Abnormalities in myocardial metabolism in patients with unstable angina as assessed by positron emission tomography

Dual-time-point myocardial 18F-FDG imaging in the detection of coronary artery disease

Background

Myocardial ¹⁸F-deoxyglucose (¹⁸F-FDG) uptake has been observed to be enhanced in patients with coronary artery disease (CAD) under fasting conditions. However, whether the increased ¹⁸F-FDG is induced by myocardial ischemia and how to discriminate ischemic from physiological ¹⁸F-FDG uptake have rarely been investigated.

Methods

Under fasting conditions, ¹⁸F-FDG PET imaging was performed in 52 patients with suspected CAD. Two ¹⁸F-FDG imaging sessions were conducted within two hours after a single administration of ¹⁸F-FDG (dual-time-point imaging), and with an intervention of an exercise test after the first imaging. Abnormal ¹⁸F-FDG uptake was determined by the classification of the ¹⁸F-FDG distribution pattern, and the changes of the ¹⁸F-FDG distribution between the two PET imaging sessions were analyzed. ^99mTc-sestamibi was injected at peak exercise and myocardial perfusion imaging (MPI) was conducted after ¹⁸F-FDG imaging. Coronary angiography was considered the reference for diagnosing CAD.

Results

Overall, 54.8% (17/31) of CAD patients and 36.2% (21/58) of stenotic coronaries showed exercise-induced abnormal uptake of ¹⁸F-FDG. Based on the classification of the ¹⁸F-FDG distribution pattern, the sensitivity and specificity of exercise ¹⁸F-FDG imaging to diagnose CAD was 80.6% and 95.2% by patient analysis, 56.9% and 98.0% by vascular analysis, respectively. Compared with MPI, ¹⁸F-FDG imaging had a tendency to have higher sensitivity (80.6% vs 64.5%, P = 0.06) on the patient level.

Conclusion

Myocardial ischemia can induce ¹⁸F-FDG uptake. With the classification of the ¹⁸F-FDG distribution pattern, dual-time-point ¹⁸F-FDG imaging under fasting conditions is efficient in diagnosing CAD.

Use of resting myocardial 18F-FDG imaging in the detection of unstable angina

OBJECTIVE

Increased myocardial glucose metabolism occurs with the onset of myocardial ischemia and may persist even after the restoration of blood flow, termed as 'ischemic memory'. Previous studies have demonstrated that 18F-fluorodeoxyglucose (18F-FDG) is a sensitive marker of myocardial ischemia and may have potential utility in diagnosing unstable angina (UA). This study aimed to explore the value of F-FDG PET/CT in diagnosing UA.

PATIENTS AND METHODS

Thirty-four patients (17 male patients; mean age, 59 ± 6 years) with suspected UA were prospectively recruited. Resting myocardial F-FDG PET/CT imaging was performed 21 ± 9 h (2-46 h) after the latest onset of angina pectoris. Resting or exercise myocardial perfusion imaging (MPI) and coronary angiography were performed. 'Focal' or 'focal on diffuse' myocardial F-FDG uptake was defined as abnormal, whereas other patterns of myocardial uptake, including 'focal' uptake on the basal segments, were considered as normal. The final diagnosis of UA was based on a comprehensive analysis of ECG, MPI, and coronary angiography.

RESULTS

Of the 21 patients with a final diagnosis of UA, 18 had increased 18F-FDG uptake (sensitivity 85.7%), whereas, of the 13 patients without UA, only one had abnormal 18F-FDG uptake (specificity 92.3%). The sensitivity of resting 18F-FDG imaging was higher than that of resting MPI (85.7 vs. 52.4%, P=0.016). Moreover, six UA patients with only exercise-induced ischemia showed abnormal F-FDG uptake at rest.

CONCLUSION

This pilot study demonstrated that resting 18F-FDG PET/CT imaging is an accurate and sensitive technique for the identification of UA.

