Effects of coronary collaterals on regional myocardial function during temporary coronary occlusion and hypoxic...

The effects of coronary collaterals on regional myocardial function during temporary ischemia and hypoxia were studied in 12 open-chest dogs. Using an ultrasonic dimension gauge, systolic segment shortening in the left anterior descending coronary artery (LAD) area was measured at 1 min after the following three experimental conditions: LAD occlusion and LAD hypoxic perfusion with nonoxygenated solutions at two different pressures (60 mmHg and 120 mmHg). Collateral function was assessed by both LAD diastolic retrograde pressure and the percentage of increase in left circumflex coronary flow at 1 min after LAD occlusion. Systolic segment shortening decreased less with hypoxic perfusion than with occlusion, however, this beneficial effect on regional contraction was greater at a perfusion pressure of 60 mmHg than at one of 120 mmHg. The magnitude of decrease of systolic shortening was variable among individual dogs but correlated linearly with each of the two collateral function indexes, not only during occlusion but also during hypoxic perfusion. In conclusion, the preventive effect of hypoxic coronary perfusion on the early decline of regional myocardial function, in comparison to the changes seen during ischemia, may depend on coronary collaterals in addition to its washout effect on metabolites. In order to maintain myocardial function, perfusion pressure should be at an optimal level.