ACUTE EFFECTS OF RV PACING ON SYSTOLIC AND DIASTOLIC FUNCTION

Purpose. Comparing the acute hemodynamic effects of RV pacing applied in apex or mid-septum, looking for an indicator of the most suitable pacing site.
Methods.During dual-chamber implantation procedures in 32 patients affected by SSS and/or AVB with preserved pump function (EF>50%), the V lead was sequentially positioned in RV apex and mid-septum. The transvalvular impedance (TVI) waveform was recorded by an external device (Medico, Italy), while a full echocardiographic assessment was performed and LV pressure was measured by a Mikro-Tip catheter (Millar, USA) in the presence of intrinsic activity and sequential RV pacing at either site (80 ms AV delay).
Results. RVP increased the QRS duration from 101±25 ms with intrinsic AV conduction (IAVC) to 166±17 and 147±18 ms, respectively, with apical and septal stimulation (RVAP, RVSP; P<0.001 in pacing site comparison). LVdP/dt max decreased from 1406±251 mmHg/s (IAVC) to 1319±250 mmHg/s with RVAP and 1303±257 mmHg/s with RVSP (P<0.005 vs IAVC with either pacing site). EF was mildly affected, averaging 59±5%, 566% and 55±6%, repectively, with IAVC, RVAP (P<0.07) and RVSP (P<0.05). In contrast, a clear-cut reduction was observed in the velocity of mitral annulus displacement in early diastole, which was 7.5±1.4 cm/s with IAVC, 5.9±0.9 cm/s with RVAP (P<0.005) and 6.1±1.5 cm/s with RVSP (P<0.05). The E-wave deceleration time was correspondingly increased: 156±32 ms with IAVC, 199±54 ms with RVAP (P<0.01) and 188±39 ms with RVSP (P<0.05). The transition from IAVC to RV pacing induced deep morphologic alterations in TVI waveform in 10 cases out of 25 with RVAP (P<0.01).
Conclusions. Sequential RV pacing produced mild acute effects on the systolic function, while diastolic indices were more severely affected. The QRS was shorter and the RV contraction pattern was less affected with septal than apical stimulation.