The mechanisms underlying hibernating myocardium are poorly understood, but appear to involve both acute and chronic feedback whereby reduced energy supply induces decreased contractile function and attendant reduced energy consumption. By maintaining the balance between supply and demand, ischemia is avoided and tissue survival is possible. Although often difficult to distinguish from hibernating myocardium with routine testing, stunned myocardium connotes a reversible ischemic injury in contrast to hibernating myocardium in which no injury is thought to occur. Clinically applicable measures of metabolism (e.g., with PET scanning) are depressed in hibernating myocardium but normal in stunned myocardium. Thus, PET scanning is an excellent way to identify poorly contracting but viable myocardium. Other useful approaches include dobutamine echocardiography, thallium redistribution studies, and ''scar imaging'' with nuclear magnetic resonance. Revascularization in patients with depressed but viable myocardium has been shown to improve function, and is therefore appropriate therapy for CHF. With the following exception, there are no special considerations in the identification and management of hibernating myocardium in diabetic compared with nondiabetic patients. The BARI study showed that diabetic patients with multivessel coronary disease with indications for revascularization fared much better in terms of survival when revascularization was accomplished surgically rather than percutaneously by balloon angioplasty. Coronary stenting combined with new approaches to prevention of restenosis (especially brachy-therapy) may modify this conclusion, but for the time being diabetic patients with low-ejection-fraction CHF, significant areas of viable myocardium, and multivessel coronary disease should generally be treated with surgical rather than percutaneous revascularization.

Transplantation and Mechanical Assist Devices. Cardiac transplantation is appropriate treatment for the relatively small number of severely compromised CHF patients for whom suitable donor organs can be identified. In the past, diabetic patients had been considered to be suboptimal candidates for transplantation. However, with improvements in immunosuppressive regimens, the outlook for diabetic patients undergoing transplantation, providing they do not have extensive end organ damage, has become quite acceptable. As transplantation has come of age, great strides have been made in the development of ventricular assist devices. These devices now have portable power supplies and are being used increasingly for prolonged periods of time with acceptably low complication rates, although their role remains primarily that of a bridge to transplantation. As further advances in this technology occur, including continued development of a totally implantable mechanical heart, mechanical assist devices are likely to emerge as viable treatment approaches independent of transplantation for both diabetic and nondiabetic patients.

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