THE INFLUENCE OF INTERATRIAL CONDUCTION TIME (IACT) ON LEFT-HEART AV SEQUENCE (LAV) AND LEFT-HEART HEMODYNAMIC PERFORMANCE IN PATIENTS DURING DUAL-CHAMBER STIMULATION

Dual chamber stimulation is physiological pacing which mostly coordina tes electrical function and is important in atrial and ventricular con traction. Atrio-ventricular stimulation preserving a normal activation sequence could significantly improve LV systolic function and patient 's feeling. If left atrial activation is delayed the programmed AV int erval may not provide adequate time for effective left atrial systole before LV systole and in extreme cases left atrial systole may actuall y begin after the onset of LV systole. The effect of synchronous dual chamber pacing (DDD) on left ventricular function was evaluated in a g roup of 21 patients with third degree AV block and 17 patients with si ck sinus syndrome. The 38 patients (22 men, 16 women, mean age 61 +/- 11 years) were examined at rest by esophageal ECG and echocardiography during DDD pacing while changing the pacing rate (70,80,90 ppm) and A V delay (100, 150, 200ms). Right heart pacing is known to cause delays in the depolarization of left heart chamber, leading on to abnormal l eft heart AV sequence (LAV). The put-pose of our study was to assess t he left ventricular systolic function during DDD stimulation and to ex amine the influence of interatrial conduction time (IACT), AV delay (R AV) and heart rate on LV performance. Interatrial conduction time, lef t atrial dimension (LA-D), cardiac index (CI) and stroke volume index (SVI) were measured. We found high statistically significant correlati on between interatrial conduction time and left atrial dimension (p<0. 001). Our results show that LA-D must be kept in mind when choosing a mode of stimulation and determining the pacing parameters. The IACT wa s measured from the stimulus artifact to the left atrial deflection. M ean IACT was 82 +/- 18ms. A positive correlation between AV delay and left heart AV sequence was found (p<0.001). During all AV delays which were explored we found high significant negative correlation between IACT and LAV (p<0.001). There was a significant correlation between IA CT and heart rate (p<0.05). The values of cardiac index (CI) and strok e volume index (SVI) changed significantly during successive changes i n DDD pacing modes. Our study demonstrates a positive correlation betw een LAV and CI (p<0.01). Doppler echocardiography demonstrated the nee d to preserve a normal ventricular activation sequence and optimal atr ioventricular synchrony in permanent pacing. AV synchronous pacing is the preferred mode because it maintains the atrial contribution to ven tricular filling. It is concluded that IACT should be accounted for wh en programming DDD pacemaker to provide physiological LAV. As interatr ial conduction varies automatically changing AV interval can provide a n optimal hemodynamic response to sequential pacing.