The purpose of this study was to determine the feasibility and safety of terminating sustained ventricular tachycardia by low-energy, synchronized shocks delivered through transvenous, intracardiac catheter electrodes. Adult mongrel dogs underwent 2-hour 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) ≥ 200 msec. One of 5 sustained ventricular tachycardias with CLs < 200 msec was terminated by ≤ 1.0 J. During ventricular tachycardias with a CL ≥ 200 msec, 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 ≥ 0.008 J in the T wave (9 of 85) or ≥ 0.5 J in the QRS of ventricular tachycardias with CLs < 200 msec (2 of 17) produced ventricular fibrillation. Atrial flutter or atrial fibrillation, usually terminating within 3 seconds, occurred in 9% of shocks ≥ 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 ventricular apex (cathode) and coronary sinus (anode). We conclude that transvenous, intracardiac, R-wave-synchronous shocks ≤ 1.0 J safely terminate sustained ventricular tachycardia with CLs ≥ 200 msec in dogs.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine
- Physiology (medical)