Cardiac resynchronization therapy produces a long-term improvement in the clinical symptoms of patients with HF who have a ventricular conduction delay. The differences between optimized biventricular and univentricular therapy appear to be small for short-term treatment.

Background-Previous studies of pacing therapy for dilated congestive heart failure (CHF) have not established the relative importance of pacing site, AV delay, and patient heterogeneity on outcome. These variables were compared by a novel technique that evaluated immediate changes in hemodynamic function during brief periods of atrial-synchronous ventricular pacing. Methods and Results-Twenty-seven CHF patients with severe left ventricular (LV) systolic dysfunction and LV conduction disorder were implanted with endocardial pacing leads in the right atrium and right ventricle (RV) and an epicardial lead on the LV and instrumented with micromanometer catheters in the LV, aorta, and RV. Patients in normal sinus rhythm were stimulated in the RV, LV, or both ventricles simultaneously (BV) at preselected AV delays in a repeating 5-paced/15-nonpaced beat sequence. Maximum LV pressure derivative (LVϩdP/dt) and aortic pulse pressure (PP) changed immediately at pacing onset, increasing at a patient-specific optimal AV delay in 20 patients with wide surface QRS (180Ϯ22 ms) and decreasing at short AV delays in 5 patients with narrower QRS (128Ϯ12 ms) (PϽ0.0001). Overall, BV and LV pacing increased LVϩdP/dt and PP more than RV pacing (PϽ0.01), whereas LV pacing increased LVϩdP/dt more than BV pacing (PϽ0.01). Conclusions-In this population, CHF patients with sufficiently wide surface QRS benefit from atrial-synchronous ventricular pacing, LV stimulation is required for maximum acute benefit, and the maximum benefit at any site occurs with a patient-specific AV delay. (Circulation. 1999;99:2993-3001.)

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These data suggest that ICD implantation as first choice is preferable to the conventional approach in survivors of cardiac arrest caused by old myocardial infarction. Conventionally treated patients are likely to end up with an ICD, and those who remain on AD as sole therapy have a high risk of death regardless of efficacy assessment, including PES.