Multiple episodes of ischemic preconditioning are not associated with loss of benefit: preliminary clinical experience.

Background: As a clinical analogue of ischemic preconditioning (IP), preinfarction angina (PA) shares a well-documented protective effect in the setting of acute myocardial infarction (AMI) by reducing infarct size, preserving left ventricular function and improving prognosis. In the experimental setting, multiple cycles of IP may induce the loss of this protection.

Objective: To evaluate the effect of repeated cycles of PA on clinical outcomes in patients exhibiting a first AMI.

Methods: Seventy-four consecutive patients with AMI, in whom PA was the surrogate of experimental IP, were studied prospectively. All patients had poor or no collaterals. The patients were divided into three groups: group 1 (n=32) comprised patients without PA (control subjects); groups 2 (n=24) and 3 (n=18) comprised patients reporting one to four and more than four episodes of new-onset PA, respectively (preconditioned groups). Both of the preconditioned groups were compared with the control subjects with regard to creatine kinase-MB release, corrected Q-T interval (QTc) at discharge and major in-hospital complications.

Results: Compared with the control subjects, groups 2 and 3 exhibited reduced creatine kinase-MB release (75+/-26 IU/L and 85+/-22 IU/L versus 172+/-13 IU/L, P=0.004 and P=0.024, respectively), lower discharge QTc values (418+/-15 ms and 422+/-19 ms versus 443+/-38 ms, P=0.004 and P=0.031, respectively), and a reduced incidence of postinfarction angina (25% and 11% versus 44%, P<0.05), arrhythmias (0% and 0% versus 22%, P<0.05) and pulmonary edema (4% and 0% versus 28%, P<0.05).

Conclusions: Regardless of the number of recurrences, IP seems to be a powerful intervention to reduce infarct size, limit QTc at discharge and improve the outcome in patients with AMI.