[Thallium scintigraphy for determining myocardial vitality. Evaluation of the "stunned and hibernating myocardium"].

Myocardial uptake of 201thallium is not only a function of regional myocardial blood flow, but also reflects cellular uptake by intact cell membranes and thus can not be merely regarded a signal of perfusion but also of structural cell integrity. Especially in the setting of severely depressed left ventricular function evidence of viable but dysfunctional myocardium has impact on recovery potential and prognosis after myocardial revascularization. Hibernating myocardium, a reversible chronically ischemic state of reduced aerobic metabolism and depressed contractile function, may be identified after injection of 201thallium at rest and rest-redistribution SPECT imaging. Since 201thallium uptake in initial defect areas may occur as a function of time allowed for redistribution, even partial late uptake may be considered a reliable signal for viable, but hibernating tissue, 75% of which demonstrating contractile recovery after revascularization. Uptake of 201thallium at rest or with redistribution, thus, is indicative of myocardial viability irrespective of function. Conversely, lack of 201thallium uptake after stress and redistribution does not always indicate necrosis, since 45 to 83% of myocardium with no uptake may improve function after revascularization. These defects, however, often resolve with reinjection of 201thallium and subsequent imaging at rest. This observation led to a triphasic imaging protocol including conventional rest-redistribution imaging and a third set of images after reinjection of 1 mCi 201thallium at rest. This concept ensures uptake of 201thallium in 31 to 49% of presumably persistent defects and increases sensitivity for detection of viable tissue. In 80 to 87% of areas with reinjection 201thallium uptake function improved after revascularization compared to 0 to 8% of segments with no uptake at all. Redistribution imaging should not be omitted for logistical reasons, since important information not only on ischemia but also on viability may be lost. Useful imaging protocols for detection of both ischemia and viability comprise either a sequence of stress, redistribution and reinjection imaging or a series of stress, reinjection and 24 hour redistribution images; both protocols have similar sensitivity for detection of tissue viability. In the setting of stunned myocardium mainly after thrombolytic therapy the assessment of residual viability may be important for both additional therapeutic and prognostic reasons. 201Thallium uptake preferentially using a re-redistribution protocol may help to differentiate viable from non-viable myocardium; however 201 thallium imaging should be performed after the hyperemic phase following successful thrombolysis (> or = 24 to 48 hours after thrombolysis).(ABSTRACT TRUNCATED AT 400 WORDS)