Mayo Clinic Proceedings Home

Second-Degree Atrioventricular Block: A Reappraisal

      In this review, we discuss the various forms and causes of second-degree atrioventricular (AV) block and the reasons they remain poorly understood. Both type I and type II block characterize block of a single sinus P wave. Type I block describes visible, differing, and generally decremental AV conduction. Type II block describes what appears to be an all-or-none conduction without visible changes in the AV conduction time before and after the blocked impulse. Although the diagnosis of type II block is possible with an increasing sinus rate, absence of sinus slowing is an important criterion of type II block because a vagal surge (generally a benign condition) can cause simultaneous sinus slowing and AV nodal block, which can superficially resemble type II block. The diagnosis of type II block cannot be established if the first postblock P wave is followed by a shortened PR interval or is not discernible. A pattern resembling a narrow QRS type II block in association with an obvious type I structure in the same recording (eg, Holter) effectively rules out type II block because the coexistence of both types of narrow QRS block is exceedingly rare. Concealed His bundle or ventricular extrasystoles confined to the specialized conduction system without myocardial penetration and depolarization can produce electrocardiographic patterns that mimic type I and/or type II block (pseudo-AV block). All correctly defined type II blocks are infranodal. A narrow QRS type I block is almost always AV nodal, whereas a type I block with bundle branch block barring acute myocardial infarction is infranodal in 60% to 70% of cases. A 2:1 AV block cannot be classified in terms of type I or type II block, but it can be nodal or infranodal. Infranodal blocks require pacing regardless of form or symptoms. The widespread use of numerous disparate definitions of type II block appears primarily responsible for many of the problems surrounding second-degree AV block. Adherence to the correct definitions provides a logical and simple framework for clinical evaluation.


      ACC ( American College of Cardiology), AHA ( American Heart Association), AV ( atrioventricular), ECG ( electrocardiogram), WHO ( World Health Organization)
      To read this article in full you will need to make a payment


        • Barold SS
        • Barold HS
        Pitfalls in the characterization of second-degree AV block. HeartWeb [serial online]. April 1997. Article 97040001.
        (Accessed September 13, 2000.)
        • Gillespie ND
        • Brett CT
        • Morrison WG
        • Pringle SD
        Interpretation of the emergency electrocardiogram by junior hospital doctors.
        J Accid Emerg Med. 1996; 13: 395-397
        • Phibbs BP
        Advanced ECG: Boards and Beyond: What You Really Need to Know About Electrocardiography. Little, Brown and Co, Boston, Mass1997: 110-124
        • Hay J
        Bradycardia and cardiac arrhythmia produced by depression of certain of the functions of the heart.
        Lancet. 1906; 1: 139-143
        • Mobitz W
        Uber die unvollstandige storung der erregungsuberleitung zwischen vorhof und kammer des menschlichen herzems.
        Z Ges Exp Med. 1924; 41: 180-237
        • Katz LN
        • Pick A
        Clinical Electrocardiography. Lea & Febiger, Philadelphia, Pa1956
        • Langendorf R
        • Cohen H
        • Gozo Jr, EG
        Observations on second degree atrioventricular block, including new criteria for the differential diagnosis between type I and type II block.
        Am J Cardiol. 1972; 29: 111-119
        • Barold SS
        • Friedberg HD
        Second degree atrioventricular block: a matter of definition.
        Am J Cardiol. 1974; 33: 311-315
        • Chou T-C
        • Knilans TK
        Electrocardiography in Clinical Practice: Adult and Pediatric. 4th ed. WB Saunders Co, Philadelphia, Pa1996: 448-470
        • Chung EK
        Principles of Cardiac Arrhythmias. 4th ed. Williams & Wilkins, Baltimore, Md1989: 273-345
        • Albarran-Sotelo R
        • American Heart Association
        • et al.
