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Key Features

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  • First-degree AV block: Prolongation of the PR interval

  • Second-degree AV block

    • Mobitz type I (Wenckebach)

      • Recognized by progressive prolongation of the PR interval until there is no QRS following a P wave

    • Mobitz type II

      • No progressive lengthening of the PR interval before the dropped beat

  • Congenital complete AV block

    • Most common form

    • Occurs in a fetus or infant with an otherwise normal heart

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Clinical Findings

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  • Most patients have an innocent flow murmur from increased stroke volume

  • In symptomatic patients

    • Heart can be quite enlarged

    • Pulmonary edema may be present

  • If the heart rates are sufficiently low, then there will be low cardiac output, decreased cardiac function, and the development of hydrops fetalis.

  • Postnatal adaptation largely depends on the heart rate; infants with heart rates < 55 beats/min are at significantly greater risk for

    • Low cardiac output

    • Heart failure

    • Death

  • First-degree AV block may be associated with

    • Structural congenital heart defects, namely AV septal defects and congenitally corrected transposition of the great arteries (ccTGA)

    • Diseases such as rheumatic carditis

  • Second-degree AV block

    • Mobitz type I occurs in normal hearts at rest and is usually benign

    • Mobitz type II is frequently associated with organic heart disease

  • Complete AV block

    • Primary finding in infants and children is a significantly low heart rate for age

    • Associated with maternal systemic lupus erythematosus antibodies and some form of congenital heart disease

    • Patients may be asymptomatic

    • Presyncope, syncope, or fatigue may be present

    • Atria and ventricles beat independently

    • Ventricular rates can range from 40 to 80 beats/min, whereas atrial rates are faster

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Diagnosis

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  • The diagnosis is often made prenatally when fetal bradycardia is documented

  • An ultrasound is then conducted as well as a fetal echocardiogram of the heart

  • Complete cardiac evaluation, including ECG, echocardiography, and Holter monitoring, is necessary to assess the patient for ventricular dysfunction and to relate any symptoms to concurrent arrhythmias

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Treatment

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  • When diagnosis of complete atrioventricular block is made in a fetus, the treatment depends on

    • Gestational age

    • Ventricular rate

    • Presence or absence of hydrops

  • In some instances (eg, fetus has associated heart failure), some experts advocate that mothers should receive

    • Corticosteroids

    • Intravenous immune globulin (IVIG) and/or

    • β-Adrenergic stimulation treatment

  • Emergent delivery is sometimes warranted

  • Postnatal treatment for neonates or older patients in whom significant symptoms are present and immediate intervention is required includes temporary

    • Support by the infusions of isoproterenol

    • Transvenous pacing wires

    • Transcutaneous pacemakers if needed

  • Long-term treatment involves the placement of a permanent pacemaker

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