EFFECT OF ELECTRODE LENGTH ON ATRIAL DEFIBRILLATION THRESHOLDS

Electrode Length for Atrial Defibrillation. Introduction: Catheter-bas ed electrodes have been used previously to terminate episodes of atria l fibrillation in animals and man. Typically, these electrodes span 6 to 7 cm, and lowest energy requirements are achieved when these electr odes are positioned in the dietal coronary sinus and in the right atri um. The purpose of this study was to evaluate the use of longer electr ode lengths for atrial defibrillation. Methods and Results: In 15 pati ents, two decapolar catheters were inserted, one into the distal coron ary sinus and one in the right atrium. To provide longer electrodes le ngths, a third catheter was inserted and alternated positioned in the right atrium or coronary sinus. A 6-cm electrode span was obtained by using the distal 8 rings on the coronary sinus catheter or 8 consecuti ve electrodes on the right atrial catheter and increased from 6 to 11 cm by connecting 5 consecutive, nonoverlapping rings of the third cath eter with the 10 rings of the initial right atrial or coronary sinus c atheter. Atrial defibrillation thresholds were determined twice, in a randomized order, in each patient for each of the three combinations o f electrode lengths. All 15 patients could be successfully converted t o sinus rhythm without complications; however, one patient could be co nverted reproducibly with only 2 of the 3 electrode combinations. Mean thresholds were 306 +/- 102 V, 5.9 +/- 4.0 J for the 6 cm/6 cm electr ode length combination with an impedance of 72 +/- 18 Omega. For the e lectrode combination using the 11-cm electrode in the right atrium, th e defibrillation threshold was 296 +/- 107 V, 5.8 +/- 3.9 J with an im pedance of 61 +/- 17 Omega and was 293 +/- 91 V, 5.6 +/- 3.6 J with an impedance of 55 +/- 11 Omega for the 11-cm electrode in the coronary sinus. There were no significant differences in defibrillation voltage or energy (P > 0.05) associated with the longer electrode lengths; ho wever, the longer electrode lengths did significantly lower shock impe dance (P < 0.05). Conclusion: The use of longer electrodes, when using the right atrium to coronary sinus shock vector, does not lower the d efibrillation requirements for restoration of sinus rhythm.