PET Radiotracers of the Cardiovascular System

Cardiovascular PET provides exquisite measurements of key aspects of the cardiovascular system and as a consequence it plays central role in cardiovascular investigation. Moreover, PET is now playing an ever increasing role in the management of the cardiac patient. Central to the success of PET is the development and use of novel radiotracers that permit measurements of key aspects of cardiovascular health such as myocardial perfusion, metabolism, and neuronal function. Moreover, the development of molecular imaging radiotracers is now permitting the interrogation of cellular and sub cellular processes. This article highlights these various radiotracers and their role in both cardiovascular research and potential clinical applications.

Recent advances in metabolic imaging

Abnormalities in myocardial substrate metabolism play a central role in the manifestations of most forms of cardiac disease such as ischemic heart disease, heart failure, hypertensive heart disease, and the cardiomyopathy due to either obesity or diabetes mellitus. Their importance is exemplified by both the development of numerous imaging tools designed to detect the specific metabolic perturbations or signatures related to these different diseases, and the vigorous efforts in drug discovery/development targeting various aspects of myocardial metabolism. Since the prior review in 2005, we have gained new insights into how perturbations in myocardial metabolism contribute to various forms of cardiac disease. For example, the application of advanced molecular biologic techniques and the development of elegant genetic models have highlighted the pleiotropic actions of cellular metabolism on energy transfer, signal transduction, cardiac growth, gene expression, and viability. In parallel, there have been significant advances in instrumentation, radiopharmaceutical design, and small animal imaging, which now permit a near completion of the translational pathway linking in-vitro measurements of metabolism with the human condition. In this review, most of the key advances in metabolic imaging will be described, their contribution to cardiovascular research highlighted, and potential new clinical applications proposed.

Translation of myocardial metabolic imaging concepts into the clinics

Flexibility in myocardial substrate metabolism for energy production is fundamental to cardiac health. This loss in plasticity or flexibility leads to overdependence on the metabolism of an individual category of substrates, with the predominance in fatty acid metabolism characteristic of diabetic heart disease and the accelerated glucose use associated with pressure-overload left ventricular hypertrophy being prime examples. There is a strong demand for accurate noninvasive imaging approaches of myocardial substrate metabolism that can facilitate the crosstalk between the bench and the bedside, leading to improved patient management paradigms. In this article potential future applications of metabolic imaging, particularly radionuclide approaches, for assessment of cardiovascular disease are discussed.

Multifocal, persistent cardiac uptake of [18-F]-fluoro-deoxy-glucose detected by positron emission tomography in patients with acute myocardial infarction

BACKGROUND

Inflammation appears to be important in the pathogenesis of acute myocardial infarction (AMI).

METHODS AND RESULTS

Cardiac [18-F]-fluoro-deoxy-glucose (FDG) uptake by positron emission tomography/computed tomography (PET/CT)-scan was investigated in 12 fasting patients with first AMI (FAMI) single-vessel disease after successful primary percutaneous coronary intervention and at 9 weeks follow-up, and in 12 controls. The average FDG uptake (aFDGu) of the 28 left ventricular (LV) wall segments defined on the PET/CT images of the 12 FAMI patients was 1.28+/-0.57-fold higher than the activity present in the LV cavity. By contrast, the aFDGu of the 12 controls was 0.70+/-22 (p<0.001). The segmental aFDGu in the FAMI was multifocal in both the culprit and non-culprit segments; it was less than LV cavity activity in 38%, 1-2-fold greater in 51.8% and more than 2-fold greater in 10.2%. At follow-up, aFDGu was significantly increased in both culprit and non-culprit segments (1.69+/-1.15, p<0.001). Statistically significant differences between FAMI and controls patients were only found for interleukin-6 plasma levels on admission (11.3+/-7.7 pg/ml vs 2.2+/-1.3 pg/ml; p<0.004).

CONCLUSION

Multifocal, non-infarct related, cardiac-FDG-uptake occurred immediately after AMI and persisted at follow-up. The cause of these striking and consistent findings is still speculative.

