CORONARY CIRCULATION IN DOGS WITH AN EXPERIMENTAL DECREASE IN AORTIC COMPLIANCE

Objectives. This study was designed to investigate the effects of decreased aortic compliance on the coronary circulation. Background. A decrease in aortic compliance due to arteriosclerosis is observed in patients with coronary artery disease. However, the effects of decreased aortic compliance on the coronary circulation have not yet been investigated sufficiently. Methods. Hemodynamics, subendocardial electrocardiogram (ECG), myocardial segmental length and myocardial blood flow were investigated in six dogs with aortic bandaging (bandaged group) and five dogs with a sham operation (control group) at rest and during pacing 4 weeks after surgery. Results. Aortic compliance in the bandaged group was less than that in the control group (0.24 +/- 0.20 vs. 0.50 +/- 0.22 ml/mm Hg, p < 0.05). Pulse pressure and the tension-time index were significantly greater in the bandaged group than in the control group, but systemic vascular resistance was not altered significantly. The subendocardial/subepicardial flow ratio was lower in the bandaged group than in the control group (0.95 +/- 0.31 vs. 1.57 +/- 0.26, p < 0.05). In the region supplied by the left circumflex artery with a stenosis that was adjusted to eliminate reactive hyperemia, rapid atrial pacing (heart rate 200 beats/min) further decreased endocardial flow and the endocardial/epicardial flow ratio in the bandaged group. Moreover, both the reduction of segmental shortening and the ST elevation on the subendocardial ECG in the left circumflex-supplied region during pacing were greater in the bandaged group. Conclusions. These results indicate that decreased aortic compliance greatly increases the risk of subendocardial ischemia in the presence of coronary stenosis.