DEFIBRILLATION THRESHOLD AND ELECTRODE CONFIGURATIONS - AN EXPERIMENTAL-STUDY TESTING 3 CONFIGURATIONS IN 12 PIGS

Objective. The choice between epicardial or subcutaneous patches remai ns unclear and depends essentially on the team's habits. This study te sted how much an additional patch can decrease defibrillation threshol d (DFT), and compared a Subcutaneous Array and an epicardial patch. To day most implantable automatic defibrillators have a transvenous endoc ardial configuration alone but when the DFT remains high an additional patch is necessary. Experimental design. Three different configuratio ns were tested with biphasic shocks in 12 pigs: Endovenous lead (Endo) , Endovenous lead + subcutaneous patch (Endo + SQ) and Endovenous lead + epicardial patch (Endo + Epi), For each animal DFTs were determined in a balanced random order for the 5 configurations. Ventricular fibr illation was induced by pacing (30 Hz, 8 V, for 5 seconds). DFT was ac curately measured with the up/down procedure until 5 reversal of defib rillation success or failure occurred. DFTs (mean +/- SD) were extract ed and compared using paired t test and analysis of variance. Results. DFTs were 14.6 +/- 11.0 J for Endo and significantly decreased (p < 0 .01) when an additional SQ (9.4 +/- 7.2 J) or epicardial patch (8.9 +/ - 6.5 J) was added to endovenous lead, without significant difference between Endo + SC and Endo + Epi configurations. Conclusions. Regardin g this important decrease of DFT (respectively -35% for Endo + SC and -39% for Endo + Epi), additional patches should be more often recommen ded in patients with low safety margin of DFT. In those cases subcutan eous patches should be preferred instead of epicardial patches. Moreov er, an additional reason to recommend this attitude could be the possi ble generator batteries saving.