Objectives: We sought to investigate the effect of intrinsic conduction over the right bundle on the maximum rate of left ventricular pressure rise (LVdP/dt(max)) during left ventricular (LV) pacing compared to biventricular (BiV) pacing.
Background: Simultaneous BiV pacing and LV pacing both improve LV function in patients with heart failure and LV asynchrony. We studied the hemodynamic effect of intrinsic conduction leading to ventricular fusion during LV pacing.
Methods: In 34 patients with New York Heart Association functional class III or IV, sinus rhythm with normal atrioventricular (AV) conduction, left bundle branch block, QRS >130 ms, and optimal medical therapy, LVdP/dt(max) was measured invasively during LV and simultaneous BiV pacing. The AV interval was varied in four steps starting (AV1) with an AV interval 40 ms shorter than the intrinsic PQ time and decreased with 25% for each step.
Results: At AV1, LVdP/dt(max) was 996 +/- 194 mm Hg/s for LV pacing and 960 +/- 200 mm Hg/s for BiV pacing (p = 0.0009), with all patients showing ventricular fusion during LV pacing. At AV2, 21 patients had ventricular fusion with a LVdP/dt(max) of 983 +/- 213 mm Hg/s and 957 +/- 202 mm Hg/s for LV and BiV pacing, respectively. In the remaining 13 patients without fusion these values were 919 +/- 164 mm Hg/s and 957 +/- 174 mm Hg/s, respectively. The difference between LV and BiV at AV2 is significantly higher when fusion is present (p = 0.01).
Conclusions: The LVdP/dt(max) is higher in LV than in BiV pacing provided that LV pacing is associated with ventricular fusion caused by intrinsic activation.