complete heart block – isolated

complete heart block(chb) occurs when atrial and ventricular contraction is completely dissociated or independent. this can be due to damage to the conducting tissue (usually caused by maternal auto-antibodies) or to abnormalities of the atrial nodes and conducting tissue, which can be a familial defect, or to congenital heart disease, particularly left atrial isomerism. in isolated chb, the fetal heart is structurally normal but the ventricular rate is sustained at less than 100 beats per minute. this is usually due to damage to the conducting tissue by circulating anti-ro antibodies (anti-ssa in some laboratories). the mother is usually asymptomatic but may have clinical sjogren’s syndrome or systemic lupus erythematosis. complete heart block may become evident at some time between 18-24 weeks gestation. it has been reported to develop later but this is rare. usually the affected fetus remains well in utero but in some cases, evidence of fetal hydrops develops. in this latter setting, the outcome tends to be poor. if the fetus survives to delivery close to term, pacing can be successfully carried out if it proves necessary. premature delivery with immediate pacemaker placement has salvaged some hydropic infants. many children do not need pacing for some years. rarely, isolated chb is due to an abnormality of the conduction tissues which is familial in aetiology. maternal antibodies are negative. this appears to have a less benign course in fetal life than those who are antibody positive.