Right ventricular cardiomyocyte apoptosis in patients with acute myocardial infarction of the left ventricular wall

Cardiac remodeling after acute myocardial infarction (AMI) is characterized by molecular and cellular mechanisms involving both the left (LV) and right ventricular (RV) walls. Cardiomyoycte apoptosis in the peri-infarct and remote LV myocardium has a central role in cardiac remodeling. Whether apoptosis also occurs in the right ventricle of patients with ischemic heart disease has not been investigated. The aim of the present study was to investigate the presence of cardiomyocyte apoptosis in the right ventricle in patients with AMI. We assessed the number of apoptotic cardiomyocytes using multiple samplings in the LV and RV walls of 12 patients selected at autopsy who died 4 to 42 days after AMI. Five patients without cardiac disease were also selected at autopsy as controls. Apoptotic rates were calculated from the number of cardiomyocytes showing double positive staining for in situ end-labeling of DNA fragmentation (TUNEL) and for activated caspase-3. Potentially false-positive results (DNA synthesis and RNA splicing) were excluded from cell counts. The apoptotic rate in the right ventricle in patients with AMI was significantly higher than in control hearts (median 0.8%, interquartile range 0.3 to 1.0 vs median 0.01%, interquartile range 0.01 to 0.03, p <0.001). RV apoptosis significantly correlated with such parameters of global adverse remodeling as cardiac diameter to LV free wall thickness (R = +0.57, p = 0.050). RV apoptosis was significantly higher in five cases (42%) with infarct involving the ventricular septum and an adjacent small area of the RV walls (median 1.0%, interquartile range 0.8 to 2.2 vs median 0.5%, interquartile range 0.2 to 1.0, p = 0.048, p <0.001 vs controls). The association between apoptotic rate in the right ventricle and cardiac remodeling was apparent even after exclusion of cases with RV AMI involvement (R = +0.82, p = 0.023 for diameter to LV wall thickness ratio and R = -0.91, p = 0.002 for RV free wall thickness). In conclusion, patients with cardiac remodeling after AMI had a significant increase in RV apoptosis even when ischemic involvement of the RV wall was not apparent.

Mechanisms leading to reversible mechanical dysfunction in severe CAD: alternatives to myocardial stunning

Patients with severe chronic coronary artery disease (CAD) exhibit a highly altered myocardial pattern of perfusion, metabolism, and mechanical performance. In this context, the diagnosis of stunning remains elusive not only because of methodological and logistic considerations, but also because of the pathophysiological characteristics of the myocardium of these patients. In addition, a number of alternative pathophysiological mechanisms may act by mimicking the functional manifestations usually attributed to stunning. The present review describes three mechanisms that could theoretically lead to reversible mechanical dysfunction in these patients: myocardial wall stress, the tethering effect, and myocardial expression and release of auto- and paracrine agents. Attention is focused on the role of these mechanisms in scintigraphically “normal” regions (i.e., regions usually showing normal perfusion, glucose metabolism, and cellular integrity as assessed by nuclear imaging techniques), in which stunning is usually considered, but these mechanisms could also operate throughout the viable myocardium. We hypothesize that reversion of these three mechanisms could partially explain the unexpected functional benefit after reperfusion recently highlighted by high-spatial-resolution imaging techniques.

PET in cardiology

Myocardial perfusion imaging with single-photon emission CT (SPECT) is a key investigation in the work-up of patients with coronary artery disease. PET, however, with inherently better spatial and temporal resolution, offers several advantages over SPECT. The last decade has witnessed extensive application of PET techniques to assess myocardial viability and has provided valuable information important in analyzing the risk: benefit ratio for several therapeutic measures. Recent advances in PET instrumentation and radiopharmaceuticals have generated considerable interest to use PET for evaluating an array of cardiovascular disease.

Widespread myocardial inflammation and infarct-related artery patency

BACKGROUND

Diffuse coronary vascular inflammation is associated with acute coronary syndromes. However, it is unknown whether inflammation also occurs within the myocardium. Therefore, this study was aimed at assessing the presence of activated cells in unaffected remote myocardium of patients with acute myocardial infarction (AMI), in comparison to the peri-infarct region from the same cases, and in comparison to myocardial specimens from control hearts.

