Influence of right ventricular stimulation site on left ventricular function in atrial synchronous ventricular pacing

OBJECTIVES The study investigates the correlation between left ventricular function and QRS duration obtained by alternate right ventricular pacing sites. BACKGROUND 1. Right ventricular apical pacing is associated with alterations of left ventricular contraction sequence. 2. stimulation producing narrow QRS complexes is supposed to provide for better left ventricular contraction patterns. METHODS Fourteen patients with third degree AV block received one ventricular pacing lead in apical position. The alternate lead was attached to that site on the septum that produced the smallest QRS complex as measured from the earliest to the last deflection in any of the orthogonal Frank leads (xyz). During atrial synchronous ventricular pacing, the AV delay was optimized individually and for each stimulation site using mitral valve doppler or impedance cardiography. By radionuclide ventriculography, the phase distribution histogram of left ventricular contraction was evaluated as are under the curve (AuC); systolic function was determined as ejection fraction (EF) and as absolute ejected counts (EC) in random order. The difference (Δ) in QRS duration between apical and septal stimulation (Δxyz) was correlated with the difference in phase distribution (ΔAuC) and ejection parameters (ΔEF, ΔEC). RESULTS QRS duration was shorter with septal than with apical pacing in 9 out of 14 patients (64%); it was longer in 4 (29%), and no difference was seen in 1 patient. There was significant positive correlation between the change in QRS duration (Δxyz) and phase distribution (ΔAuC: r = 0.66393, p = 0.010) and significant negative correlation to systolic function (ΔEF: r = 0.70931, p = 0.004; ΔEC: r = 0.74368, p = 0.002). CONCLUSIONS In atrial synchronous right ventricular pacing, if the AV delay is adapted individually, decreased QRS duration obtained by alternate pacing sites is significantly correlated with homogenization of left ventricular contraction and with increased systolic function in acute tests.