Third Degree Atrioventricular Block

Third degree, or complete, heart block is characterized by atrioventricular dissociation – atrial impulses fail to conduct to the ventricles and, therefore, the atria and ventricles act independently of each other. Perfusion is maintained only by a junctional or ventricular escape rhythm from an ectopic focus. If the block is the result of a diseased atrioventricular node, a junctional focus escapes and produces a ventricular rate between 40 and 60 bpm. However, when infra-Hisian conduction disease exists (i.e. below the bundle of His), the escape focus is ventricular in origin, slower and less reliable. Complete heart block is life-threatening and it is typical for patients with this condition to experience severe bradycardia and hypotension. If no escape rhythm is present the patient will arrest due to cardiac standstill. An external pacemaker is the necessary treatment for complete heart block.



  1. Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhyth. Circulation. 2019;140(8):e382-e482.