Effect of acute regional ischemia on pressure in the subepicardium and subendocardium.

The effects of acute ischemia on regional intramyocardial pressure were studied in eight open-chest dogs. Aortic, left ventricular, subepicardial, and subendocardial pressures were measured with catheter-tip micromanometers. During the control period subendocardial pressure during systole (180 +/- 13 mmHg; mean +/- SE) was higher than left ventricular intracavitary pressure (137 +/- 9 mmHg; P less than 0.001). Subepicardial pressure during systole was lower (95 +/- 6 mmHg; P less than 0.001). Acute ischemia caused a reduction of subendocardial pressure during systole to levels below left ventricular systolic pressure (92 +/- 7 mmHg vs. 116 +/- 6 mmHg; P less than 0.01). Ischemia also caused a reduction of systolic subepicardial pressure to 67 +/- 2 mmHg (P less than 0.001). After reperfusion all pressures returned nearly to control values. During diastole subendocardial pressure during the control period (13 +/- 1 mmHg) was high than left ventricular end-diastolic pressure (6 +/- 1 mmHg; P less than 0.001). Subepicardial pressure during diastole (29 +/- 2 mmHg) was higher than subendocardial pressure and left ventricular end-diastolic pressure (P less than 0.001). Acute ischemia had little or no effect on subendocardial pressure during diastole, whereas it caused a reduction of subepicardial diastolic pressure to 16 +/- 1 mmHg (P less than 0.001). Reperfusion of the ischemic region caused a return of all diastolic pressures nearly to control values. These observations indicate that coronary extravascular resistance is affected by ischemia and that the most prominent effects are in the subendocardium during systole and in the subepicardium during diastole.