variety of subjects by searching on "patient info" and the keyword(s) of interest.) Basics topics (see "Patient education: Bradycardia (The Basics)" and "Patient education: Heart block in adults (The Basics)") SUMMARY AND RECOMMENDATIONS Definitions 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 anatomic or functional impairment in the conduction system. In second-degree AV block, some atrial impulses fail to reach the ventricles. In Mobitz type I second-degree AV block ( waveform 1), there is progressive PR interval prolongation for several beats preceding a nonconducted P wave, whereas in Mobitz type II second-degree AV block ( waveform 2), the PR interval remains unchanged prior to a P wave that suddenly fails to conduct to the ventricles. (See 'Introduction' above and 'Definitions' above.) Etiology Mobitz type I second-degree AV block can occur in normal subjects and athletes without underlying cardiac pathology. The potential etiologies of Mobitz type I second- degree AV block also include reversible (both pathologic and iatrogenic) and idiopathic causes that are similar to other degrees of AV block ( table 1). Common potentially https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 12/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate reversible causes include certain medications, myocardial ischemia, myocarditis, and cardiomyopathies. (See 'Etiology' above.) Clinical history All patients with suspected Mobitz type I second-degree AV block should be questioned about any history of heart disease, both congenital and acquired, as well as any recent cardiac procedures or medications that could predispose to AV conduction abnormalities. (See 'Clinical history' above.) Clinical presentation Most patients with Mobitz type I second-degree AV block are asymptomatic. Mobitz type I second-degree AV block that occurs in the setting of acute myocardial ischemia or myocarditis may result in clinical deterioration if the resulting ventricular rate is inadequate to maintain cardiac output. Additionally, even in otherwise healthy patients, if the sinus rate is slow and there are fewer conducted beats (2:1 or 3:2 block), there may be a significant reduction in cardiac output resulting in symptoms of hypoperfusion (including fatigue, lightheadedness, syncope, presyncope, or angina) or heart failure. (See 'Signs and symptoms' above.) ECG findings and diagnostic maneuvers Mobitz type I second-degree AV block is identified by progressive prolongation of the PR interval for several heart beats, followed by a nonconducted P wave ( waveform 1). If 2:1 AV block is seen on the surface ECG, certain ECG features (eg, PR interval >300 ms, narrow QRS complexes, etc) may aid in differentiating Mobitz type I from Mobitz type II second-degree AV block. Additionally, because of the varying effects of vagal tone on sinus node, AV node, and His-Purkinje system properties, vagal maneuvers can identify the site of a conduction abnormality in patients with second-degree AV block. (See 'ECG findings and diagnostic maneuvers' above and 'Diagnosis' above.) Initial management The initial management of patients with Mobitz type I second- degree AV block ( algorithm 1) depends on the presence or absence of symptoms and the hemodynamic status of the patient. (See 'Initial management' above.) Symptomatic patients Hemodynamically unstable Patients who are symptomatic and hemodynamically unstable should be urgently treated with atropine (0.5 mg intravenously, which may be repeated every three to five minutes to a total dose of 3 mg) and temporary cardiac pacing if not responsive to atropine (either with transcutaneous or, if immediately available, transvenous pacing). (See 'Symptomatic and hemodynamically unstable' above.) https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 13/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate Hemodynamically stable Patients who are symptomatic and hemodynamically stable do not require urgent therapy with atropine or temporary cardiac pacing. However, patients should be continuously monitored with transcutaneous pacing pads in place ( figure 2) in the event of clinical deterioration. (See 'Symptomatic and hemodynamically stable' above.) Asymptomatic patients Patients who are asymptomatic do not require any initial treatment. Reversible causes of slowed conduction such as myocardial ischemia, increased vagal tone, and medications should be excluded. If no reversible causes are present, and the patient is asymptomatic, no specific therapy is required. (See 'Asymptomatic patients' above.) Subsequent management ( algorithm 1) (See 'Subsequent management' above.) Symptomatic patients For the rare patient with Mobitz