OBJECTIVES This study was performed to assess the atrial defibrillation thr
eshold in patients with recurrent atrial fibrillation (AF) using repeated i
nternal cardioversion.
BACKGROUND Previous studies in patients with chronic AF undergoing internal
cardioversion have shown this method to be effective and safe. However, cu
rrent energy requirements might preclude patients with longer-lasting AF fr
om being eligible for an implantable atrial defibrillator.
METHODS Internal shocks were delivered via defibrillation electrodes placed
in the right atrium (cathode) and the coronary sinus (anode) or the right
atrium (cathode) and the left pulmonary artery. After cardioversion, patien
ts were orally treated with sotalol (mean 189 +/- 63 mg/day). Eighty consec
utive patients with chronic AF (mean duration 291 +/- 237 days) underwent i
nternal cardioversion, and sinus rhythm was restored in 74 patients. Eighte
en patients underwent repealed internal cardioversion using the same electr
ode position and shock configuration after recurrence of AF (mean duration
34 +/- 25 days).
RESULTS In these 18 patients, the overall mean defibrillation threshold nas
6.67 +/- 3.09 J for the first cardioversion and 3.83 +/- 2.62 J for the se
cond (p = 0.003). Mean lead impedance was 55.6 +/- 5.1 Omega and 57.1 +/- 3
.7 Omega, respectively (not significant). For sedation, 6.7 +/- 2.9 mg and
3.9 +/- 2.2 mg midazolam were administered intravenously (p = 0.003), and t
he pain score (0 = not felt, 10 = intolerable) was 5.1 +/- 1.9 and 2.7 +/-
1.8 (p = 0.001). Uni- and multivariate analyses revealed only the duration
of AF before cardioversion to be of relevance, lasting 175 +/- 113 days bef
ore the first and 34 +/- 25 days before the second cardioversion in these 1
8 patients (p = 0.002).
CONCLUSION If the duration of AF is reduced, a significant reduction in def
ibrillation energy requirements for internal cardioversion ensues. This mig
ht extend the group of patients eligible for an implantable atrial defibril
lator despite relatively high initial defibrillation thresholds. (C) 1999 b
y the American College of Cardiology.