THE IMPORTANCE OF THE LEFT ATRIOVENTRICULAR INTERVAL DURING ATRIOVENTRICULAR SEQUENTIAL PACING

During atrioventricular (AV) sequential pacing from the right heart, t he interval between the left atrium and ventricle map vary from the pr ogrammed AV interval depending on the position of the atrial and ventr icular electrodes and interatrial and interventricular conduction. The aim of this study was to determine the hemodynamic effects of alterin g the left AV interval while keeping the programmed AV interval consta nt. Four male and 17 female patients, aged 49 +/- 15 years were studie d. The left AV interval was measured by a catheter in the coronary sin us. Stroke volume and mitral flow were measured by simultaneous echo D oppler during AV sequential pacing from the right atrial appendage and right ventricular apex at programmed ATI intervals of 100, 60, and 6 ms. The atrial catheter was then positioned on the atrial sepium and t he measurements repeated. With the atrial catheter in the right atrial appendage, interatrial activation time (118 +/- 20 ms) was similar to interventricular activation time (125 +/- 21 ms) and the left AV inte rval was almost identical to the programmed right AV interval. There w as a significant correlation between interatrial and interventricular activation rimes (r = 0.8; P < 0.001). Positioning the atrial electrod e on the septum decreased interatrial activation time by 39 +/- 12 ms and increased the left AV interval by a similar amount. At ct programm ed AV interval of 60 ms, the left AV interval increased from 67 +/- 15 ms to 105 +/- 17 ms after the atrial catheter was repositioned from t he appendage to the septum (P < 0.001). compared to pacing from the ri ght atrial appendage, atrial sept al pacing increased mitral A wave ve locity integral (2.8 +/- 1.4 vs 4.4 +/- 1.7 cm at a programmed AV inte rval of 60 ms, P < 0.01), decreased E wave velocity integral (8.1 +/- 2.2 vs 6.1 +/- 2.4 cm, P < 0.001) but did not alter stroke volume (44. 8 +/- 10.6 vs 44.9 +/- 10.1 mL). In contrast, a 40 ms decrease in the programmed right Air interval from 100 to 60 ms decreased stroke volum e from 48.0 +/- 10.0 to 44.9 +/- 10.2 mL (P < 0.001). There was a stro ng relationship between interatrial and interventricular conduction so that patients with prolonged interatrial conduction still had equival ent left and right AV intervals during atrioventricular sequential pac ing from the right atrial appendage and right ventricular apex. Positi oning the atrial electrode on the septum decreases interatrial activat ion time and increases the left AV interval by about 40 ms but has min imal hemodynamic effect in patients without heart failure.