A. Maseri

Increased uptake of 18F-fluorodeoxyglucose in postischemic myocardium of patients with exercise-induced angina.

Regional myocardial perfusion and exogenous glucose uptake were assessed with rubidium-82 (82Rb) and 18F-2-fluoro-2-deoxyglucose (FDG) in 10 normal volunteers and 12 patients with coronary artery disease and stable angina pectoris by means of positron emission tomography. In patients at rest, the myocardial uptake of 82Rb and FDG did not differ significantly from that measured in normal subjects. The exercise test performed within the positron camera in eight patients produced typical chest pain and ischemic electrocardiographic changes in all. In each of the eight patients a region of reduced cation uptake was demonstrated in the 82Rb scan recorded at peak exercise, after which uptake of 82Rb returned to the control value 5 to 14 min after the end of the exercise. In these patients, FDG was injected in the recovery phase when all the variables that were altered during exercise, including regional myocardial 82Rb uptake, had returned to control values. In all but one patient, FDG accumulation in the regions of reduced 82Rb uptake during exercise was significantly higher than that in the nonischemic regions, i.e., the ones with a normal increment of 82Rb uptake on exercise. In the nonischemic areas, FDG uptake was not significantly different from that found in normal subjects after exercise. In conclusion, myocardial glucose transport and phosphorylation seem to be enhanced in the postischemic myocardium of patients with exercise-induced ischemia.

Preoperative prediction of the outcome of coronary revascularization using positron emission tomography.

BackgroundPrevious assessments of myocardial viability using positron emission tomography (PET) relied on demonstration of glucose metabolism in hypoperfused asynergic segments using the glucose analogue [18F]2-fluoro-2-deoxyglucose (FDG). Recently, it was shown that myocardial viability could be assessed by calculating the water-perfusable tissue index (PTI) for the asynergic region. PTI represents the proportion of the myocardium that is capable of rapid transsarcolemmal exchange of water and thus perfusable by water. The aim of the present study was to assess myocardial viability by PET using PTI in patients undergoing coronary revascularization. Methods and ResultsTwelve patients with chronic coronary artery disease and previous myocardial infarction were studied. Analysis of transmission (tissue density) and 15O-labeled carbon monoxide (blood pool), and 150-labeled water (myocardial blood flow [MBF]) emission PET data enabled the simultaneous quantification of MBF (ml · min−1 · g perfusable tissue−1) and PTI (gram of perfusable tissue per gram of total anatomic tissue). In addition, PET imaging with FDG after 75-g oral glucose load was performed in eight patients. Preoperative echocardiography identified 33 hypocontractile and 26 control segments. Follow-up echocardiography performed 3 to 5 months later demonstrated 26 of 33 segments with improved wall motion (recovery) and seven of 33 segments without improvement (nonrecovery). MBF in the control segments (0.97 ± 0.22 ml · min−1 · g perfusable tissue−1) was significantly higher (p < 0.001) than in both the recovery (0.73 ± 0.18 ml min−1 g perfusable tissue−1) and the nonrecovery (0.45 ± 0.11 ml min−1 · g perfusable tissue−1) segments. PTI in the recovery regions (0.99 ± 0.15) was≥0.7 in all cases and slightly less than in control regions (1.10 ± 0.15, p < 0.02). FDG uptake in these regions was 92 ± 17% (n=13) of the uptake in control segments with normal wall motion. In the nonrecovery group, PTI was 0.62 ± 0.06 (p < 0.02 versus control and recovery) and always < 0.7. In the one patient in whom a comparison with metabolic imaging was made, FDG uptake was 46% of the uptake in a reference region with normal wall motion. ConclusionsThese data showed that contractile recovery occurred only in segments where PTI was ≥0.7, suggesting that ≥70% of myocardial tissue in a given asynergic segment should be perfusable by water to enable contractile recovery. There was good agreement between the PTI and FDG methods for predicting improvements in regional wall motion after revascularization. Although further studies should be performed in a larger patient group, the preliminary results are promising and suggest that PTI may be a good predictor of contractile recovery after coronary revascularization.

Dipyridamole vasodilator response after human orthotopic heart transplantation : quantification by oxygen-15-labeled water and positron emission tomography

To assess coronary vasodilator reserve after orthotopic heart transplantation, regional myocardial perfusion was measured with oxygen-15-labeled water and dynamic positron emission tomography in 14 cardiac allograft recipients who were not experiencing rejection and who had no angiographic evidence of epicardial coronary sclerosis 15 to 73 months (mean +/- SD 43 +/- 19) after transplantation (group I). Twelve normal men with an average age of 31 years (group II) served as a control group. Regional perfusion was measured at rest and after the intravenous administration of 0.6 mg/kg body weight of dipyridamole. Rest regional myocardial blood flow was homogeneously distributed throughout the left ventricle and was significantly higher in transplant recipients (mean 1.16 +/- 0.26 ml/g per min [range 0.8 to 1.73] than in normal subjects (mean 0.85 +/- 0.13 ml/g per min [range 0.57 to 0.99]; p = 0.001) as was rest heart rate-systolic blood pressure product (rate-pressure product 11,255 +/- 2,540 vs. 7,073 +/- 1,306; p less than 0.001). After dipyridamole, perfusion in the transplant recipients was homogeneous and slightly lower (2.73 +/- 1.03 vs. 3.40 +/- 1.09 ml/g per min; p = NS), whereas rate-pressure product was slightly higher (12,179 +/- 2,266 vs. 10,885 +/- 1,895; p = NS) than the value in normal subjects. Dipyridamole vasodilator response (dipyridamole/rest myocardial blood flow) ranged from 1.23 to 4.92 (mean 2.50 +/- 1.13) in group I and from 2.65 to 5.45 (3.97 +/- 0.89) in group II (p = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

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.