Hideyuki Yamanaka

Functional role of coronary collaterals with exercise in infarct-related myocardium

We evaluated the regional myocardial blood flow in collateral dependent infarct-related areas to examine the functional role of coronary collaterals. Regional myocardial blood flow was measured by positron emission tomography with 13N-ammonia at rest and during low-grade exercise (bicycle ergometer fixed at 25 W for 6.5 min). The study was performed in 24 subjects, consisting of 19 patients with prior myocardial infarction, and five normal individuals. Regional myocardial blood flow was calculated using the radioactivity in myocardial tissue measured by positron emission tomography and the radioactivity in arterial blood. Concerning the infarct related area, the exercise caused myocardial blood flow to decrease by 18.4% (P < 0.01) in the collateral-dependent areas (n = 8) of angiographically positive collaterals, and to increase by 14.4% (P = not significant) in the areas (n = 10) of negative collaterals. Four patients in whom the myocardial blood flow in all walls, including the normal areas, decreased with exercise were excluded from this evaluation. Myocardial blood flow in collateral-dependent infarct-related areas appeared to decrease transiently by low-grade exercise. Our results suggest that collaterals increase the incidence of exercise-induced ischemia, but may protect the infarct related but viable myocardium from necrosis.

Relation Between Exercise-Induced Myocardial Ischemia as Assessed by Nitrogen-1 3 Ammonia Positron Emission Tomography and QT Interval Behavior in Patients With Right Bundle Branch Block

Exercise-induced myocardial ischemia is difficult to detect with ST-T changes in patients with right bundle branch block (RBBB). We sought to predict exercise-induced myocardial ischemia with QT interval behavior during exercise in patients with RBBB. Twenty-two patients with angiographically proven coronary artery disease and RBBB and 9 healthy volunteers underwent nitrogen-13 ammonia positron emission tomography with bicycle ergometer exercise at a fixed workload of 25 W. Regional myocardial blood flow (RMBF) and electrocardiographic changes were measured both at rest and after 5 minutes of exercise. The QT interval was measured from the onset of the QRS complex to the offset of the T wave in lead V5. The deltaQT and deltaRMBF, which indicated values after 5 minutes of exercise minus values at rest, were negatively correlated (r = -0.74, p <0.001). Exercise-induced shortening of the QT interval (422 +/- 27 to 381 +/- 38 ms, p = 0.0020) was observed in 15 patients (group 1) and no change or prolongation (411 +/- 45 to 420 +/- 37 ms, p = NS) was observed in 7 patients (group 2). Multivessel disease was significantly more frequent but collateral circulation was significantly less in group 2 than in group 1 (p <0.01, p <0.05, respectively). Cardiac output at rest was significantly lower in groups 1 and 2 than in healthy volunteers (4.52 +/- 0.83 and 4.51 +/- 0.84 vs 6.20 +/- 0.83 L/min; p = 0.0014, p = 0.0003). Although RMBF at rest did not differ significantly among groups 1 and 2 and healthy volunteers (0.63 +/- 0.20 vs 0.69 +/- 0.13 and vs 0.77 +/- 0.14 ml/min/g), RMBF after 5 minutes of exercise was significantly lower in group 2 than in group 1 and healthy volunteers (0.78 +/- 0.11 vs 0.96 +/- 0.20 and vs 1.20 +/- 0.18 ml/min/g; p = 0.0289, p <0.0001). The number of regions of critical coronary artery disease was significantly greater in group 2 than in group 1 (4.0 +/- 1.2 vs 2.1 +/- 1.3, p = 0.0039). Our results suggest that the absence of QT interval shortening during exercise may indicate severe myocardial ischemia induced by exercise in patients with RBBB and coronary artery disease.

Correlation between exercise-induced ischemic ST-segment depression and myocardial blood flow quantified by positron emission tomography

BACKGROUND Ischemic ST-segment depression (horizontal or downsloping) is the most common manifestation of exercise-induced myocardial ischemia. The mechanisms responsible for these types of ST-segment depression are largely unknown. We investigated the relation of these 2 types of exercise-induced ST-segment depression to changes in regional myocardial blood flow (RMBF) by using exercise positron emission tomography (PET). METHODS AND RESULTS The RMBF was measured with nitrogen-13 ammonia PET both at rest and during low-level supine bicycle exercise in 27 patients with angiographically proven coronary artery disease and in 6 healthy volunteers. ST-segment depression was measured from the isoelectric PR segment 80 ms after the J point. Exercise-induced horizontal ST-segment depression > or =0.1 mV was observed in 9 patients and downsloping depression > or =0.1 mV was observed in 18 patients. Multivessel disease was more frequent and areas of exercise-induced ischemia were larger in patients with downsloping depression than in patients with horizontal depression (P < .02, P < .05). In patients with horizontal ST-segment depression, RMBF in ischemic areas and in surrounding areas increased by a similar amount (31%+/-29% and 32%+/-16%) with exercise. In patients with downsloping ST-segment depression, RMBF was unchanged or decreased in ischemic areas (10%+/-24%) but increased in surrounding areas (46%+/-27%) with exercise. In healthy volunteers, RMBF increased in all areas (56%+/-30%) with exercise. CONCLUSIONS Compared with horizontal changes in ST-segment morphology, downsloping changes may better indicate severe ischemia and greater differences in the increase of blood flow with exercise in the ischemic myocardium and in the surrounding areas.

