Atrioventricular (AV) block is defined as a delay or interruption in the transmission of an impulse from the atria to the ventricles due to an anatomical or functional impairment in the conduction system. The conduction disturbance can be transient or permanent. The conduction can be delayed, intermittent, or absent. The commonly used terminology includes first degree (slowed conduction without missed beats), second degree (missed beats, often in a regular pattern, eg, 2:1, 3:2, or higher degrees of block), and third degree or complete AV block. (See "ECG tutorial: Atrioventricular block".)
Congenital third degree, or complete, heart block (CHB) was first described in 1901 by Morquio, who also noted the familial occurrence and the association with Stokes-Adams attacks and death . The presence of fetal bradycardia (40 to 80 beats per minute) as a manifestation of CHB was first noted in 1921 and is the initial sign of this disorder in many cases . The incidence of congenital CHB in the general population varies between 1 in 15,000 to 1 in 22,000 live-born infants .
The etiology, presentation, treatment, and prognosis associated with congenital CHB will be presented here. Discussions of the etiologies of acquired AV block as well as non-congenital complete AV block are presented separately. (See "Etiology of atrioventricular block" and "Third degree (complete) atrioventricular block".)
Neonatal lupus, previously known as maternal lupus and caused by maternal antibodies that cross the placenta, is responsible for 60 to 90 percent of cases of congenital CHB overall [4-6]. It accounts for almost all cases presenting in utero or the neonatal period, but for only a few cases occurring later (5 percent in one report) . (See "Neonatal lupus".)
Other causes include myocarditis and various structural cardiac defects, particularly congenitally corrected transposition of the great arteries, atrioventricular discordance, or polysplenia with atrioventricular canal defect. Several hereditary disorders have also been identified. (See 'Non-immune congenital AV block' below and "Etiology of atrioventricular block", section on 'Familial disease'.)