METHODS AND RESULTS

Sixteen patients dying 1 to 12 weeks after AMI and 16 control subjects were selected at autopsy. Myocardial specimens were taken at remote unaffected viable regions and at peri-infarct regions in cases with AMI. Confocal microscopy was performed to measure the number of activated cells (DR+), T-lymphocytes (CD3+), and activated T-lymphocytes (CD3+/DR+). Activated cells and activated T-lymphocytes were found in remote unaffected regions in 11 of 16 cases (69%), in peri-infarct zone in all cases (100%), and in none of the control hearts (0%, P<0.001 versus others). A greater myocardial inflammatory burden in remote regions but not in peri-infarct regions was associated with persistent infarct-related artery occlusion (P<0.05).

CONCLUSIONS

This study for the first time shows the presence of activated T-lymphocytes in remote unaffected myocardial regions in approximately two thirds of patients with recent AMI. Because these cells are associated with persistent infarct-related artery occlusion, our data may suggest that an antigenic stimulus present also in the myocardium triggers an immune response that may be critical to precipitate artery occlusion.

Widespread coronary inflammation in unstable angina

BACKGROUND

Inflammation within vulnerable coronary plaques may cause unstable angina by promoting rupture and erosion. In unstable angina, activated leukocytes may be found in peripheral and coronary-sinus blood, but it is unclear whether they are selectively activated in the vascular bed of the culprit stenosis.

METHODS

We measured the content neutrophil myeloperoxidase content in the cardiac and femoral circulations in five groups of patients: two groups with unstable angina and stenosis in either the left anterior descending coronary artery (24 patients) or the right coronary artery (9 patients); 13 with chronic stable angina; 13 with variant angina and recurrent ischemia; and 6 controls. Blood samples were taken from the aorta, the femoral vein, and the great cardiac vein, which selectively drains blood from the left but not the right coronary artery.

RESULTS

The neutrophil myeloperoxidase content of aortic blood was similar in both groups of patients with unstable angina (-3.9 and -5.5, with negative values representing depletion of the enzyme due to neutrophil activation) and significantly lower than in the other three groups (P<0.05). Independently of the site of the stenosis, the neutrophil myeloperoxidase content in blood from the great cardiac vein was significantly decreased in both groups of patients with unstable angina (-6.4 in those with a left coronary lesion and -6.6 in those with a right coronary lesion), but not in patients with stable angina and multiple stenoses, patients with variant angina and recurrent ischemia, or controls. There was also a significant transcoronary reduction in myeloperoxidase content in both groups with unstable angina.

CONCLUSIONS

The widespread activation of neutrophils across the coronary vascular bed in patients with unstable angina, regardless of the location of the culprit stenosis, challenges the concept of a single vulnerable plaque in unstable coronary syndromes.

Enhanced myocardial 18F-2-fluoro-2-deoxyglucose uptake after orthotopic heart transplantation assessed by positron emission tomography

OBJECTIVES

We sought to assess the relation between glucose metabolism, myocardial perfusion and cardiac work after orthotopic heart transplantation.

BACKGROUND

The metabolic profile of the transplanted cardiac muscle is affected by the lack of sympathetic innervation, impaired inotropic function, chronic vasculopathy, allograft rejection and immunosuppressive therapy. In relation to myocardial perfusion and cardiac work, glucose metabolism has not previously been studied in heart transplant recipients.

METHODS

Regional myocardial blood flow (ml.min-1.g-1) and 18F-2-fluoro-2-deoxyglucose (18FDG) uptake rate (ml.s-1.g-1) were measured after an overnight fast in 9 healthy male volunteers (mean age +/- SD 32 +/- 7 years) and in 10 male patients (mean age 50 +/- 10 years) who had a nonrejecting heart transplant, normal left ventricular function and no angiographic evidence of epicardial coronary sclerosis. Measurements were made by using dynamic positron emission tomography (PET) with 15O-labeled water and 18FDG, respectively. Heart rate and blood pressure were also measured for calculation of rate-pressure product.

