Fetal complete atrioventricular block

A fetal congenital complete heart block (CAVB) is a rare cardiac conduction abnormality which is associated with high morbidity and mortality. It is considered the commonest of fetal bradyarrhymias.

Epidemiology

The estimated prevalence of complete heart block in newborns is at ~  1 in 20,000.

Pathology

It results from either anatomic or electric discontinuity in the conducting tissues connecting the atria and ventricles. Congenital heart block is is often classified into cases with cardiac structural abnormalities (often complex) and those with structurally normal hearts.

The etiology of congenital heart block when the heart is structurally normal is most often a fetal immune inflammatory response, caused by the binding of antibodies to the fetal cardiac conduction system.

Associations 

• mothers of these fetuses can be shown to have anti-SS-A (anti-Ro) and anti-SS-B (anti-La) antibodies to ribonucleoproteins.
• congenital cardiac anomalies : 35 - 53 % ^1-2
  • L type transposition of the great arteries
• situs anomalies : heterotaxy syndrome

Radiographic features

Ultrasound - echocardiography

On M mode ultrasound the atrial impulses can be seen in their own rate none of which are tramissed to the ventricles. The ventricular rates are often overy slow at ~ 40 - 70 bpm.

Complications

• development of hydrops fetalis

Prognosis

The prognosis of complete heart block is worsened by the presence of hydrops, a ventricular rate of < 55 beats / mm and by an associated cardiac anomaly.