Study Population
The present study cohort comprised 412 patients from MADIT-CRT with non-LBBB and complete information on baseline clinical, echocardiographic, and laboratory variables was available. The rationale and design of the MADIT-CRT trial was previously published.14 Briefly, MADIT-CRT was designed to determine whether CRT with a defibrillator (CRT-D) would reduce the risk of death or HF events in patients with mild HF symptoms, a reduced ejection fraction, and wide QRS complex compared with ICD therapy. Patients were randomly assigned in a 3:2 ratio to receive either CRT-D or ICD. From December 22, 2004, through April 23, 2008, a total of 1820 patients were enrolled at 110 hospital centers. The protocol was approved by the institutional review board at each of the participating centers. Patients of either sex who were at least 21 years of age were enrolled in the study if they had ischemic cardiomyopathy (NYHA class I or II) or non-ischemic cardiomyopathy (NYHA class II only), sinus rhythm, an ejection fraction of ≤0.30, and prolonged intraventricular conduction with a QRS duration of ≥130 milliseconds. All eligible subjects met guideline indications for ICD therapy. Of the 412 patients without LBBB who were included in the present study, 215 were randomized to CRT-D therapy and 197 were randomized to ICD-only therapy.

End points and rhythm adjudication

The primary end point of this study was the first occurrence of VTA. Secondary endpoints were; composite of VTA or death (whichever comes first) and appropriate defibrillator shock therapy. All device therapies delivered were blindly adjudicated by 2 experienced electrophysiologists. VTA were defined as any ICD-recorded, treated or monitored sustained ventricular tachycardia (VT) faster or equal to 180 bpm or ventricular fibrillation (VF).