RESULTS

18FDG uptake was similar in all heart regions in the patients and volunteers (intrasubject regional variably 12 +/- 8% and 16 +/- 12%, respectively, p = 0.51). Regional myocardial blood flow was similarly evenly distributed (intrasubject regional variability 14 +/- 10% and 12 +/- 8%, respectively, p = 0.67). Mean 18FDG uptake and myocardial blood flow values for the whole heart are given because no regional differences were identified. 18FDG uptake was on average 196% higher in the patients than in the volunteers (2.90 +/- 1.79 x 10(-4) vs. 0.98 +/- 0.38 x 10(-4) ml.s-1.g-1, p = 0.006). Regional myocardial blood flow and rate-pressure product were similarly increased in the patient group, but by only 41% (1.14 +/- 0.3 vs. 0.81 +/- 0.13 ml.min-1.g-1, p = 0.008) and 53% (11,740 +/- 2,830 vs. 7,689 +/- 1,488, p = 0.001), respectively.

CONCLUSIONS

18FDG uptake is homogeneously increased in normally functioning nonrejecting heart transplants. This finding suggests that glucose may be a preferred substrate in the transplanted heart. The magnitude of this observed increase is significantly greater than that observed for myocardial blood flow or cardiac work. In the patient group, the latter two variables were increased to a similar degree over values in control hearts, indicating a coupling between cardiac work load and myocardial blood flow. The disproportionate rise in 18FDG uptake may be accounted for by inefficient metabolic utilization of glucose by the transplanted myocardium or by the influence of circulating catecholamines, which may stimulate glucose uptake independently of changes in cardiac work load.

Prognostic value of an increase in fluorine-18 deoxyglucose uptake in patients with myocardial infarction: comparison with stress thallium imaging

OBJECTIVES

This study was undertaken to evaluate the prognostic value of an increase in fluorine (F)-18 deoxyglucose uptake compared with clinical, angiographic and stress thallium findings in patients with myocardial infarction.

BACKGROUND

Positron emission tomography (PET) imaging using F-18 deoxyglucose has been applied to assess tissue viability in patients with coronary artery disease. We hypothesized that patients with a myocardial segment with augmented F-18 deoxyglucose uptake are at high risk for a future cardiac event.

METHODS

One hundred fifty-eight consecutive patients with myocardial infarction referred for F-18 deoxyglucose PET and stress thallium scans were studied. Follow-up was obtained in 84 patients at a mean interval of 23 months to investigate prognostic implications of radionuclide studies.

RESULTS

Seventeen patients had a cardiac event during the follow-up interval. Univariate analysis showed that an increase in F-18 deoxyglucose uptake was the best predictor of a future cardiac event (p = 0.0006), followed by the number of stenosed vessels (p = 0.008). In the multivariate analysis, when an increase in F-18 deoxyglucose uptake was entered into the model, only angiographic variables had an independent prognostic value, whereas no other radionuclide variables showed significant prognostic value. Among patients who did not show redistribution, a future cardiac event was observed more often in patients with than in those without an increase in F-18 deoxyglucose uptake (p < 0.05).

CONCLUSIONS

Thus, an increase in F-18 deoxyglucose uptake seemed to be the best predictor of a future cardiac event among all clinical, angiographic and radionuclide variables in this study of stable patients with myocardial infarction. Even when a stress thallium-201 scan does not show redistribution, those patients who have an increase in F-18 deoxyglucose uptake in a PET study may be at risk for a future cardiac event, and these patients may need aggressive treatment to prevent a future cardiac event.

Altered coronary vasodilator reserve and metabolism in myocardium subtended by normal arteries in patients with coronary artery disease

OBJECTIVES

The aim of this study was to investigate coronary vasodilator reserve and metabolism in myocardium subtended by angiographically normal arteries remote from ischemia.

