Effect of shock polarity on the efficacy of transthoracic XXXX .

@entity1 @entity955
BACKGROUND: The energy requirement for internal ventricular defibrillation is reduced by reversal of shock polarity. The influence of shock polarity on the efficacy of transthoracic @entity955 is unknown. METHODS: This prospective, randomized study enrolled 110 consecutive @entity1 who were referred for elective cardioversion of persistent @entity955 ( @entity955 ). The electrodes were placed in the anteroposterior position. The @entity1 were randomized to receive either standard (anterior pad = cathode) or reversed polarity (anterior pad = anode) shocks with a damped sinusoidal monophasic waveform. A step-up protocol was used to estimate the cardioversion threshold. The initial shock energy was 50 J, with subsequent increments to 100, 200, 300, and 360 J in the event of cardioversion failure. RESULTS: Sixty-four percent of the @entity1 population were @entity1 , with a mean age of 66 +/- 13 years and a mean duration of @entity955 of 242 +/- 556 days. The overall success rates of cardioversion were 84% for standard polarity and 78% for reversed polarity (P not significant). Among the @entity1 who were successfully cardioverted, the mean @entity955 threshold was 198 +/- 103 J for standard polarity and 212 +/- 107 J for reversed polarity (P not significant). CONCLUSIONS: Reversal of shock polarity does not improve transthoracic cardioversion efficacy with a standard damped sinusoidal monophasic waveform. Alternate strategies should be considered for @entity1 who fail external cardioversion, such as adjunctive pharmacologic treatment, use of a biphasic shock waveform, or internal cardioversion.
