In Utero Diagnosis of Long QT Syndrome by Magnetocardiography

Abstract

Background The electrophysiology of long QT syndrome (LQTS) in utero is virtually unstudied. Our goal here was to evaluate the efficacy of fetal magnetocardiography (fMCG) for diagnosis and prognosis of fetuses at risk of LQTS. Methods and Results We reviewed the pre/postnatal medical records of 30 fetuses referred for fMCG due to a family history of LQTS (n=17); neonatal/childhood sudden cardiac death (n=3) and/or presentation of prenatal LQTS rhythms (n=12): 2° AVB, ventricular tachycardia, heart rate < 3rd percentile. We evaluated heart rate and reactivity, cardiac time intervals, T-wave characteristics, and initiation/termination of Torsade de Pointes (TdP), and compared these with neonatal ECG findings. After birth, subjects were tested for LQTS mutations. Based on accepted clinical criteria, 21 subjects (70%; 9 KCNQ1, 5 KCNH2, 2 SCN5A, 2 other, 3 untested) had LQTS. Using a threshold of QTc= 490 ms, fMCG accurately identified LQTS fetuses with 89% (24/27) sensitivity and 89% (8/9) specificity in 36 sessions. Four fetuses (2 KCNH2 and 2 SCN5A), all with QTc ≥ 620 ms, had frequent episodes of TdP, which were present 22–79% of the time. While some episodes initiated with a long-short sequence, most initiations showed QRS aberrancy and a notable lack of pause dependency. T-wave alternans was strongly associated with severe LQTS phenotype. Conclusions QTc prolongation (≥490 ms) assessed by fMCG accurately identified LQTS in utero; extreme QTc prolongation (≥620 ms) predicted TdP. FMCG can play a critical role in the diagnosis and management of fetuses at risk of LQTS.

Diagnosis and Treatment of Fetal Cardiac Disease

“…435 Management of the fetus with suspected LQTS includes close observation, postnatal evaluation, and measurement of the QTc by fMCG or fetal electrocardiography if available. 436 Fetal treatment is not recommended for bradycardia; however, torsades de pointes and ventricular tachycardia (VT) require treatment if they occur (Tables 13 and14). 435 Maternal electrolyte abnormalities, especially hypomagnesemia and hypocalcemia, should be avoided, as well as drugs and anesthetic agents that lengthen the QT interval.…”

“…353 Unfortunately, although terbutaline may increase fetal rates and prolong pregnancy, no studies have shown survival benefit. Although there is merit to the notion, because of significant technical limitations, fetal pacing has not been shown to be successful in improving survival or prolonging gestation 436 and therefore at present is experimental and not recommended as part of usual care.…”

Utility of High-Resolution Magnetocardiography to Predict Later Cardiac Events in Nonischemic Cardiomyopathy Patients With Normal QRS Duration

“…Multichannel MCG has been used clinically for the detection and diagnosis of fetal arrhythmias, 20 and for analysis in healthy adults as well as detection of abnormalities in various heart diseases. 7,21-23 Korhonen et al have reported the usefulness of QRS fragmentation detected quantitatively using the time-waveforms of MCG for predicting MACE in patients with previous myocardial infarction.…”

Clinical Features of Long QT Syndrome in Children

“…11 In addition to a low baseline heart rate, nonreactive heart rate patterns are also suggestive in LQTS fetuses and may be explained by lower-than-normal right sympathetic cardiac activity or a blunted response to a sympathetic drive, as seen postnatally. 8 LQTS with 2:1 AVB is commonly observed during the fetal and neonatal periods, 9,10 but rarely observed in childhood and adulthood. In neonates with LQT2 and LQT3, 2:1 AVB was observed in 55% and 83% of the patients, respectively (Figure 1).…”

“…10 AVB may be caused by functional block of the ventricle, because of prolongation of the ventricular refractory period, and in the majority of patients the atrioventricular conduction returns with a significant decrease in the QTc interval during the follow-up period. 8 That may explain the rare occurrence of AVB in older children and adults with LQTS.…”