Distribution of intramyocardial blood flow during pericardial tamponade: Correlation with microscopic anatomy and intrinsic myocardial contractility

Abstract

Pericardial tamponade was produced in a dog model, and measurements were made at the first decrease in blood pressure and when pressure had fallen to a mean of 35 mm. Hg. Radionuclide-labeled microspheres were used to determine total and transmural myocardial blood flow. Intrinsic cardiac contractility and cardiac output were calculated, and histologic sections were assessed for evidence of subendocardial hemorrhage and zonal lesions. Contractility initially increased even though total blood flow and the subendocardial/subepicardial flow ratio decreased significantly. In late tamponade the subendocardial/subepicardial flow ratio stayed the same, and there was a large decrease in total coronary flow and contractility. When compared with findings in dogs in hemorrhagic shock at the same arterial pressure, coronary blood flow was a significantly smaller per cent of the cardiac output in the tamponade dogs. All the tamponade dogs developed zonal lesions, and the 3 dogs with the lowest subendocardial/subepicardial flow ratios developed subendocardial hemorrhage. These studies emphasize the role of myocardial ischemia in the evolution of cardiac decompensation associated with progressive increases in pericardial pressure.