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R-wave-synchronous radionuclide angiography provides time-activity curve information that is assumed to be proportional to ventricular volumes. We performed serial 2-minute time-activity curves and simultaneous Fick cardiac outputs before and during graded, maximal, supine exercise in nine normal sub- jects; each subject exercised without drug intervention, after nitroglycerin and after intravenous propranolol. Imaging was performed using an R-wave-synchronized gamma camera-computer system, a high-sensitivity collimator and autologous 99mTc-labeled red blood cells. Fick cardiac output was determined from pulmonary and radial artery blood samples and oxygen consumption. Changes in count-derived cardiac output, expressed as percent change from baseline, closely paralleled changes in Fick output at all levels of exercise for nondrug and nitroglycerin studies. After propranolol, agreement was maintained between both methods for low-tomoderate levels of exercise. Changes in count-defined end-diastolic volume, end-systolic volume and stroke volume agreed well with simultaneous heart rate, wedge pressure and Fick measurements and were in accord with known hemodynamic effects of exercise, nitroglycerin and propranolol. We conclude that radionuclide count data accurately reflect true hemodynamic change as determined by the Fick technique and may aid in defining the mechanisms of ventricular dysfunction in coronary and valvular heart disease, thereby providing a better understanding of the effects of interventions in these disorders.
Sorensen et al. (Sat,) studied this question.