Regional myocardial blood flow during cardiac tamponade in hearts with chronic coronary artery occlusion.

The effects of increased pericardial pressure on blood flow to collateral dependent and normal myocardium were investigated and the mechanisms responsible for these effects evaluated in 10 anaesthetised dogs after collateral inducement by gradual occlusion of a coronary artery. Regional myocardial blood flows were measured with radioactive microspheres during control conditions, mild tamponade, severe tamponade, and severe tamponade with aortic blood pressure held at the control value by blood volume expansion. Mild tamponade increased heart rate by 10% and decreased aortic blood pressure by 15%. Left atrial and central venous blood pressures were moderately increased, and indices of cardiac function were reduced. Blood flow to collateral dependent and normally perfused myocardium was not significantly altered, but the endocardial to epicardial flow ratio was significantly decreased in collateral dependent myocardium. Severe tamponade decreased aortic blood pressure by 45% and cardiac index by 62%. Left atrial and central venous blood pressures were appreciably increased and cardiac function indices considerably depressed. Blood flow to collateral dependent and normally perfused myocardium was decreased similarly (by 54-57%), but the endocardial to epicardial flow ratio was decreased by a greater degree in collateral dependent myocardium. During severe tamponade at control aortic blood pressure, left atrial and central venous blood pressures were further increased, but blood flow to collateral dependent and normally perfused myocardium returned to within 84% of control and endocardial to epicardial flow ratios were normal. Total peripheral vascular resistance increased during severe tamponade, but coronary vascular resistance remained constant. Thus blood flow to collateral dependent and normally perfused myocardium varied according to net coronary perfusion pressure.(ABSTRACT TRUNCATED AT 250 WORDS)