Hemodynamic effects of long-term cardiac resynchronization therapy - Analysis by pressure-volume loops

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 < 35%, left bundle-branch block, and QRS duration > 120 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 3.1 +/- 0.5 to 2.1 +/- 0.8; quality-of-life score change from 44 +/- 12 to 31 +/- 16; and 6-minute hall-walk distance increased from 260 +/- 149 to 396 +/- 129 m; all P < 0.001), improved LV ejection fraction (from 29 +/- 10% to 40 +/- 13%, P < 0.01), decreased end-diastolic pressure (from 18 +/- 8 to 13 +/- 6 mm Hg, P < 0.05), and reverse remodeling (end-diastolic volume decreased from 257 +/- 67 to 205 +/- 54 mL, P < 0.01). Previously reported acute improvements in LV function remained present at 6 months: dP/dt(max) increased 18%, -dP/dt(min) increased 13%, and stroke work increased 34% (all P < 0.01). 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, P < 0.01) and improved mechanical efficiency (44% increase, P < 0.01). Conclusions - Hemodynamic improvements with CRT, previously shown in acute invasive studies, are maintained chronically. In addition, ventricular-arterial coupling, mechanical efficiency, and chronotropic responses are improved after 6 months of CRT. These findings may help to explain the improved functional status and exercise tolerance in patients treated with CRT.