Differential effect of preconditioning on post-ischaemic myocardial performance in the absence of substantial infarction and in extensively infarctedrat hearts

Objectives: There is controversy concerning the beneficial effects of ischa emic preconditioning during short periods of ischaemia (stunning). The aim of the study was to investigate post-ischaemic myocardial performance after various periods of ischaemia in both non-preconditioned and preconditioned hearts and to compare these results with infarct volume estimation. Method s: Isolated perfused rat hearts were subjected to various periods of sustai ned ischaemia (15, 20, 30, and 45 min). Haemodynamic parameters, infarct si ze and lactate dehydrogenase (LDH) leakage were recorded in both preconditi oned and non-preconditioned hearts. Results: After lj min of ischaemia, pre conditioned hearts revealed significantly lower developed pressure than non -preconditioned hearts (80 +/- 4.1 vs. 95 +/- 0.3%, P = 0.02). In the 20 mi n ischaemia group, preconditioning resulted in non-significantly lower deve loped pressure (76 +/- 3.1% in preconditioned hearts vs. 87 +/- 5.3% in non -preconditioned hearts, P = 0.11). In these groups infarct volume was small and not different between non-preconditioned and preconditioned hearts. Af ter 30 min of ischaemia, preconditioning significantly improved developed p ressure (66 +/- 3.1% in preconditioned and 44 +/- 5% in non-preconditioned hearts, P = 0.002). LDH leakage was significantly higher in non-preconditio ned hearts compared with preconditioned hearts (16 +/- 2.3 vs. 9.0 +/- 1.3, P = 0.04), whereas infarct volume was not (12.5 +/- 0.8 and 9.8 +/- 1.5, r espectively, P = 0.1). Non-preconditioned hearts of this group, subjected t o inotropic stimulation at the end of reperfusion responded poorly. Signifi cantly higher developed pressure was attained by preconditioned hearts (150 +/- 3.1 vs. 123 +/- 7.5%, P = 0.01). After 45 min of ischaemia, preconditi oning resulted in 69% limitation of infarct volume (P < 0.0001) and 53% red uction in LDH release (P = 0.009). Developed pressure was 57 +/- 8.5% in pr econditioned hearts and 32 +/- 4.5% in non-preconditioned hearts (P = 0.02) . Conclusions: When ischaemic insult results in minimally lethal injuries, preconditioned hearts do not have the advantage of not being prone to stunn ing rather than non-preconditioned. If ischaemic insult is potentially able to produce extensive infarction, improvement in post-ischaemic myocardial function is mainly due to infarct size limitation evoked by preconditioning . (C) 2001 Elsevier Science B.V. All rights reserved.