The effect of a synchronous dual chamber pacing mode (DDD) on left ven
tricular function was evaluated in group 38 patients (21 patients with
third degree A-V block and 17 patients with Sick Sinus Syndrome). Thi
rty eight patients (22 men, 16 women)mean age 61 10.7 were examined at
rest, by esophageal ECG and echocardiography during DDD pacing mode c
hanging the pacing rate (70, 80, 90ppm), and A-V delay (100, 150, 200
ms). Right heart chambers pacing is known to cause delays in the depol
arization of left heart chambers, leading to abnormal left heart A-V s
equence (LAV). The purpose of this study was to assess the left ventri
cular (LV) systolic function during DDD pacing and to explore the infl
uence of interatrial conduction time, A-V delay(RAV) and heart rate on
LV performance. Interatrial conduction time (IACT), left atrial diame
ter (LAD), cardiac index (CI) and stroke volume index(SVI) were measur
ed. The positive significant relationship between IACT and LAD (p < 0.
001, r = 0.436) was found. Our results show that LAD must be kept in m
ind when choosing a mode of stimulation and determining the pacing par
ameters. The IACT was measured from the stimulus artifact to the left
atrial deflection. Mean IACT was 82.2 18.5ms. Doppler echocardiography
demonstrated necesity of preserving normal ventricular activation seq
uence and optimal atrioventricular (A-V) synchrony in permanent pacing
. Optimalization of pacing rate and A-V delay improved CI by mean 47%
(p < 0.001) compared with the worst CI value. A-V synchronous pacing i
s the preferred mode because it maintains the atrial contribution to v
entricular filling. It is concluded that IACT should be accounted for
when programming DDD pacemaker to provide physiological LAV. Because i
nteratrial conduction varies automatically changing A-V interval can p
rovide an optimal hemodynamic response to sequential pacing.