Experimental myocardial infarction. II. Acute depression and subsequent recovery of left ventricular function: serial measurements in intact conscious dogs.

Acute myocardial infarction causes depression of left ventricular function, but the capacity of the ventricle to recover from such an injury remains unknown. This problem was explored by measuring left ventricular function in eight intact conscious dogs before, 1 hr after, and again 6-8 days after myocardial infarction. Acute myocardial infarction was produced using a technique which entails gradual inflation over an average period of 1 hr of a balloon cuff previously implanted around the left anterior descending coronary artery. Occurrence of anterior wall infarction was detected electrocardiographically and later confirmed by postmortem examination. Left ventricular function was evaluated from the relationship between left ventricular developed pressure (left ventricular peak systolic pressure minus left ventricular end-diastolic pressure) and left ventricular end-diastolic pressure during transient aortic occlusion with a balloon catheter. Left ventricular function curves were obtained by plotting left ventricular-developed pressure at increasing left ventricular end-diastolic pressures up to 50 mm Hg. Acute myocardial infarction caused marked depression of left ventricular function measured 1 hr after onset of infarction, but 1 wk later all eight animals showed improvement with return of function toward the control levels. A small but significant descending limb was noted at left ventricular end-diastolic pressures above 35 mm Hg. Quantitatively, the descending limb was similar before, 1 hr after, and 1 wk after myocardial infarction. Hemodynamic data revealed evidence of left ventricular failure in all animals, but variability in individual hemodynamic parameters was noted. The data indicate that the marked depression of left ventricular function observed immediately after experimental acute myocardial infarction undergoes considerable resolution within 1 wk, but that functional recovery remains incomplete.