Effect of bipolar electrode spacing on phrenic nerve stimulation and left ventricular pacing thresholds: an acute canine study.
BACKGROUND
Phrenic nerve stimulation (PNS) is a common complication of cardiac resynchronization therapy when left ventricular (LV) pacing occurs via a coronary vein. The purpose of this study was to evaluate the effects of bipolar electrode spacing on PNS and LV pacing thresholds.


RESULTS
Electrophysiology catheters with standard (2 mm-5 mm-2 mm) or modified (1 mm-5 mm-1 mm) interelectrode spacing was, respectively, inserted in a posterior/lateral cardiac vein in a randomized order in 6 anesthetized dogs via jugular access. The phrenic nerve was dissected via a left minithoracotomy and repositioned over the vein as close as possible to one of the electrodes. The presence of PNS was verified (ie, PNS threshold <2 V at 0.5 ms in unipolar configuration). Bipolar pacing was delivered using the electrode closest to the phrenic nerve as the cathode, and multiple bipolar electrode spacing configurations were tested. During bipolar pacing, PNS threshold increased as bipolar electrode spacing was reduced (P<0.05), whereas LV pacing thresholds did not change significantly (P>0.05). Compared with a standard bipolar electrode spacing of 20 mm for LV leads, 1 and 2 mm bipolar electrode spacing resulted in a PNS threshold increase of 5.5±2.2 V (P=0.003) and 2.8±1.7 V (P<0.001), respectively. Similarly, PNS threshold increased by 6.5±3.7 V with 1 mm and by 3.8±1.9 V with 2 mm bipolar pacing (both P<0.001), compared with unipolar pacing.


CONCLUSIONS
This study suggests that reducing LV bipolar electrode spacing from the standard 20 mm to 1 or 2 mm may significantly increase the PNS threshold without compromising LV pacing thresholds.
Institute of Cardiology, University of Bologna, Bologna, Italy. mauro.biffi@aosp.bo.it
Mauro
M
Biffi
Laurie
L
Foerster
William
W
Eastman
Michael
M
Eggen
Nathan A
NA
Grenz
John
J
Sommer
Tiziana
T
De Santo
Tarek
T
Haddad
Annamaria
A
Varbaro
Zhongping
Z
Yang
D000200:Action Potentials; D000818:Animals; D058406:Cardiac Resynchronization Therapy / Q000009:adverse effects / Q000379:methods*; D058409:Cardiac Resynchronization Therapy Devices / Q000009:adverse effects; D017023:Coronary Angiography; D004210:Dissection; D004285:Dogs; D004867:Equipment Design; D023421:Models, Animal; D010523:Peripheral Nervous System Diseases / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D010791:Phrenic Nerve / Q000503:physiopathology* / Q000601:surgery; D013908:Thoracotomy; D013997:Time Factors; D016277:Ventricular Function, Left