BACKGROUND

After infarction, structural and functional changes occur in remote myocardium often subtended by normal arteries. Whether changes occur in regions remote from ischemic but noninfarcted myocardium is unknown.

METHODS

Coronary vasodilator reserve was measured with positron emission tomography in 12 patients with single-vessel disease using intravenous dipyridamole (0.56 mg/kg for 4 min). In another 10 patients, simultaneous arterial/great cardiac vein catheterization was performed during atrial pacing to measure myocardial metabolism in regions subtended by diseased or normal arteries.

RESULTS

Basal myocardial blood flow in stenosis-related regions was comparable to that in remote regions but was lower after dipyridamole administration (1.73 +/- 0.91 vs. 2.89 +/- 0.93 ml/min per g, p < 0.01), giving coronary vasodilator reserve values of 1.80 +/- 0.82 and 2.73 +/- 0.89 (p < 0.01). In normal control subjects, basal myocardial blood flow was 0.92 +/- 0.13 and 3.67 +/- 0.94 ml/min per g in the basal state and after dipyridamole (both p < 0.05 vs. values in remote regions), and coronary vasodilator reserve was 4.07 +/- 0.98 (p < 0.01) vs. values in remote regions). During pacing there was net lactate release in diseased regions (-18 +/- 27%, p < 0.05 vs. values in remote regions and control subjects) and extraction in remote regions (38 +/- 17%) and in normal control subjects (26 +/- 11%). Glucose and alanine extraction were increased in diseased (8 +/- 6% and 6 +/- 6%) and remote regions (6 +/- 3% and 4 +/- 3%), compared with values in normal control subjects (2 +/- 3% and -1 +/- 3%, both p < 0.05 vs. diseased and remote regions).

CONCLUSIONS

Coronary vasodilator reserve is reduced and glucose and alanine metabolism is abnormal in regions subtended by normal arteries remote from ischemic but noninfarcted myocardium.

Glucose utilization in a patient with hepatoma and hypoglycemia. Assessment by a positron emission tomography

Tumor glucose use in patients with non-islet-cell tumors has been difficult to measure, particularly in hepatoma, because of hepatic involvement by neoplasm. We studied a patient with nonhepatic recurrence of hepatoma after successful liver transplantation. Tumor tissue contained messenger RNA for insulin-like growth factor-II (IGF-II), and circulating high molecular weight components and E-peptide of IGF-II were increased. Glucose use measured by isotope dilution with [3-3H]glucose was 7.94 mg/kg fat-free mass per min, and splanchnic glucose production was 0.93 mg/kg fat-free mass per min. Glucose uptake and glucose model parameters were independently measured in tissues by positron emission tomography with 18F-fluoro-2-deoxy-D-glucose. Glucose uptake by heart muscle, liver, skeletal muscle, and neoplasm accounted for 0.8, 14, 44, and 15% of total glucose use, respectively. Model parameters in liver and neoplasm were not significantly different, and glucose transport and phosphorylation were twofold and fourfold greater than in muscle. This suggests that circulating IGF-II-like proteins are partial insulin agonists, and that hypoglycemia in hepatoma with IGF-II production is predominantly due to glucose uptake by skeletal muscle and suppression of glucose production.

Hibernation and myocardial ischemia: clinical detection by positron emission tomography

Regions of myocardium supplied by severely diseased epicardial arteries may develop chronic ischemia at rest and exhibit reduced contractility, contributing to a reduction in global left ventricular function. However, after revascularization, contractility in these regions may return to normal. These regions of asynergy are described as "hibernating myocardium." Such myocardium in which normal contractility may be restored often coexists with areas of infarcted, or scar, tissue, leading to the definition of hypoperfused hibernating myocardium as viable myocardium. It is important to identify viable myocardium, as revascularization of these areas should lead to the greatest improvement in left ventricular function and, thus, improvement in survival. Positron emission tomography is the best noninvasive method for quantifying regional myocardial blood flow and metabolism. Using 18F-fluorodeoxyglucose, which measures myocardial glucose utilization, it is possible to identify myocardial tissue that is hypoperfused at rest with preserved or increased glucose uptake. This mismatch of blood flow to metabolism has a high predictive accuracy in the recovery of contractile function. In order to reduce the need for metabolic imaging in documenting myocardial viability, a regional index of perfusable tissue derived from imaging with 15O water has been recently developed that also allows the quantification of tissue viability.