type I second-degree AV block and symptomatic bradycardia that is not due to a reversible etiology, we recommend implantation of a permanent pacemaker (Grade 1A). We implant a dual chamber DDD pacemaker whenever possible in an effort to maintain physiologic AV synchrony. Asymptomatic patients For the large majority of patients with Mobitz type I second- degree AV block and asymptomatic bradycardia, we suggest not implanting a permanent pacemaker (Grade 2B). This is particularly true in younger patients and those patients in whom the AV block is felt to be supra-Hisian in nature (ie, within the AV node). These patients should have regularly follow-up, including a surface ECG, every 6 to 12 months. ACKNOWLEDGMENT The UpToDate editorial staff acknowledges Leonard Ganz, MD, FHRS, FACC, who contributed to an earlier version of this topic review. Use of UpToDate is subject to the Terms of Use. REFERENCES 1. Wenckebach, KF . Zur Analyse der unregelm ssigen Pulses. Ztschr klin Med 1899; 36:181. 2. Mobitz, W . ber die unvollst ndige St rung der Erregungs berleitung zwischen Vorhof und Kammer des menschlichen Herzens. Z Gesamte Exp Med 1924; 41:180. https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 14/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate 3. JOHNSON RL, AVERILL KH, LAMB LE. Electrocardiographic findings in 67,375 asymptomatic subjects. VII. Atrioventricular block. Am J Cardiol 1960; 6:153. 4. 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. 5. Dickinson DF, Scott O. Ambulatory electrocardiographic monitoring in 100 healthy teenage boys. Br Heart J 1984; 51:179. 6. 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. 7. Viitasalo MT, Kala R, Eisalo A. Ambulatory electrocardiographic recording in endurance athletes. Br Heart J 1982; 47:213. 8. 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. 9. 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. 10. Young D, Eisenberg R, Fish B, Fisher JD. Wenckebach atrioventricular block (Mobitz type I) in children and adolescents. Am J Cardiol 1977; 40:393. 11. 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. 12. 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. 13. Oliveira E, Ribeiro AL, Assis Silva F, et al. The Valsalva maneuver in Chagas disease patients without cardiopathy. Int J Cardiol 2002; 82:49. 14. Friedman HS, Gomes JA, Haft JI. An analysis of Wenckebach periodicity. J Electrocardiol 1975; 8:307. 15. Denes P, Levy L, Pick A, Rosen KM. The incidence of typical and atypical A-V Wenckebach periodicity. Am Heart J 1975; 89:26. 16. Callans DJ. Josephson's Clinical Cardiac Electrophysiology: Techniques and Interpretations, 6 th ed, Wolters Kluwer, Philadelphia 2020. 17. Aksu T, Gopinathannair R, Bozyel S, et al. Cardioneuroablation for Treatment of Atrioventricular Block. Circ Arrhythm Electrophysiol 2021; 14:e010018. 18. Link MS, Berkow LC, Kudenchuk PJ, et al. Part 7: Adult Advanced Cardiovascular Life Support: 2015 American Heart Association Guidelines Update for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2015; 132:S444. https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 15/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate 19. Brignole M, Auricchio A, Baron-Esquivias G, et al. 2013 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy: the Task Force on cardiac pacing and resynchronization therapy of the European Society of Cardiology (ESC). Developed in collaboration with the European Heart Rhythm Association (EHRA). Eur Heart J 2013; 34:2281. 20. 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 Rhythm Society. J Am Coll Cardiol 2019; 74:e51. 21. Shaw DB, Gowers JI, Kekwick CA, et al. Is Mobitz type I atrioventricular block benign in adults? Heart 2004; 90:169. 22. 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. Topic 909 Version 38.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 16/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate GRAPHICS Electrocardiogram showing Mobitz type I (Wenckebach) atrioventricular block Single-lead electrocardiogram showing Mobitz type I (Wenckebach) second-degree atrioventricular block with 5:4 conduction. The characteristics of this arrhythmia include: a progressively increasing PR interval until a P wave is not conducted (arrow), a progressive decrease in the increment in the PR interval, a progressive decrease in the RR interval, and the RR interval that includes the dropped beat (0.96 sec) is less than twice the RR interval between conducted beats (0.53 to 0.57 sec). Courtesy of Morton Arnsdorf, MD. Graphic 73051 Version 6.0 Normal rhythm strip Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright. Courtesy of Morton F Arnsdorf, MD. Graphic 59022 Version 3.