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Second degree atrioventricular block: Mobitz type I (Wenckebach 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, either transient or permanent, from the atria to the ventricles due to an anatomic or functional impairment in the conduction system. The conduction can be delayed, intermittent, or absent. The commonly used terminology includes first degree AV block (slowed conduction without missed beats), second degree AV block (missed beats, often in a regular pattern, eg, 2:1, 3:2, or higher degrees of block), and third degree or complete AV block.

In second degree AV block, some atrial impulses fail to reach the ventricles. Wenckebach described progressive delay between atrial and ventricular contraction and the eventual failure of an atrial beat to reach the ventricles [1]. Mobitz subsequently divided second degree AV block into two subtypes, as determined by the findings on the electrocardiogram (ECG) [2]:

Mobitz type I AV block, in which progressive PR interval prolongation precedes a non-conducted P wave.

Mobitz type II AV block, in which the PR interval remains unchanged prior to a P wave that suddenly fails to conduct to the ventricles.

Advanced second degree AV block, in which two or more consecutive P waves are non-conducted. In contrast to third degree or complete heart block, however, some P waves continue to be conducted to the ventricle.


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Literature review current through: Oct 2015. | This topic last updated: Jul 2, 2014.
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  1. Wenckebach KF. Zur Analyse der unregelmässigen Pulses. Ztschr klin Med 1899; 36:181.
  2. Mobitz W. Über die unvollständige Störung der Erregungsüberleitung zwischen Vorhof und Kammer des menschlichen Herzens. Z Gesamte Exp Med 1924; 41:180.
  3. Peuch P, Groileau 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, Leiden, 1976. p.467.
  4. Friedman HS, Gomes JA, Haft JI. An analysis of Wenckebach periodicity. J Electrocardiol 1975; 8:307.
  5. Denes P, Levy L, Pick A, Rosen KM. The incidence of typical and atypical A-V Wenckebach periodicity. Am Heart J 1975; 89:26.
  6. JOHNSON RL, AVERILL KH, LAMB LE. Electrocardiographic findings in 67,375 asymptomatic subjects. VII. Atrioventricular block. Am J Cardiol 1960; 6:153.
  7. Brodsky M, Wu D, Denes P, et al. Arrhythmias documented by 24 hour continuous electrocardiographic monitoring in 50 male medical students without apparent heart disease. Am J Cardiol 1977; 39:390.
  8. Dickinson DF, Scott O. Ambulatory electrocardiographic monitoring in 100 healthy teenage boys. Br Heart J 1984; 51:179.
  9. Meytes I, Kaplinsky E, Yahini JH, et al. Wenckebach A-V block: a frequent feature following heavy physical training. Am Heart J 1975; 90:426.
  10. Viitasalo MT, Kala R, Eisalo A. Ambulatory electrocardiographic recording in endurance athletes. Br Heart J 1982; 47:213.
  11. Zeppilli P, Fenici R, Sassara M, et al. Wenckebach second-degree A-V block in top-ranking athletes: an old problem revisited. Am Heart J 1980; 100:281.
  12. Zehender M, Meinertz T, Keul J, Just H. ECG variants and cardiac arrhythmias in athletes: clinical relevance and prognostic importance. Am Heart J 1990; 119:1378.
  13. Young D, Eisenberg R, Fish B, Fisher JD. Wenckebach atrioventricular block (Mobitz type I) in children and adolescents. Am J Cardiol 1977; 40:393.
  14. Stein R, Medeiros CM, Rosito GA, et al. Intrinsic sinus and atrioventricular node electrophysiologic adaptations in endurance athletes. J Am Coll Cardiol 2002; 39:1033.
  15. Meimoun P, Zeghdi R, D'Attelis N, et al. Frequency, predictors, and consequences of atrioventricular block after mitral valve repair. Am J Cardiol 2002; 89:1062.
  16. Oliveira E, Ribeiro AL, Assis Silva F, et al. The Valsalva maneuver in Chagas disease patients without cardiopathy. Int J Cardiol 2002; 82:49.
  17. Josephson, ME. Atrioventricular Conduction. In: Clinical Cardiac Electrophysiology, 4th, Lippincott, Philadelphia 2008. p.93.
  18. 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.
  19. Vardas PE, Auricchio A, Blanc JJ, et al. Guidelines for cardiac pacing and cardiac resynchronization therapy. The Task Force for Cardiac Pacing and Cardiac Resynchronization Therapy of the European Society of Cardiology. Developed in collaboration with the European Heart Rhythm Association. Europace 2007; 9:959.
  20. Shaw DB, Gowers JI, Kekwick CA, et al. Is Mobitz type I atrioventricular block benign in adults? Heart 2004; 90:169.
  21. Coumbe AG, Naksuk N, Newell MC, et al. Long-term follow-up of older patients with Mobitz type I second degree atrioventricular block. Heart 2013; 99:334.