Identifying sites for catheter ablation of ventricular tachycardia
Stevenson, W.G.; Sager, P.; Nademanee, K.; Hassan, H.; Middlekauff, H.R.; Saxon, L.A.; Wiener, I.
Herz 17(3): 158-170
1992
ISSN/ISBN: 0340-9937 PMID: 1639335 Document Number: 397124
The approach to localizing sites for catheter ablation of ventricular tachycardia foci depends on the type of tachycardia. In large reentry circuits such as those arising from infarct scars, areas of slow conduction in and around the scar should be targeted. During sinus rhythm, these can be suspected from the presence of fractionated electrograms and, at some sites, long stimulus to QRS delays during pacing. Slow conduction areas can be classified as: central slow conduction zone sites, exists from the slow conduction zone, entrances to the slow conduction zone, and bystander areas which are not involved in the tachycardia circuit. In the central slow conduction zone stimulation entrains or resets tachycardia with a long stimulus to QRS (S-QRS) delay (40 to > 300 ms) without altering the QRS morphology (entrainment with concealed fusion). At slow conduction zone exists, presystolic electrograms are recorded during VT, the pace-man matches the VT OQS morphology, and with pacing during VT the S-QRS interval is relatively short and VY may or may not be entrained. At entrances to the slow conduction zone electrogram timing is variable but early diastolic electrograms are expected and the pace-map QRS may differ from the VT QRS morphology. Relatively late stimuli or slow trains of stimuli entrain VT with concealed fusion with a relatively longer S-QRS interval than observed in the central slow conduction zone. Early stimuli may entrain VT while altering the QRS morphology due to propagation of the stimulated antidromic wavefront out of the scar from a site other than the tachycardia exit. At bystander sites electrogram timing, pace-mapping, and the effects of programmed stimulation are variable but may occasionally mimic reentry circuit sites. Relatively late stimuli are likely to capture the site without altering the VT. If discrete electrograms are present, analysis of these during pacing may provide further evidence that the site is not in the reentry circuit. Catheter ablation will probably be most effective at central slow conduction zone sites. When VT originates from a small focus surrounded by normal myocardium, such as is likely for idiopathic RV outflow tract and some idiopathic left ventricular tachycardias, presystolic electrical activity and pace-mapping are likely to identify the tachycardia focus. For macrororeentry involving the bundle branches, the right bundle branch can be easily targeted.