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 17/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate Single lead electrocardiogram (ECG) showing Mobitz type II second degree atrioventricular (AV) block The third and sixth P waves are not conducted through the AV node (there is no associated QRS complex). The PR interval is constant prior to and after the non-conducted beats. Graphic 58649 Version 4.0 Sinus rhythm The normal P wave in sinus rhythm is slightly notched since activation of the right atrium precedes that of the left atrium. The P wave is upright in a positive direction in leads I and II. A P wave with a uniform morphology precedes each QRS complex. The rate is between 60 and 100 beats per minute and the cycle length is uniform between sequential P waves and QRS complexes. In addition, the P wave morphology and PR intervals are identical from beat to beat. Graphic 69872 Version 2.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 18/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate Single-lead electrocardiogram (ECG) showing sinus rhythm with third degree (complete) AV block Sinus rhythm with third degree (complete) heart block. There is independent atrial (as shown by the P waves) and ventricular activity, with respective rates of 83 and 43 beats per minute. The wide QRS complexes may represent a junctional escape rhythm with underlying bundle branch block or an idioventricular pacemaker. Courtesy of Ary Goldberger, MD. Graphic 72863 Version 6.0 Normal rhythm strip Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright. Courtesy of Morton F Arnsdorf, MD. Graphic 59022 Version 3.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 19/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate Major causes of atrioventricular (AV) block Physiologic and pathophysiologic Increased vagal tone Progressive cardiac conduction system disease With fibrosis and/or sclerosis (Lenegre disease) With calcification (Lev disease) Ischemic heart disease, including acute myocardial infarction Cardiomyopathy Infiltrative processes (eg, sarcoidosis, amyloidosis, hemochromatosis, malignancy, etc) Other non-ischemic cardiomyopathies (eg, idiopathic, infectious, etc) Infections (eg, viral myocarditis, Lyme carditis) Congenital AV block Related to structural congenital heart disease As part of neonatal lupus syndrome Other Hyperkalemia, severe hypo- or hyperthyroidism, trauma, degenerative neuromuscular diseases Iatrogenic Drugs Beta blockers, calcium channel blockers, digoxin, adenosine, antiarrhythmic drugs Cardiac surgery Post valvular surgery, post surgical correction of congenital heart disease Transcatheter aortic valve implantation Catheter ablation of arrhythmias Transcatheter closure of VSD Alcohol septal ablation for HCM VSD: ventricular septal defect; HCM: hypertrophic cardiomyopathy. Graphic 62885 Version 6.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 20/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate Electrocardiogram (ECG) showing concurrent Mobitz type I (Wenckebach) atrioventricular (AV) block and inferior myocardial infarction (MI) This rhythm strip shows a Mobitz type I (Wenckebach) atrioventricular block with 4:3 and 3:2 conduction and progressive prolongation of the PR intervals of conducted beats. The marked ST segment elevation suggests acute inferior wall ischemia or infarction that may be responsible for the arrhythmia. Courtesy of Ary Goldberger, MD. Graphic 62040 Version 3.0 Normal rhythm strip Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright. Courtesy of Morton F Arnsdorf, MD. Graphic 59022 Version 3.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 21/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate Normal conduction system Schematic representation of the normal intraventricular conduction system (His- Purkinje system). The Bundle of His divides into the left bundle branch and right bundle branch. The left bundle branch divides into anterior, posterior, and, in some cases, median fascicles. AV: atrioventricular; RA: right atrium; LA: left atrium; RV: right ventricle; LV: left ventricle. Graphic 63340 Version 6.