Effect of limb lead electrodes location on ECG and localization of idiopathic outflow tract tachycardia: a prospective study

Role of ECG in Localization of OT‐VT. Background: Different kinds of the surface ECG limb electrode positions may affect the limb lead vector and therefore the accuracy of the 12‐lead ECG in localization of outflow tract ventricular tachycardia (OTVT). This study was intended to evaluate and compare the accuracy of the standard and the modified 12‐lead ECG for localization of OTVT using the current published criteria. Methods and Results: Twenty consecutive patients (10 men, mean age, 51.6 ± 13.4 years) with OT‐VT were included. A standard ECG with the distal placement of the limb lead electrodes and a modified ECG with the limb electrodes placed on the torso were recorded during the OT‐VT and were used for localization by 2 electrophysiologists who were blinded to the successful ablation site to compare the accuracy of the 2 ECGs. The R wave amplitude during OT‐VT in lead I of the standard 12‐lead ECG was significantly higher compared to the modified surface ECG (0.225 ± 0.145 mV vs 0.139 ± 0.111 mV, P = 0.032). The S wave in aVR during OT‐VT was significantly more negative compared to the modified surface ECG (?0.682 ± 0.182 mV vs ?0.527 ± 0.228 mV, P = 0.017). The rate of accurate localization of the successful ablation sites in the anterior versus posterior outflow tract by the 2 observers using standard ECG (70% and 80%) were higher compared to modified ECG (50% and 60%, P = 0.042). Conclusion: The R wave amplitude in lead I and the depth of the S wave amplitude in lead aVR of the standard surface ECG during OT‐VT is significantly larger compared to the modified surface ECG. As the QRS morphology of the OT‐VT is usually the first clue to the possible site of successful ablation, the standard 12‐lead ECG should be used for more accurate localization of the origin of the OT‐VT. (J Cardiovasc Electrophysiol, Vol. 22, pp. 886‐891, August 2011)