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Factors determining success and energy requirements for cardioversion of atrial fibrillation
G W Dalzell1, J Anderson, A A Adgey
1Regional Medical Cardiology Centre, Royal Victoria Hospital, Belfast, N. Ireland.
Insights
Cardioversion success for atrial fibrillation is linked to shorter duration of the condition and prior digoxin use. Shorter atrial fibrillation duration predicts success with low-energy shocks.
Area of Science:
- Cardiology
- Electrophysiology
Background:
- Atrial fibrillation (AF) is a common arrhythmia requiring cardioversion.
- Predictors of successful cardioversion and energy requirements remain areas of investigation.
Purpose of the Study:
- To identify factors influencing the success and energy needs for cardioversion of atrial fibrillation.
- To analyze the impact of patient characteristics, electrode positioning, and prior medications on cardioversion outcomes.
Main Methods:
- 80 patients undergoing cardioversion for atrial fibrillation were studied.
- Transthoracic impedance was measured using self-adhesive pads in anteroposterior (AP) or anteroapical (AA) positions.
- Cardioversion success and energy levels were recorded, with statistical analysis performed on various potential predictors.
Main Results:
- Overall cardioversion success rate was 91.2% (73/80).
- Low-energy shocks (≤200 J) were successful in 56.2% (45/80) of patients.
- Prior digoxin treatment and shorter duration of atrial fibrillation (24 hours to 3 years) were significant predictors of success, particularly for low-energy shocks.
- Higher transthoracic impedance was associated with lower success rates for low-energy shocks.
Conclusions:
- Shorter duration of atrial fibrillation is a key predictor of successful cardioversion, especially with low-energy shocks.
- Prior digoxin treatment also positively influences cardioversion success.
- Transthoracic impedance and electrode pad positioning may affect energy requirements.
Abstract:
Factors thought to affect the success of and energy requirements for cardioversion of atrial fibrillation were studied in 80 (49 male, 31 female) patients aged 21-88 (mean 61.5 years). Transthoracic impedance was measured in advance of the countershock using a 30 kHz low amplitude AC current passed through self-adhesive ECG/defibrillator pads (diameters 8-12 cm) applied to the chest in the antero-posterior (AP) position in 57 patients and the anteroapical (AA) position in 23 patients. Mean transthoracic impedance for all patients was 69.3 +/- 16 (SD) ohms (range 39-131 ohms), but transthoracic impedance was significantly greater in the AA than the AP position (75.4 +/- 13 vs. 66.7 +/- 16 ohms, p = 0.02). Initial energy was 50 J (delivered) and was gradually increased to a maximum of 360 J if required. Cardioversion was successful in 73 of 80 (91.2 per cent), and low energy shocks (less than or equal to 200 J) were successful in 45 of 80 (56.2 per cent) patients. Using single factor analysis, sex, left atrial enlargement, electrode pad positions, aetiology of atrial fibrillation, presence of left ventricular failure, and prior treatment with verapamil or beta-adrenergic blockers were not significant determinants of cardioversion success or success of low energy shocks but prior treatment with digoxin was, both for cardioversion success and success at low energies. In patients with transthoracic impedance less than or equal to 70 ohms, low energy shocks were more often successful (33 or 50, 66 per cent) than in patients with transthoracic impedance greater than 70 ohms (12 of 30, 40 per cent), p = 0.04. Using univariate analysis, cardioversion success with low energy shocks was not only significantly associated with prior treatment with digoxin but also with the duration of atrial fibrillation (24 hours to one month and one month to three years) and for shocks of less than or equal to 100 J, with prior treatment with amiodarone. Multifactorial linear regression analysis selected, in rank order, only duration of atrial fibrillation of 24 hours to less than one month and one month to three years as significant predictors of both cardioversion success irrespective of shock strength, and success of low energy shocks.