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(Circulation. 1998;98:64-72.)
© 1998 American Heart Association, Inc.

Basic Science Reports

Effects of Postshock Atrial Pacing on Atrial Defibrillation Outcome in the Isolated Sheep Heart

A. C. Skanes, MD; R. A. Gray, PhD; C. L. Zuur; ; J. Jalife, MD

From the Department of Pharmacology, SUNY Health Science Center, Syracuse, NY. Dr Gray is now at the Department of Bioengineering, University of Alabama at Birmingham.

Correspondence to Dr J. Jalife, MD, Department of Pharmacology, SUNY Health Science Center at Syracuse, 766 Irving Ave, Syracuse, NY 13210. E-mail jalifej{at}vax.cs.hscsyr.edu

Background—Failed atrial defibrillation shocks are associated with organization of postshock activity and a substantial postshock electrical quiescence. We investigated the ability of a train of pacing stimuli to capture or locally entrain atrial myocardium during the quiescent period after low-energy shocks and to alter defibrillation outcome.

Methods and Results—High-resolution video imaging of near-defibrillation-threshold atrial shocks was performed in 12 Langendorff-perfused sheep hearts. A train of 10 pacing stimuli (10-ms pulse width, 200-ms cycle length) was coupled to the shock at various delays in 7 hearts. Coupling intervals of 40 to 130 ms were investigated for feasibility of capture of the first pacing stimulus. The success rate of capture was 0, 0.08±0.08, 0.43±0.13, 0.73±0.13, and 0.11±0.1 for 40-, 60-, 80-, 100-, and 120-ms coupling intervals, respectively (P<0.001). In 5 experiments, the coupling interval was fixed at 100 ms (highest success, see above), and the pacing stimulus amplitude was varied between 1.0, 2.0, and 4.0 V. Successful capture rates were 0.38±0.08, 0.75±0.08, and 0.64±0.08, respectively (P<0.003 for 1.0 versus 2.0 V, P=0.2 for 2.0 versus 4.0 V). Rates of successful defibrillation for the groups without and with pacing were 0.56±0.07 and 0.64±0.04, respectively (P=0.3). With capture of the first pacing stimulus, the rate of successful defibrillation rose to 0.75±0.05 (P<0.01); it remained unchanged without capture (0.48±0.07 versus 0.56±0.07 for no pacing).

Conclusions—Pacing during the quiescent period that follows defibrillation shocks is feasible. A pacing train whose first pacing stimulus successfully captures during the quiescent period of near-defibrillation-threshold shocks appears to alter the outcome.

Key Words: pacing • electrophysiology • defibrillation • atrium