        Textbook of Advanced Cardiac Life Support. 2nd ed. American Heart Association, Dallas, Tex1987: 45-87
        • Pick A
        • Langendorf R
        Interpretation of Complex Arrhythmias. Lea & Febiger, Philadelphia, Pa1979: 217-365
      1. Definition of terms related to cardiac rhythm.
        Am Heart J. 1978; 95: 796-806
        • Surawicz B
        • Uhley H
        • Borun R
        • et al.
        The quest for optimal electro-cardiography, task force I: standardization of terminology and interpretation.
        Am J Cardiol. 1978; 41: 130-145
        • Rardon DP
        • Miles WM
        • Zipes DP
        Atrioventricular block and dissociation.
        in: Zipes DP Jalife J Cardiac Electrophysiology: From Cell to Bedside. 3rd ed. WB Saunders Co, Philadelphia, Pa2000: 451-459
        • O'Keefe Jr, JH
        • Hammill SC
        • Zolnick MR
        • Steinhaus DM
        • Vatterott PJ
        Electrocardiography study guide: scoring criteria and definitions.
        in: Murphy JG Mayo Clinic Cardiology Review. Futura Publishing Co Inc, Armonk, NY1997: 427-445
        • Lange HW
        • Ameisen O
        • Mack R
        • Moses JW
        • Kligfield P
        Prevalence and clinical correlates of non-Wenckebach narrow-complex second-degree atrioventricular block detected by ambulatory ECG.
        Am Heart J. 1988; 115: 114-120
        • Wolbrette DL
        • Naccarelli GV
        Bradycardias: sinus nodal dysfunction and AV conduction disturbances.
        in: Topol EJ Comprehensive Cardiovascular Medicine. Vol 2. Lippincott-Raven, Philadelphia, Pa1998: 1803-1826
        • Barold SS
        Pacemaker treatment of bradycardias and selection of optimal pacing modes.
        Contemp Treat Cardiovasc Dis. 1997; 2: 123-164
        • Massie B
        • Scheinman MM
        • Peters R
        • Desai J
        • Hirschfeld D
        • O'Young J
        Clinical and electrophysiologic findings in patients with paroxysmal slowing of the sinus rate and apparent Mobitz type II atrioventricular block.
        Circulation. 1978; 58: 305-314
        • Motté G
        • Dinanian S
        • Sebag C
        Classification and pitfalls of atrioventricular blocks [in French].
        Arch Mal Coeur Vaiss. 1997; 90: 47-55
        • Zaman I
        • Moleiro F
        • Rozanski JJ
        • Pozen R
        • Myerburg RJ
        • Castellanos A
        Multiple electrophysiologic manifestations and clinical implications of vagally mediated AV block.
        Am Heart J. 1983; 106: 92-99
        • Rosen KM
        • Loeb HS
        • Gunnar RM
        • Rahimtoola SH
        Mobitz type II block without bundle-branch block.
        Circulation. 1971; 44: 1111-1119
        • Yeh BK
        • Tao P
        • DeGuzman N
        Mobitz type II A-V blocks as a manifestation of digitalis toxicity.
        J Electrocardiol. 1972; 5: 74-77
        • Kastor JA
        Atrioventricular block.
        in: Kastor JA Arrhythmias. WB Saunders Co, Philadelphia, Pa1994: 145-200
        • Josephson ME
        • Zimetbaum P
        • Marchlinski FE
        • Buxton AE
        The bradyarrhythmias: disorders of sinus node function and AV conduction disturbances.
        in: Fauci AS Braunwald E Isselbacher KJ 14th ed. Harrison's Principles of Internal Medicine. Vol 1. McGraw-Hill, New York, NY1998: 1253-1261
        • Kusumoto FM
        • Goldschlager N
        Cardiac pacing.
        N Engl J Med. 1996; 334: 89-97
        • Bayés de Luna A
        Clinical Electrocardiography: A Textbook. 2nd ed. Futura Publishing Co Inc, Armonk, NY1998: 319-436
        • Kocovic DZ
        • Friedman PL
        Atrioventricular nodal block.
        in: Podrid PJ Kowey PR Cardiac Arrhythmia: Mechanisms, Diagnosis, and Management. Williams & Wilkins, Baltimore, Md1995: 1039-1050
        • Goldschlager N
        • Goldman MJ
        Principles of Clinical Electrocardiography. 13th ed. Appleton & Lange, Norwalk, Conn1989: 195-205
        • Grolleau R
        • Messner P
        • Leclercq F
        • Carabasse D
        Electrocardiography of atrioventricular block [in French].
