Effect of electrode configuration and capacitor size on internal atrial defibrillation threshold using leads currently used for ventricular defibrillation.

Background: Previous studies have shown that endocardial atrial defibrillat ion, using lead configurations specifically designed for ventricular defibr illation, is feasible but the substantial patient discomfort might prevent the widespread use of the technique unless significant improvements in shoc k tolerability are achieved. It has been suggested that the peak voltage or the peak current but not the total energy delivered determines the patient pain perception and therefore, lower defibrillating voltage and current ac hieved with modifications in lead and waveforms may increase shock tolerabi lity. This study was undertaken to evaluate the effect, on the atrial defib rillation threshold (ADFT), of the addition of a patch electrode (mimicking the can electrode) to the right ventricle (RV)-superior vena cava (SVC) le ad configuration. The influence of capacitor size on ADFT using the RV-SVCskin patch configuration was also assessed. Methods: In 10 patients (pts) (Group 1) cardioversion thresholds were evalu ated using biphasic shocks in two different configurations: 1) right ventri cle (RV) to superior vena cava (SVC); 2) RV to SVC+skin patch. In a second group of twelve patients (Group 2) atrial defibrillation thresholds of biph asic waveforms that differed with the total capacitance (90 or 170 mu F) we re assessed using the RV to SVC+skin patch configuration. Results: In Group 1 AF was terminated in 10/10 pts (100 %) with both config urations. There was no significant difference in delivered energy at the de fibrillation threshold between the two configurations (7.1 +/- 5.1 J vs 7.1 +/- 2.6 J; p > 0.05). In group 2 AF was terminated in 12/12 pts (100%) wit h both waveforms. The 170 mu F waveform provided a significantly lower defi brillating voltage (323.7 +/- 74.6 V vs 380 +/- 70.2 V; p < 0.03) and curre nt (8.1 +/- 2.7 A vs 10.0 +/- 2.3 A; p < 0.04) than the 90 mu F waveform. A ll pts, in both groups, perceived the shock of the lowest energy tested (18 0 V) as painful or uncomfortable. Conclusions: The addition of a patch electrode to the RV-SVC lead configura tion does not reduce the ADFT. Shocks from larger capacitors defibrillate w ith lower voltage and current but pts still perceive low energy subthreshol d shocks as painful or uncomfortable.