Low-energy electrical catheter ablation of the A-V junction in dogs: Physiologic and histologic findings
Abstract
Damped sine wave defibrillator shocks applied through an intracardiac catheter are presently used to damage myocardium to achieve arrhythmia control. We compared effectiveness of damped sine wave shocks with capacitor discharge shocks to produce transient A-V block using equal, low energies. The His-bundle ablation catheter was anchored in place by suction, and positioned in twelve anesthetized dogs (22-33 kg) using fluoroscopy, intracardiac recording, and pacing criteria. The shocks were delivered between a catheter-mounted electrode and an 8-cm diameter plate (anode) on the left chest wall. Two low-energy shocks of about 1.3 J each were delivered first, one of the pair being a damped sine wave, and the other being a capacitor discharge. Progressively higher, equal-energy, paired shocks were applied, with adequate time allowed after each shock for return of sinus rhythm. Block was measured from shock delivery to return of sinus rhythm. Delivered energy was calculated from voltage and current waveforms. When a shock produced complete A-V block lasting 3 hours, no additional shocks were delivered and the dog was monitored for 6 days. In 34 of 36 paired shocks, the capacitor discharge produced longer block than the damped sine wave (P $<$ 0.05). Five dogs remained in block for 6 days. In four, the last shock delivered was the capacitor discharge (energies of 1.1, 3.5, 3.6 and 7.3 J), and in one, the last shock was a 3.9J damped sine wave. In a second study, twenty dogs (23-37 kg) were used to determine the efficacy of single, low-energy, capacitor discharge shocks. Each animal received a single shock of predetermined energy: 5.6J, 13.2J, or 22.5J. For the lowest energy group, 1 of 6 (17%) remained in complete A-V block for 6 days. Two of 6 (33%) remained in block for the 13.2 J group, and 5 of 8 (64%) for the 22.5 J group. The 64% rate of 22.5 J is similar to published clinical rates. Histopathologic changes in the myocardium at the site of shock delivery resembled those from defibrillator shock overdose, but lesions were small, with only minor damage to the atrial and ventricular septae. Valve damage was minimal, and the minor endocardial disruption at the site of catheter attachment resolved quickly. Lesion size correlated positively with delivered energy. In conclusion, the capacitor discharge is more effective at producing transient block and permanent block can be produced in 2/3 of subjects with 22.5 J or less with minimal damage to non-conducting cardiac structures.
Degree
Ph.D.
Advisors
Tacker, Purdue University.
Subject Area
Biomedical research
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