SURFACE COVERAGE EFFECTS ON DEFIBRILLATION IMPEDANCE FOR TRANSVENOUS ELECTRODES

Transvenous defibrillation electrodes are constructed by wrapping cond uctive elements around an insulating base. However, these conductive e lements do not cover the entire area of the base. The effects of varyi ng the surface area coverage on the defibrillation impedance (DZ) are unknown. To understand the effects, four transvenous right ventricular test leads were specially fabricated. A ring design was used with 3 m m diameter cylinders equally spaced along a 5 cm length, ending 11 mm from the pacing tip. Three leads consisted of 4, 8, and 15 rings each of length approximate to 2.4 mm so that the coverages were 20%, 40%, a nd 70%, respectively. The fourth lead used 8 rings of length approxima te to 1.2 mm each and had a coverage of 20%. DZ for each lead was obta ined using three methods: (i) computer simulation; (ii) in vitro measu rement in a tank; and (iii) in vivo measurement in nine dogs during de fibrillation testing. The DZs from either of the first two methods cor related very well (r = 0.98) with the mean DZs from the third method, indicating that in vivo DZs can be predicted from computer and in vitr o models. The study shows that: (i) at the same ring length, DZ decrea ses as coverage (number of rings) increases; (ii) at the same coverage , DZ decreases as ring length decreases; and (iii) in vivo, a statisti cally significant difference was observed in DZ between the leads with 20% coverage and the leads with higher coverages. No statistically si gnificant difference was observed between leads with coverages >40%.