Ablation of Idiopathic Ventricular Tachycardia in Two Separate Regions of the Outflow Tract: Prevalence and Electrocardiographic Characteristics

Few studies have clarified the prevalence and characteristics of idiopathic outflow tachycardia (OT‐VT) with an altered QRS morphology after radiofrequency catheter ablation (RFCA), requiring additional RFCA applications at a different portion of the outflow tract (OT) to abolish the OT‐VT. Among 344 patients (97 VTs and 247 premature ventricular contractions), 12 (3.5%; VTs‐7, PVCs‐5; 6 women) had dynamic QRS morphology changes following the RFCA, requiring additional RFCA applications at a different portion to abolish the OT‐VT. In 8 of 12 patients (67%), this phenomenon occurred following RFCA at right (RVOT; n=7) or left ventricular (LVOT; n=1) endocardial sites of the OT: The second OT‐VT was consistently associated with an increase in the R‐wave amplitude in the inferior leads, and in five it was finally abolished by RFCA at the left sinus of Valsalva (LSV). Conversely, in four patients (33%), the second OT‐VT appeared after RFCA at the LSV: two required additional RFCA applications at the LVOT to abolish the second OT‐VT, and one at the RVOT, and all were associated with a decrease in the R‐wave amplitude in the inferior leads. This kind of dynamic QRS morphology change was often observed when RFCA was applied to either the first or second OT‐VT at a right or left ventricular endocardial site, with the other site being the LSV. A detailed continuous observation of the QRS morphology, especially of the R‐wave in the inferior leads, is important for identifying changes in the QRS morphology during RFCA.