Pediatric Second-Degree Atrioventricular Block Treatment & Management

Presentation of second-degree atrioventricular (AV) block varies. In general, patients with Mobitz I (Wenckebach) AV block are asymptomatic. However, when 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. Patients with Mobitz I (Wenckebach) AV block secondary to increased vagal tone may respond to theophylline, glycopyrrolate, or scopolamine. Pacemaker therapy is rarely required when medications fail to control symptoms.

Infusion of inotropes and temporary pacing are usually performed in a suitable hospital environment with facilities for continuous nursing and monitoring.

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.^[14]

In fetuses with anti-Ro/La, bradycardia secondary to second (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 are used. Some reported immediate postnatal use of intravenous immunoglobulin with good results.^[15]

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.

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 perfusing 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.

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.^[16]

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).

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.