Determinants of first-shock success for atrial implantable cardioverter defibrillators

The aim of this study was to identify determinants of first-shock success for defibrillation of spontaneous atrial fibrillation (AF) in ambulatory patients with an atrial implantable cardioverter defibrillator (ICD). The determinants of first-shock success in ambulatory patients with atrial ICDs are unknown.

We used the generalized estimating equation method to analyze determinants of first-shock success in 50 consecutive atrial ICD recipients in whom DFT+ (weakest shock that defibrillates on two consecutive trials) was determined at implant and spontaneous AF was shocked with shock strength > or = 2 x DFT+. DFT+ was 6.2 +/- 3.1 J. Of 470 first shocks, 407 were successful (generalized estimating equation 85%, confidence interval 79% to 90%). Determinants of first-shock success were use of coronary sinus electrode (univariate P = 0.02; multivariate P < 0.001, relative risk 5.0), absence of a Class III antiarrhythmic drug (univariate P = 0.06; multivariate P < 0.001, relative risk 3.2), absence of early recurrence of atrial fibrillation (ERAF; univariate P = 0.06; multivariate P = 0.02, relative risk 2.9), and longer duration of AF prior to shock > or = 3 hours (univariate: P = 0.02; multivariate P = NS). Sinus rhythm >1 minute persisted after 93% of first shocks in patients without documented ERAF but after only 58% of shocks in patients with documented ERAF (P < 0.001).

Reducing ERAF is critical to achieving a clinically acceptable rate of persistent sinus rhythm after first shocks. For first shocks > or = 2 x DFT +, success is not increased by programming stronger shocks. Early cardioversion does not increase first-shock success.