Bang for the buck: the importance of modifiable factors for electrical cardioversion of atrial fibrillation

This commentary refers to ‘Maximum-fixed energy shocks for cardioverting atrial fibrillation’, by A.S. Schmidt et al., on page 626. The Comparison of High vs. Escalating Shocks (CHESS) trial randomized 276 patients with persistent atrial fibrillation (AF) to low-escalating (125-150-200 J) vs. maximum-fixed energy (360-360-360 J) biphasic shocks.1 The authors report higher cardioversion success at 1 min and higher first shock success with the maximum-fixed energy strategy (88% vs. 66% and 75% vs. 34%, respectively) and no difference in safety endpoints. We congratulate our colleagues for their important contribution to this topic. However, one should keep in mind that the CHESS trial examined energies for first and subsequent shocks without addressing other potentially influential variables. We recently reported the results of the Ottawa AF cardioversion protocol (OAFCP),2 which we developed, implemented, and evaluated prospectively at our centre. The OAFCP similarly consists of up to three sequential shocks (200-200-360 J) and was evaluated in patients with persistent AF using the same defibrillator as that used in CHESS. However, it incorporates the application of manual pressure on anterolateral self-adhesive electrodes for the second and third shocks. The OAFCP acutely restored sinus rhythm in 386/389 consecutive cases (99.2%) and sustained sinus rhythm as documented on a 12-lead electrocardiogram prior to hospital discharge in 351/383 (91.6%). In a substudy of the Cardioversion-BMI trial, Voskoboinik et al. 3 similarly found that applying manual pressure to electrodes could successfully cardiovert patients with morbid obesity in whom 200 J shocks had failed. Therefore, although we agree that shock energy is associated with cardioversion success, we argue that substantial improvements can also be achieved by applying manual pressure, potentially by reducing transthoracic impedance. We hope that the important emphasis on shock energy that this trial is expected to elicit does not detract from the attention paid to other modifiable factors. After all, maximum-energy shocks failed in nearly one in eight patients in the trial despite being delivered by knowledgeable clinicians with an interest in cardioversions. In our opinion, the takeaway message from the CHESS trial is therefore that high-energy shocks are frequently effective and appear to be safe. However, we believe that our data and that of others suggest that especially in cases of failed high-energy shocks, clinicians should consider repeating shocks while applying manual pressure. The Canadian Institutes of Health Research (CIHR) Frederick Banting and Charles Best Canada Graduate Scholarship to F.D.R.; CIHR Banting Postdoctoral Fellowship to F.D.R.; the Royal College of Physicians and Surgeons of Canada Detweiler Travelling Fellowship to F.D.R.; CIHR to D.H.B.; the University of Ottawa Heart Institute Leadership Chair in Electrophysiology to D.H.B.; the Tier 1 University of Ottawa Chair in Electrophysiology Research to D.H.B.; and the Cardiac Arrhythmia Network of Canada (CANet) as part of the Networks of Centres of Excellence to F.D.R., M.M.S., and D.H.B. Conflict of interest: none declared.

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