title: Fetal heart rate predictors of long QT syndrome.
abstract: BACKGROUND
  Fetal long QT syndrome (LQTS) is associated with complex arrhythmias including torsades de pointes and 2° atrioventricular block. Sinus bradycardia has also been associated with fetal LQTS, but little is known of this rhythm manifestation. Our purpose was to characterize the fetal heart rate (FHR)/gestational age (GA) profile of fetal LQTS.
  
  
  RESULTS
  We ascertained fetal LQTS subjects by family history (Group 1) or fetal arrhythmia referral (Group 2). We compared FHR in LQTS subjects versus normal fetuses. To identify FHR predictors of LQTS, we calculated a bradycardia index as % of LQTS FHR recordings either ≤110 beats per minute (obstetric standard) or ≤3(rd) percentile for GA. Among 42 LQTS subjects, 26 were in Group 1 and 16 in Group 2. There were 536 normal fetuses. The bradycardia index was only 15% for FHR ≤110 beats per minute, but 66% for FHR ≤3rd percentile for GA. Ten fetuses with complex arrhythmias also had severe and sustained sinus bradycardia throughout gestation. Identifying a fetal proband in Group 2 resulted in LQTS diagnosis in 9 unsuspected members of 6 families.
  
  
  CONCLUSIONS
  FHR varies by GA in both normal and LQTS fetuses. Postnatal evaluation of neonates with FHR ≤3(rd) percentile for GA may improve ascertainment of LQTS in fetuses, neonates, and undiagnosed family members.
authors.affiliation: The Heart Institute for Children, Hope Children's Hospital, 4440 W 95th Street, Oak Lawn, IL 60453, USA.
authors.forename: Jason L
authors.initials: JL
authors.lastname: Mitchell
authors.forename: Bettina F
authors.initials: BF
authors.lastname: Cuneo
authors.forename: Susan P
authors.initials: SP
authors.lastname: Etheridge
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Horigome
authors.forename: Hsin-Yi
authors.initials: HY
authors.lastname: Weng
authors.forename: D Woodrow
authors.initials: DW
authors.lastname: Benson
mesh_terms: D001919:Bradycardia / Q000175:diagnosis / Q000503:physiopathology; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006340:Heart Rate, Fetal / Q000502:physiology*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008133:Long QT Syndrome / Q000175:diagnosis* / Q000503:physiopathology*; D011237:Predictive Value of Tests; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods*