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-ii/print 15/25 7/5/23, 10:37 AM Second-degree atrioventricular block: Mobitz type II - 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-ii/print 16/25 7/5/23, 10:37 AM Second-degree atrioventricular block: Mobitz type II - 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-ii/print 17/25 7/5/23, 10:37 AM Second-degree atrioventricular block: Mobitz type II - UpToDate Electrocardiogram (ECG) showing complete heart block in a patient with syncopal episodes who previously had shown Mobitz II type AV block The first two beats are paced. After the pacemaker is turned off, a normally conducted beat followed with a PR interval of 0.19 sec and a LBBB morphology. The next eight P waves fail to conduct and no lower pacemaker appears to assume control of the ventricles. Restarting the artificial pacemaker led to the QRS complex at the end of the rhythm strip. LBBB: left bundle branch block. Courtesy of Morton Arnsdorf, MD. Graphic 64261 Version 4.0 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-ii/print 18/25 7/5/23, 10:37 AM Second-degree atrioventricular block: Mobitz type II - UpToDate Electrocardiographic and electrophysiologic features of Mobitz type II second-degree atrioventricular block The PR and RR intervals are constant, but the third atrial beat (A) is not conducted (arrow). His bundle electrocardiography (HBE) shows constant AH (85 msec) and HV (95 msec) intervals and normal AH but no HV conduction in the nonconducted beat. The last finding indicates that the block is distal to the His bundle, in contrast with the more proximal location of Mobitz type I atrioventricular block. Adapted from: Josephson ME, Clinical Cardiac Electrophysiology: Techniques and nd Interpretations, 2 ed, Lea & Febiger, Philadelphia 1993. Graphic 79539 Version 7.0 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-ii/print 19/25 7/5/23, 10:37 AM Second-degree atrioventricular block: Mobitz type II - 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-ii/print 20/25 7/5/23, 10:37 AM Second-degree atrioventricular block: Mobitz type II - UpToDate Overview of acute management of Mobitz type II second-degree AV block This algorithm discusses the acute management of Mobitz type II second-degree AV block. Refer to UpToDate content on subsequent management of this condition. AV: atrioventricular. Hemodynamic instability is identified by signs and symptoms of inadequate tissue perfusion, which include hypotension, lightheadedness, altered mental status, poor peripheral perfusion, and other signs of shock. Temporary cardiac pacing is performed with transcutaneous or transvenous pacing. Transcutaneous pacing may be initiated while access for transvenous pacing is obtained. Beta adrenergic agents which may be used in this setting include isoproterenol, dopamine, dobutamine, and epinephrine. Refer to UpToDate content regarding use of these chronotropic agents. Atropine is generally avoided in patients with Mobitz type II second-degree block as it is unlikely to be beneficial and may worsen infranodal block by increasing sinus rate without improving conduction. Graphic 140931 Version 1.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-ii/print 21/25 7/5/23, 10:37 AM Second-degree atrioventricular block: Mobitz type II - UpToDate Mobitz type II second-degree AV block: Identifying candidates for permanent pacemaker placement This algorithm is an aid to identifying which patients with Mobitz type II second-degree AV block require a permanent pacemaker. Patients with persistent Mobitz type II second-degree AV block are at high risk for progressing to symptomatic Mobitz type II second- degree AV block or complete heart block and therefore are candidates for permanent pacemaker placement. Dual-chamber (AV) pacing is generally preferred to maintain AV synchrony. For additional details, refer to UpToDate content on management of Mobitz type II second-degree AV block. AV: atrioventricular. The time course for response to treatment of reversible causes varies depending upon the specific cause of AV conduction delay and other clinical factors. Graphic 140930 Version 1.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-ii/print 22/25 7/5/23, 10:37 AM Second-degree atrioventricular block: Mobitz type II - 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-ii/print 23/25 7/5/23, 10:37 AM Second-degree atrioventricular block: Mobitz type II - UpToDate Graphic 71370 Version 4.0 https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-ii/print 24/25 7/5/23, 10:37 AM Second-degree atrioventricular block: Mobitz type II - 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-ii/print 25/25