991-73 Ultrarapid Subthreshold Stimulation Delivered via Epicardial Patches can Terminate Reentrant Ventricular Tachycardia in a Canine Model

Although Ultrarapid subthreshold stimulation (USTS) delivered via endocardial electrodes to a critical site of a tachycardia circuit is able to terminate reentrant arrhythmias, it requires detailed electrophsyiologic mapping. We evaluated USTS given via epicardial patches to terminate ventricular tachycardia (VT).MethodsCanines underwent coronary artery ligation to produce apical infarction. 3–5 days after infarct, two defibrillator patches were sutured epicardially and pacing thresholds determined. VT was induced and USTS was applied at 90% threshold, with a train of 10 stimuli, cycle length 50ms, and pulse width 2ms. If there was no effect, increasing trains and pulse widths were used. Threshold was re-tested post-termination to insure subthreshold output. Six dogs survived and had 136 VTs induced.Results91/136 (67%) of induced VT episodes were terminated. 41 (30%) terminated after 1 delivery of USTS; 50 (37%) terminated after 2–17 sets of USTS; 22 (16%) were reset; 23 (17%) were unaffected. Of 91 terminations, there was a 66% probability of VT termination within the first three sets of USTS delivery.ConclusionsUSTS may be successfully applied via epicardial patches to terminate induced reentrant VT in the canine model, without the need for extensive mapping of the VT circuit