Postextrastimulus delay of ventricular tachycardia return cycle: Indicator of a good ablation site

A 67-year-old man was referred for catheter ablation of incessant ventricular tachycardia (VT). He had suffered a myocardial infarction 10 years earlier. VT had occurred 2 years ago, prompting insertion of an implantable cardioverter-defibrillator (ICD). He began having palpitations followed by shocks. ICD interrogation showed VT episodes [cycle length (CL) 450 ms] terminated by a single shock each after failed antitachycardia pacing attempts. Intravenous amiodarone was administered. Episodes became more frequent and then became incessant but slower (CL 590 ms). VT ablation was attempted after retrograde aortic access to the left ventricle. Based on the ECG morphology of VT, the inferobasal free wall was mapped. An electrogram in this region showed early and late diastolic components (Abl_d, Figure 1). Burst pacing at this site resulted in entrainment with concealed fusion with a stimulus-to-QRS interval equal to the electrogram-to-QRS interval and a postpacing interval equal to VT CL. Single extrastimuli were delivered from this site to ascertain if termination would occur. At relatively long coupling intervals, resetting occurred with a stimulated QRS identical to VT. At short coupling intervals, the extrastimulus (S) caused delay of the next VT complex (again with identical QRS; asterisk in Figure 1). Intervals in the figure correspond to R-R intervals in the right ventricular (RV) recording. Based on these findings, radiofrequency energy was delivered at this site. VT terminated after 4 seconds and sinus rhythm resumed. VT could not be reinitiated thereafter. At 6-month follow-up, the patient was free of palpitations, and ICD interrogation showed no episodes.