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Pediatric Second-Degree Atrioventricular Block Treatment & Management

  • Author: M Silvana Horenstein, MD; Chief Editor: P Syamasundar Rao, MD  more...
 
Updated: Mar 02, 2016
 

Approach Considerations

Presentation of second-degree atrioventricular (AV) block varies. In general, patients with Mobitz I (Wenckebach) AV block are asymptomatic; if it is thought to be a normal finding, such as in highly trained athletes or during sleep, no treatment is necessary. However, when symptomatic bradycardia is present, intravenous medications such as isoproterenol and atropine may be helpful. These agents must be administered in a hospital setting with cardiac monitoring.

Infusion of inotropes and temporary pacing should be performed in a suitable hospital environment with facilities for continuous monitoring. Patients with Mobitz type II AV block may have a reversible cause (ie, myocarditis, transplant rejection) and thus they may respond after treating the baseline disease. However, if no reversible cause can be found or if medications fail to control symptoms, pacemaker therapy is required.

High-grade AV block may be reversible if it is secondary to acute myocarditis or rheumatic fever or irreversible (eg, lupus, after cardiac surgery). Therefore, these patients require pacemaker implantation. Patients who do require pacemaker implantation should be evaluated for retrograde VA conduction to avoid pacemaker-mediated tachyarrhythmias.[15]

A unique and rare cause of second-degree AV block is a severe infantile form of long-QT syndrome. The prognosis in such long-QT syndromes is very guarded, even if patients are treated with beta blockers, pacing, and stellate ganglionectomy. It has been suggested that the prognosis of patients with high-grade AV block is similar to that of patients with complete AV block and that management should be the same for the two.[16]

In fetuses with anti-Ro/La, bradycardia secondary to second-degree (Mobitz type II) or complete AV block may lead to congestive heart failure, hydrops, and, eventually, fetal demise. Although no standard approach to treatment exists, fluorinated steroids have been used. Treatment of the fetus with transplacental digoxin and dexamethasone was also reported with resultant resolution of both second-degree AV block and atrial flutter.[17] Such treatment options are worth a trial in the management of second-degree AV block secondary to fetal exposure to maternal anti-Ro (SS-A) and anti-La (SS-B) antibodies.[17]  Some investigators reported immediate postnatal use of intravenous immunoglobulin with good results.[18]

Consultations

Patients with a second-degree AV block should be evaluated by a cardiologist even when they are asymptomatic, to assess for any associated congenital heart disease, to identify sinus node dysfunction, and to determine whether it may progress to worrying symptoms, such as low heart frequency and syncope.

Activity

Activity should be tailored to the patient's physical capabilities. A 24-hour Holter monitor and an exercise stress test may aid in determining recommendations in this regard. In addition, an exercise stress test helps to determine who likely requires a pacemaker; in patients who already have a pacemaker, it helps to reprogram the device according to the patient's needs.

Transfer

Transfer of patients with second-degree AV block should include attained intravenous access, available short-term medications and pacing systems, and accompaniment by individuals familiar with the administration of these medications and application of these systems.

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Pharmacologic Therapy

In symptomatic patients, initiation of short-term therapy with a chronotropic agent, such as isoproterenol, is reasonable. However, isoproterenol may exacerbate the condition by accelerating the atrial rate, which results in a higher grade of AV block by increasing myocardial oxygen demand, by reducing diastolic and coronary perfusion pressure, or by initiating ventricular dysrhythmias. If a vagal mechanism is suspected as the cause of acute symptomatic heart block, atropine may also be used. Arrangements for a stable temporary pacing system are necessary because drug therapy is usually only a temporizing measure for symptomatic heart block.

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Temporary and Permanent Pacing Systems

Asymptomatic patients with Wenckebach or non-Wenckebach AV block do not require immediate pacemaker therapy. However, they should be monitored periodically because of the possibility of cardiovascular syncope or Stokes-Adams attacks in cases of a very slow escape rhythm. Because these patients may be at risk for sudden death, pacemaker therapy is indicated. Pacemaker therapy is also indicated in asymptomatic patients who have AV block within the His bundle (demonstrated by electrophysiologic study) and in those whose Wenckebach AV block persists for more than 7 days after cardiac surgery.[19]

Temporary pacing may be initiated using a noninvasive transcutaneous pacing system; however, the potential for discomfort in all patients and skin burns in newborns must be recognized, and arrangements for transvenous (or epicardial) pacing are usually initiated simultaneously. If the cause of the symptomatic second-degree AV block is unlikely to be reversible, permanent pacing can be initiated. However, in most patients, permanent pacing is reserved for those who do not demonstrate resolution of their conduction disorder after a reasonable period of observation.

