Coronary artery hemodynamics in conscious dog during cardiac tamponade.

We tested the hypothesis that coronary artery blood flow is sufficient to meet myocardial requirements throughout cardiac tamponade in a conscious euvolemic canine model recovered from surgery. Seven mongrel dogs were chronically instrumented to measure ascending aortic blood flow (electromagnetic flowmeter); intrapericardial, right atrial, and aortic blood pressures; regional myocardial blood flow (radionuclide labelled microspheres); and myocardial consumption of lactate, pyruvate, and oxygen. Data were collected during progressive cardiac tamponade induced by intrapericardial saline infusion to the point of hemodynamic decompensation. Decompensated cardiac tamponade (DCT) was defined as a decline in mean aortic blood pressure to 70% of the level present when the pericardial space was drained of fluid (baseline) and was produced in all animals within 25 minutes. Cardiac tamponade caused a continuous decline in coronary artery blood flow from 1.26 +/- 0.35 (baseline, mean +/- SD) to 0.53 +/- 0.15 ml/min/g (DCT, p less than 0.01), which was associated with a decrease in myocardial oxygen consumption from 1.26 +/- 0.35 (baseline) to 0.74 +/- 0.27 ml/min/g (DCT, p less than 0.05) and a slight increase in myocardial oxygen extraction from 71 +/- 3 (baseline) to 81 +/- 4% (DCT, p less than 0.05). This change in oxygen extraction occurred because of both an increase in arterial and a decrease in coronary venous oxygen content. At all degrees of cardiac tamponade, the lactate-pyruvate ratio did not change significantly from baseline (7.56 +/- 2.31), there was no evidence of lactate production, and the normal endocardial to epicardial blood flow ratio present at baseline (1.41 +/- 0.23) was preserved.(ABSTRACT TRUNCATED AT 250 WORDS)