Blood flow to acutely ischaemic myocardium during pericardial tamponade: dominant influence of aortic blood pressure.

The effect of increased pericardial pressure on blood flow to acutely ischaemic and normal myocardium was investigated and the mechanisms responsible for this effect evaluated in eight open chest anaesthetised dogs. After coronary artery occlusion regional myocardial blood flows were estimated from the tissue content of radioactive microspheres administered systemically during control conditions, mild tamponade (pericardial pressure 8.4(1.0) mmHg), severe tamponade (pericardial pressure 13.3(1.4) mmHg), and severe tamponade (pericardial pressure 13.5(1.6) mmHg) with aortic blood pressure held constant by blood volume expansion. Mild tamponade decreased aortic blood flow by 20% and aortic pressure by 90%. Right and left atrial blood pressures were moderately increased. Blood flow to ischaemic and normal myocardium was not significantly altered. Severe tamponade decreased aortic blood flow by 50% and aortic pressure by 35%. Heart rate increased by 18%, and right and left atrial pressures were appreciably increased. Blood flow to ischaemic and normal myocardium decreased in proportion to the decrease in aortic pressure, but the transmural distribution of flow in ischaemic myocardium was not altered. During severe tamponade with constant aortic pressure, right and left atrial blood pressures were further increased, but blood flow to ischaemic and normal myocardium was similar to that observed under pre-tamponade control conditions. These results show that blood flow to acutely ischaemic myocardium during tamponade is determined primarily by aortic pressure.