Notch Timing (NT): A novel criterion to predict the site of origin in Outflow Tract PVCs
A Jaouadi, O Ekrem Turan, Y Yilancioglu, E Evren OzcanAbstract
Background
The Outflow Tracts (OT) represent a critical site of arrhythmogenesis for idiopathic premature ventricular contractions (PVCs). Accurately predicting the PVC's site of origin (SOO) for ablation is hindered by the region's intricate and highly variable anatomy. This has led to the development of numerous ECG algorithms, which, unfortunately, are plagued by a trade-off between diagnostic accuracy and clinical practicality.
Objective and hypothesis
The notching phenomenon in PVCs remains understudied, with current assessment largely confined to its topographic location on the 12-lead ECG. To enhance its predictive value for localizing the SOO in OT arrhythmias, this study introduces and systematically evaluates Notch Timing (NT)—a novel, quantitative ECG marker designed to differentiate between right ventricular outflow tract (RVOT) and left ventricular outflow tract (LVOT) origins. We hypothesize that due to fundamental anatomical differences, including myocyte fiber arrangement and a greater distance from the interventricular septum, PVCs originating from the RVOT will demonstrate a longer NT than those from the LVOT. The performance of this parameter will be rigorously compared against established ECG criteria.
Methods
This is a retrospective study that includes 95 patients who underwent a successful ablation of outflow tract PVCs (57 RVOT PVCs and 38 LVOT PVCs). All PVCs exhibited a left bundle branch block (LBBB) morphology with negative polarity in leads aVL and aVR, and featured a consistent < 20 millisecond notch in at least one lead. Notch Timing (NT) was defined as the interval from the earliest ventricular deflection on the surface ECG to the peak of the notch. To mitigate the influence of cardiac rotation, the latest-occurring notch across the 12 leads was analyzed when notches were asynchronous. The diagnostic performance of the NT criterion was compared against the V2S/V3R index using receiver operating characteristic (ROC) curve analysis and the area under the curve (AUC).
Results
The NT was significantly longer in RVOT PVCs compared to LVOT PVCs (94,33 milliseconds vs. 75,45 milliseconds, p <0.001). The AUC by an ROC analysis was 0,823. Using the Youden index, an optimal cutoff of 80 milliseconds predicts an RVOT origin with an 87,7% sensitivity and 65,8% specificity (PPV= 79,4% NPV= 78,1%). The performance of NT was comparable or superior to the V2S/V3R index, particularly in the subgroup of patients with precordial transition in lead V3 (n=76).
Conclusion
The novel Notch Timing (NT) criterion differentiates RVOT from LVOT origins as effectively as the established V2S/V3R index, while offering the unique benefits of robustness against cardiac rotation and precordial lead placement variability.Visual Abstract 1Visual Abstract 2