A method was devised to quantitate regional capillary perfusion in the human heart by measuring the clearance constants (k) of Xenon-133 washout from multiple areas of the myocardium with a multiple-crystal scintillation camera. In 17 subjects, 133Xe was injected into the right or left coronary artery or both and counts per second (cps) were recorded simultaneously on magnetic tape from each of 294 scintillation crystals viewing the precordium through a multichannel collimator. Data were processed by a digital computer. Crystals detecting the myocardial washout of 133Xe were distinguished from those monitoring pulmonary excretion by positioning radioactive markers at the cardiac margins, and by a computer printout of the peak cps recorded by each crystal and its time after isotope injection into the coronary artery. The slopes of the initial segment of the multiple 133Xe curves obtained in each study were calculated by the method of least squares using a monoexponential model. Myocardial blood flow rates in the cardiac regions viewed by the individual crystals were calculated (assuming a blood to myocardium partition coefficient of 0.72) along with the SD of every flow measurement. The pattern of myocardial perfusion rates so obtained was superimposed over a tracing of the subject's coronary arteriogram. Scintiphotographs showing the arrival and washout of isotope from various regions of myocardium and the area of tissue perfused by each coronary artery were obtained by replaying the data tape on an oscilloscope. Significant regional variations in local myocardial perfusion rates were observed in hearts with normal coronary arteries. When capillary flow measurements from crystals overlying the various cardiac chambers were averaged in each subject, the mean myocardial blood flow rate of the left ventricle in 17 patients, 64.1 ±13.9 (SD) ml/100 g·min, significantly exceeded that of the right ventricle, 47.8 ±10.9 ml/100 g·min, and of the right atrial region, 33.6 ±10.3 ml/100 g·min. The approach may facilitate more objective assessment of: myocardial capillary perfusion in patients with angina pactoris, the pharmacology of antianginal drugs, and the efficacy of surgical procedures to revascularize ischemic myocardium.
Paul J. Cannon, Ralph B. Dell, Edward M. Dwyer Jr.