The biology of myocardial hibernation

Patients with chronic coronary artery disease frequently have contractile d ysfunction that recovers upon reperfusion, The concept of myocardial hibern ation views the observed reduction in contractile function not as the resul t of an ongoing energetic deficit, but as an adaptive down-regulation that serves to maintain myocardial integrity and viability. In the experiment, s ustained perfusion-contraction matching, recovery of energy and substrate m etabolism during ongoing ischemia, the potential for recruitment of inotrop ic reserve, lack of necrosis, and therefore recovery of function upon reper fusion are established features of hibernation. Apart from reduced calcium responsiveness, the underlying mechanisms are still unclear. In patients, t he importance of reduced baseline blood flow vs. that of superimposed repet itive stunning is somewhat controversial; however, in most studies blood fl ow is reduced and the myocardium must be ischemic often enough to have pers istent dysfunction. Morphologically, hibernating myocardium displays featur es of dedifferentiation, with loss of cardiomyocytes and myofibrils, and of degeneration, with increased interstitial fibrosis, Patients with hibernat ing myocardium must be identified and undergo revascularization. With a bet ter understanding of the underlying mechanisms of hibernation, these adapti ve responses to ischemia can potentially be recruited and reinforced pharma cologically to delay impending myocardial infarction. (C) 2001, Elsevier Sc ience Inc.