Low energy conversion of atrial fibrillation in the sheep.
OBJECTIVE
In this study, the feasibility, efficacy and safety of low energy internal atrial cardioversion were investigated in a sheep model. The relation between the level of energy used for atrial defibrillation and the probability of successful cardioversion was examined.


BACKGROUND
Atrial fibrillation is a common clinical arrhythmia that frequently recurs after termination with high energy external cardioversion. In some patients with drug-refractory and poorly tolerated atrial fibrillation, an automatic implantable cardioverter may prove useful by providing rapid restoration of sinus rhythm.


METHODS
In 16 pentobarbital-anesthetized sheep, a right atrial spring electrode was implanted percutaneously and a left thoracic cutaneous patch electrode was placed on the thorax. Sustained atrial fibrillation was induced by rapid atrial pacing and terminated by biphasic cathodal shocks synchronized to the R wave of the surface electrocardiogram (ECG).


RESULTS
During 768 defibrillation attempts in 16 sheep, the percent of successful cardioversion attempts increased in a dose-response manner, reaching a plateau at the average energy level of 5 J. With greater than or equal to 1.5 and greater than or equal to 2.5 J energy levels, cardioversion was achieved, respectively, in greater than 50% and greater than 80% of attempts. Ventricular fibrillation occurred in 18 (2.4%) of 768 cardioversion attempts; in all 18 cases, the shock was poorly synchronized with the ECG R wave.


CONCLUSIONS
Low energy cardioversion of atrial fibrillation to sinus rhythm is feasible with use of a right atrial spring/cutaneous patch electrode configuration. The percent of successful cardioversion attempts depends on the level of energy output, and there is a risk of ventricular fibrillation if cardioversion is poorly synchronized with ventricular depolarization.
Powell
A C
AC
Harvard Medical School, Boston, Massachusetts.
Garan
H
H
McGovern
B A
BA
Fallon
J T
JT
Krishnan
S C
SC
Ruskin
J N
JN
D000818:Animals; D001281:Atrial Fibrillation / Q000628:therapy*; D004554:Electric Countershock / Q000009:adverse effects / Q000379:methods*; D005240:Feasibility Studies; D006325:Heart Atria / Q000473:pathology; D012756:Sheep; D014693:Ventricular Fibrillation / Q000209:etiology