High afterload during 10 min of regional ischaemia affects diastolic creep but not systolic function in reperfused (stunned) myocardium.

The effect of afterload during regional ischaemia on myocardial stunning was studied in 15 pentobarbital anaesthetized cats. 10 min occlusion of the left anterior descending artery (LAD) was followed by 60 min of reperfusion. Afterload was decreased by intravenous infusion of nitroglycerine 3-8 micrograms kg-1 min-1 in group I (n = 8); left ventricular peak systolic pressure (LVSP) 84 +/- 4 mmHg (mean +/- SEM) during coronary artery occlusion. In group II (n = 7) LVSP was increased to 188 +/- 10 mmHg by inflating an intraaortic balloon during coronary artery occlusion. Regional function in the LAD perfused region was evaluated by cross-oriented sonomicrometry. Myocardial tissue blood flow was evaluated by radio-labelled microspheres. Afterload alterations did not affect regional systolic shortening (10.8 +/- 2.0% vs. 11.0 +/- 1.5% in group I and II, respectively, after 60 min of reperfusion). However, increased end-diastolic dimensions (diastolic creep) in both the circumferential and longitudinal segments were markedly more pronounced in the high afterload group (group II). Also important, the markedly increased myocardial tissue blood flow during reperfusion in group II as compared with group I (2.30 +/- 0.18 vs. 1.34 +/- 0.08 mL min-1 g-1 and 2.58 +/- 0.23 vs. 1.49 +/- 0.07 mL min-1 g-1 in subepicardial and subendocardial layers in the LAD perfused region) suggests that increased diastolic creep increased metabolic demands. This study indicates that passive stretching of the ischaemic area during coronary artery occlusion is an important mechanism behind diastolic creep.