        Arch Mal Coeur Vaiss. 1992; 85: 45-49
        • Akhtar M
        Cardiac arrhythmias with supraventricular origin.
        in: Goldman L Bennett JC Cecil Textbook of Medicine. 21st ed. WB Saunders Co, Philadelphia, Pa2000: 233-241
        • Bigger Jr, JT
        Cardiac arrhythmias.
        in: Bennett JC Plum F Cecil Textbook of Medicine. 20th ed. WB Saunders Co, Philadelphia, Pa1996: 231-253
        • Williams ES
        • Fisch C
        Cardiac arrhythmias.
        in: Stein JH Internal Medicine. 4th ed. Mosby, St Louis, Mo1994: 94-116
        • Lévy S
        • Mogensen L
        Diagnosis of bradycardias.
        in: Julian DG Camm AJ Fox KM Hall RJC Poole-Wilson PA Diseases of the Heart. 2nd ed. WB Saunders Co, London, England1996: 648-659
        • Sutton R
        • Bourgeois I
        The Foundations of Cardiac Pacing, Part I: An Illustrated Practical Guide to Basic Pacing. Futura Publishing Co Inc, Mount Kisco, NY1991: 15-43
        • Ellenbogen KA
        • Peters RW
        Indications for permanent and temporary cardiac pacing.
        in: Ellenbogen KA Cardiac Pacing. 2nd ed. Blackwell Science, Cambridge, Mass1996: 1-36
        • Goldberger AL
        Clinical Electrocardiography: A Simplified Approach. 6th ed. Mosby, St Louis, Mo1999: 178-187
        • El-Sherif N
        • Aranda J
        • Befeler B
        • Lazzara R
        Atypical Wenckebach periodicity simulating Mobitz II AV block.
        Br Heart J. 1978; 40: 1376-1383
        • Friedman HH
        Diagnostic Electrocardiography and Vectorcardiography. 3rd ed. McGraw-Hill, New York, NY1985: 403-618
        • Friedman HS
        • Gomes JAC
        • Haft JI
        An analysis of Wenckebach periodicity.
        J Electrocardiol. 1975; 8: 307-315
        • Denes P
        • Levy L
        • Pick A
        • Rosen KM
        The incidence of typical and atypical A-V Wenckebach periodicity.
        Am Heart J. 1975; 89: 26-31
        • Miles WM
        • Klein LS
        Sinus nodal dysfunction and atrioventricular conduction disturbances.
        in: Naccarelli GV Cardiac Arrhythmias: A Practical Approach. Futura Publishing Co Inc, Mount Kisco, NY1991: 243-282
        • Puech P
        • Grolleau R
        • Guimond C
        Incidence of different types of A-V block and their localization by His bundle recordings.
        in: Wellens HJJ Lie KI Janse MJ The Conduction System of the Heart: Structure, Function, and Clinical Implications. Lea & Febiger, Philadelphia, Pa1976: 467-484
        • Puech P
        • Grolleau R
        L'Activité du Faisceau de His Normale et Pathologique. Sandoz, Paris, France1972: 138-141
        • Puech P
        • Wainwright RJ
        Clinical electrophysiology of atrioventricular block.
        Cardiol Clin. 1983; 1: 209-224
        • Narula OS
        Cardiac Arrhythmias: Electrophysiology, Diagnosis, and Management. Williams & Wilkins, Baltimore, Md1979: 85-113
        • Narula OS
        Clinical concepts of spontaneous and induced atrioventricular block.
        in: Mandel WJ Cardiac Arrhythmias. 3rd ed. JB Lippincott, Philadelphia, Pa1995: 441-459
        • Ursell S
        • Habbab MA
        • El-Sherif N
        Atrioventricular and intraventricular conduction disorders: clinical aspects.
        in: El-Sherif N Samet P Cardiac Pacing and Electrophysiology. 3rd ed. WB Saunders Co, Philadelphia, Pa1991: 140-169
        • Gomes JA
        • El-Sherif N
        Atrioventricular block: mechanism, clinical presentation, and therapy.
