Fetal Heart Rate and Long QT Syndrome | Journal Scan

Study Questions:

What is the association between fetal heart rate (FHR) and long QT syndrome (LQTS) genotype and the value of the former to predict the latter?


This was a retrospective collection of third trimester FHR measurements from two large founder populations identified through prior cascade screening to carry either the p.Y111C or the p.R518X mutations associated with LQTS type 1. LQTS mutation carriers were compared to family members without LQTS mutation carriage.


Data from 184 pregnancies (87 mothers) resulting in 110 mutation carriers and 74 noncarriers were analyzed. Mean measured FHRs were significantly associated with mutation carrier status: no mutation FHR 143 ± 5 bpm, single mutation 134 ± 8 bpm, double mutation 111 ± 6 bpm. Postnatal disease severity correlated with FHR (worse = lower FHR) especially for double mutation carriers. LQTS genotype was the strongest determinate of FHR in a multivariate maximum likelihood model that accounted for 65% of the variance in FHR.


The authors support the use of FHR for early detection and risk stratification for LQTS.


The association of bradycardia with LQTS is well known; evident by the fact that bradycardia is a criterion on the ‘Schwartz score’ for LQTS diagnosis. Prior work by Mitchell et al. (Circulation 2012;126:2688-95) has correlated severe postnatal LQTS with fetal bradycardia. The current work analyzes this association further by identifying significant differences in mean FHRs dependent on mutation carriage in a larger population. The predictive value of FHR to determine LQTS status outside of the two specific mutations present in this study is not validated. Sustained fetal bradycardia (HR <110 bpm) should prompt consideration for postnatal electrocardiogram evaluation. However, the mean FHR in nearly all single mutation carriers was within the normal range. Interestingly, nearly all normal fetuses in this and the Mitchell study had FHR >130 bpm, perhaps making this a specific, but not sensitive threshold to raise suspicion for underlying LQTS.

Clinical Topics: Arrhythmias and Clinical EP, Congenital Heart Disease and Pediatric Cardiology, Heart Failure and Cardiomyopathies, Implantable Devices, Genetic Arrhythmic Conditions, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Congenital Heart Disease, CHD & Pediatrics and Arrhythmias, CHD & Pediatrics and Quality Improvement

Keywords: Arrhythmias, Cardiac, Bradycardia, Cost of Illness, Electrocardiography, Fetus, Genotype, Heart Conduction System, Heart Defects, Congenital, Heart Rate, Fetal, Long QT Syndrome, Mutation, Phenotype, Pregnancy Trimester, Third, Retrospective Studies, Romano-Ward Syndrome

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