Myocardial blood flow during cardiac tamponade in dogs with coronary occlusion: Effects of isoproterenol

Abstract

To determine the effects of cardiac tamponade in dogs with ligation of the left anterior descending coronary artery, fluid was introduced into the pericardial space to raise right and left atrial and pericardial pressures, first to 7 to 9 mm Hg and then to 11 to 12 mm Hg. Normal and ischemic myocardial blood flow fell approximately 20% to 25% during mild tamponade (1.27 ± 0.16 to 1.00 ± 0.06 ml/min/gm and 0.52 ± 0.12 to 0.39 ± 0.08 ml/min/gm, respectively) and by 50% during moderate tamponade (0.66 ± 0.08 and 0.23 ± 0.05 ml/min/gm, respectively). The inner/outer left ventricular wall blood flow ratio decreased modestly from 1.16 to 1.08 ( p < 0.025) in normal areas but increased from 0.53 to 0.61 ( p < 0.05) in the ischemic regions, suggesting possible epicardial vessel compression. Isoproterenol resulted in prompt decreases in pericardial and filling pressures, 16% increase in aortic pressure, and 200% rise in cardiac output. Normal myocardial blood flow more than doubled (1.55 ± 0.12 ml/min/gm, p < 0.001). Although average ischemic blood flow rose slightly to 0.42 ± 0.10 ml/min/gm, the increase was not significant. Furthermore, changes in ischemic blood flow were heterogeneous with frank decrease in one dog. Therefore, although isoproterenol has salutary hemodynamic effects, its unpredictable action on myocardial blood flow should cause one to use it cautiously in those with tamponade who are believed to have coronary occlusive disease.