Exercise-induced ST-segment changes permit prediction of improvement in left ventricular ischemic dysfunction after revascularization: Evaluation with positron emission tomographic measurements of regional myocardial blood flow and cardiac output☆

BackgroundPrediction of the recovery of left ventricular (LV) ischemic dysfunction after revascularization is important in patients with coronary artery disease (CAD). We investigated whether the improvement in LV ischemic dysfunction after revascularization could be predicted preoperatively by exercise-induced ST-segment changes.Methods and ResultsRegional myocardial blood flow (RMBF) and cardiac output were measured with nitrogen 13-ammonia positron emission tomography at rest and during low-level exercise in 28 patients with angiographically proven CAD before and after successful revascularization and in 9 normal subjects. Before revascularization, exercise-induced upsloping ST-segment depression <1 mm 80 msec after the J-point was observed in 11 patients (group 1), horizontal depression of 1 to 1.5 mm was observed in 0 patients (group 2), and downsloping depression ≥1.5 mm was observed in 8 patients (group 3). The number of regions of critical CAD was greater in group 3 than in groups 1 and 2 (3.6±1.4 vs 1.6±0.7 and 2.2±1.1, p<0.001, p<0.02). Increase of RMBF in regions of critical CAD with exercise was lower in group 3 than in groups 1 and 2 (0.15±0.01 vs 0.22±0.01 and 0.18±0.02 ml/min per gram, p<0.0001, p <0.01). After revascularization, RMBF in regions of critical CAD both at rest and during exercise improved in groups 1 (0.49±0.15 to 0.60±0.18, 0.70±0.26 to 0.86±0.33 ml/min per gram, both p<0.05) and 2 (0.50±0.15 to 0.62±0.19, 0.67±0.26 to 0.89±0.31 ml/min per gram, both p<0.02), but was unchanged in group 3 (0.47±0.09 to 0.47±0.15, 0.62±0.17 to 0.64±0.23 ml/min per gram, both p=NS). Cardiac output at rest improved in groups 1 (4.98±0.43 to 5.35±0.50 L/min, p<0.02) and 2 (5.08±0.52 to 5.53±0.28 L/min, p<0.02), but was unchanged in group 3 (4.76±0.48 to 4.88±0.82 L/min, p=NS).ConclusionsOur results suggest that marked downsloping ST-segment depression induced by preoperative low-level exercise may predict a lack of improvement in LV ischemic dysfunction after revascularization.

Thallium-201 and I-123 beta-methyl iodophenyl-pentadecanoic acid dual isotope single photon emission computed tomography for evaluating reperfusion injury after successful reperfusion therapy.

We report a reperfusion injury after rotational coronary atherectomy (RA) in a 66-year-old man with coronary artery disease. Submaximal exercise with thallium-201 single photon emission computed tomography (SPECT) imaging before reperfusion showed partially reversible perfusion defects in the apex and reversible perfusion defects in the anteroseptal area. Thallium-201 and I-123 beta-methyl iodophenyl-pentadecanoic acid (BMIPP) dual isotope SPECT was performed 5 days before and 1 hour after RA, and 1 month after RA. SPECT images at 1 hour after recovery of no reflow phenomenon after RA revealed enlargement of the defect sizes on thallium-201 and BMIPP uptakes in the anteroseptal area including the apex compared with those before RA. The defect size of thallium-201 uptake was progressively improved on 5 hour delayed redistribution imaging and 1 month after reperfusion compared with that of BMIPP uptake. In conclusion, the changes for the worse of thallium-201 uptake and fatty acid metabolism immediately after the no reflow phenomenon may indicate an injured membrane integrity with altered myocardial metabolism rather than myocardial ischemia. Thallium-201 and I-123 BMIPP dual isotope SPECT is useful for evaluating reperfusion injury after successful reperfusion therapy in a patient with acute coronary syndrome.