Hemodynamic characteristics of critical stenosis in canine coronary arteries.

To determine the hemodynamic characteristics of critical stenosis of coronary arteries, mean left circumflex coronary artery (LCCA) flow, myocardial peak reactive hyperemic response (PRHR), myocardial PO2 and PCO2 electrocardiograms, and aortic pressure were monitored at precise degrees of LCCA stenosis in 18 dogs. Stepwise LCCA constriction by a specially designed occluder resulted in a gradual drop in PRHR but little change in other variables. When PRHR was reduced 96 per cent, critical stenosis was achieved, and further constriction caused pronounced and sudden changes in all parameters. When critical stenosis occurred, LCCA diameter had been reduced by 74 plus or minus 2 per cent. Mean LCCA flow was reduced from a base-line level of 42 plus or minus 2 to 34 plus or minus 2 c.c. per minute. PO2 in the myocardium was reduced from 24 plus or minus 1.5 to 16 plus or minus 1.6 mm. Hg. PCO2 increased from 43 plus or minus 5 to 55 plus or minus mm. Hg. T waves in Lead II because isoelectric. The myocardium was well perfused and able to regulate flow through an artery narrowed up to 74 per cent. Beyond this point of critical stenosis, the vascular bed was maximally dilated and further narrowing caused ischemia. These findings indicate that PRHR may be useful at operation to determiine whether all significant lesions are bypassed and whether graft flow is adequate.