INITIAL CLINICAL-EXPERIENCE WITH AN IMPLANTABLE HUMAN ATRIAL DEFIBRILLATOR

Low energy biatrial shock is an effective means of restoring sinus rhy thm in patients with atrial fibrillation (AF). Ventricular proarrhythm ia is avoided provided that shocks are well synchronized to R wave tha t are not at closely coupled intervals or preceded by long-short cycle s. Based on these principles, an implantable atrial defibrillator has been developed and was implanted in three patients with drug refractor y paroxysmal AF. The device detects AF via an actively fixed right atr ial and a self-retaining coronary sinus defibrillating leads, and deli vers 3/3 ms biphasic shocks up to 300 V synchronized to the R wave. Th e mean implant threshold (ED50) was 195 V (1.8 J), and minimum voltage at conversion during follow-up assessments at 1, 3, and 6 months were 260 V, 2.5 J, 250 V, 2.3 J, and 300 V, 3.0 J respectively. Detection of AF was 100% specific and shocks were 100% synchronized, although on ly a proportion of synchronized R waves were considered suitable for s hock delivery primarily because of closely coupled cycles. Three patie nts had 9 spontaneous AF episodes, 8/9 (89%) successfully defibrillate d by shocks of 260-300 V. Sedation was not used in 4 out of 9 (45%) ep isodes. Backup ventricular pacing was initiated by the device in 6 out of (67%) episodes. One patient had more frequent AF after lead placem ent, which subsided after a change of medication. There was no ventric ular proarrhythmia. It is concluded that an implantable atrial defibri llator is a viable therapy for selected patients with paroxysmal AF. T he device is capable of accurate AF detection, R wave synchronization and ventricular support pacing after successful defibrillation of AF.