Ischemic Heart Failure: Radionuclide Imaging and Clinical Implications

Ischemic heart failure: pathophysiological aspects Under certain conditions, when viable myocytes are subject to ischemia, prolonged alterations in regional or global LV function may occur and this dysfunction may be completely reversible. This condition may be related to two pathophysiological states: stunned and hibernating myocardium. Stunned myocardium refers to the state of persistent regional dysfunction after a transient period of ischemia that has been followed by reperfusion, and is mainly present in acute coronary syndromes. Myocardial hibernation refers to persistent regional LV dysfunction secondary to prolonged, subacute or chronic myocardial hypoperfusion under resting conditions in which myocytes remain viable but regional contractility is reduced to match the reduced blood supply [1,2] . It has been suggested that during hibernation a new state of equilibrium is reached between blood flow (oxygen supply) and contraction (oxygen demand) whereby myocardial necrosis is prevented. Therefore, hibernation is considered a protective response of decrease oxygen demand in the setting of decrease oxygen availability [3]. Early studies suggested that resting blood flow is severely reduced in hibernating myocardium. However, more recent data obtained with quantitative measurements of myocardial blood flow indicate that during hibernation resting blood flow may be normal or only moderately reduced, with a disproportional decline in contractile function [4,5] . hese findings suggest that myocardial hibernation may involve, at least in part, repetitive myocardial stunning, which determines protracted contractile dysfunction. Moreover, it is conceivable that somecases of presumed hibernation may represent stunning and other cases may represent intermittent stunning with hibernation, in which chronically underperfused myocardium becomes transiently ischemic (regional oxygen supply-demand imbalance).