The natural history of fetal long QT syndrome

• Published in: Journal of electrocardiology 2016-11, Vol.49 (6), p.807-813
• Main Authors: Cuneo, Bettina F., MD, Strasburger, Janette F., MD, Wakai, Ronald T., PhD
• Format: Article
• Language: English
• Subjects: Arrhythmia; Cardiovascular; Disease Progression; Electrocardiography; Electrocardiography - methods; Female; Fetal Diseases - diagnosis; Fetal Monitoring - methods; Fetus; Fetuses; Humans; KCNH2 mutation; Long QT syndrome; Long QT Syndrome - diagnosis; Long QT Syndrome - embryology; Magnetocardiography - methods; Male; Mutation; Reproducibility of Results; Sensitivity and Specificity; Signal processing; Studies; Torsades de pointes
• ISSN: 0022-0736; 1532-8430
• DOI: 10.1016/j.jelectrocard.2016.07.023

Abstract Introduction Fetal magnetocardiography (fMCG), the magnetic analog of ECG, has provided invaluable insight into the mechanisms of fetal arrhythmias. In the past 15 years, we have evaluated over 300 fetuses with arrhythmia by fMCG. We review the unique characteristics and natural history of the long QT syndrome (LQTS) rhythms. Methods We reviewed the fMCGs of subjects referred with suspected LQTS based on either a positive family history or echo diagnosis of the LQTS rhythms ( sinus bradycardia, ventricular tachycardia, or 2:1 AV conduction) to the Biomagnetism laboratory in the Department of Medical Physics, UW-Madison. We recorded fMCGs using a 37-channel (Magnes, 4D Neuroimaging, Inc., San Diego, CA) superconducting quantum interference device (SQUID) biomagnetometer, housed in a magnetically-shielded room for 1200 to 6000 s. Signal processing was used to remove maternal interference. Cardiac intervals (R-R, p, QRS, QT) were measured and compared to published normals. We correlated fetal heart rate (FHR) patterns and effects of fetal movement on FHR and rhythm using actocardiography. Results 39 fetuses were studied at a mean of 28 (19–28) weeks of gestation. All had structurally normal hearts. One was on amiodarone for suspected supraventricular tachycardia and hydrops. Five had serial fMCGs. Isolated sinus bradycardia with a QTc > 490 ms was found in 35: 33 had a KCNQ1 mutation one each was a false positive./false negative. Four fetuses had torsades de pointes and 3 had periods of 2:1 conduction and either KCNH2 or SCN5A mutations. TdP was rarely initiated with a preceding long-short pattern and did not degenerate into ventricular fibrillation. One fetus with TdP died in utero, 2 with fetal TdP had postnatal cardiac arrest. Conclusion Fetal LQTS is diagnosed by an fMCG QTc > 490 ms (89% sensitivity and specificity). TdP are seen with uncharacterized, KCNH2 or SCN5A R1623q mutations. Fetal TdP occurs when QTc ≥620 ms. Identifying fetal LQTS and defining its rhythms by fMCG risk stratifies postnatal management.