Introduction: Phrenic Nerve Stimulation (PNS) is a challenging problem of transvenous left ventricular (LV) pacing. Leads and devices that allow multiple pacing vectors may reduce or eliminate PNS.
Methods: The study involved 6 centers and 98 patients (mean age 70 ± 8 years, 74 males) who received a quadripolar LV lead (QuartetTM, St Jude Medical) for cardiac resynchronization (CRT) according to standard indications. The mean LV ejection fraction was 29 ± 5%, and the mean QRS was 161 ± 22ms. Twenty-six patients were in chronic atrial fibrillation. In 18 cases the quadripolar LV lead was implanted in a postero-lateral coronary vein, and in 67 patients in a lateral vein. The prevalence of PNS was determined at the time of implantation and at mid-term follow-up. Rise in pacing threshold was also evaluated at mid-term follow-up.
Results: At implantation the mean final pacing threshold was 1.27 ± 0.94 V at 0.5ms and mean pacing impedance was 805 ± 299 ohms. PNS (at 5V, 0.5ms) was reported in 31 patients (32%) at a site where the pacing threshold was satisfactory. With alteration of the pacing vector, PNS was eliminated in all the patients without repositioning the LV lead. Pacing vectors involving proximal electrodes were also used in 7 more patients, due to better anatomical position of the electrodes.
At mid-term follow up (4 ± 3 months), 28 patients (29%) experienced a new onset of PNS (14 pts, 14%, spontaneous, at programmed output) or a rise in LV pacing threshold (14 pts, 14%, more than 1V above the value measured at implant). PNS and high pacing threshold were managed by reprogramming the LV pacing vector, with a new final mean threshold, in all patients, of 1.5 ± 1.2 V at 0.5 ms and LV pacing impedance of 780 ± 263 ohm.
Conclusions: Quadripolar LV leads and device programmability are useful in CRT patients for the management of PNS and high pacing threshold.