Ischaemic preconditioning causes increased myocardial vascular resistance but no myocardial contractility changes in pigs after OPCAB

Abstract

The coronary vascular resistance (CVR) after off pump coronary bypass (OPCAB) surgery has never been clarified and ways of preventing stunning are wanted. We wished to investigate the effect of ischaemic preconditioning (IPC) on the CVR and stunning in the postoperative period after OPCAB. In 20 pigs (80 kg), 7 piezo-electric crystals were placed on the left ventricle to assess global and local myocardial contractility. Coronary vascular resistance was measured as the relation between perfusion pressure and coronary artery blood flow. IPC was obtained in ten pigs with one period of 10 min of coronary occlusion, followed by 15 min of reperfusion and 20 min of ischaemia. Ten control animals were exposed to 20 min of ischaemia only. Reperfusion was allowed for 120 min. The CVR was higher in the IPC group (measured by the slopes of the curves in the reperfusion period) (IPC: -0.33 (CI: (-0.62)-(-0.03)); 0.31 (CI: (-0.03)-(0.67)), P<0.005. There was no difference in the local myocardial contractility (slopes of the curves in the reperfusion period) (IPC: -0.004+/-0.01; -0.005+/-0.01). In conclusion, there was no alteration in myocardial contractility, but increased CVR in the early reperfusion period in animals preconditioned before sustained ischaemia.