Radiofrequency Ablation Of Idiopathic Left Ventricular Tachycardia With Significant Changing Of Surface ECG Morphology

Objective:To study electrophysiological mechanism of the changing of surface ECG morphology from superior to inferior axis deviation or from inferior to superior axis deviation during ablation of idiopathic left ventricular tachycardia (ILVT).Methods:Between March 2000 and September 2009, a total of 122 consecutive patients with verapamil-sensitive idiopathic left ventricular tachycardia underwent electrophysiologic study and radiofrequency catheter ablation at General Hospital of Shenyang Military Region. Radiofrequency current was delivered at the site with the earliest Purkinje potential (PP) or the late diastolic potential (DP) during VT. Eleven (mean age 35.5±15.7 years) of 122 patients have significant change of surface ECG morphology during ablation (radiofrequency current was applied during VT) or after ablation (radiofrequency current was applied during sinus rhythm). Analyses of the electrophysiological mechanism through mapping the earliest PP, DP and His bundle potential (H), measuring the extent of frontal plane QRS axis changing during VT or in sinus rhythm, and comparing the cycle length change of VT before and after the changing of cardiac axis.Results:The PP was recorded in all 11 patients, the DP in 2 of 11 patients, the H in 6 of 11 patients. The PP-V intervals were 14-40 (24.8±8.7) ms and 24-52 (32.8±10.0) ms before and after the changing of cardiac axis. DP-V intervals were 61,60 ms and 70,71ms seprately before and after the changing of cardiac axis in 2 patients. However the PP-H intervals had no changes [15-33(24.0±6.8)ms VS 17-32(24.2±6.0)ms]. In 4 of the 11 patients, a phenomenon was observed that the cardiac axis changed from superior to inferior axis deviation gradually with the PP-V interval longer and longer. In 3 of 11 patients cardiac axis changes were observed from superior to inferior axis deviation without the PP-V interval change. The frontal plane QRS axis changes during sinus rhythm before and after VT cardiac axis change were also observed. The cardiac axis changes were significant in 5 patients, slight in 4 patients and middle (between the "significant" and the "light") in 2 patients. In all the 11 patients the finally successful ablation sites were close to previous sites of ablation. But these successful ablation sites were more proximal than those before the cardiac axis change of VT. The patients had been followed up for 11-113 months without antiarrhythmic drugs. VT recurred in 2 patients. The recurred VTs were the same as the VTs in the previous precedures which were eliminated at the second precedure without recurrence. All the 11 patients had no complications.Conclusion:Ablation of ILVT had a high success rate by targeting the earliest Purkinje potential (PP) or the diastolic potential (DP) during VT. The occurrence of obvious change of frontal plane QRS axis during VT was not rare, accounting for about nine precent of patients underwnet ablation of ILVT. The most likely electrophysiological mechanism was that the damage of radiofrequency energy led to conduction delay or block of the left posterior fascicle, so the activation could not transmit through the left posterior fascicle but through the left anterior fascicle. So the ECG morphology of ILVT changed from superior to inferior axis deviation, and vice versa.