        Med Clin North Am. 1984; 68: 955-967
        • Goodfriend MA
        • Barold SS
        Tachycardia-dependent and bradycardia-dependent Mobitz type II atrioventricular block within the bundle of His.
        Am J Cardiol. 1974; 33: 908-913
        • Artigou JY
        • Leclercq JF
        • Slama R
        Mobitz type II suprahisian atrioventricular block: block in the subnodal-suprahisian (NH) zone? [in French].
        Arch Mal Coeur Vaiss. 1984; 77: 283-291
        • Gregoratos G
        • Cheitlin MD
        • Conill A
        • et al.
        ACC/AHA guidelines for implantation of cardiac pacemakers and antiarrhythmia devices: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Pacemaker Implantation).
        J Am Coll Cardiol. 1998; 31: 1175-1209
        • Hayes DL
        • Barold SS
        • Camm AJ
        • Goldschlager NF
        Evolving indications for permanent cardiac pacing: an appraisal of the 1998 American College of Cardiology/American Heart Association Guidelines.
        Am J Cardiol. 1998; 82 (A6): 1082-1086
        • El-Sherif N
        • Scherlag BJ
        • Lazzara R
        Pathophysiology of second degree atrioventricular block: a unified hypothesis.
        Am J Cardiol. 1975; 35: 421-434
        • Wharton JM
        • Ellenbogen KA
        Atrioventricular conduction system disease.
        in: Ellenbogen KA Kay GN Wilkoff BL Clinical Cardiac Pacing. WB Saunders Co, Philadelphia, Pa1995: 304-320
        • Barold SS
        • Falkoff MD
        • Ong LS
        • Vaughan MJ
        • Heinle RA
        Atrioventricular block.
        in: Barold SS Mugica J New Perspectives in Cardiac Pacing 2. Futura Publishing Co Inc, Mount Kisco, NY1991: 23-52
        • Sumiyoshi M
        • Nakata Y
        • Yasuda M
        • et al.
        Clinical and electro-physiologic features of exercise-induced atrioventricular block.
        Am Heart J. 1996; 132: 1277-1281
        • Halpern MS
        • Nau GJ
        • Chiale PA
        • et al.
        Mechanism of Mobitz II periodicities.
        in: Rosenbaum MB Elizari MV Frontiers of Cardiac Electrophysiology. Martinus Nijhoff, Boston, Mass1983: 465-487
        • Marriott HJL
        Practical Electrocardiography. 8th ed. Williams & Wilkins, Baltimore, Md1988: 382-399
        • Marriott HJL
        Rhythm Quizlets: Self Assessment. 2nd ed. Williams & Wilkins, Baltimore, Md1996
        • Marriott HJL
        Emergency Electrocardiography. Trinity Press, Naples, Fla1997: 94-100
        • Marriott HJL
        • Myerburg RJ
        Recognition of cardiac arrhythmias and conduction disturbances.
        in: Hurst JW Schlant RC Rackley CE Sonnenblick EH Wenger NK The Heart, Arteries and Veins. 7th ed. McGraw-Hill, New York, NY1990: 483-534
        • Marriott HJL
        • Conover MB
        Advanced Concepts in Arrhythmias. 3rd ed. Mosby, St Louis, Mo1998: 311-328
        • Waugh RA
        • Rotman M
        Bradycardias due to failure of atrioventricular conduction.
        in: Waugh RA Wagner GS Ramo BW Gilbert M Cardiac Arrhythmias: A Practical Guide for the Clinician. 2nd ed. FA Davis Co, Philadelphia, Pa1994: 320-343
        • Mudge Jr, GH
        Manual of Electrocardiography. Little, Brown and Co, Boston, Mass1981: 85-109
        • Wagner GS
        Marriott's Practical Electrocardiography. 9th ed. Williams & Wilkins, Baltimore, Md1994: 379-395
        • 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: 555-573
      2. Guidelines for clinical intracardiac electrophysiologic studies: a report of the American College of Cardiology/American Heart Association Task Force on assessment of diagnostic and therapeutic cardiovascular procedures (Subcommittee to Assess Clinical Intracardiac Electrophysiologic Studies).
