The influence of right atrial septal pacing on the interatrial contraction sequence.

UNLABELLED: Right atrial septal pacing yields shorter interatrial conduction delays than conventional right atrial pacing at the free wall or the right atrial appendage. However, the hemodynamic effects of right atrial septal pacing are less well known. This study measured the delay between right and left atrial contractions during right atrial septal pacing (n = 21), conventional right atrial pacing (n = 32) and atrial multisite pacing (n = 6) by pulse Doppler echocardiography of transtricuspidal and transmitral blood flow. The effects of right atrial septal pacing (n = 14) versus conventional right atrial pacing (n = 22) on the optimal AV delay during dual chamber pacing was examined in patients with high degree atrioventricular (AV) block. Compared to sinus rhythm, conventional right atrial pacing increased P wave duration from 119 +/- 21 ms to 137 +/- 24 ms (P < 0.001), whereas both right atrial septal pacing (119 +/- 10 ms before, 106 +/- 13 ms during pacing, P = 0.002) and atrial multisite pacing (123 +/- 20 ms before, 112 +/- 11 ms during pacing, P = 0.5) shortened P wave duration. Atrial pacing caused a significant (P < 0.002) prolongation of atrial contraction [corrected] delays from 24 +/- 21 ms to 41 +/- 26 ms during conventional right atrial pacing, and reversed the right-to-left into a left-to-right contraction sequence in 20 of 21 patients during right atrial septal pacing (atrial conduction delay during sinus rhythm: 34 +/- 23 ms vs -37 [corrected] +/- 26 ms during atrial pacing, P < 0.0001). Atrial multisite pacing caused a nonsignificant shortening of the usual right-to-left contraction delay from 22 +/- 34 ms to 11 +/- 18 ms. The optimal left heart AV delay during AV sequential pacing was significantly (P = 0.002) shorter during right atrial septal pacing (108 +/- 38 ms) than during conventional right atrial pacing (152 +/- 33 ms). During conventional right atrial pacing the optimal right heart AV delay was significantly (P = 0.029) shorter than the optimal left heart AV delay. The opposite relation was observed for right atrial septal pacing (P = 0.033). CONCLUSIONS: Interatrial septal pacing does not synchronize right and left atrial contractions. It reverses the atrial mechanical timing from a right-to-left to a left-to-right contraction sequence, and requires the setting of shorter AV delays during dual chamber pacing if based on the optimization of left heart timing. Interatrial septal pacing is a technique which allows pacing of the left atrium from a right atrial site, rather than a single site approach to biatrial pacing.