One of the challenges in device-based management of AT/AF is the issue of early recurrences of atrial fibrillation (ERAF). ERAF occurs when an AT/AF episode terminates (either spontaneously or in response to a therapy) and is shortly followed by another episode of AT/AF. The time interval over which a recurrence may be classified as ERAF is somewhat arbitrary. The incidence of ERAF following an atrial shock has been reported to be 17% within 1m, 30% within 1h, and 43% within 1 day.125 Very sudden ERAF can confuse the device into thinking that a therapy was unsuccessful when in fact it was effective in terminating the arrhythmia (albeit briefly). The EGM tracing in Fig. 14a shows an AT/AF episode that is treated with an ICD shock. The arrhythmia converts to sinus rhythm for two beats and then quickly reverts to AT/AF. The device reported this as an unsuccessful shock since the device-based definition for successful termination (five beats of sinus rhythm) was not satisfied. Without an EGM tracing at the time of therapy delivery, the physician may have incorrectly concluded that the shock energy was not sufficient to defibrillate the heart. In actuality, the shock was successful in terminating the arrhythmia, but its effect was short-lived due to almost instantaneous ERAF. The EGM tracing in Fig. 14b is from the same patient and same episode. After waiting a longer period of time, a shock with identical energy output is able to successfully terminate the episode without ERAF, and the device declares that the episode was successfully terminated after five beats of sinus rhythm. This example illustrates the findings of earlier studies that reported that the incidence of ERAF could be decreased by delaying a shock for 24 h instead of shocking the arrhythmia within a few hours of its initiation and that the most potent predictor of ERAF was an episode duration less than 3h.125'126 Another implication of ERAF is that the true efficacy of an episode's first shock may actually be higher than the ^85% that has been reported based on device classification alone.127
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