[Ischemic preconditioning. Is it always a beneficial phenomenon?]

Hearts exposed to reversible ischemia stand a subsequent prolonged episode of coronary artery occlusion (ischemic preconditioning) better. The reduction of infarct size by means of preconditioning has been amply demonstrated, but the relationship between preconditioning and contractile function remains less well defined. In this study we assess the effect of a later ischemia on the regional contractility in a stunned-preconditioned myocardium.

We analyze the shortening fraction in the ischemic (dependent on the left anterior descending coronary artery), periischemic and control zone (dependent on the left circumflex coronary artery), using chronic implants of ultrasonic crystals in 17 adult mongrel dogs. In the control series, we quantified the effects of partial (30-60% reduction of coronary flow from the basal) and transitory (15 minutes) ischemic episode in the regional myocardial function in a "virgin" myocardium. In two other series, the myocardium was previously stunned-preconditioned through brief and repeated ischemias. Afterwards, at 5th day (series B) and at 15th day (series C), the dogs were subjected to ischemic episode similar to control ones.

After comparing the results with the control series, we observed that the shortening fraction of the ischemic zone was decreased by 107% (p < 0.01) during partial ischemic episode when it was induced on the 5th day of the stunning-preconditioning (series B).

In dogs, the brief and repeated episodes of ischemia could condition the contractile function so that a later partial and transitory reduction of coronary flow could induce a severe affectation of contractility expressed as a diskinetic area.