OPTIMIZATION OF VENTRICULAR-FUNCTION BY IMPROVING THE ACTIVATION SEQUENCE DURING VENTRICULAR PACING

(bnormal electrical activation occurring during;ventricular pacing red uces left ventricular (LV) pump function. Two strategies were compared to optimize LV function using ventricular pacing, minimal asynchrony and optimal sequence of electrical activation. ECG and hemodynamics ao rtic flowprobe, thermodilution cardiac output, LV pressure and its max imal rates of rise (LVdP/dtpos) and fall (LVdP/dtneg) were measured in anesthetized open-chest dogs (n = 7) with healthy hearts. The QRS dur ation la measure of asynchrony of activation) was 47 +/- 5 ms during s inus rhythm and increased to 110 +/- 12 ms during DDD pacing at the ri ght ventricular (RV) apex with a short AV interval. During pacing at t he LV apex and LV base, the QRS duration was 8% +/- 7% and 15% +/- 7% (P < 0.05) longer than during RV apex pacing, respectively. Stroke vol umes, LVdP/dtpos and LVdP/dtneg, however, were higher during LV apex ( 15% +/- 16%, 10% +/- 12% [P < 0.05], and 15% +/- 10%, respectively) an d LV base pacing (11% +/- 12% [P < 0.05], 3% +/- 12%, and 3% +/- 11%, respectively) than during RV apex pacing. Systolic LV pressure was not influenced significantly by the site of pacing. Biventricular pacing (RV apex together with one or two LV sites) decreased the QRS duration by approximately 20% as compared with RV apex pacing, however, it did not improve Stroke volumes, LVdP/dtpos and LVdP/dtneg beyond those du ring pacing at the LV apex alone. In conclusion, the sequence of elect rical activation is a stronger determinant of ventricular function tha n the synchrony of activation. For optimal LV function the selection o f an optimal single pacing site, like the LV apex, is more important t han pacing from multiple sites.