Time course of recovery of left atrial mechanical dysfunction after cardioversion of spontaneous atrial fibrillation with the implantable atrial defibrillator

S cardioversion of atrial fibrillation (AF) is associated with left atrial (LA) mechanical dysfunction and may predispose the atria to thrombus formation.1–4 The occurrence and time course of recovery of atrial mechanical dysfunction appear to be related to the duration of AF.1,2,4 These findings suggest that prompt termination of AF may prevent LA mechanical dysfunction and its sequelae may be reduced. The implantable atrial defibrillator (IAD) is a safe and effective device for prompt cardioversion of AF.3–7 The purpose of this study was to determine whether the timing of cardioversion of spontaneous AF with an IAD affects the time course of recovery of LA mechanical dysfunction seen after cardioversion. • • • From November 1995 to December 1998, 9 of the 11 patients (7 men and 2 women, mean age 57 6 12 years) treated with an IAD (Metrix, InControl Inc., Redmond, Washington) for symptomatic drug-refractory AF and with stable sinus rhythm for at least 4 weeks to allow a baseline echocardiographic assessment of LA function were included in this study. The mean left ventricular ejection fraction was 0.56 6 0.09, and the mean LA diameter by echocardiography was 4.3 6 0.8 cm. After the device implant, patients received concomitant antiarrhythmic drugs (amiodarone 5 8, sotalol 5 1) and anticoagulation (warfarin 5 8) as needed. Four patients had no cardiovascular disease, 4 patients had hypertension, and 1 patient had congenital heart disease. In all, 46 spontaneous AF episodes were treated with the IAD in these patients during the follow-up period between 14 and 37 months after implantation. The study protocol was approved by the ethics committee of the University of Hong Kong, and written informed consent was obtained from all patients. All echocardiography studies were conducted with a commercially available machine (System Five; VingMed Sound, Horton, Norway). Transmitral pulsed Doppler inflow velocities were recorded from the apical 4-chamber view using a 3.5-MHz transducer with the sample volume positioned between the tips of the mitral leaflet during quiet respiration. All echocardiographic data were digitally stored in a Macintosh PowerPC computer for subsequent off-line quantitative analysis. Peak velocity, mean acceleration, and deceleration of the transmitral flow during atrial contraction (A wave) were obtained.8,9 An average of 3 to 5 consecutive beats was used for analysis. The technique for implantation and features of Metrix IAD have been described elsewhere.5–7 In this study, the IAD was programmed in a monitoring mode to document the cardiac rhythm every 2 hours, with data logged into the device memory each time AF was detected. Each patient was evaluated by the physician in the outpatient clinic every 3 months and the device was interrogated to determine the number and total duration of AF episodes. Patients were instructed to come to the hospital or clinic for prompt treatment during each episode of symptomatic AF. All the atrial defibrillation shocks were delivered under a physician’s supervision. During follow-up, a baseline echocardiogram was recorded after the patients were in sinus rhythm for at least 4 weeks (mean 1,207 6 502 hours, range 702 to 2,064). Then a 300-V R-wave synchronized biphasic shock was delivered during sinus rhythm in each patient to evaluate the effect of atrial defibrillation shock on LA mechanical function. Echocardiographic studies were performed at 1 minute, 20 minutes, and 4 hours after shock delivery. When the patients sought treatment of a symptomatic AF episode or a spontaneous AF episode was detected during routine followup, atrial defibrillation shock programmed at 300 V was delivered for cardioversion. In patients with spontaneous AF episodes that were successfully treated with the IAD and maintained in stable sinus rhythm, echocardiographic studies were performed at 1 minute, 20 minutes, 4 hours, and 1 week after cardioversion. Continuous variables are expressed as mean 6 1 SD. Statistical comparisons were performed with Student’s t test or Fisher’s exact test as appropriate. Analysis of serial changes in transmitral Doppler variables at baseline and after cardioversion was performed by analysis of variance for repeated measures. A p value ,0.05 was considered statistically significant. At baseline, the mean peak A-wave velocity was 62 6 11 cm/s, the mean acceleration of the A wave was 625 6 170 cm/s and the mean deceleration of the A wave was 785 6 308 cm/s. There was no significant change in these parameters at 1 minute, 20 minutes, and 4 hours after a 300-V atrial shock delivered From the Division of Cardiology, Department of Medicine, and the Institute of Cardiovascular Science and Medicine, University of Hong Kong, Queen Mary Hospital, Hong Kong, China; and InControl Inc, Redmond, Washington. Dr. Lau’s address is: Division of Cardiology, Department of Medicine, University of Hong Kong, Queen Mary Hospital, Hong Kong, China. E-mail: cplau@hkucc.hku.hk. Manuscript received March 9, 2000; revised manuscript received and accepted May 9, 2000.