Coronary extravascular compression influences systolic coronary blood flow

The purpose of this study was to determine whether a relation exists between systolic coronary blood flow and systolic coronary extravascular compressive forces. Studies were performed in seven open-chest dogs in which the left anterior descending coronary artery was cannulated and perfused from the left carotid artery. Pressure within the left ventricular subepicardium, a measure of coronary extravascular compression in the subepicardium, was measured with a 1-mm-diameter catheter-tip micromanometer inserted directly into the myocardium in the region of perfusion. Systolic extravascular compressive forces were augmented by a local intracoronary injection of 1 microgram isoproterenol. Measurements were made in the presence of coronary vasomotor tone and were repeated following local maximal vasodilatation with adenosine. In the regulated coronary bed, systolic coronary flow decreased (18 +/- 4 vs -2 +/- 4 ml/min, P less than 0.01) as intramyocardial pressure increased (127 +/- 5 vs 222 +/- 12 mmHg, P less than 0.001). Similarly, in the maximally vasodilated coronary bed, systolic coronary flow decreased (103 +/- 16 vs 38 +/- 11 ml/min, P less than 0.001) as intramyocardial pressure increased (112 +/- 6 vs 204 +/- 16 mmHg, P less than 0.001). These observations indicate that an augmentation of coronary extravascular compressive forces during systole is accompanied by a diminution of systolic coronary flow irrespective of coronary vasomotor tone.