Cardioversion in Obese Patients

By Michael H. Crawford, MD, Editor

SYNOPSIS: A multicenter, single-blind, randomized clinical trial of dual vs. single defibrillator shocks for cardioverting obese patients with atrial fibrillation showed that dual defibrillation was significantly more effective without any increase in adverse events.

SOURCE: Aymond JD, Sanchez AM, Castine MR, et al. Dual vs single cardioversion of atrial fibrillation in patients with obesity: A randomized clinical trial. JAMA Cardiol 2024; May 22. doi:10.1001/jamacardio.2024.1091. [Online ahead of print].

Because obesity is a risk factor for atrial fibrillation (AF), it is not uncommon to encounter obese patients requiring direct current cardioversion (DCCV) when pursuing a rhythm control strategy. Traditional DCCV with maximum biphasic energy delivery fails in 20% to 35% in obese patients, compared to 10% of nonobese individuals. One approach to this problem has been the use of two defibrillators simultaneously, but this approach has not been systematically studied prospectively. Thus, these investigators from three medical centers in Louisiana conducted a multicenter, single-blind (the patient), randomized controlled trial between 2020 and 2023 of elective dual vs. single defibrillator DCCV in obese AF patients (body mass index [BMI] ≥ 35) who were taking anticoagulants and underwent transesophageal echocardiograms to exclude left atrial (LA) thrombus.

The researchers applied two sets of electrode patches to each patient in an anterior-posterior position diagonally in a crisscross fashion. For those undergoing a single shock, they used the anterior upper right side of sternum patch to the posterior patch over the lower left scapula area. Dual DCCV employed single shock electrodes and the opposite patches with simultaneous defibrillator discharges from two devices each set to deliver the maximum of 200 Joules.

If the first shock failed, up to two repeat dual shocks could be used. There was no manual pressure on the pads and the shocks were not coordinated with respiration. Of the 2,079 patients undergoing DCCV during the study period at the three centers, 276 patients (13%) met the inclusion/exclusion criteria and 210 patients consented to the study. Of these, 10 patients dropped out, four because of spontaneous conversion, three because of the presence of LA thrombus, and three for other reasons.

Of the remaining patients, 101 were randomized to a single shock and 99 were randomized to dual shocks. The median age of the patients was 68 years; 37% were women and 20% were Black. The primary outcome of successful cardioversion after one shock occurred in 87% of the single-shock patients and 98% of the dual-shock patients (P = 0.002). The adjusted (for clinical characteristics) odds ratio for success with one dual shock vs. a single shock was 6.7 (95% confidence interval, 3.3-13.6; P = 0.01). Of the 14 patients from the two groups who failed the first shock, a second dual shock was successful in 12 and a third shock was successful in the remaining two. There was no difference in chest pain after the procedure or any safety endpoint between the two groups. The authors concluded that dual DCCV in AF patients with obesity resulted in more cardioversion success than the traditional one defibrillator method without any differences in patient comfort or other complications.

COMMENTARY

Despite the advance of biphasic energy defibrillators, cardioverting obese patients with AF is a common clinical problem. Several approaches to overcoming this problem have been deployed, including manual pressure on the pads, the use of paddles instead of pads, adjusting electrode placement, increasing the shock energy to maximum, timing the shock to end-expiration, and pre-cardioversion drug administration.

This randomized trial combined two of these approaches: maximizing energy delivered and varied pad position by using dual defibrillators and a crisscross pad orientation. This proved to be successful in 98% of the obese patients who met the more robust definition of a BMI of 35 or more. Also, there was no significant increase in adverse events, including bradycardia, chest pain, stroke, myocardial infarction, or death. In fact, there were no adverse events reported in either of the two groups.

There were some caveats to this study. It was single-blind, and the physicians administering the DCCV interpreted the post-shock electrocardiogram. The researchers used only the Zoll R-series defibrillators, which can only deliver a maximum of 200 Joules. One center contributed 93% of the cases. The researchers used only BMI to determine obesity and did not consider other factors, such as chest circumference.

The single defibrillator group used only one pad position: right upper anterior chest to left subscapular posterior chest. I have found that a left anterior chest pad and a posterior pad between the scapula and the spine creates a direct current line through the atria and improves AF DCCV success compared to the often-deployed right parasternal left apical pad position used for ventricular defibrillation.

Finally, in my experience, rustling up a second defibrillator often is not that easy. Thus, to optimally deploy the dual defibrillator strategy, one would need to have two defibrillators stationed in the DCCV room.