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).