Congenital atrioventricular block is defined (Yater) as a documented conduc
tion defect in a young subject with unquestionable bradycardia in the absen
ce of a history of infection which might have caused the condition after bi
rth. It is a rare condition (1 out of 20 000 births) and may be isolated or
associated with another congenital malformation. Four cardiac malformation
s are classically associated : endomyocardial fibrosis, morphological abnor
malities close to the conduction system : corrected transposition, left iso
merism; patent ductus arteriosus and atrial septal defect apparently unrela
ted but the most common; the association of mitral regurgitation in adults,
although the significance is not very clear. Isolated block is often obser
ved in patients with mothers suffering from autoimmune disease, often clini
cally latent.
Anti Ro/SS-A and La/SS-B antibodies cross into the foetal circulation and c
ause inflammation of the conduction tissues but the causal mechanism is not
known. The diagnosis of the conduction defect is sometimes made during foe
tal life by echocardiography. After birth, the diagnosis is made by electro
cardiography but the block is not always complete or permanent, its degree
often increasing with time. In addition, in advanced degrees of block, the
escape rhythm tends to slow down. Longterm follow-up studies have revised t
he previously considered good prognosis of isolated congenital atrioventric
ular block but advances in cardiac pacing provide satisfactory treatment. I
n the foetus, isolated atrioventricular block is usually associated with an
escape rhythm > 60/min and enables normal vaginal delivery; a low heart ra
te < 55/min and anasarca carry a poor prognosis. In the neonate, pacing is
indicated in babies with cardiac failure and a heart rate < 55/min. Follow-
up by Hotter monitoring, exercise testing and echocardiography is justified
in children and adolescents; the patients may become symptomatic at any ag
e. Pacing is essential in symptomatic cases (malaise, ventricular dysfuncti
on) and useful in cases with long QT intervals, frequent ventricular extras
ystoles and wide ventriculogrammes. Pacing is not always easy in children.
Epicardial pacing by thoracotomy or an epigastric approach is possible but
endocavitary pacing is to be preferred using thin pacing catheters introduc
ed via the subclavian vein and small pacemakers implanted in a sub or prepe
ctoral site. A pacing mode which restores the normal atrioventricular seque
nce is theoretically superior to single ventricular pacing even if rate res
ponsive frequency.