Low-energy synchronous cardioversion of ventricular tachycardia using a catheter electrode in a canine model of subacute myocardial infarction.

Abstract

The feasibility and safety of terminating sustained ventricular tachycardia by low-energy, synchronized shocks delivered through transvenous, intracardiac catheter electrodes were determined. Adult mongrel dogs underwent 2-h occlusion-release of the left anterior descending coronary artery. Programmed electrical stimulation 3-8 days later in 14 of 24 surviving dogs induced 627 episodes of sustained ventricular tachycardia that had 35 morphologically distinct contours. Truncated exponential shocks, timed from the bipolar R wave recorded in the right ventricular apex, were delivered between the right ventricular apex (cathode) and superior vena cava (anode). Shocks of 0.008-1.0 J (median 0.5 J) reproducibly terminated 25 of 30 (83%) sustained ventricular tachycardias that had a cycle length (CL) .gtoreq. 200 ms. One of 5 sustained ventricular tachycardias with CL < 200 ms was terminated by .ltoreq. 1.0 J. During ventricular tachycardias with a CL .gtoreq. 200 ms, only 12 of 748 (1.6%) shocks of 0.008-1.0 J applied within the first 80% of the QRS produced repetitive ventricular responses, and none accelerated the ventricular tachycardia or produced ventricular fibrillation shocks .gtoreq. 0.008 J in the T wave (9 of 85) or .gtoreq. 0.5 J in the QRS of ventricular tachycardias with CL < 200 ms (2 of 17) produced venticular fibrillation. Atrial flutter or atrial fibrillation, usually terminating within 3 s, occurred in 9% of shocks .gtoreq. 0.5 J. The energy required to terminate sustained ventricular tachycardia was decreased 20-250-fold using an epicardial apex cone electrode for the cathode and the superior vena cava electrode for the anode, but was not significantly altered when the shock was delivered between electrodes in the right ventricualr apex (cathode) and coronary sinus (anode). Transvenous, intracardiac, R-wave-synchronous shocks .ltoreq. 1.0 J safely terminate sustained ventricular tachycardia with CL .gtoreq. 200 ms in dogs.