510 Similar degree of mechanical left ventricular dyssynchrony between RV outflow tract and apex pacing for permanent pacemaker site: studied by strain Doppler image

Abstract

Purpose: The long term right ventricular (RV) apex pacing has been associated with left ventricular (LV) systolic dysfunction. These may be the result of abnormal myocardial shearing forces and stress vectors. However, in RV outflow tract (RVOT) pacing ventricular activation may not be changed from that occurring over the normal His-Purkinje network to that originating from site of the ventricular lead. So we hypothesized that the degree of mechanical LV dyssynchrony in RVOT pacing is less than that in RV apex pacing. Methods: We enrolled 15 controls, 9 patients with RV pacing and 9 patients with LBBB. In RV pacing group, we paced at 2 sites (RV apex and RVOT) with 500 msec for 3 minutes. At the end of each pacing, we had the echocardiographic images in the apical 4 and 2 chamber views. We measured the time from QRS onset to compression/expansion crossover point in the strain image. The degree of dyssynchrony was evaluated by the difference between the longest and shortest parameters. We compared mechanical dyssynchrony in 12 segment of LV among different groups. Results: The degree of mechanical dyssynchrony was similar in RV apical, RVOT pacing and LBBB groups (figure 1). Detailed data are in the table. Conclusion: The RVOT pacing, though it may be recommended as an alternative site, might have an adverse effect on long term LV function.