests performed before and 3 months after angioplasty in 118 patients with single-vessel coronary artery disease.

RESULTS

Ninety-two (78%) of the 118 patients had ST changes in the same lead before and after angioplasty, whereas the remaining 26 (22%) patients had ST changes in other leads in the postangioplasty test when compared with the preangioplasty exercise test. Restenosis was found in 44 (48%) of the 92 patients with ST changes in the some lead but in only four (15%) of the 26 patients with ST changes in other leads.

CONCLUSIONS

Exercise-induced ST-segment changes are not reliable markers of restenosis 3 months after angioplasty. ST-segment changes observed in other leads after angioplasty compared with the preangioplasty exercise test may show a false-positive result.

Downregulation of immunodetectable connexin43 and decreased gap junction size in the pathogenesis of chronic hibernation in the human left ventricle

BACKGROUND

The regional wall motion impairment and predisposition to arrhythmias in human ventricular hibernation may plausibly result from abnormal intercellular propagation of the depolarizing wave front. This study investigated the hypothesis that altered patterns of expression of connexin43, the principal gap junctional protein responsible for passive conduction of the cardiac action potential, contribute to the pathogenesis of hibernation.

METHODS AND RESULTS

Patients with poor ventricular function and severe coronary artery disease underwent thallium scanning and MRI to predict regions of normally perfused, reversibly ischemic, or hibernating myocardium. Twenty-one patients went on to coronary artery bypass graft surgery, during which biopsies representative of each of the above classes were taken. Hibernation was confirmed by improvement in segmental wall motion at reassessment 6 months after surgery. Connexin43 was studied by quantitative immunoconfocal laser scanning microscopy and PC image software. Analysis of en face projection views of intercalated disks revealed a significant reduction in relative connexin43 content per unit area in reversibly ischemic (76.7+/-34.6%, P<.001) and hibernating (67.4+/-24.3%, P<.001) tissue compared with normal (100+/-30.3%); ANOVA P<.001. The hibernating regions were further characterized by loss of the larger gap junctions normally seen at the disk periphery, reflected by a significant reduction in mean junctional plaque size in the hibernating tissues (69.5+/-20.8%) compared with reversibly ischemic (87.4+/-31.2%, P=.012) and normal (100+/-31.5%, P<.001) segments; ANOVA P<.001.

CONCLUSIONS

These results indicate progressive reduction and disruption of connexin43 gap junctions in reversible ischemia and hibernation. Abnormal impulse propagation resulting from such changes may contribute to the electromechanical dysfunction associated with hibernation.

Reliability of exercise-induced ST segment changes to detect restenosis 3 months after coronary angioplasty: significance of the appearance in other leads

Exercise-induced ST-segment changes 3 months after angioplasty sometimes may show a false-positive result. We therefore analyzed the ST changes observed during the exercise tests performed before and 3 months after angioplasty in 118 patients with single-vessel coronary artery disease. Ninety-two (78%) of the 118 patients had ST changes in the same lead before and after angioplasty, whereas the remaining 26 (22%) patients had ST changes in other leads in the postangioplasty exercise test when compared with the preangioplasty test. Restenosis was found in 44 (48%) of the 92 patients with ST changes in the same lead but in only 4 (15%) of the 26 patients with ST changes in other leads. We conclude that exercise-induced ST segment changes are not reliable markers of restenosis 3 months after angioplasty. ST segment changes observed in other leads after angioplasty may show a false-positive result when compared with the preangioplasty exercise test.

Serial changes in response of hibernating myocardium to inotropic stimulation after revascularization: a dobutamine echocardiographic study

OBJECTIVES

We sought to evaluate the serial changes in the response of the hibernating myocardium to dobutamine stimulation after revascularization.

BACKGROUND

An improvement in myocardial contraction during dobutamine stress echocardiography (DSE), particularly a biphasic response, predicts recovery of rest function. However, little is known about the changes in the response of the myocardium to dobutamine after revascularization.

METHODS

Thirty-four patients with stable coronary artery disease and regional left ventricular dysfunction underwent DSE before, early (within 1 week) and late (>6 weeks) after coronary angioplasty. Dobutamine was given in incremental doses from 2.5 to 40 microg/kg body weight per min.

RESULTS

Of 180 revascularized segments with severe rest dysfunction, recovery of rest function was seen in 56 segments (31%) late after angioplasty, 80% of which had early recovery. Ventricular function during DSE was similar early and late after revascularization. Patients who showed a biphasic response to DSE before revascularization (n = 12) had the most improvement in function at rest (mean [+/-SD] wall motion score index [WMSI] 1.98 +/- 0.75 vs. 1.35 +/- 0.54, p < 0.05) and during DSE (2.11 +/- 0.67 vs. 1.21 +/- 0.41, p < 0.05) late after revascularization. Patients with sustained improvement during DSE before revascularization had no significant change in wall motion during DSE after angioplasty. However, patients without improvement in function at low dose DSE, who demonstrated worsening of function at a high dose, had significant augmentation in wall motion during DSE after revascularization (WMSI 2.16 +/- 0.50 vs. 1.60 +/- 0.57, p < 0.05). Patients who had no recovery of rest function had significant improvement in wall motion response to DSE, particularly when ischemia was inducible before revascularization.

CONCLUSIONS

In myocardial hibernation, the majority of recovery of rest function occurs early after revascularization. Although patients who recover rest function show the most marked improvement in wall motion during DSE, those without recovery of rest function also have improved function during DSE, particularly when there is evidence of ischemia before revascularization.

[Clinical usefulness of positron emission tomography (PET) in the evaluation of myocardial viability]

Positron emission tomography (PET) is a radionuclide imaging technique that allows quantitative assessment of regional myocardial function. It is mainly used in clinics to assess viability of dissynergic myocardium, by means of combined images of flow (with ammonia) and metabolism (with fluordeoxyglucose). The mismatch pattern, with an increase in fluordeoxyglucose metabolism in hypoperfused regions, is indicative of viability. The match pattern (a decrease in flow and metabolism in the same areas) is indicative of necrosis. Viability can also be assessed with water or fluordeoxyglucose independently quantified. Other promising methods are based in the study of oxygen consumption with 11C acetate and the study of hypoxia with 18F-misonidazole.