Mapping the Terrain of Competing Risk Following Primary Prevention Defibrillator Implantation

Abstract

Landmark clinical trials have firmly established implantable cardioverter defibrillator (ICD) therapy as the cornerstone of sudden death prevention in patients with systolic heart failure stemming from both ischemic and nonischemic cardiomyopathies.1,2 Despite the widespread use of ICDs, a recent analysis of the Get With The Guidelines Heart Failure Registry suggested that an ICD may be indicated to prolong survival for an additional 800 000 patients with heart failure in the United States.3 Guideline recommendations for primary prevention ICD therapy are based on efficacy demonstrated among highly selected outpatient trial participants with stable, mild-to-moderate heart failure symptoms. These efficacy data have in turn been used to generate estimates of cost-effectiveness.4 In contrast to those patients enrolled in the pivotal trials, a substantial proportion of real-world ICD recipients are older, hospitalized at implant, or have a greater burden of comorbid medical conditions.5,6 Each of these factors may increase the risk of nonarrhythmic death and attenuate the incremental survival benefit conferred by primary prevention ICDs in otherwise eligible patients.7 Clearer identification of those patients whose dominant risk is from decompensated heart failure or noncardiac comorbidities will allow more focused ICD therapy in those for whom the device promises to provide meaningful prolonging of life. Article see p 927 Most primary prevention ICD recipients never experience an appropriate defibrillator shock. Multiple strategies have been studied to better target ICD therapy to those at highest risk. Sophisticated tools, such as magnetic resonance imaging, invasive electrophysiology study, and surface ECG analysis, have unfortunately proven to be neither a practical nor an efficient means of stratifying sudden death risk.8 Only a persistently reduced left ventricular ejection fraction ≤35% has endured in the guidelines as the central risk marker to triage candidates with chronic heart failure to a …