Assessment of Myocardial Viability: An Effective Gatekeeper for Coronary Revascularization?

Abstract

Heart failure is an emerging worldwide epidemic. In the USA alone, there are an estimated 4.8 million Americans with heart failure, 10% of persons aged 70 years or greater and 400,000 new cases annually [1]. Heart failure is the most common diagnosis in hospitalized patients aged 65 years and older. There is an exceedingly high mortality rate associated with heart failure; approximately 50% of patients diagnosed with heart failure will be dead within 5 years. As the population ages, with more cardiac patients living longer with their disease, the opportunity for developing heart failure increases. The economic costs of heart failure are substantial with an estimated US$23.2 billion society costs per year in the USA. Coronary artery disease (CAD) is the most common cause of left ventricular (LV) systolic dysfunction leading to heart failure [2]. It was previously thought that loss of myocardial contractility after myocardial infarction was caused by the destruction of myocardium and the development of irreversible scarring. With the subsequent development of coronary artery bypass grafting (CABG), clinical observations showed that in some individuals, the function of hypo or akinetic segments could improve following revascularization [3]. The contractile regional dysfunction seen in patients may be either transient (stunning) or prolonged (hibernation). In reality, the spectrum of myocardial dysfunction is probably a continuum extending from myocardial ischemia to programmed cell death and apoptosis. A proportion of patients with heart failure will confer viability by symptomatic angina or ischemia demonstrated by myocardial perfusion imaging [4]. However, most patients with LV systolic dysfunction due to CAD have a heterogeneous mixture of stunned, hibernating and scarred myocardium in various proportions. Given many considerations, it is clear that patients with heart failure due to CAD should pursue treatment options to prevent future coronary events. These therapies include treatment of heart failure, myocardial ischemia, and myocardial stunning and hibernation. Standard treatment of patients with heart failure due to LV systolic dysfunction include angiotensin-converting enzyme (ACE) inhibitors, angiotensinreceptor blockers, β-blockers and aldosterone antagonists [5–8]. Many cardiologists, and some guidelines [9], recommend evaluating patients with CAD and heart failure to identify patients suitable for coronary revascularization, although this strategy is not evidence based. It is often believed that the presence of viable but dysfunctional myocardium is an indication for revascularization, although very few patients with heart failure undergo viability testing.