ESC 2019: Maximum-fixed energy shocks are more effective than low-escalating energy shocks for cardioverting AF

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Anders Sjoerslev Schmidt

A study that compared the use of maximum-fixed energy and low-escalating energy shocks for cardioversion in patients with atrial fibrillation (AF) found that maximum-fixed shocks were significantly more effective at cardioverting AF. No differences were found in any safety endpoints included in the study between patients treated with either method.

Results from the study were presented by Anders Sjoerslev Schmidt (Randers Regional Hospital, Randers; Aarhus University, and Aarhus University Hospital, Denmark) in a Hotline Session at the European Society of Cardiology Congress (ESC 2019; 31 August–4 September, Paris, France). He stated: “We found that when using maximum-fixed shocks the cardioversion efficacy was 88% compared with 66% when using a more standard low-escalating approach. This was a 22% absolute difference and statistically significant.”

Direct-current cardioversion of AF is one of the most commonly performed clinical procedures in cardiology, emergency, and critical care medicine. However, the 2016 ESC guidelines on the management of AF do not specify which energy levels to use when performing the procedure.

Schmidt explained: “It is common practice to use low initial energy shocks with escalating shocks, if necessary. This protocol was originally introduced to improve safety in the era of monophasic shocks. Now we more commonly use biphasic shocks for cardioversion, which are more effective than monophasic shocks and safer in terms of not inducing myocardial injury or skin burns. Therefore the advantage of the low-escalating approach of biphasic shocks is now less clear.”
Researchers at Randers Regional Hospital in Denmark therefore aimed to investigate the use of maximum-fixed versus low-escalating energy shocks for cardioverting AF. In this single-centre study, patients were randomised 1:1 to undergo cardioversion using either low-escalating shocks or maximum-fixed shocks.

All shocks were delivered using a truncated exponential waveform with the LifePak 20 device (Physio-Control). The maximum-fixed shocks used the maximum available setting on the device of 360J, while the low-escalating shock protocol escalated to a maximum strength of 200J (125–150–200J).

Patients were eligible for inclusion in the trial if they were scheduled for elective cardioversion of AF, were ≥18 years old, and able to sign informed consent. Patients were excluded if they had non-AF arrhythmias or haemodynamically unstable AF, if they had untreated hyperthyroidism, were pregnant, or had previously been enrolled in the trial.

The primary endpoint was sinus rhythm one minute after cardioversion. Secondary safety endpoints were cases of arrhythmia, myocardial injury (measured with high-sensitive troponin I changes), skin redness or burns, and patient-reported discomfort or pain using a visual analogue scale.
In all, 276 patients were randomised; 129 to maximum-fixed shocks and 147 to low-escalating shocks.

Investigators found that the percentage of patients in sinus rhythm one minute after cardioversion was 88% for those who had received maximum-fixed shocks, compared with 66% for those who had received low-escalating shocks—a statistically significant difference of 22% in shock efficiency (95% confidence interval [CI ]13–32, p<0.001). Similarly, the efficacy to discharge—the proportion of patients in sinus rhythm four hours after the procedure—was 85% for the maximum-fixed shock group compared with 63% for the low-escalating shock group, a 22% difference in cardioversion efficacy (95% CI 12–32, p<0.001).

Schmidt said: “The maximum-fixed energy group only needed a median number of one shock to achieve cardioversion compared with a median number of two shocks for the patients treated with low-escalating energy shocks. The average procedure duration was shorter for the maximum-fixed energy group at a median time of 1.9 minutes, with IQR [interquartile range] of 1.5–2.7, compared with 2.2 minutes, with an IQR of 1.7–3, for the low-escalating energy group.”

“Importantly,” he continued, “there were no major harms reported in this study. The same number of cases of arrhythmia were reported in each group and there was no significant change in high-sensitive troponin I levels after cardioversion. There were no incidents of skin burns in any patients and comparable numbers of mild redness were found in both groups. A comparable proportion of patients in each group also reported any pain or discomfort.”

There were some limitations: the study only took place in one centre using only one device for cardioversion and, because of the nature of the study, the physician carrying out cardioversion was not blinded to the energy level used. Also acute cardioversions were not included.

Although the study was powered for efficacy rather than safety endpoints, Schmidt noted that “it was very reassuring to see comparable outcomes for all the included safety endpoints.”

He concluded: “Using maximum-fixed energy shocks can optimise cardioversion efficacy. We would suggest a change in clinical practice to use the maximum energy available rather than the existing practice of using low-escalation shocks.”


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