Examples of positive and negative ΔQRS in different native QRS categories and illustration of the global QRS measurement method with electrophysiological system. (A) LBBB QRS narrows from 186 to 142 ms, (B) LBBB QRS widens from 170 to 220 ms, (C) RBBB QRS of 196 ms narrows to 166 ms, (D) IVCD QRS of 136 ms widens to 204 ms. QRS duration measurements were done with paper speed of 100 mm/s, amplitude augmentation of 16 times, and digital callipers on Bard/Boston Scientific electrophysiology LAB system. Please note that measuring QRS duration in a single lead might have resulted in QRS duration underestimation as QRS is initially isoelectric in several leads (circles); at the same time, QRS end is difficult to ascertain in many leads (circles). Global QRS measurement method with simultaneous recording of 12 leads and digital callipers overcomes these difficulties. IVCD, intraventricular conduction delay; LBBB, left bundle branch block; NIVCD, non-specific intraventricular conduction delay; RBBB, right bundle branch block; ΔQRS (−), no QRS shortening; ΔQRS (+), QRS shortening.