HIBERNATING AND STUNNED MYOCARDIUM

The term ''hibernating'' myocardium has been introduced to indicate the presence of regional asynergy due to persistent hypoperfusion, which can be reversed after revascularization. The mechanisms underlying the 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 important role. The identification of hibernating myocardium may have therapeutic implications, since it has been demonstrated that the revascularization of hibernating myocardial territories may lead to regional and global improvement of systolic left ventricular function. The noninvasive identification of hibernating myocardium can be accomplished by positron emission tomography, which demonstrates the presence of preserved metabolic activity in hibernating myocardial territories. However, exercise thallium-201 scintigraphy, using the reinjection technique, with a quantitative regional analysis of thallium-201 uptake, has also been reported to provide information comparable to that obtained by positron 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 of function after ischemia are still not completely understood. Experimental data suggest in this case a reduced Ca++ affinity of the myofibrils and a reduced maximal calcium-activated force.