Circulation: Clinical Summaries

Long QT syndrome (LQTS) is among the most common causes of sudden cardiac death in the young. Although its role in sudden infant death syndrome has been known for more than a decade, a very recent study by Crotti and colleagues suggests that LQTS may also be responsible for >10% of unexplained fetal death. This finding implies that many lives might be saved if LQTS could be accurately diagnosed and effectively treated in utero. Our study demonstrates that both are possible. Using fetal magnetocardiography (fMCG), the magnetic analog of ECG, we show that fetal QTc has diagnostic value for identification of fetuses with LQTS and prognostic value for prediction of a severe phenotype. In addition, fMCG was invaluable for definitive detection of the signature lethal rhythm of LQTS, Torsades de Pointes. The fMCG findings not only prompted successful in utero pharmacological treatment to restore sinus rhythm and postpone the delivery of a premature fetus, but also guided anticipatory neonatal care. Because of the known association between LQTS and low heart rate, some fetuses with an isolated finding of lowfor-gestational-age heart rate (< 3%) were referred for fMCG testing and were found to have LQTS. This led to the identification of LQTS in several unsuspecting first-degree relatives. Currently, fMCG is not readily accessible to clinicians because of the cost and complexity of the instrumentation; however, a new technology, based on atomic magnetometers, has the potential to rectify this situation. See p 2183.