LEFT-VENTRICULAR DYSFUNCTION DUE TO THE NEW ISCHEMIC OUTCOMES - STUNNING AND HIBERNATION

Several potential manifestations and outcomes are associated with myoc ardial ischemia and reperfusion. When ischemia is severe and prolonged , irreversible damage occurs and there is no recovery of contractile f unction. When ischemia is less seven or shorter in duration, recovery of contraction may occur instantaneously or more commonly, after consi derable delay, which is the condition recognized as ''stunned myocardi um.'' Stunning is defined as a transient left ventricular dysfunction that persists after reperfusion despite the absence of irreversible da mage and restoration of normal or near-normal coronary flow. Oxidative stress and alteration of calcium homeostasis during reperfusion an th e probable causes of stunning. Clinically, stunning may occur after ac ute infarction, successful thrombolysis, unstable angina, angioplasty, resolution of coronary spasm, open-heart surgery, or transplantation, It can be treated with interventions aimed at prevention or reversal. When ischemia is prolonged but less severe, myocytes may remain viabl e but exhibit depressed contraction. Under these conditions, reperfusi on restores normal contractile performance. This type of ischemia, lea ding to a reversible, chronic left ventricular dysfunction, has been t ermed ''hibernating myocardium,'' The intrinsic mechanisms of this con dition are unknown. Clinically, it is very important to diagnose hiber nation because reperfusion of the hibernating myocardium by angioplast y or heart surgery restores contraction, and this correlates with long term survival. A number of methods are available to access the hiberna ting myocardium. These include cardiac imaging techniques that evaluat e myocardial viability, such as positron emission tomography and thall ium myocardial imaging, or methods that evaluate contractile reserve, such as low-dose dobutamine echocardiography. Interestingly, reperfusi on of patients with end-stage ischemic cardiomyopathy and hibernating myocardium can be considered an alternative to transplantation.