From 30% to 40% of heart failure patients with QRS duration >120 ms do not exhibit left ventricular dyssynchrony, which may explain the nonresponse to CRT. Alternatively, 27% of patients with heart failure and a narrow QRS complex show significant left ventricular dyssynchrony and may be candidates for CRT.

Background-Acute hemodynamic effects of cardiac resynchronization therapy (CRT) were reported previously, but detailed invasive studies showing hemodynamic consequences of long-term CRT are not available. Methods and Results-We studied 22 patients scheduled for implantation of a CRT device based on conventional criteria (New York Heart Association class III or IV, left ventricular [LV] ejection fraction Ͻ35%, left bundle-branch block, and QRS duration Ͼ120 ms). During diagnostic catheterization before CRT, we acquired pressure-volume loops using conductance catheters during atrial pacing at 80, 100, 120, and 140 bpm. Studies were repeated during biventricular pacing at the same heart rates after 6 months of CRT. Our data show a significant clinical benefit of CRT (New York Heart Association class change from 3.1Ϯ0.5 to 2.1Ϯ0.8; quality-of-life score change from 44Ϯ12 to 31Ϯ16; and 6-minute hall-walk distance increased from 260Ϯ149 to 396Ϯ129 m; all PϽ0.001), improved LV ejection fraction (from 29Ϯ10% to 40Ϯ13%, PϽ0.01), decreased end-diastolic pressure (from 18Ϯ8 to 13Ϯ6 mm Hg, PϽ0.05), and reverse remodeling (end-diastolic volume decreased from 257Ϯ67 to 205Ϯ54 mL, PϽ0.01). Previously reported acute improvements in LV function remained present at 6 months: dP/dt max increased 18%, ϪdP/dt min increased 13%, and stroke work increased 34% (all PϽ0.01). Effects of increased heart rate were improved toward more physiological responses for LV ejection fraction, cardiac output, and dP/dt max . Moreover, our study showed improved ventricular-arterial coupling (69% increase, PϽ0.01) and improved mechanical efficiency (44% increase, PϽ0.01). Conclusions-Hemodynamic

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