Meaningful Outcome Measures in Cardiac Surgery

Abstract

The most common cardiac surgical procedures are coronary artery bypass graft surgery and aortic or mitral valve repair or replacement. Underlying conditions include coronary artery disease and heart failure, manifesting as exertional angina, dyspnea, and poor exercise tolerance. The major goals of surgery are to alleviate symptoms and improve patient survival. These, therefore, should inform the choice of primary outcome measures in clinical studies enrolling patients undergoing cardiac surgery. Studies focusing on surrogate outcome measures are relied on all too often. Many are of questionable significance and often have no convincing relationship with patient outcome. Traditional “hard endpoint” outcome measures include serious complications and death with the former including myocardial infarction (MI) and stroke. Such serious adverse outcomes are commonly collected in registries, but because they occur infrequently, they need to be large to reliably detect true associations and treatment effects. For this reason, some investigators combine several outcomes into a single composite endpoint. Cardiovascular trials commonly use major adverse cardiac events (MACEs) as a composite primary endpoint. However, there is no standard definition for MACE. Most include MI, stroke, and death; others include rehospitalization for heart failure, revascularization, cardiac arrest, or bleeding complications. An influential trial in noncardiac surgery found that perioperative β-blockers reduced the risk of MI but increased the risk of stroke and death. Such conflicting findings challenge the veracity of such composite endpoints and raise a far more important question: which of these endpoints, or even others that were unmeasured, are most important to a patient recovering from surgery? Given the primary aims of cardiac surgery are to relieve symptoms and improve good quality survival, it is disability-free survival that is the ultimate outcome measure. The question then becomes: what is disability and how should it be quantified after cardiac surgery?