Antenatal Presentation of Congenital Long QT Syndrome: A Prenatal Diagnosis Not To Be Missed

Abstract

We focus attention on the antenatal diagnosis of long QT syndrome (LQTS). Recent data show that a diagnosis of LQTS is possible at an early stage of life, namely, the fetal period, and that LQTS, now well established as capable of explaining some sudden infant death syndromes (SIDS), can explain some fetal loss [2, 8]. This new medical perspective implies strong preventative implications. Long QT syndrome is an heterogeneous inherited arrhythmia. To date, 10 responsible genes have been identified [7, 9]. The genetic prevalence is 1 to 2,000, but considering that most mutation carriers remain asymptomatic, clinical prevalence is less important [9]. Because LQTS is characterized by an abnormal prolongation of QT interval on electrocardiogram, it poses an increased risk of sudden death, usually due to ventricular fibrillation [9]. Echocardiography shows no heart structural abnormality [7, 9], and 25% of unexpected fetal loss cases remain unexplained after autopsy [6]. According to recent reports, LQTS can be diagnosed in utero. An M-mode echocardiogram or magnetocardiography, if available, can reveal sustained fetal bradycardia, decreased heart rate variability, 2:1 atrioventricular block, and ventricular arrhythmias [3–5, 10]. Fetal bradycardia is defined as a heart rate slower than 100 beats/min [4]. Recently, waveforms of torsade de pointes recorded on fetal magnetocardiogram at 28 weeks of gestation have been reported [6]. Parallel to these new fetal rhythm investigation methods, LQTS appears to be a silent killer among fetuses and newborns [8, 13]. An abnormal QT prolongation is associated with SIDS [11]. According to recent molecular screening studies, LQTS could be a strong contributor to SIDS, being responsible for 9.5% of them [1]. These findings suggest that abnormality in fetal rhythm compatible with LQTS (i.e., sustained fetal bradycardia, 2:1 atrioventricular block, or ventricular arrhythmias), even if there is no family history of sudden death, must require careful evaluation because of the risk for fetal loss, SIDS, or life-threatening events later in life. When LQTS is evoked, pregnancy should be managed in a medical center with cardiac facilities to allow preventive care such as beta-adrenergic blockers, adapted multidisciplinary follow-up assessment, identification of previously undiagnosed relatives, and early parental education with infant cardiopulmonary resuscitation and contraindicated medications. Beta-blocking therapy is known to be effective for children with LQTS [12], and some authors have reported prenatal treatment of fetal LQTS with beta-adrenergic blockers [3]. Further studies are needed to determine whether prenatal administration of this medication can be recommended.