HIBERNATING AND STUNNED MYOCARDIUM

The term ''hibernating'' myocardium has been introduced to indicate th e presence of regional asynergy due to persistent hypoperfusion, which can be reversed after revascularization. The mechanisms underlying th e prolonged functional adaptation of myocardial cells to hypoperfusion are still not clear, although preliminary experimental data indicate that a reduced availability of intracellular Ca++ may play an importan t role. The identification of hibernating myocardium may have therapeu tic implications, since it has been demonstrated that the revasculariz ation of hibernating myocardial territories may lead to regional and g lobal improvement of systolic left ventricular function. The noninvasi ve identification of hibernating myocardium can be accomplished by pos itron emission tomography, which demonstrates the presence of preserve d metabolic activity in hibernating myocardial territories. However, e xercise thallium-201 scintigraphy, using the reinjection technique, wi th a quantitative regional analysis of thallium-201 uptake, has also b een reported to provide information comparable to that obtained by pos itron emission tomography. ''Stunning'' of the myocardium indicates a condition of transient impaired regional systolic function, following an episode of ischemia. The mechanisms determining the slow recovery o f function after ischemia are still not completely understood. Experim ental data suggest in this case a reduced Ca++ affinity of the myofibr ils and a reduced maximal calcium-activated force.