Atrioventricular (AV) Block

Key Features

• 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

Clinical Findings

• 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

Diagnosis

• 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

Treatment

• 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