Separation of overlap and collateral perfusion of ischemic canine myocardium: important considerations in the analysis of vasodilator-induced coronary steal.

Coronary steal was studied in dogs with a left anterior descending (LAD) coronary artery occlusion by use of a special technique to exclude contamination from overlapping circulations with true collateral blood flow. Different degrees of vasodilation in nonischemic myocardium were produced by the selective coronary dilator, chromonar, at a constant heart rate and aortic blood pressure. A map of the ischemic area was made, and criteria used to identify ischemic tissue samples included: (1) all samples within the LAD perfusion area, as defined by a dye technique; (2) tissue samples with blood flows less than 25% normal area flow; (3) samples from within the central ischemic zone; and (4) tissue samples with overlap blood flow less than 2% normal area flow. When criteria 1 and 2 were used to identify ischemic myocardium, chromonar (5 and 7.5 mg/kg, i.v.) produced no change in ischemic blood flow. On the other hand, when tissue samples from the central ischemic zone or those which had less than 2% overlap flow (criteria 3 and 4) were used to identify ischemic myocardium, chromonar produced a dose-related decrease (p less than 0.01) in transmural collateral perfusion (25 +/- 4 and 33 +/- +/- 5;33 +/- 3 and 41 +/- 6%, respectively). Other indices of collateral function, peripheral coronary pressure (23 +/- 4 and 25 +/- 3%), retrograde flow (20 +/- 3 and 26 +/- 4%), and retrograde conductance (21 +/- 4 and 30 +/- 4%), also decreased significantly. These results indicate that moderate to maximal coronary vasodilation produces a true coronary steal in the absence of changes in aortic pressure and heart rate. In addition, these data demonstrate that significant amounts of overlap flow are contained in superior, inferior, and lateral borders of the ischemic zone, and that strict criteria to identify ischemic myocardium are needed when studying the effect of drugs on true coronary collateral blood flow.