Transvenous internal cardioversion for atrial fibrillation: a randomized study on defibrillation threshold and tolerability of asymmetrical compared with symmetrical shocks

The aim of the study was to compare, according to a randomized cross-over d esign, two different biphasic waveforms (6.5/2.5 ms and 3.0/3.0 ms phases d uration, respectively) for low energy internal atrial cardioversion with re gard to energy requirements for cardioversion and shock induced discomfort. Methods: Nineteen patients with chronic persistent atrial fibrillation (AF )(mean duration 16+/-20 months) were submitted to internal atrial cardiover sion (shock delivery between catheters in right atrium and coronary sinus, respectively) and were randomly allocated to baseline cardioversion with an asymmetrical biphasic shock (6.5/2.5 ms) or with a symmetrical biphasic sh ock (3.0/3.0 ms), according to a step up protocol. After baseline cardiover sion, a sustained AF was reinduced and the patients crossed to the alternat ive waveform. The procedure was performed without routine administration of sedatives and shock induced discomfort was monitored by a subjective score (1 to 5). Sedatives or anesthetics were administered at patient's request. Results: The procedure was effective in all the patients and was performed without need for sedatives/anesthetics in 17/19 patients (89%). Leading ed ge voltage of effective shocks resulted lower for asymmetrical shocks compa red to symmetrical shocks (290+/-76 vs. 337+/-104 V, P<0.001) with no stati stically significant differences in delivered energy (7.74+/-4.25 vs. 8.65/-5.94 J). Moreover shock induced discomfort resulted lower for asymmetrica l shocks compared to symmetrical (pain score=4.18+/-0.73 vs. 4.59+/-0.62, P <0.02). Shock impedence of effective shocks was 59+/-10 ohms for both wavef orms. No significant complications occurred during the procedure and no ven tricular arrhythmia was observed after atrial cardioversion. Transient brad ycardia requiring support ventricular pacing was observed in one patient. C onclusions: Delivery of biphasic asymmetrical shocks (6.5/2.5 ms) results i n lower leading edge voltage of effective shocks and better patients tolera bility compared with conventional biphasic symmetrical shocks (3.0/3.0 ms). These findings are of interest both for transvenous internal cardioversion of chronic persistent AF and for implantable atrial defibrillators. (C) 19 99 Elsevier Science Ireland Ltd. All rights reserved.