Does Electrode Position Affect the Results of Cardioversion?
By Michael H. Crawford, MD, Editor
SYNOPSIS: A randomized trial of anteroposterior vs. anterolateral electrode positioning for the biphasic energy cardioversion of atrial fibrillation showed the anterolateral positioning is most effective.
SOURCE: Schmidt AS, Lauridsen KG, Møller DS, et al. Anterior-lateral versus anterior-posterior electrode position for cardioverting atrial fibrillation. Circulation 2021;144:1995-2003.
Using contemporary biphasic shocks, there is controversy regarding the position of the electrodes. When it comes to monophasic shocks, anterior-posterior (AP) positioning could be more effective than anterior-lateral (AL) positioning. But which position really is best?
Schmidt et al conceived and conducted the Electrode Position In Cardioverting Atrial Fibrillation (EPIC) trial, a multicenter, randomized, open-label, blinded-outcome assessment study. They randomized 467 patients undergoing elective cardioversions for atrial fibrillation (AF) at three medical centers to AP or AL electrode positioning. Two-thirds were men, and the average BMI for all was 29 kg/m2. The physician performing the cardioversion was not blinded to the electrode position. Up to four shocks of increasing energy (100 J, 150 J, 200 J, and 360 J) were used as necessary after propofol anesthetization. The primary outcome was the proportion of patients in sinus rhythm one minute after the first shock. The secondary outcome was the proportion after the final shock. The outcomes were assessed blindly by an investigator reviewing the recorded electrograms. Safety outcomes included arrhythmias during or for up to two hours after cardioversion on continuous monitoring.
Investigators’ review of the precardioversion ECG found eight patients were in atrial flutter but were included in the intention-to-treat analysis. The primary outcome was achieved in 54% of AL patients and 33% of AP patients (P < 0.001). The number of patients in sinus rhythm after the final shock was 93% in the AL group and 85% in the AP group. There was no significant difference in any safety outcome. The authors concluded that for biphasic cardioversion of atrial fibrillation, AL electrode positioning was more effective than AP.
My current practice is to use AP positioning; in my experience, this works better. My practice originated in the monophasic defibrillator era, but based on the EPIC trial results, the situation may be different in the biphasic defibrillator era. Also, the monophasic defibrillators we used included handheld paddles or foil electrodes, not the current self-adhesive ones. The well-done EPIC study will change my practice.
Notably, the position of the electrodes in this study was somewhat different from what I have observed clinically. The AL positioning uses an electrode in the upper right chest and one in the midaxillary line. Often, when I see where the support staff have placed the electrodes, the lateral one is centered at the cardiac apex. Standard AP positioning is left upper chest anteriorly and centered on the medial edge of the scapula posteriorly. The AP position supposedly targets the atria; it is unclear why the AL positioning was superior in the EPIC study. Interestingly, a subgroup analysis of EPIC showed AL positioning was particularly successful in obese patients vs. non-obese patients (P = 0.03).
Schmidt et al used a graded incremental energy application of up to four shocks. If the first shock had been made at the maximum allowed energy application (or close to it), the results could have been affected, since the difference in success rate of the two positions decreased with higher energy shocks (22% difference at 100 J compared with 8% at 360 J). The number of patients at the highest shock level was much smaller than at the first level. Many patients had converted with the first three shocks. Even if the difference between AL and AP positioning was minimal using a higher first shock energy protocol, there are other advantages to the AL positioning. In an emergency, the electrodes would be easier to place quickly. Also, if the need to cardiovert arose during surgery or other procedures, the AL leads would be easier to apply. In addition, if temporary pacing is needed, the AL position is the one recommended for pacing. Finally, some practitioners like to add manual pressure to the electrodes, especially on obese subjects, and AL positioning would facilitate this. For the cardioversion of atrial fibrillation today, AL electrode positioning with a high initial energy application seems to be the best approach.
A randomized trial of anteroposterior vs. anterolateral electrode positioning for the biphasic energy cardioversion of atrial fibrillation showed the anterolateral positioning is most effective.
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