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Third degree (complete) atrioventricular block

William H Sauer, MD
Section Editor
Leonard I Ganz, MD, FHRS, FACC
Deputy Editor
Brian C Downey, MD, FACC


Atrioventricular (AV) block is defined as a delay or interruption in the transmission of an impulse from the atria to the ventricles due to an anatomical or functional impairment in the conduction system. The conduction disturbance can be transient or permanent. The conduction can be delayed, intermittent, or absent. The commonly used terminology includes first degree (slowed conduction without missed beats), second degree (missed beats, often in a regular pattern, eg, 2:1, 3:2, or higher degrees of block), and third degree or complete AV block. (See "ECG tutorial: Atrioventricular block".)

The clinical manifestations and management of third degree AV block will be discussed here. Congenital complete heart block, the etiology of AV block in general, and the management of other specific types of AV block are discussed separately. (See "Etiology of atrioventricular block" and "Congenital third degree (complete) atrioventricular block" and "First degree atrioventricular block" and "Second degree atrioventricular block: Mobitz type I (Wenckebach block)" and "Second degree atrioventricular block: Mobitz type II".)


No atrial impulses reach the ventricle in third degree or complete heart block (waveform 1). The block can exist in the AV node or in the infranodal specialized conduction system [1-3]. A His-bundle electrocardiographic study can determine the site of block quite accurately, but the escape rhythm provides important clues.

Escape rhythms — Escape rhythms occur when a pacemaker other than the sinus node has sufficient time to depolarize, attain threshold, and produce a depolarization. In complete heart block, the escape rhythm that controls the ventricles can occur at any level below that of the conduction block and the morphology of the QRS complex can help to determine the location at which this is occurring.

If third degree AV block occurs within the AV node, about two-thirds of the escape rhythms have a narrow QRS complex, ie, a junctional or AV nodal rhythm (waveform 2) [4-6].


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Literature review current through: Jun 2015. | This topic last updated: Aug 7, 2014.
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  1. Narula OS, Javier RP, Samet P, Maramba LC. Significance of His and left bundle recordings from the left heart in man. Circulation 1970; 42:385.
  2. Narula OS, Scherlag BJ, Javier RP, et al. Analysis of the A-V conduction defect in complete heart block utilizing His bundle electrograms. Circulation 1970; 41:437.
  3. Guimond C, Puech P. Intra-His bundle blocks (102 cases). Eur J Cardiol 1976; 4:481.
  4. Peuch P, Grolleau R, Guimond C. Incidence of different types of A-V block and their localization by His bundle recordings. In: The Conduction System of the Heart, Wellens HJJ, Lie KI, Janse MJ (Eds), Stenfert Kroese, Leiden 1976. p.467.
  5. Narula OS. Current concepts of atrioventricular block. In: His Bundle Electrocardiography and Clinical Electrophysiology, Narula OS (Ed), Davis, Philadelphia 1975. p.139.
  6. Rosen KM, Dhingra RC, Loeb HS, Rahimtoola SH. Chronic heart block in adults. Clinical and electrophysiological observations. Arch Intern Med 1973; 131:663.
  7. Schweitzer P, Mark H. The effect of atropine on cardiac arrhythmias and conduction. Part 1. Am Heart J 1980; 100:119.
  8. Schweitzer P, Mark H. The effect of atropine on cardiac arrhythmias and conduction. Part 2. Am Heart J 1980; 100:255.
  9. Narula OS, Scherlag BJ, Samet P, Javier RP. Atrioventricular block. Localization and classification by His bundle recordings. Am J Med 1971; 50:146.
  10. Lie KI, Wellens HJ, Schuilenburg RM, Durrer D. Mechanism and significance of widened QRS complexes during complete atrioventricular block in acute inferior myocardial infarction. Am J Cardiol 1974; 33:833.
  11. Bär, FW, Den Dulk, K, Wellens, HJJ. Atrioventricular dissociation. In: Comprehensive Electrocardiology: Theory and Practice in Health and Disease, MacFarlane, PW, Lawrie, TDV (Eds), Pergamon Press, New York, 1989, p. 933.
  12. Josephson, ME. Clinical Cardiac Electrophysiology: Techniques and Interpretations. 2nd ed., Lea & Febiger, Philadelphia, 1993.
  13. Wellens HJ, Brugada P, Bär FW. The role of intraventricular conduction disorders in precipitating sudden death. Ann N Y Acad Sci 1982; 382:136.
  14. Ezri M, Lerman BB, Marchlinski FE, et al. Electrophysiologic evaluation of syncope in patients with bifascicular block. Am Heart J 1983; 106:693.
  15. Zipes DP, DiMarco JP, Gillette PC, et al. Guidelines for clinical intracardiac electrophysiological and catheter ablation procedures. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Clinical Intracardiac Electrophysiologic and Catheter Ablation Procedures), developed in collaboration with the North American Society of Pacing and Electrophysiology. J Am Coll Cardiol 1995; 26:555.
  16. Epstein AE, DiMarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices): developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons. Circulation 2008; 117:e350.