        J Am Coll Cardiol. 1989; 14: 1827-1842
        • Vlay SC
        A Practical Approach to Cardiac Arrhythmias. 2nd ed. Little, Brown and Co, Boston, Mass1996: 84-128
        • Barold SS
        • Zipes DP
        Cardiac pacemakers and antiarrhythmic devices.
        in: Braunwald E 5th ed. Heart Disease: A Textbook of Cardiovascular Medicine. Vol 1. WB Saunders Co, Philadelphia, Pa1997: 705-741
        • Barold SS
        Narrow QRS Mobitz type II second-degree atrioventricular block in acute myocardial infarction: true or false?.
        Am J Cardiol. 1991; 67: 1291-1294
        • Barold SS
        • Barold HS
        Infranodal AV block in acute inferior myocardial infarction. HeartWeb [serial online]. April 1997. Article 97040002.
        (Accessed September 14, 2000.)
        • Scheinman MM
        • Gonzalez RP
        Fascicular block and acute myocardial infarction.
        JAMA. 1980; 244: 2646-2649
        • Sclarovsky S
        • Strasberg B
        • Hirshberg A
        • Arditi A
        • Lewin RF
        • Agmon J
        Advanced early and late atrioventricular block in acute inferior wall myocardial infarction.
        Am Heart J. 1984; 108: 19-24
        • Behar S
        • Zissman E
        • Zion M
        • SPRINT Study Group
        • et al.
        Prognostic significance of second-degree atrioventricular block in inferior wall acute myocardial infarction.
        Am J Cardiol. 1993; 72: 831-834
        • Zipes DP
        Second-degree atrioventricular block.
        Circulation. 1979; 60: 465-472
        • Barold SS
        • Barold HS
        Internet diagnosis of second-degree AV block: a cybercase report. HeartWeb [serial online]. March 2000. Article 00010001.
        (Accessed September 14, 2000.)
        • Baron SB
        • Huang SK
        Cough syncope presenting as Mobitz type II atrioventricular block-an electrophysiologic correlation.
        Pacing Clin Electrophysiol. 1987; 10: 65-69
        • Nakagawa S
        • Koiwaya Y
        • Tanaka K
        Vagally mediated paroxysmal atrioventricular block presenting as “Mobitz type II” block [letter].
        Pacing Clin Electrophysiol. 1988; 11: 471-474
        • Barold SS
        Cardiac pacing in special and complex situations: indications and modes of stimulation.
        Cardiol Clin. 1992; 10: 573-591
        • Barold SS
        • Jais P
        • Shah DC
        • Takahashi A
        • Haissaguerre M
        • Clementy J
        Exercise-induced second-degree AV block: is it type I or type II?.
        J Cardiovasc Electrophysiol. 1997; 8: 1084-1086
        • Damato AN
        • Varghese PJ
        • Caracta AR
        • Akhtar M
        • Lau SH
        Functional 2:1 A-V block within the His-Purkinje system: simulation of type II second-degree A-V block.
        Circulation. 1973; 47: 534-542
        • Langendorf R
        • Mehlman JS
        Blocked (nonconducted) A-V nodal premature systoles imitating first and second degree A-V block.
        Am Heart J. 1947; 34: 500-506
        • Rosen KM
        • Rahimtoola SH
        • Gunnar RM
        Pseudo A-V block secondary to premature nonpropagated His bundle depolarizations: documentation by His bundle electrocardiography.
        Circulation. 1970; 42: 367-373