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 22/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate Electrocardiogram (ECG) showing atypical Mobitz type I (Wenckebach) atrioventricular (AV) block Single lead electrocardiogram (ECG) strip showing an atypical Mobitz type I (Wenckebach) AV block with 18:17 ratio. The last three cycles of the group, the skipped beat (with the P wave lost in the T wave; arrow), and the first three cycles of the next group are shown. The last three cycles had a PR interval of 0.36 sec while the first three cycles showed PR intervals of 0.23, 0.32 and 0.34 sec with a decreasing R-R interval. This demonstrates the importance of comparing the PR interval of the last beat before the dropped QRS to the PR interval of the first and second beats of the new cycle. The PR interval is the longest in the beat before the dropped beat, shortest in the first beat of the cycle, and increases in the second beat. Courtesy of Morton Arnsdorf, MD. Graphic 78766 Version 3.0 Normal rhythm strip Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright. Courtesy of Morton F Arnsdorf, MD. Graphic 59022 Version 3.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 23/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate Single-lead electrocardiogram (ECG) showing first degree atrioventricular (AV) block I Electrocardiogram of lead II showing normal sinus rhythm, first degree atrioventricular block with a prolonged PR interval of 0.30 seconds, and a QRS complex of normal duration. The tall P waves and P wave duration of approximately 0.12 seconds suggest concurrent right atrial enlargement. Courtesy of Morton Arnsdorf, MD. Graphic 67882 Version 5.0 Normal rhythm strip Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright. Courtesy of Morton F Arnsdorf, MD. Graphic 59022 Version 3.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 24/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate Algorithm management Mobitz I second degree AV block in adults AV: atrioventricular; ECG: electrocardiogram; CHB: complete heart block; BP: blood pressure; HF: heart failure; IV: intravenous; PPM: permanent pacemaker. The initial dose of atropine is 0.5 mg IV. This dose may be repeated every three to five minutes to a total dose of 3 mg. https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 25/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate While transcutaneous pacing may be initially successful in stabilizing the patient, it may not be consistently reliable. Central venous access should be considered in the event that urgent transvenous pacing is required. Dopamine IV infusion typically begins at a dose of 3 mcg/kg/minute and can be titrated up to 20 mcg/kg/minute if needed for heart rate and blood pressure augmentation. Dobutamine IV infusion typically begins at a dose of 5 mcg/kg/minute and can be titrated up to 20 mcg/kg/minute if needed for heart rate and blood pressure augmentation. Graphic 109617 Version 1.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 26/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate Adult bradycardia algorithm 2020 update Reprinted with permission. ACLS Provider Manual. Copyright 2020 American Heart Association, Inc. Graphic 130748 Version 10.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 27/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate Options for hands-free pacemaker/defibrillator pad positioning Positioning options for hands-free pacemaker/defibrillator pads showing anterior/lateral positioning (left) and anterior/posterior positioning (right). Graphic 103268 Version 2.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 28/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate Selection of pacemaker systems for patients with atrioventricular block Decisions are illustrated by diamonds. Shaded boxes indicate type of pacemaker. AV: atrioventricular. Reproduced with permission from: 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. J Am Coll Cardiol 2008; 51(21):e1-e62. Illustration used with permission of Elsevier Inc. All rights reserved. Copyright 2008 Elsevier Inc. https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 29/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate Graphic 71370 Version 4.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 30/31 7/5/23, 10:36 AM Second-degree atrioventricular block: Mobitz type I (Wenckebach block) - UpToDate Contributor Disclosures William H Sauer, MD Grant/Research/Clinical Trial Support: Biosense-Webster [Catheter ablation]; Boston Scientific [Catheter ablation]. All of the relevant financial relationships listed have been mitigated. Mark S Link, MD No relevant financial relationship(s) with ineligible companies to disclose. Susan B Yeon, MD, JD, FACC No relevant financial relationship(s) with ineligible companies to disclose. Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these are addressed by vetting through a multi-level review process, and through requirements for references to be provided to support the content. Appropriately referenced content is required of all authors and must conform to UpToDate standards of evidence. Conflict of interest policy https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block/print 31/31