392. Features of PACs vs. PVCs July 6th, 2008 by reuben in arrhythmia ashman pac pvc Back Top Tags: card 391. What determines QRS width in 3rd degree AV block? / Congenital vs. acquired 3rd degree AV block / Most common cause of a pause on ECG 393. What does the ECG show for a PJC? Causes of PVCs and ventricular tachycardia / When does a PVC appear narrow? Leave a Reply Cancel reply Please post any discussion to the emupdates Reddit page.