Importance of diagnosing hibernating myocardium: how and in whom?

Hibernating myocardium (1–3) can be described by the clinical situation, that is, it is impaired left ventricular (LV) function at rest that is reversible by revascularization. Hearse (4) has defined hibernating myocardium as “exquisitely regulated tissue successfully adapting its activity to prevailing circumstances. ” Initially, the two clinical syndromes diagnosed in patients with coronary artery disease (CAD) were angina and myocardial infarction (MI). Subsequently, it was recognized that these two conditions could be painless, and the syndromes of unstable angina and non-Q wave MI were also diagnosed. Hibernating myocardium is one of three myocardial states of new ischemic syndromes (5) (Fig. 1) and is one of the myocardial states that may be present in patients in areas of LV dysfunction at rest (Table 1). There is a considerable body of evidence (which is progressively increasing) showing that hibernating myocardium is a result of, and is associated with, reduced myocardial blood flow (MBF) or reduced myocardial perfusion at rest and that hibernating myocardium is normalized or improved with increasing MBF, reperfusion or myocardial revascularization (6,7). Hibernating myocardium, if revascularized, is associated with a lower cardiovascular event rate (8). Coronary bypass surgery, if it increases or normalizes MBF, reduces or eliminates the frequency and severity of angina and the need for pharmacologic treatment (9). Randomized trials in selected patients have documented better survival in those “assigned to” coronary bypass surgery than in those “assigned to” medical treatment in patients with left main CAD; three-vessel CAD with normal LV function; and two-vessel CAD if one of the vessels was the proximal left anterior descending coronary artery (2,10,11). In patients with LV dysfunction at rest, randomized trials of coronary bypass surgery have shown an improved survival (2,10), particularly in patients with threevessel CAD (12). Complete revascularization is important for improving the long-term outcome of severely symptomatic patients with three-vessel CAD and LV dysfunction (13). Percutaneous transluminal coronary angioplasty has been documented in randomized trials of selected patients to have results (both short term and intermediate up to 5 years) similar to those of coronary bypass surgery (14–17). The conclusions from these studies were that revascularization was of benefit in patients with hibernating myocardium and that it was also needed in selected patients with CAD to improve survival and the symptomatic state. As a result, the “conventional wisdom” developed that if patients had LV dysfunction at rest and had unstable angina or stable chronic angina and left main or three-vessel CAD, they should undergo revascularization by interventional techniques, without the need for documenting the presence and extent of hibernating myocardium. In the current issue of the Journal, Haas et al. (18) describe their findings in patients with “advanced” three-vessel CAD and severe LV dysfunction (LV ejection fraction [LVEF] #0.35) who underwent coronary bypass surgery. Thirty-five patients had coronary bypass surgery on the basis of clinical presentation and angiographic data (group A), and 34 patients had coronary bypass surgery on the basis of positron emission tomographic (PET) findings in addition to the clinical presentation and angiographic data (group B). The PET findings included presence of viable myocardium (see later) and subjectively determined the extent of necrosis and viable tissue. Group B patients had a lower hospital mortality rate (0% vs. 11.4%, p 5 0.04), a lower rate of complicated postoperative recovery (33% vs. 67%, p 5 0.05), a lower incidence of low output syndrome (3% vs. 17%, p 5 0.05) and a lower proportion of patients who needed catecholamine support (0% vs. 29%, p 5 0.002). Furthermore, the 1-year survival rate was better (97 6 8% vs. 79 6 8%, p , 0.01); and, in selected patients studied postoperatively, the LVEF increased from 26% to 35% (p 5 0.003) in group B, but the change in LVEF in group A (30% to 34%) was not statistically significant. These data support the notion that testing for hibernating myocardium is important in determining improved patient outcomes in patients with three-vessel CAD and severe LV dysfunction (LVEF # 0.35). However, there are limitations to the study of Haas et al. (18), some of which the authors themselves have described: 1) The study was a retrospective review of the patients, which means that it is uncertain whether the two groups were identical, even though there were no statistically significant differences in the preoperative characteristics that were examined, and that the patients in this study were a highly select subgroup; 2) whether the symptomatic state was due to angina or heart failure, or both, was not well documented; 3) LVEF was assessed preoperatively by contrast LV angiography and postoperatively by radionuclide angiography, and only threefourths of the surviving patients had postoperative studies (postoperative LVEF in patients who subsequently died was not documented); 4) the functional outcome of regional myocardial segments after coronary bypass surgery was not inves*Editorials published in Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology. From the Griffith Center, Division of Cardiology and Department of Medicine, University of Southern California, Los Angeles County and University of Southern California Medical Center, Los Angeles, California. Address for correspondence: Dr. Shahbudin H. Rahimtoola, Distinguished Professor, University of Southern California, 2025 Zonal Avenue, Los Angeles, California 90033. JACC Vol. 30, No. 7 December 1997:1701–6 1701