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Implantable atrial defibrillators are able to deliver shocks immediately after the onset of paroxysmal atrial fibrillation (PAF). It is anticipated that rapid restoration of sinus rhythm may allow electrical remodeling and thus reduce PAF recurrence ("sinus rhythm begets sinus rhythm"). Methods: 8 patients with atrial defibrillators (Metrix 3020, InControl) were studied for a mean of 11.6+/-3.7 (range 8-18) months. Data were prospectively collected by device telemetry and patient diary. Patient characteristics, PAF episodes and results of device therapy were recorded. Results: All patients had failed >2 medical therapies. 6/8 patients had structurally normal hearts, 2/8 had dilated left atria and hypertension. Mean number of PAF episodes per month prior to implant was 3.0 (range 0.25-8.0). Post-implant, patients had a mean of 15.4+/-9 (range 0-28) AF episodes during follow-up, with 12.6+/-10.8 attempted therapies with a success rate of 74%. The most common cause of failure of therapy was early recurrence of AF (i.e. within 60 seconds). Following device implant. 1 patient had no further episodes of PAF despite 16 months follow up. 3 patients had decreasing frequency of episodes and 4 patients had increasing frequency of episodes (2 of whom will no longer use their device). Of those patients with an increasing frequency of PAF episodes, 3/4 had a 100% success rate with shock therapy and 1/4 suffered episodes of early recurrence of AF. No patient or arrhythmia characteristics were able to distinguish those whose PAF episodes decreased from those whose episodes increased. Conclusions: Although atrial defibrillators may successfully cardiovert almost all PAF episodes, prompt restoration of sinus rhythm does not appear to alter the electrophysiological substrate and prevent future events in a significant proportion of patients. Event frequency may increase to the point that patients may no longer wish to use their device for repeated shocks. It is not yet possible to identify those patients whose frequency of PAF will reduce following repeated shock therapies.


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