BackgroundVentricular arrhythmias (VA) arising from arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) and idiopathic right ventricular outflow tract ventricular arrhythmias (RVOT‐VA) share the pattern of left bundle branch block (LBBB)/inferior axis. The existence of QRS notching showed a discriminating effect of the two conditions in recent research; however, there are little data regarding the difference in the distribution of QRS notching. The aim of this study was to compare the VA morphology between the two conditions, especially evaluating the diagnostic role of QRS notching.MethodsElectrocardiographic (ECG) recordings of VA episode with LBBB/inferior axis of 16 ARVD/C and 45 idiopathic RVOT‐VA patients (30 originated from the septum, 15 from the free‐wall) were gathered and compared.ResultsARVD/C had longer mean QRS duration in all 12 leads, and significant differences existed in leads Ⅰ,Ⅱ,Ⅲ, aVL, aVF, and V1 (P < 0.05). Lead Ⅰ had the largest mean difference of 25.1 ± 5.8 ms. In addition, ARVD/C had more R‐wave transition in lead V5 or later (37.5% vs 8.9%, P < 0.01).The presence of QRS notching (15/16 [93.8%] vs 36/45 [80.0%], P = 0.20) and the total number of leads expressing notching (2.88 ± 2.0 vs 2.80 ± 2.0, P = 0.90) were not different between ARVD/C and idiopathic RVOT‐VA. However, QRS notching existing simultaneously in leads I and aVL was more common in ARVD/C (43.8% vs13.3%, P = 0.011).ConclusionLonger QRS duration, later precordial R/S transition, and QRS notching in lateral leads (leads Ⅰ and aVL) are useful in discriminating ARVD/C from idiopathic RVOT‐VA.