HIBERNATING, STUNNING AND ISCHEMIC PRECONDITIONING OF THE MYOCARDIUM - THERAPEUTIC IMPLICATIONS

Hibernating myocardium, as a compensatory mechanism to chronic ischemi a caused by a tight coronary stenosis is best treated by restoration o f blood flow. Hence in this condition the therapeutic implications are rather obvious and the problem is how to diagnose hibernating myocard ium. Provocation tests and/or scintigraphic methods are usually used t o show viability of an akinetic myocardial area. These tests, however, can be expected to be clearly positive only if hibernating myocardium is not mixed with patchy scar tissue. Physicians should be aware of m yocardial stunning, when left ventricular function remains impaired im mediately after revascularization, for example, after cardiac surgery of the totally ischemic organ or after thrombolytic therapy of acute m yocardial infarction. Due to the self-recovery of this condition, ther apeutic implications are given only when symptoms and signs of impaire d ventricular function are present. Positive inotropic agents have bee n shown to be effective in experimental conditions and are widely acce pted to be beneficial in clinical use. Based on experimental observati ons the term ''ischemic preconditioning'' has been introduced to descr ibe a condition of increased ischemic tolerance after a short precedin g period of ischemia and reperfusion. This condition, however, has nev er been proven to be of clinical significance in the treatment of pati ents with ischemic heart disease. According to some clinical observati ons, repeated episodes of ischemia are even associated with a worse pr ognosis. Therapeutic implications may arise from understanding the mec hanisms involved in this cardioprotective process, for example, activa tion of adenosine A(1) receptors.