Rectilinear biphasic cardioversion (Bi-DC) has been shown to be very effective for restoration of sinus rhythm in patients with persistent atrial fibrillation (AF). There is, however, limited information on factors influencing effectiveness of the initial energy of 50 J for Bi-DC of atrial fibrillation.
Aim of the study: Evaluation of efficacy of 50 J shock of Bi-DC for restoration sinus rhythm and development of point score system to predict high conversion rate of 50 J shock in persistent atrial fibrillation.
Material and methods: The study group was composed of 502 consecutive Bi-DC in-patients with persistent atrial fibrillation who underwent cardioversion according to the standard protocol (50 J --> 1 J/kg m.c. --> 2 J/kg m.c. --> 200 J). Factors influencing effectiveness of 50 J shock were defined.
Results: Rectilinear biphasic cardioversion of shock of 50 J was successful in 157 (31%) patients. In multivariate analysis independent factors associated with efficacy of 50 J shock were: atrial fibrillation duration < 7 months (OR: 14.3, CI: 5.83 - 35.2, p < 0.001), left ventricular ejection fraction--LVEF > 40% (OR: 5.67, CI: 1.22 - 26.3, p = 0.027), body weight < 78 kg (OR: 3.17, CI: 1.52 - 6.59, p = 0.002), permanent pacemaker (OR: 2.98, CI: 1.20 - 7.40, p = 0.018), LA diameter < 4.5 cm (OR: 2.80, CI: 1.19 - 6.58, p = 0.02). A simplified point score system was developed to predict the chance for termination of atrial fibrillation (the score gives 5 points for atrial fibrillation duration < 7 months; 2 points for EF > 40%; 1 point for pacemaker, body weight < 78 kg and LA < 4.5 cm, each). High effectiveness (65%) of 50 J shock was achieved in patients with > 9 points of scoring system and 80% in this group when atrial fibrillation duration is shorter than 3 months. Effectiveness of 50 J shock was very low in the remaining group (0 points--0%; 1-3 points--5%; 4-6 points--21%; 7-8 points--34%, respectively).
Conclusion: The efficacy of initial shock of 50 J for termination of atrial fibrillation is limited and is not recommended for general population of patients with atrial fibrillation referred for Bi-DC. 50 J might be considered in patients with pacemakers without factors associated with failure of 50 J to terminate atrial fibrillation: atrial fibrillation duration > 7 months, lower LVEF increased LA diameter, body weight > 78 kg. The shock of 50 J is effective in more than 60% of patients, if they achieved 9 or 10 points in proposed score. The highest efficacy of 50 J shock (80%) is possible to reach in this group if atrial fibrillation duration is shorter than 3 months.