QRS notch timing in idiopathic outflow tract premature ventricular complexes

The precise preprocedural localization of outflow tract premature ventricular contractions (OT-PVCs) remain essential yet challenging, owing to the region's complex and variable anatomy, particularly for left-sided origins. Although numerous electrocardiographic localization algorithms have been proposed, most are constrained by a trade-off between diagnostic accuracy and clinical practicality. QRS notching is a frequently observed but largely overlooked feature in OT-PVCs, and it remains understudied in the context of idiopathic ventricular arrhythmias. This study aims to move beyond a simple analysis of notch distribution across leads by leveraging QRS notching as a functional marker of ventricular activation to enhance site of origin localization.

This retrospective observational study included 105 patients who underwent successful catheter ablation for symptomatic OT-PVCs. The cohort consisted of 57 right ventricular outflow tract (RVOT) and 48 left ventricular outflow tract (LVOT) PVCs. All PVCs exhibited a left bundle branch block morphology with an inferior axis, defined by a dominant R-wave in the inferior leads and a QS complex in leads aVL and aVR. Furthermore, each PVC demonstrated a single, reproducible notch with a duration of ≤20 ms. Notch Timing (NT) was defined as the interval from the earliest onset of the global PVC QRS complex to the nadir of the identifiable notch. When notches were asynchronous across the 12 leads, the timing of the latest-occurring notch was recorded for analysis. The diagnostic performance of the NT criterion for differentiating RVOT from LVOT origins was evaluated and compared against the V2S/V3R index using receiver operating characteristic (ROC) curve analysis, with the area under the curve (AUC) serving as the primary metric of comparison.

Of 105 patients (45.6 ± 13.4 years, 55% male), 57 had RVOT and 48 had LVOT PVCs. NT robustly differentiated origins, with RVOT PVCs demonstrating significantly later notches than LVOT PVCs (94.3 ± 15.0 ms vs. 74.5 ± 15.6 ms, p < 0.001). An NT >80 ms favored an RVOT origin with 87.7% sensitivity and 68.8% specificity (PPV = 76,9%, NPV = 78,1%, AUC 0.838). The diagnostic performance of NT was comparable to the established V2S/V3R index (AUC 0.828). Characteristic lead distribution patterns augmented localization, though extensive notching across both the inferior and lateral precordial leads was not specific for a free-wall RVOT origin.

This study introduces the first structured framework for QRS notch analysis-defining its characteristics, timing, and distribution-to improve arrhythmia localization. This represents a shift from descriptive morphology to mechanistic interpretation, where a novel notch timing metric robustly discriminates RVOT from LVOT origins by quantifying delayed transeptal conduction.