Table 3

Randomized Trials of CRT in Narrow QRS Duration

Trial (Ref. #)nStudy DesignEnrollment QRS Duration, msEnrollment NYHA Functional Class/HF EtiologyEnrollment LVEF, %SR/AF Included?Primary Endpoint
RethinQ (34)172Parallel control CRT-D with CRT pacing on or off<130NYHA III
Ischemic and nonischemic
≤35SRPeak VO2 on CPET
NARROW CRT (35)120CRT-D vs. DDD-ICD<120II/III
Ischemic only
≤35SRHF clinical composite response
EchoCRT (33)809Parallel control CRT-D with CRT pacing on or off<130III/IV
Ischemic and nonischemic
≤35SRAll-cause or first hospitalization for worsening HF
LESSER EARTH (32)85Parallel control
CRT-D with CRT pacing on or off
<120Symptoms of HF and a 6-min walk ≤400 m
Ischemic and nonischemic
≤35SRExercise capacity and LV reverse remodeling

DDD-ICD = dual-chamber implantable cardioverter-defibrillator; EchoCRT = Echocardiography Guided Cardiac Resynchronization Therapy; LESSER-EARTH = Evaluation of Resynchronization Therapy for Heart Failure; NARROW CRT = Narrow QRS Ischemic Patients Treated With Cardiac Resynchronization Therapy; RethinQ = Resynchronization Therapy in Normal QRS; other abbreviations as in Table 1.