Selecting the appropriate patients for coronary artery bypass grafting in ischemic cardiomyopathy-importance of myocardial viability

Abstract

Patients who undergo coronary artery bypass graft (CABG) surgery in ischemic cardiomyopathy have a survival advantage over medical therapy at 10 years. The survival advantage of CABG over medical therapy is due to its ability to reduce future myocardial infarction, and by conferring electrical stability. The presence of myocardial viability does not provide a differential survival advantage for CABG over medical therapy. Presence of angina and inducible ischemia are also less predictive of outcome. Moreover, CABG is associated with significant early mortality. Hence, careful patient selection is more important for reducing the early mortality and improving the long-term outcome than relying on results of myocardial viability. Younger patients with good exercise tolerance benefit the most, while patients who are frail and patients with renal dysfunction and dysfunctional right ventricle seem to have very high operative mortality. Elderly patients, because of poor life expectancy, do not benefit from CABG, but the age cutoff is not clear. Patients also need to have revascularizable targets, but this decision is often based on experience of the surgical team and heart team discussion. These recommendations are irrespective of the myocardial viability tests. Optimal medical treatment remains the cornerstone for management of ischemic cardiomyopathy.

Keywords: CABG; Coronary artery bypass grafting; Ischemic cardiomyopathy; Left ventricular dysfunction; STICH trial.

Fig. 1

A conceptual construct for the stages of hibernation. After a short period of ischemia, which is alleviated before irreversible damage has taken place, contractile dysfunction can persist for hours to days; this is termed stunning. If the cell is exposed to repeated episodes of hypo-perfusion, it can enter early- or “short-term” hibernation with metabolic adaptation and early histological changes becoming apparent: at this point, function remains persistently abnormal between episodes of ischemia, unless the stimulus is withdrawn for an extended period. Over a longer duration, more extensive histological change occurs, some myocytes are lost with fibrotic replacement, while others enter advanced hibernation with cellular adaptations and remodeling. Conversely, infarction, usually caused by a single prolonged period of ischemia, results in complete cellular necrosis and replacement of normal tissue with fibrous scar (reproduced with permission from Ryan et al. [29])

Fig. 2

Algorithm for selection of patients for CABG in ischemic cardiomyopathy

Fig. 3

Revascularization in heart failure: proposed contributing factors influencing the decision for revascularization in patients with severe left ventricular dysfunction (reproduced with permission from Velazquez and Bonow [5])