TRANSTHORACIC DEFIBRILLATION - DOES ELECTRODE ADHESIVE PAD POSITION ALTER TRANSTHORACIC IMPEDANCE

Successful termination of ventricular fibrillation by transthoracic sh ocks is dependent on achieving adequate current flow, which in turn is governed by transthoracic impedance (TTI). The American Heart Associa tion (AHA) Advanced Cardiac Life Support textbook recommends three ele ctrode positions for defibrillation: (1) anterior-apex, (2) apex-poste rior and (3) anterior-posterior. However, there are few data available comparing TTI of these positions. To study this, we applied large (78 cm(2)) self-adhesive monitor-defibrillator pads to 20 subjects (ten m ale, ten female, ages 21-79) and measured TTI using a validated test-p ulse technique which does not require actual shocks. We performed two studies. In Study 1 tall 20 subjects) the electrode pads were applied in the three positions recommended by the AHA, with the posterior elec trode placed in the right infrascapular location. All TTI measurements were made at end-expiration and body surface area (BSA) was recorded. The results (TTI, Omega, mean +/- S.D.) for the respective positions were the following: anterior-apex, 82.0 +/- 24.7, apex-posterior, 71.2 +/- 23.5; anterior-posterior, 77.0 +/- 24.7 (P NS). In Study 2 (six s ubjects) we compared the effect of right vs. left infrascapular poster ior electrode placement (TTI, Omega): apex-right infrascapular (RIS), 76.8 +/- 18.4; apex-left infrascapular (LIS), 72.1 +/- 18.7; anterior- RIS, 72.5 +/- 19.4; anterior-LIS, 71.6 +/- 18.6 (P NS). Correlation of TTI (anterior-apex placement) with BSA: TTI = 15.9 (BSA) + 46.7, r = 0.60, P < 0.01; the correlations of TTI and BSA were similar in the ot her two electrode positions. Thus, the three AHA-recommended electrode positions for transthoracic defibrillation have equivalent and accept able TTIs, current flow should be similar using any of these positions . Furthermore, the posterior electrode may be placed in either the rig ht or the left infrascapular position without affecting TTI. TTI is re lated to BSA in any of the three recommended positions, patients with high BSA and TTI may require higher energy selection to achieve defibr illation. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.