Difference in the relation between infarct and occluded bed in pentobarbital-anesthetized and conscious dogs
The relationship between myocardial infarct size (IS) and occluded bed size (OBS) in pentobarbital-anesthetized (A, n = 16) and conscious (C, n = 20) dog models were compared. IS and OBS (postmortem coronary arteriography) were measured by computerized planimetry of weighed left ventricular (LV) rings 7 days after permanent left anterior descending (LAD, n = 19) or circumflex (LC, n = 17) coronary artery occlusion. For both A and C groups, IS was directly related to OBS (p < 0.001) and no infarcts developed for small occluded beds. For either LAD or LC subgroups, infarcts were larger in A than C dogs (49 ± 18 vs. 30 ± 19% OBS, p < 0.025), with greater slope of the linear regression between IS and OBS (p < 0.001) and less epicardial sparing on topographic mapping (p < 0.05). Although postocclusion mean arterial and left atrial pressures were similar in A and C groups, heart rates were greater in the A dogs, both pre- (125 vs. 88 beats/min, p < 0.001) and post-occlusion (151 vs. 108 beats/min, p < 0.001). Endocardial flows (radioactive microspheres) in infarct centers and margins were less in A than C dogs. Also, endocardial/epicardial (endo/epi) flow ratios in all regions were less in A than C dogs, both pre- and post-occlusion. Increasing heart rate in 10 other C dogs with LAD occlusion to that of the A group (151 beats/min) by right ventricular pacing resulted in larger infarcts with greater slope of the linear regression and less endo/epi flow ratios, as in the A group. Thus, infarcts are larger in A than C dog models. The effect appears to be related to increased myocardial oxygen demands and transmural maldistribution of flow associated with tachycardia.