ATRIAL DEFIBRILLATION USING TEMPORARY EPICARDIAL DEFIBRILLATION STAINLESS-STEEL WIRE ELECTRODES - STUDIES IN THE CANINE STERILE PERICARDITIS MODEL

Objectives. This study sought to determine whether temporary epicardia l wire electrodes can be used safely and effectively to defibrillate t he atria with low energy shocks in the absence of anesthesia. Backgrou nd. Atrial fibrillation after open heart surgery is a significant clin ical problem. Methods. Twelve dogs with sterile pericarditis were stud ied. In the first group (6 dogs, bilateral thoracotomy group), a wire electrode, insulated except for the distal 6 cm, was placed on the epi cardial free mall of each atrium. Each end of the bare wire was then s utured to the parietal pericardium. In the second group (6 dogs, media n sternotomy group), the wire electrodes were kept in place by a doubl e loop of Prolene placed around the distal tip of the bare wire and se wn to the overlying parietal pericardium. In the bilateral thoracotomy group, atrial defibrillation thresholds (defined as < 90% and > 10% s uccessful defibrillation of 20 shocks at a given delivered energy) wer e obtained in anesthetized dogs using the wire electrodes with the che st closed and open and using two transvenously placed catheters with c oil electrodes in the distal 6 cm (one in the coronary sinus and the o ther in the right atrial appendage) with the chest open. In the median sternotomy group, thresholds were obtained in minimally sedated anima ls without reopening the chest. A 25% increase above threshold shock w as also used to determine a new percent success. After 4 days, the wir e electrodes were removed by pulling on the external ends. At the time of removal, blood pressure and heart rate were monitored for 30 min, after,which dogs were killed and their hearts sent for histopathologic study. For all dogs, chest radiographs were obtained postoperatively and on study days. Results. Atrial defibrillation using the wire elect rodes was successful in all dogs at a mean (+/- SE) voltage of 112 +/- 9 V, with an energy level of 0.46 +/- 0.07 J and an impedance of 59.3 +/- 5 ohms. The mean percent success at the atrial defibrillation thr eshold was 36 +/- 5%. The 25% increase in defibrillation voltage impro ved the mean percent success to 73% (mean energy 0.66 +/- 0.19 J). No clinical or hemodynamic complications were observed during shock deliv ery, and no ventricular arrhythmias mere induced during the shocks. No complications followed wire electrode removal. Histopathologic analys is showed no structural damage. Conclusions. The atrial defibrillation threshold obtained using temporary epicardial wire electrodes for atr ial defibrillation is < 1 J in dogs. Atrial defibrillation using tempo rary epicardial wire electrodes can be performed safely, quickly and r eliably without the need for anesthesia or antiarrhythmic agents. The wire electrodes can be removed without adverse hemodynamic or structur al consequences. These data provide a basis for testing atrial defibri llation using epicardial wire electrodes in patients after open heart surgery.