Efficacy of transthoracic cardioversion of atrial fibrillation using a biphasic, truncated exponential shock waveform at variable initial shock energies

A South Australian registry of biphasic cardioversions of atrial arrhythmias: efficacy and predictors of success

BACKGROUND

Restoration of sinus rhythm by biphasic cardioversion is an established strategy for patients in atrial arrhythmias. This study aimed to investigate the real-life practice of cardioversions throughout a local hospital to determine frequency and predictors of success and use of high energy (> 200 joules).

METHODS

Prospective analysis of consecutive biphasic cardioversions from 2009-2013. Patient demographics, medical history and cardioversion data were collected.

RESULTS

484 cardioversions from 379 patients were included in the final analysis. The majority (73%) of cardioversions were immediately successful after a single shock; overall success was 88% (1-5 shocks). Exploratory analyses revealed that single-shock success was significantly associated with lighter weight (OR 1.19, 95% CI 1.0-1.4, p<0.05). If a second shock was required, energy escalation was significantly associated with success (OR 3.11, 95% CI 1.43-6.77, p<0.05). Increasing weight was the strongest predictor of receiving high energy (10kg increase OR 1.43, 95% CI 1.13-1.81, p<0.05).

CONCLUSIONS

This prospective analysis reflects the real-life heterogeneous practice of biphasic cardioversions of atrial arrhythmias throughout a local hospital. These findings highlight the importance of first shock energy selection with careful consideration of patient weight. We emphasise the recommendation to escalate energy, highlighting the need for high-energy defibrillators in 'hard-to-cardiovert' patients.

When, how, and why should sinus rhythm be restored in patients with persistent atrial fibrillation?

The results of the AFFIRM (Atrial Fibrillation Follow-up Investigation of Rhythm Management) trial indicate that the rate control strategy is preferred for the majority of patients with paroxysmal and persistent atrial fibrillation (AF). If the patient remains symptomatic despite adequate rate control or if rate control cannot be achieved, then rhythm control therapies are indicated. The most likely explanation for the disappointing results of the AFFIRM trial is the poor efficacy and excessive toxicity of rhythm control medications, because the presence of sinus rhythm was associated with a favorable prognosis in AFFIRM. As a result, there is currently great interest in nonpharmacologic therapies such as AF ablation and development of new drugs for AF with a more favorable efficacy and toxicity profile. AF ablation should be reserved for patients who fail an initial trial of a rhythm control medication until additional clinical trial information is available to justify the use of AF ablation as first-line therapy. When rhythm control therapy is indicated, the choice of antiarrhythmic medication should be dictated by the presence or absence of structural heart disease, congestive heart failure, renal dysfunction, or other comorbidities in order to maximize efficacy and minimize the chance of proarrhythmia or extracardiac toxicity.