The effects of intermittent ischemic arrest on the perfusion of myocardium supplied by collateral coronary arteries.

Six weeks after placement of an ameroid constrictor on the circumflex coronary artery, blood flow in a collateral region was compared with flow in myocardium supplied by normal arteries during cardiopulmonary bypass (80 mm Hg). Myocardial blood flow was determined using radionuclide-labeled microspheres (8 to 10 mu) before 10 minutes of ischemic arrest and after 1, 5, and 10 minutes of reperfusion. The retrograde circumflex pressure was monitored continuously and served as an additional index of perfusion of the collateral region. During reperfusion, endocardial flow in the collateral region remained unchanged despite a threefold increase in a similar layer having normal arteries (p less than 0.01). Following ischemic arrest, mean transmural and subendocardial hyperemic responses both persisted for longer than 10 minutes in normal regions. Simultaneously, peripheral circumflex pressures decreased at 1 and 5 minutes of reperfusion (p less than 0.001) but returned to control within 10 minutes. Persistently elevated endocardial flow in the normal arteries and the absence of a hyperemic response in the collateral region during an associated decrement in retrograde circumflex pressure may indicate incomplete flow repayment even after 10 minutes of reperfusion. Marked transmural flow imbalances despite adequate coronary perfusion pressures suggest that intermittent ischemic arrest may cause cumulative ischemia, and this occurrence may be detrimental especially in collateral regions of myocardium.