Discussion

Complete congenital heart block is the most common and severe atrio-ventricular block usually detected in utero, at birth or within the first month. ^{Reference Brito-Zerón, Izmirly, Ramos-Casals, Buyon and Khamashta3} Risk factors include maternal diseases (diabetes mellitus), viral infections (coxsackie, adenovirus), and drugs (anti-epileptics, lithium). Fetal factors such as cardiac malformations and genetic channelopathies are also implicated. Isolated CCHB is more common in infants of mothers with autoimmune disease and/or auto-antibodies positivity. Asymptomatic antibody carrier status in mother of index case was similar to a systematic review of 856 mothers, where over 50% were asymptomatic despite having anti-Ro and anti-La antibodies. ^{Reference Brito-Zerón, Izmirly, Ramos-Casals, Buyon and Khamashta3} These mothers could be immunologically positive even years before clinical symptoms appear, making a definitive diagnosis of SLE or Sjogren difficult. However, risk of recurrence is nearly 20% in subsequent pregnancies especially when both auto-antibodies are present, ^{Reference Buyon, Hiebert and Copel2} necessitates strict follow-up. Auto-antibodies transferred trans-placentally impede clearance of apoptotic fetal cardiocytes, causing inflammation, fibrosis, and rhythm impairment. ^{Reference Ho, Esscher, Anderson and Michaëlsson4} Often non-cardiac manifestations involving blood, liver, and skin are observed, which resolve at approximately 6 months postnatally, coinciding with waning maternal autoantibodies from infant’s circulation. ^{Reference Buyon, Hiebert and Copel2} Our infant showed none of these manifestations. To decrease the recurrence risk of CCHB in mothers with autoantibodies, use of hydroxychloroquine and fluorinated steroids in antenatal period has been demonstrated, however, current recommendations emphasise on serial echocardiograms every 1-2 weeks from 16^th week gestation, to detect premature atrial contractions and moderate pericardial effusion and then initiate preventive therapies. ^{Reference Brucato5} IVIG used in a recent trial also showed no reduction in recurrence. ^{Reference Friedman, Llanos and Izmirly6}

Most cases are diagnosed in the fetal period, with 82% before 30 weeks of gestation. ^{Reference Buyon, Hiebert and Copel2} Antenatal therapeutic strategies include maternal steroids, sympathomimetics, and plasmapheresis. ^{Reference Buyon, Clancy and Friedman7} In our case however, due to irregular antenatal visits, the detection was possibly delayed with no window for antenatal intervention. Shokrzadeh performed longitudinal analysis of fetal heart rates and showed an increased risk of perinatal death, severe fetal bradyarrhythmia, and need of emergency pacing with ventricular rates below age-specific mean. ^{Reference Shokrzadeh, Maltret and Morel8} A ventricular rate <55 bpm is considered critical with guarded fetal prognosis. ^{Reference Brito-Zerón, Izmirly, Ramos-Casals, Buyon and Khamashta3} Our neonate, despite having a nadir of 43 bpm, did not develop hydrops, and had an uncomplicated perinatal course, similar to a few case reports in literature. ^{Reference Reid, Coleman and Doig9} Tunaoglu et al described a term neonate where the nadir heart rates were 39 bpm and pacing was not required till reporting at 8 years. ^{Reference Tunaoglu, Yildirim and Vurali10}

The overall mortality of CCHB is approximately 20–30%, with upto 70% deaths in utero. ^{Reference Buyon, Hiebert and Copel2,Reference Brito-Zerón, Izmirly, Ramos-Casals, Buyon and Khamashta3} Risk factors for mortality include fetal diagnosis, hydrops, endocardial fibroelastosis, and delivery ≤32 weeks. ^{Reference Jaeggi, Hamilton, Silverman, Zamora and Hornberger11} The mortality in the presence of either dilated cardiomyopathy or endocardial fibroelastosis is >50%, increasing to 100% if both are present. Pacemaker insertion is recommended in asymptomatic cases with ventricular rate <50 bpm, broad QRS escape rhythm, prolonged QT interval, or complex ventricular ectopy. Haemodynamic instability with ventricular dysfunction attributable to bradycardia mandates emergency pacing. ^{Reference Glikson, Nielsen and Kronborg12} Buyon et al reported 63% of 107 children born alive had pacemakers inserted, of which 35 required it within the first 9 days of life, while 15 additional were paced in infancy, and 17 after 1 year. This highlights the ability of some children to tolerate bradycardia quite well for some time, while others require cardiac pacing in the first few days of life and decision of permanent pacing requires detailed diagnostics.

Our infant is currently 14 months old and doing well without pacing.