(26)
In our study; programming the pacemakers from AS-VP mode (group I) to AP-VP mode at rate of 100 b/min in (group II) showed a significant decrease in both global and regional LV LSS.
Hettrick et al observed that atrial pacing has been shown to reduce overall LV stroke volume due to impaired filling caused by atrial dysfunction. (27) In Liang et al . study, atrial pacing in DDD mode resulted in sub-optimal ventricular diastolic filling and consequently stroke volume compared to intrinsic atrial derived rhythm in VDD mode. In addition, they also demonstrated atrial mechanical dysfunction reflected by decreased active atrial strain caused by atrial pacing in DDD mode.(25) In their study, although LVEF was not statistically different between VDD (ventricular only pacing) and DDD (dual chamber pacing) modes, the more sensitive strain measurements demonstrated statistically significant differences in global strain of LV. This indicated that LV systolic function is indeed lower in DDD mode due to direct deleterious effect of atrial pacing on the atrium leading to indirect effects on the LV strain. Therefore, they concluded that atrial pacing in DDD mode led to atrial dysfunction causing decreased LV preload and consequently reduced LV systolic mechanics, resulting in sub-optimal LV performance when compared to VDD mode.