Published online before print March 11, 2004, doi: 10.1161/01.RES.0000125628.57672.CF
© 2004 American Heart Association, Inc.
Integrative Physiology |
Hibernating Myocardium
Chronically Adapted to Ischemia but Vulnerable to Sudden Death
From the VA Western New York Health Care System (J.M.C.Jr., M.B., J.A.F.) and the Departments of Medicine (J.M.C.Jr., G.S., M.D.B., J.A.F.) and Physiology/Biophysics (J.M.C.Jr.), University at Buffalo, Buffalo, NY, and the Department of Pathology and Cellular and Molecular Biology (F.V.), Cardiovascular Research Institute, University of Maastricht, The Netherlands.
Correspondence to John M. Canty, Jr, MD, Biomedical Research Building, Room 347, Department of Medicine/Cardiology, University at Buffalo, 3435 Main St, Buffalo, NY 14214. E-mail canty{at}buffalo.edu
The inability to reproduce spontaneous ventricular fibrillation in an animal model of chronic coronary artery disease has limited advances in understanding mechanisms of sudden cardiac death (SCD). Swine with hibernating myocardium arising from a chronic left anterior descending coronary artery (LAD) occlusion have a high rate of SCD that parallels the poor clinical survival of medically treated patients with hibernating myocardium. Kaplan-Meier analysis (n=426) demonstrated a cumulative mortality of 49% after 5 months that was almost entirely attributable to spontaneous SCD. Using implantable loop recorders, ventricular fibrillation was documented as the arrhythmic mechanism of death in all animals (n=10) and was usually preceded by ventricular tachycardia (n=8). Physiological studies before SCD (n=7) demonstrated total LAD occlusion and collateral-dependent myocardium (n=5), excluding acute occlusion as a major trigger of arrhythmia. The physiological substrate of hibernating myocardium was present before SCD, with reductions in LAD perfusion (SCD 0.79±0.13 versus 0.80±0.08 mL/min per g) and wall thickening (SCD 28±3% versus 22±3%) that were similar to survivors (n=14). Triphenyltetrazolium chloride infarcts among animals with SCD were infrequent (4 of 32) and small, averaging 4.6% of LV mass. Histology (n=4) showed postmortem changes but no acute inflammation nor contraction band necrosis. These data support the notion that hibernating myocardium is a pathophysiological substrate at high risk of SCD. This is independent of changes in functional stenosis severity, acute myocardial necrosis, or fibrotic scar. Thus, regional adaptations that promote myocyte survival in the setting of chronic repetitive ischemia result in a substrate with enhanced vulnerability to lethal arrhythmias and SCD.
Key Words: hibernating myocardium • sudden cardiac death • ventricular fibrillation
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