Myocardial metabolism in ischemic heart disease: basic principles and application to imaging by positron emission tomography

The human heart in the fasting state extracts FFA, glucose, lactate, pyruvate, and ketone bodies from the systemic circulation. Of these substrates, FFA utilization accounts for the greater part of oxygen consumption and energy production. The oxidative use of lipid (FFA) and carbohydrate (glucose and lactate) fuels is reciprocally regulated through the operation of Randle's cycle. Feeding, by increasing both insulin and glucose concentration, shifts myocardial metabolism towards preferential carbohydrate usage, both for oxidative energy generation and for glycogen synthesis. During conditions of reduced oxygen supply, the oxidation of all substrates is decreased while anaerobic metabolism is activated. In patients with coronary artery disease and stable angina pectoris, lactate release in the CS can be demonstrated during pacing stress. However, this occurs in only 50% of patients, and no relationship can be demonstrated between lactate production and the severity of ischemia. In patients with chronic angina, a significant release of alanine in the CS and an increased myocardial uptake of glutamate could be demonstrated at rest and following pacing. These two phenomena result from increased transamination of excess pyruvate to alanine with glutamate serving as NH2 donor. In addition, release of citrate (a known inhibitor of glycolysis) in the CS can be demonstrated following pacing in patients with stable angina. The introduction of PET has made it possible to study regional myocardial perfusion and metabolism in humans noninvasively. Two basically different patterns of myocardial glucose utilization have been observed in patients with coronary artery disease studied at rest using 18F-flurodeoxyglucose. In patients with stable angina on exercise but studied at rest, regional myocar- dial glucose utilization was homogeneously low and comparable with that of a group of normals. In contrast, in patients with unstable angina, myocardial glucose utilization at rest was increased even in the absence of symptoms and ECG signs of acute ischemia. In patients with stable angina, a prolonged increase in glucose uptake could be demonstrated in the post-ischemic myocardium in the absence of perfusion abnormalities, and a state of chronic metabolic ischemia is proposed. PET imaging has also allowed prospective differentiation between viable and nonviable segmental function in patients with recent myocardial infarction and in those undergoing coronary artery surgery; in both cases viable segments have relatively maintained glucose uptakes, whereas nonviable segments have depressed glucose uptakes.

Pharmacology of acute effort angina

From the pharmacologic point of view, each of the major types of antianginal agents--calcium antagonists, beta-blockers, and nitrates--seem to act at least in part by an improvement of the myocardial blood supply. The recently elucidated mechanism of action of nitrates, acting on a common pathway with the endothelium-derived relaxation factor (EDRF), suggests an important role for guanylate cyclase and cyclic GMP in maintaining coronary artery patency in patients with coronary atheroma. The efficacy of calcium antagonists, even in effort-induced angina, is in accord with a current hypothesis that physical exercise in the presence of coronary stenosis can cause relative coronary vasoconstriction, or at the least, failure of full dilation. Therefore, calcium antagonists all act, at least in part, on the "supply" side of the supply-demand equation. Beta-adrenergic blockers appear to have as their major mode of action a reduction of heart rate, which not only reduces the oxygen demand but, through an anti-ischemic effect, also appears to improve the endocardial blood supply (in relation to the heart rate). Thus beta-blockade indirectly enhances the supply side of the equation. The intriguing situation arises whereby all three major types of antianginal compounds may also act by a common mechanism of anginal relief, namely, improvement in the coronary blood supply, in addition to the diverse mechanisms specific to each type of compound. That conclusion does not mean the the "demand" side of the equation can be ignored. Rather, the critical importance of a reduced myocardial blood supply in the production of anginal syndromes is highlighted.