Author + information
- Received September 5, 1991
- Revision received April 7, 1992
- Accepted April 15, 1992
- Published online September 1, 1992.
- Anne C. Powell, MB, BS, PhD1,
- Hasan Garan, MD, FACC∗,
- Brian A. McGovern, MD,
- John T. Fallon, MD, PhD,
- Subramaniam C. Krishnan, MD and
- Jeremy N. Ruskin, MD, FACC
- ↵∗Address for correspondence: Hasan Garan, MD, Cardiac Unit, Massachusetts General Hospital, Boston, Massachusetts 02114.
Objectives. 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 doseresponse manner, reaching a plateau at the average energy level of 5 J. With ≥ 1.5 and ≥ 2.5 J energy levels, cardioversion was achieved, respectively, in > 50% and > 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.
- Received September 5, 1991.
- Revision received April 7, 1992.
- Accepted April 15, 1992.