Thallium-201 myocardial imaging during maximal and submaximal exercise: comparison of submaximal exercise with...

Propranolol is an effective drug for patients with angina and has been shown to favorably alter exercise ejection fraction and myocardial perfusion images in patients with coronary disease. A characteristic effect of propranolol is reduction in exercise heart rate (HR). Twenty men with coronary disease (10 with prior infarction), angina-limited exercise tests, abnormal myocardial blood flow distribution images (MBFDI) (201thallium) during exercise, and normal resting ejection fractions underwent treadmill exercise testing with imaging on three occasions. Control maximal exercise was performed initially with measurement of MBFDI. Propranolol, 40 mg by mouth four times a day, was administered for a week with exercise repeated to the same workload. A third study, with men off propranolol, was undertaken with exercise continued only to the HR obtained while the men were taking propranolol (submaximal exercise). All men had improvement in MBFDI while receiving propranolol (men without infarction +780 +/- 88 [average +/- SEM] normalized count rate difference between control and propranolol; men with infarction +724 +/- 73 normalized counts). Greater count differences were noted when control exercise and HR-controlled, submaximal exercise MBFDI were compared with a greater difference in men with infarction (+1094 +/- 89 normalized counts) than for men without infarction (+896 +/- 88 normalized counts). Results suggest that propranolol improves MBFDI during exercise in men with angina, but that submaximal exercise results in more normal MBFDI than does propranolol for exercise to the same HR.