Interventricular septum angle obtained from cardiac computed tomography for origin differentiation of outflow tract ventricular arrhythmia between left and right

Aims Our objective was to explore whether the accuracy of the transitional zone index (TZI) for outflow tract ventricular arrhythmias (OT-VAs) origin is affected by cardiac rotation and the additive value of interventricular septum angle (IVSa) obtained from coronary computed tomography angiography (CCTA). Methods Standard 12-lead ECGs of OT-VAs with inferior axis in consecutive patients undergoing both CCTA examination and successful ablation were retrospectively analyzed. The IVSa was defined as an angle between the long axis of IVS and sagittal axis of the body from CCTA. Results 64 patients (31 men; mean age 54.2 +/- 11.6 years) were enrolled. The OT-VAs exhibited right ventricular outflow tract origin in 46 (71.9%) patients and 36 (78.3%) were diagnosed correctly by TZI. The left ventricular outflow tract origin OT-VAs was observed in 18 (28.1%) patients and 16 (88.9%) were diagnosed correctly by TZI. The patients were then divided into TZI correct group (n = 52) and TZI incorrect group (n = 12). In the TZI incorrect group, 11/12 (91.7%) cases were R/S transition in lead V3 with the TZ score during premature ventricular contractions [2.8(2.5-3.4)], and the TZI between -1.5 and 0. The IVSa was significantly larger in the TZI incorrect group than correct group (52.0 +/- 6.9 degrees vs. 39.0 +/- 6.1 degrees; p < .0001). The IVSa >= 46 degrees predicted TZI incorrect with 92% sensitivity, 94% specificity, and 94% accuracy. Conclusion The IVSa is a novel cardiac rotation index that reliably improves TZI to differentiate the OT-VAs origin, especially for the OT-VAs with lead V3 R/S transition.