MYOCARDIAL PRECONDITIONING - A MODEL OR A PHENOMENON

A brief ischemic episode (ischemic preconditioning) limits myocardial necrosis produced by a prolonged period of coronary artery occlusion a nd reperfusion. In absence of infarction, lack of cumulative ATP deple tion, and ventricular arrhythmias and dysfunction ''stunning'' in mode ls of intermittent ischemia and reperfusion also could be a component of an adaptive response to brief ischemia (preconditioning). Nonischem ic stimuli also precondition the myocardium against ventricular arrhyt hmias and infarction by activating endogenous mechanism(s) of protecti on similar to that induced by ischemic preconditioning. Preservation o f myocardial ATP, abolishing purine release, attenuation of free radic al production, activation of adenosine receptors and K-ATP channels, a nd induction of heat shock proteins are common responses to ischemic a nd nonischemic stimuli of preconditioning. Although a significant redu ction in myocardial infarction is critical to myocardial salvage and p atient survival, it is equally important to have a functioning heart t hat can sustain systemic pressure without inotropic support or assist devices. It is scientifically challenging and clinically important to elucidate the mechanisms of myocardial preconditioning. However, it is necessary to expand the definition of myocardial preconditioning to i nclude nonischemic stimuli of preconditioning and other important moni tors of myocardial protection such as ventricular function and electro physiological stability in addition to that of infarction.