Novel electrocardiogram and electrophysiological findings for differentiating idiopathic left posterior papillary muscle and left posterior fascicular ventricular arrhythmias

Purpose: Differentiation between idiopathic left posterior fascicular ventricular arrhythmias (LPF-VAs) and posterior papillary muscle (PPM) VAs is of clinical value. This study aimed to develop an algorithm to distinguish PPM-VAs from LPF-VAs. Methods: This study enrolled 73 consecutive cases, including 31 with PPM-VAs and 42 with LPF-VAs, undergoing successful ablation by using 3D mapping and intracardiac echography to confirm the origin of the VAs. Electrocardiographic and electrophysiological parameters were compared between two groups. Results: The 12-lead electrocardiography of the PPM-VAs was characterized by a longer QRS duration than that in LPF-VAs (154.4 ± 14.5 vs. 132.3 ± 13.1 ms, P < 0.001). A QRS duration ≥133 ms was observed in all patients (100%) with PPM-VAs and 13/42 (31.0%) patients with LPF-VAs. The conduction duration from the earliest left ventricular activation site of the VA to the proximal right bundle branch (VA-RBB) was longer in patients with PPM-VAs than LPF-VAs (51.3 ± 12.2 vs. 23.6 ± 7.7 ms, P < 0.001). Based on the ROC analysis, a VA-RBB >36 ms was recognized in 28/31 patients with PPM-VAs (90.3%) and 2/42 with LPF-VAs (4.8%). An algorithm incorporating a QRS duration of ≥133 ms with a conduction duration of a VA-RBB of >36 ms could yield a sensitivity of 90.3% and specificity of 100% for discriminating PPM-VAs from LPF-VAs. Conclusions: The novel algorithm incorporating a QRS duration of ≥133 ms with a conduction duration of the VA-RBB of >36 ms could be useful in differentiating PPM-VAs from LPF-VAs.