Arrhythmic complications of electrical cardioversion: Relationship to shock energy☆

https://doi.org/10.1016/j.ijcard.2006.12.014Get rights and content

Abstract

Background

Existing guidelines for electrical cardioversion (ECV) of atrial arrhythmias suggest starting at a low energy setting on the grounds that shocks of high energy might damage the myocardium or trigger more serious arrhythmias. We hypothesised that more powerful shocks would exceed the upper limit of vulnerability for inducing ventricular fibrillation. The initial use of higher energy could therefore reduce arrhythmic complications.

Methods

We collected data on the sequence of shocks delivered and the resulting changes in cardiac rhythm in 1896 patients who underwent transthoracic ECV. Rhythm strips derived from 200 consecutive ECV attempts were studied to verify the accuracy of the synchronisation of the shocks delivered.

Results

In 2522 attempts at transthoracic ECV, 6398 shocks were delivered, 1243 in atrial flutter or atrial tachycardia, the others in AF. Ventricular fibrillation was significantly more common after shocks of < 200 J (5 of 2959 vs. 0 of 3439 shocks, p < 0.05, Fischer's exact test). Conversion of atrial flutter or atrial tachycardia to AF was also more common at < 200 J (20 of 930 shocks vs. 1 of 313 shocks at ≥ 200 J, p < 0.05, χ2 test). Sinus bradycardia or sinus arrest complicated 0.95% of cardioversion attempts, but none required emergency pacing. The incidence of bradycardia was not related to the energy used.

Conclusions

Shocks of > 200 J are associated with fewer tachyarrhythmic complications, and do not increase the risk of other serious complications. Bradycardia after cardioversion is very rarely of clinical importance.

Section snippets

Background

The earliest accounts of electrical cardioversion (ECV) described the initial use of a 100 J direct current (DC) shock, increasing in steps to a maximum of 400 J if initial shocks failed [1]. This tentative approach which has entered standard guidelines [2] was based on a fear that shocks of higher energy might damage the myocardium or other tissues, and an assumption that tissue damage would be proportional to the intensity of the most powerful shock delivered. Although more recent guidelines

Methods

In 13 hospitals in 3 European countries, we used the hospital computer system, ward admission records or an existing database to identify patients who underwent direct current cardioversion of atrial arrhythmias over a period of 7 years during the 1990s. The period chosen preceded the introduction of biphasic defibrillators to any of the hospitals involved. We examined the hospital records of these patients, noting the rhythm present immediately before cardioversion, the schedule of shocks

Results

Our search identified 2754 patients as having had an attempted ECV. We reviewed the hospital records of 2401 (87.2%). After excluding patients in whom there was no record of transthoracic ECV having been performed for an atrial arrhythmia we collected data pertaining to 2522 attempts at transthoracic ECV in 1896 patients (69.4% male, aged 15.1–101.3, mean 63.1 ± 12.6 years, weight 35–153 kg, mean 80.4 ± 17.2) in which the full sequence of shocks and the rhythm present after each shock was recorded

Discussion

It has been shown that the initial use of a higher energy setting reduces the number of shocks required to effect cardioversion and in many cases reduces the total energy delivered [8]. In the past, a low initial energy setting has been favoured on the grounds that higher energy shocks might damage the myocardium. Myocardial damage by direct current shock has been demonstrated in animal models but these involved shocks of far greater energy than are used in man [9], [10], or shocks of similar

Limitations

These data were collected retrospectively, and in many cases there was no rhythm strip available to confirm the sequence of events described in the notes pertaining to the cardioversion. We were therefore dependent on the interpretation of the cardiac rhythm by the physician who performed or supervised the procedure, and on the accurate recording of events in the case notes. The data are derived exclusively from DC rather than biphasic cardioversion, so the applicability to modern practice is

Conclusions

Ventricular fibrillation is a rare but potentially important complication of electrical cardioversion. The initial use of a shock of 200–360 J for DC cardioversion instead of the traditional 50–100 J may reduce the incidence of tachyarrhythmic complications without altering the incidence of other complications. Bradycardia is seldom a serious problem after ECV so prophylactic temporary pacing should be used sparingly.

Acknowledgements

By Centre:

Cork University Hospital, Ireland: WH Fennell, PP Kearney, P Nash

Crawley Hospital, Crawley, UK: JF Sneddon

Epsom Hospital, Epsom, UK: S Odamuya

Guy's Hospital, London, UK: LA Corr, JS Gill

Mayday University Hospital, Croydon, UK: SP Joseph, R Canepa-Anson, K Baig, A Crowther

Northwick Park University Hospital, London, UK: SA Allard, R Senior, NG Stevens

Royal Surrey County Hospital, Guilford, UK: TH Foley, JH Goldman, EW Leatham

Royal Sussex County Hospital, Brighton, UK: SR Holmberg, J

References (16)

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Supported by the British Heart Foundation Project Grant PG/96138.

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