Aims: To assess the acute side-effects of right ventricular (RV) stimulation applied in apex and mid-septum, in order to establish the optimal lead location in clinical practice.
Methods: During pacemaker implantation, the ventricular lead was temporarily fixed in the apex and then moved to mid-septum. In both positions, surface and endocardial electrograms and transvalvular impedance (32 cases), left ventricular (LV) pressure (23), and transthoracic echocardiography (10) were acquired with intrinsic activity and VDD pacing.
Results: A larger increase in QRS duration was noticed with apical than septal pacing (65±25 vs. 45±29 ms; P<10(-4)). The proportion of cases where RV stimulation affected the transvalvular impedance waveform was higher with apical lead location (56% vs. 20%; P<0.02). VDD pacing at either site reduced the maximum dP/dt by 6% with respect to intrinsic AV conduction (IAVC; P<0.005). The maximum pressure drop taking place in 100 ms was reduced by 6 and 8%, respectively, with apical and septal pacing (P<0.01 vs. IAVC). Apical VDD decreased mitral annulus velocity in early diastole (E') from 7.5±1.4 to 5.9±0.9 cm/s (P<0.02) and prolonged the E-wave deceleration time (DT) from 156±33 to 199±54 ms (P<0.02), while septal pacing induced non-significant modifications in E' and DT.
Conclusion: Ventricular stimulation acutely impairs LV systolic and diastolic performance, independent of the pacing site. Septal lead location preserves RV contraction mechanics and reduces the electrical interventricular delay.