External Cardioversion in Patients With Persistent Atrial Fibrillation A Reappraisal of the Effects of Electrode Pad Position and Transthoracic Impedance on Cardioversion Success.

Abstract

SUMMARYThe optimal methods to perform external cardioversion of atrial fibrillation (AF) have yet to be conclusively determined. This study was performed to examine the relative efficacy of different pad positions on cardioversion success and the relationship between the transthoracic impedance (TTI) and energy requirement for AF cardioversion.Seventy patients with persistent AF undergoing elective cardioversion were randomly assigned to an electrode pad position situated either over the ventricular apex-right infraclavicular area (AL group, n = 31) or over the right lower sternal border-left infrascapular area close to the spine (AP group, n = 39). Energy was delivered at an initial 100 joules (J) and then increased to 150 J, 200 J, 300 J, and 360 J if needed. Energy and TTI readings were recorded.Mean TTI was significantly lower in the AP group than in the AL group. However, the cumulative success rates at each energy level were similar in the two groups (23% vs 19.4%, 41% vs 45.2%, 66.7% vs 74.2%, 79.5% vs 77.4%, and 84.6% vs 83.9% at 100 J, 150 J, 200 J, 300 J and 360 J, respectively). In the AP group, converters showed slightly lower TTI compared to nonconverters. In the AL group, converters showed significantly lower TTI compared to nonconverters. However, for all patients as a group, TTI was the only predictor for cardioversion success and showed a significant relationship to the energy required for cardioversion, which can be described by a quadratic equation.Rather than pad position, TTI is the single factor that significantly affects cardioversion and correlates with energy requirement. The relationship between energy requirement and TTI further allows estimation of energy requirements to achieve a successful cardioversion. (Jpn Heart J 2003; 44: 921-932) Key words: Atrial fibrillation, Cardioversion, Impedance, Electrode pad position EXTERNAL direct current (DC) cardioversion, which is useful for cardioversion of atrial fibrillation (AF), has conventionally been performed by delivering an energy shock starting at 100 joules (J) followed by 200 J, 300 J, and 360 J,

Role of transthoracic impedance on the success of electrical synchronized cardioversion

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“…A successful defibrillation requires depolarization of 95% of the heart cells. Therefore TTI has become an important predictor for successful defibrillation, since the current reaching the heart to achieve this depolarization is inversely related to impedance [7 ], While a high amplitude current shock ensures depolarization of the myocardium, it may cause damage to the cardiac tissue [5 ]. Thus, a successful cardioversion entails lower TTI and delivery of an optimal current based on the patient's TTI.…”

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