Until the heart rate has improved, second-degree AV block related to transient phenomena, such as myocardial infarction, infections, or toxins, should be supported with temporary pacing if the patient is symptomatic. Heart block occurring above the His bundle, most commonly in a Wenckebach pattern, is usually more benign than heart block occurring below the His bundle (most commonly in a non-Wenckebach pattern).

Second-degree AV block occurring in the hemifascicles of the specialized conduction system may have a very low escape pacemaker rate if it progresses to complete AV block. Prophylactic pacemaker placement may be warranted in conditions such as Kearns-Sayre syndrome, a mitochondrial genetic disorder characterized by external ophthalmoplegia and progressive fascicular block.

Before the decision is made regarding whether to treat patients with a permanent pacing system, posttraumatic second-degree AV block should usually be monitored and supported for 7-10 days to assess whether the condition is resolving or progressing.

In patients with synchronous temporary or permanent pacing systems in place, avoid sources of electromagnetic interference, such as electrocautery or magnetic resonance imaging (MRI).

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Long-Term Monitoring

Patients receiving a permanent pacemaker should have arrangements for repeat pacemaker assessment in 6-12 weeks, in 6 months, and biannually or annually, depending on their pacemaker mode, time from implant, and pacemaker dependency.

Patients without a pacemaker but with the potential for progression of AV block severity should receive periodic monitoring, including ECG and Holter monitoring. This is particularly important for patients with mitochondrial disorders, such as Kearns-Sayre syndrome, who may develop rapid and unpredictable progression of AV block.

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Contributor Information and Disclosures
Author

M Silvana Horenstein, MD Assistant Professor, Department of Pediatrics, University of Texas Medical School at Houston; Medical Doctor Consultant, Legacy Department, Best Doctors, Inc

M Silvana Horenstein, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, American Medical Association

Disclosure: Nothing to disclose.

Coauthor(s)

Robert Murray Hamilton, MD, MSc, FRCPC Electrophysiologist, Senior Associate Scientist, Physiology and Experimental Medicine, Labatt Family Heart Centre; Professor, Department of Pediatrics, University of Toronto Faculty of Medicine

Robert Murray Hamilton, MD, MSc, FRCPC is a member of the following medical societies: American Heart Association, Canadian Medical Association, Ontario Medical Association, Royal College of Physicians and Surgeons of Canada, Canadian Medical Protective Association, Heart Rhythm Society, Canadian Cardiovascular Society, Cardiac Electrophysiology Society, Pediatric and Congenital Electrophysiology Society, Society for Pediatric Research

Disclosure: Nothing to disclose.

Chief Editor

P Syamasundar Rao, MD Professor of Pediatrics and Medicine, Division of Cardiology, Emeritus Chief of Pediatric Cardiology, University of Texas Medical School at Houston and Children's Memorial Hermann Hospital

P Syamasundar Rao, MD is a member of the following medical societies: American Academy of Pediatrics, American Pediatric Society, American College of Cardiology, American Heart Association, Society for Cardiovascular Angiography and Interventions, Society for Pediatric Research

Disclosure: Nothing to disclose.

Acknowledgements

Charles I Berul, MD Professor of Pediatrics and Integrative Systems Biology, George Washington University School of Medicine; Chief, Division of Cardiology, Children's National Medical Center

Charles I Berul, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, American Heart Association, Cardiac Electrophysiology Society, Heart Rhythm Society, Pediatric and Congenital Electrophysiology Society, and Society for Pediatric Research

Disclosure: Johnson & Johnson Consulting fee Consulting

Alvin J Chin, MD Professor of Pediatrics, University of Pennsylvania School of Medicine; Attending Physician, Cardiology Division, Children's Hospital of Philadelphia

Alvin J Chin, MD, is a member of the following medical societies: American Association for the Advancement of Science, American Heart Association, and Society for Developmental Biology

Disclosure: Nothing to disclose.

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

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A common pattern of second-degree atrioventricular (AV) block consists of gradual prolongation of the PR interval leading up to a nonconducted P wave; this pattern is known as Wenckebach AV block, or Mobitz I AV block. This rhythm strip is an example of classic Mobitz I, or Wenckebach, AV block, in which the PR interval prolongs by sequentially smaller increments, with consequent shortening of the RR intervals until the blocked beat occurs. However, classic Wenckebach block is present in only a minority of cases. Wenckebach block is most easily diagnosed by comparing the PR interval following the blocked beat with the PR interval preceding the blocked beat; if the PR interval shortens following the blocked beat, the block is most likely of the Wenckebach type.
If there is no progressive prolongation of the PR interval and the PR interval fails to shorten following a blocked beat, non-Wenckebach AV block (or Mobitz II AV block) is said to be present. This block is usually located more distally in the His bundle or the His bundle branches, or both, and the escape rates are usually slower and less stable.
 
 
 
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