Fetal Bradycardia Prompting the Diagnosis and Management of Parental Long QT Syndrome

Long QT syndrome (LQTS) is primarily an inherited condition associated with the risk of sudden cardiac death. Due to variable phenotypic expression, a prolonged QT interval on a 12-lead ECG is not always present. LQTS may present in the fetus with persistent bradycardia, including sinus bradycardia or functional 2:1 atrioventricular block. We report our experience of persistent fetal bradycardia prompting parental assessment for congenital LQTS.

From January 1, 2018 to November 1, 2023, 20 parents (20 mothers; 20 fathers) of fetuses presenting with persistent bradycardia and suspected congenital LQTS were assessed. Autoimmune-mediated atrioventricular block, diagnosed in the presence of maternal anti-Ro/anti-La antibodies, and fetuses with ventricular tachycardia were excluded. Parental ECGs were acquired in the remainder, with comprehensive evaluation, including genomic testing, performed in 12 mothers and 11 fathers.

Among 20 fetuses, 16 had sinus bradycardia and 4 had 2:1 atrioventricular block (intermittent=2; persistent=2). Pathogenic LQTS genetic variants were found in 11 fetuses (KCNQ1=8; KCNE1=1; KCNH2=1; CALM2 [calmodulin 2]=1), 9 mothers (KCNQ1=7; KCNE1=1; KCNH2=1) and 1 father (KCNQ1=1). Maternal corrected QT interval was higher in those with pathogenic variants compared with those who did not undergo genomic testing (456.9±11.6 versus 425.9±28.7 ms, P=0.009) but <400 ms in the paternal carrier. After review, 5 mothers with pathogenic variants were commenced on β-blockers (prepartum=4; postpartum=1). Provocation testing with a treadmill exercise test led to the initiation of β-blockade postnatally in one further case.

The first indication of parental LQTS may be persistent fetal bradycardia. This should prompt consideration of this diagnosis even with a normal maternal corrected QT interval and lead to the initiation of specific management strategies for pregnancy, delivery, and the postpartum period before the results of genomic testing are available.