Biventricular pacing improves the blunted force-frequency relation present during univentricular pacing in patients with heart failure and conduction delay.
BACKGROUND
In patients with chronic heart failure (CHF) and conduction delay, biventricular (BiV) and left ventricular (LV) pacing similarly improve systolic function at resting heart rates. We hypothesized that BiV and univentricular pacing differentially affect contractile function at increasing heart rates.


METHODS AND RESULTS
Twenty-two patients (aged 66+/-2 years, QRS 179+/-8 ms, LV ejection fraction 23+/-1%) underwent cardiac catheterization before device implantation to measure LV hemodynamics at baseline (rate 68+/-2 bpm; sinus rhythm n=18; atrial fibrillation n=4) and during BiV, LV, and right ventricular (RV) stimulation at 80, 100, 120, and 140 bpm. BiV and LV pacing at 80 bpm equally augmented dP/dtmax as compared with baseline and RV pacing (P<0.001). Stimulation rate significantly interacted with the effect of BiV, LV, and RV pacing on LV end-diastolic pressure (LVEDP), systolic pressure (LVSP), and dP/dtmax. Increasing the rate from 80 to 140 bpm enhanced dP/dtmax from 913+/-28 to 1119+/-50 mm Hg/s during BiV stimulation (P<0.001) but had no significant effect on contractility during single-site LV (951+/-47 versus 1002+/-54 mm Hg/s) or RV (800+/-46 versus 881+/-49 mm Hg/s) pacing. At 140 bpm, LVEDP was lower and LVSP higher during BiV pacing than during RV and LV pacing (LVEDP 12+/-1 versus 17+/-1 and 16+/-1 mm Hg, P<0.001; LVSP 112+/-5 versus 106+/-5 and 108+/-6 mm Hg, P<0.01 and P=0.09; BiV versus RV and LV pacing, respectively).


CONCLUSIONS
Different modes of ventricular stimulation alter the in vivo force-frequency relation of CHF patients. In contrast to single-site LV and RV pacing, contractile function improves with increasing heart rates during BiV stimulation. This effect may contribute to the enhanced exercise capacity during BiV pacing and could provide a functional benefit over LV-only pacing in patients for whom resynchronization therapy is indicated.