OPTIMAL ELECTRODE POSITION FOR TRANSVENOUS DEFIBRILLATION - A PROSPECTIVE RANDOMIZED STUDY

Objectives. This study was performed to determine the optimal position for the proximal electrode in a two-electrode transvenous defibrillat ion system. Background. Minimizing the energy required to defibrillate the heart has several potential advantages. Despite the increased use of two-electrode transvenous defibrillation systems, the optimal posi tion for the proximal electrode has not been systematically evaluated. Methods. Defibrillation thresholds were determined twice in random se quence in 16 patients undergoing implantation of a ho lead transvenous defibrillation system; once with the proximal mal electrode at the ri ght atrial-superior vena cava junction (superior vena cava position) a nd once with the proximal electrode in the left subclavian-innominate vein (innominate vein position). Results. The mean (+/- SD) defibrilla tion threshold with the proximal electrode in the innominate vein posi tion was significantly lower than with the electrode in the superior v ena cava position (13.4 +/- 5.7 J vs. 16.3 +/- 6.6 J, p = 0.04). Defib rillation threshold with the proximal electrode in the innominate vein position was lower or equal to that achieved in the superior vena cav a position in 75% of patients. In patients with normal heart size (car diothoracic ratio less than or equal to 0.55), the improvement in defi brillation threshold with the proximal electrode in the innominate vei n position was more significant than in patients with an enlarged hear t (innominate vein 13.0 +/- 6.5 J vs. superior vena cava 17.9 +/- 5.1 J, p < 0.01). In patients with an enlarged heart, no difference betwee n the two sites was observed (innominate vein 13.9 +/- 4.5 J vs. super ior vena cava 13.6 +/- 8.3 J, p = NS). Conclusions. During implantatio n of a two-lead transvenous defibrillation system, positioning the pro ximal defibrillation electrode in the subclavian-innominate vein will lower defibrillation energy requirements in the majority of patients.