Effectiveness of Cardiac Resynchronization Therapy by QRS Morphology in the Multicenter Automatic Defibrillator Implantation Trial–Cardiac Resynchronization Therapy (MADIT-CRT)

Study Questions:

Is the response to cardiac resynchronization therapy (CRT) affected by QRS morphology in patients enrolled in the MADIT-CRT trial?

Methods:

The baseline electrocardiogram was analyzed in 1,817 patients (mean age 65 years) with cardiomyopathy, an ejection fraction (EF) ≤30%, New York Heart Association class I-II symptoms, and QRS duration ≥130 ms. Sixty percent were randomly assigned to receive an implantable cardioverter-defibrillator (ICD) with CRT (CRT-D), and the remainder received an ICD. The mean duration of follow-up was 29 months. The primary endpoint was a heart failure event or death.

Results:

Seventy percent of patients had a left bundle branch block (LBBB) and the remainder had a non-LBBB (right bundle branch block [RBBB] in 13% and nonspecific interventricular conduction delay [IVCD] in 17%). In the LBBB group, CRT-D therapy was associated with a 53% reduction in the primary endpoint compared to the ICD therapy. There was not a significant reduction in the primary endpoint with CRT-D in the non-LBBB group. CRT was associated with a greater reduction in left ventricular end-diastolic volume in patients with LBBB (23%) than with non-LBBB (16%), and a greater absolute improvement in EF (12% vs. 9%, respectively).

Conclusions:

CRT-D therapy is associated with a significant reduction in the risk of a heart failure event or death in patients with an EF ≤30% and class I-II heart failure who have an LBBB, but not in those who have a non-LBBB QRS morphology.

Perspective:

The greater benefit of CRT in patients with LBBB most likely reflects the greater degree of left ventricular dyssynchrony associated with LBBB than with RBBB or nonspecific IVCD.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Implantable Devices, EP Basic Science, SCD/Ventricular Arrhythmias, Acute Heart Failure

Keywords: Follow-Up Studies, Heart Failure, Bundle-Branch Block, Electrocardiography, New York, Heart Ventricles, Defibrillators, Implantable, Cardiac Resynchronization Therapy


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