Cardiac resynchronization therapy: “Nonresponders” and “hyperresponders”

Abstract

Cardiac resynchronization therapy (CRT) is a recognized treatment modality for patients with dilated cardiomyopathy (DCM), left bundle branch block, and severe cardiac failure. However, 30% of patients are "nonresponders." Intriguingly, the opposite case has not been reported until recently: Do some patients treated with CRT have a "complete" recovery and thus can be considered "hyperresponders"? The purpose of this study was to investigate patients treated with CRT who have a "complete" functional recovery, with normalization of left ventricular function after therapy. Eighty-four consecutive patients with DCM, sinus rhythm, and left bundle branch block in New York Heart Association functional class III and IV who were implanted with a CRT device were prospectively followed. Patients were considered to be "hyperresponders" if they concurrently fulfilled two criteria: functional recovery and left ventricular ejection fraction > or = 50%. Among the 84 patients with DCM, 11 (13%) were "hyperresponders" within 6 to 24 months after CRT (left ventricular ejection fraction increased from 25% +/- 8% to 60% +/- 6.5%, P = .001). Comparison of baseline parameters between "hyperresponders" and the remaining patients showed that only etiology of the DCM was statistically discriminative. All "hyperresponders" belonged to the group of patients with nonischemic DCM (18% vs 0%, P = .05). In a subset of patients successfully implanted with a CRT device, "complete" functional recovery associated with normalization of LV function was observed, giving rise to the concept of "hyperresponders." This finding is observed exclusively in the subgroup of patients with nonischemic DCM and suggests that left bundle branch block may be the causal factor of DCM in this subgroup of patients.