The ECG may simply show sinus rhythm or sinus bradycardia. This is different than a first-degree atrioventricular, or AV, block, which shows a prolonged PR interval. Second-degree sinoatrial exit ...

is a form of third-degree heart block. This occurs when AV dissociation is present; however, intermittently some sinus node action potentials (P waves) are randomly conducted to the ventricles.