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Congenital Complete Heart Block

M-mode echocardiogram demonstrating a ventricular rate of 51 bpm

Spectral Doppler interrogation of the umbilical artery reveals a heart rate of 52 bpm


The M-mode fetal echocardiogram on the left demonstrates a ventricular rate of 51 bpm. While many examiners think of Doppler interrogation of the umbilical arteries only in terms of resistance to flow, important information about cardiac rate can be ascertained from the spectral tracing. The image on the right from the same patient reveals a cardiac rate of 52 bpm.


Congenital complete heart block occurring in the fetus is a rare cardiac abnormality which is associated with high morbidity and mortality. 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 prevalence of complete heart block in newborns is said to be 1 in 20,000. The actual prevalence is difficult to ascertain due to the fetal loss rate when heart block occurs in association with structural heart disease.

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. Mothers of these fetuses can be shown to have anti-SS-A (anti-Ro) and anti-SS-B (anti-La) antibodies to ribonucleoproteins. The median gestational age for identification of fetal complete heart block due these antibodies is 23 weeks' gestation with the earliest reports at 16 and 17 weeks' gestation.

A report by Baschat et al is an excellent discussion of the structural abnormalities associated with congenital heart block. As they describe; "The cardiac anomalies associated with complete heart block may be seen in in heterotaxy syndromes, congenitally corrected transposition of the great arteries, atrial and ventricular septal defects, tetralogy of Fallot and pulmonary stenosis.

Heterotaxy syndromes are characterized by abnormal development of embryonic symmetry resulting in cardiac, vascular and visceral abnormalities. Bilateral left sidedness, or left isomerism, is associated with polysplenia, interrupted inferior vena cava with an azygous or hemiazygous vein continuation into the superior vena cava and heart block in the presence of structural cardiac disease in approximately 90% of cases. The inferior vena cava may have normal drainage into the atrium in up to 30% of cases with left isomerism. The high incidence of complete heart block in left atrial isomerism appears to be due to hypoplasia of the sinoatrial node and/or disruption of nodoventricular conduction continuity caused by abnormal atrioventricular node formation. Cardiac conduction tissue and the myocardium arise from neural crest tissue. Abnormal migration of these progenitor cells in embryonic life may therefore play a role in the pathogenesis of hererotaxy and defects in the endocardial cushion and conducting tissue.

Transposition of the great arteries (ventriculo-atrial discordance) in combination with switching of the ventricles (atrioventricular discordance) results in physiologically congenitally corrected transposition of the great arteries. A ventricular septal defect and/or varying degrees of outflow tract obstruction may coexist with this condition. In these patients the atrioventricular conduction tissue has a long and vulnerable course prone to disruption. Corrected transposition is also a well-recognized cause of complete heart block. However, complete heart block is not usually present at birth, and the incidence of this association increases with age during childhood. Progression of second- to third-degree heart block attributed to interrup-tion of the atrioventricular conduction system by fibrous tissue has been described in heterotaxy syndrome with additional discordance of the ventricles. Alternating second/third-degree AV-block in utero progressing to a complete heart block after the first month of life has also been described in congenitally corrected transposition of the great arteries. In contrast, progression from sinus rhythm to heart block in left atrial isomerism may have been observed but is certainly not commonly recognized.

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. Increased nuchal translucency in association with cardiac anomalies may be considered a mild variant of fetal hydrops, as both are thought to result from imparied lymphatic drainage of interstitial fluid." However, most fetuses with complete heart block survive when this is an isolated phenomenon, regardless of any association with maternal connective tissue disease.

Although some authors reported successful prenatal treatment of complete heart block, no generally accepted therapeutic approach is presently available. Several investigators have successfully treated congenital heart block with the maternal administration of varying forms of steroids. Though not universally successful, some cases have shown dramatic response. Attempted direct fetal cardiac pacing has failed to prevent death. Transvenous intracardiac pacing may prove to be a better approach to complete heart block in the fetus.



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Ho SY, Fagg N, Anderson RH, Cook A, Allan L. Disposition of the atrioventricular conduction tissues in the heart with isomerism of the atrial appendages: its relation to congenital complete heart block J Am Coll Cardiol 1992; 20:904-10

Poelmann RE, Girtenberger-de Groot AC. A subpopulation of apoptosis-prone cardiac neural crest cells targets to the venous pole: multiple functions in heart development? Dev Biol 1999;207:271-86

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Anderson RH, Becker AE, Arnold R, Wilkinson JL. The conducting tissues in congenitally corrected transposition. Circulation 1974;50:911-18

Huhta IC, Maloney JD, Ritter DG, Ilstrup DM, Feldt RH. Complete atrioventricular block in patients with atrio-ventricular discordance. Circulation 1 983;67: 1374-7

Hyett JA, Perdu M, Sharland GK, Snijders RS, Nicolaides KH. Increased nuchal translucency at 10-14 weeks of gestation as a marker for major cardiac defects. Ultrasound Obstet Gynecol 1997;10:242-6

Hyett JA, Noble PL, Snijders RS, Montenegro N, Nicolaides KH. Fetal heart rate in trisomy 21 and other chromosomal abnormalities at 10-14 weeks gestation. Ultrasound Obstet Gynecol 1996;7:239-44

Snijders RJ, Noble P, Sebire N, Souka A. Nicolaides KH. UK multiicentre project on assessment of risk of trisomy 21 by maternal age and fetal nuchal-translucency thickness at 10-14 weeks of gestation. Fetal Medicine Foundation First Trimester Screening Group. Lancet 1998;352:343-6

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California