Enhancement of cardiac contractility by refractory period stimulation in conjunction with cardiac resynchronization therapy

Background: Cardiac resynchronization therapy (CRT) improves cardiac function in patients with heart failure by synchronizing contraction of the right and left ventricles (RV, LV). This study was to determine if electrical stimulation during the refractory period of bi-ventricular (BiV) pacing would provide additional LV mechanical improvement. Methods: 16 patients receiving CRT-ICD devices were enrolled. After the CRT leads were in place, the leads were connected to an EP stimulator for acute delivery of electrical stimuli during the absolute refractory period of each cardiac beat for a 30-sec interval. Four types of refractory period stimulation were delivered: stimulation at the local LV pacing site during intrinsic rhythm, at the local RV pacing site during intrinsic rhythm, at the local LV pacing site during BiV pacing, and simultaneously at LV and RV during BiV pacing. The LV pressure was recorded for dp/dtmax measurement to assess changes of cardiac contractility. Results: Overall LV dp/dtmax increased to 1453 ± 522 mmHg/Sec during refractory period stimulation from a baseline of 1383 ± 476 mmHg/Sec (P=0.013). The LV dp/dtmax was significantly increased by an average 12.8% when refractory period stimulation was simultaneously delivered at the LV free wall and the RV apex during BiV pacing. There was no significant improvement in LV dp/dtmax by other three types of stimulation. Conclusion: Refractory period stimulation, when delivered to both RV and LV simultaneously, can improve LV mechanical function on top of BiV pacing, which may provide additional benefits for CRT patients.