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

oftheleft anterior descending coronaryartery. Programmed electrical stimulation 3-8dayslater in14of24surviving dogsinduced 627 episodes ofsustained ventricular tachycardia thathad35morphologically distinct contours. Truncated exponential shocks, timedfromthebipolar R wave recorded intheright ventricular apex,weredelivered between theright ventricular apex(cathode) andsuperior venacava(anode). Shocks of0.008-1.0 J(median 0.5J)reproducibly terminated 25of30(83%)sustained ventricular tachycardias thathada cycle length (CL)- 200msec.Oneoffive sustained ventricular tachycardias withCLs 200msec,only12of748(1.6%) shocks of0.008-1.0 J applied within thefirst 80%oftheQRSproduced repetitive ventricular responses,andnoneaccelerated the ventricular tachycardia orproduced ventricular fibrillation. Shocks ¢0.008 JintheTwave (nine of85)or 3 0.5JintheQRSofventricular tachycardias withCLs 200msec indogs. PERMANENTpatient-activate d orautomatic ventricularpacemakers delivering single stimuli' 2 or rapid bursts2'7 havebeenusedsuccessfully totreatdrugresistant recurrent sustained ventricular tachycardia. However, single ventricular stimuli often fail toterminateventricular tachycardia (primarily intachycardias faster than170beats/min),3 Sl"l andburst ventricular pacing may result inacceleration ofventricular tachycardia orventricular fibrillation inasmany as43%of patients.3 6.7.9,11 Based on thesafety andsuccessofsynchronized transthoracic direct-current cardioversion'2- andthe feasibility ofadministering intracardiac shocks, 16-25 we reasoned that ventricular tachycardia mightbesafely andeffectively terminated bysynchronized shocks of verylowenergydelivered through intracardiac electrodes. Thepurposeofthis study was totestthis hypothesis using a canine modelinwhichprogrammed electrical stimulation induced sustained ventricular tachycardia 3-8daysafter coronaryocclusion-reperfusion.26 Weused aspecially designed catheter electrode because ifthetechnique werefeasible, implantation by a transvenous routewouldhaveobvious advantages.