The immediate effects of pacemaker-related electric remodelling on left ventricular function in patients with sick sinus syndrome

The immediate effects of electric remodelling on the left ventricular (LV) function by dual-chamber pacemakers remain unknown. The purpose of our study was to assess the interaction between heart rates and right ventricular pacing (VP) on LV contractility and diastolic function.

Twenty-five patients with dual-chamber pacemakers and sick sinus syndrome were evaluated. Echocardiographic examinations included standard and tissue-Doppler echocardiography at bilateral mitral annulus margins under either the intrinsic atrio-ventricular sequential conduction (ventricular sensing; VS) mode or right ventricular apical pacing (VP) mode. Under either mode, we accelerated the pacing rate at an increment of 15 b.p.m. step-by-step from 60 to 90/min. The tissue-Doppler echocardiography of mitral annulus showed that under the VS status, accelerating atrial pacing rate from 60 to 90 b.p.m. enhanced A′-wave velocity ( P ≦ 0.002), whereas no significant change of LV ejection fraction (LVEF) and E′-wave velocity were noted. Under the VP status, acceleration of pacing rates exerted no effect on the LVEF, E′-, and A′-wave ( P = NS). While shifting the pacemaker mode from VS to VP, the E′-wave velocity ( P ≦ 0.002) and E ′/ A ′ ratio decreased significantly ( P ≦ 0.001). The A′-wave velocity also increased significantly during shifting to VP mode at 60 b.p.m. ( P ≦ 0.004).

At fixed pacing rates, shifting from VS to VP mode impaired LV diastolic function immediately with preserved LV contractility. The acceleration of heart rate impaired LV diastolic function under VS mode.