Potential utility of pulsed‐wave Doppler for prenatal diagnosis of fetal ventricular tachycardia secondary to long QT syndrome

We describe here a case of fetal ventricular tachycardia secondary to long QT syndrome (LQTS) treated successfully with maternal intravenous magnesium sulfate. Its prenatal diagnosis using echocardiography was compared with that using magnetocardiography. A 32-year-old woman, gravida 4, para 3, was referred to our institution at 28 weeks of gestation with fetal bradycardia. Cardiac evaluation revealed a structurally normal fetal heart, but ventricular function was reduced with cardiomegaly. Fetal echocardiography and magnetocardiography showed a basal ventricular rhythm of 60 bpm with 2:1 atrioventricular block (Figure 1a), and non-sustained ventricular tachycardia (VT) with a ventricular rate of 220 bpm (Figure 1b). Serial Doppler recordings showed irregular VT with a ventricular rate of 190–220 bpm, suggesting torsade de pointes (TdP) (Figure 1c). Corrected QT (QTc) prolongation of 591 ms was confirmed on fetal magnetocardiography. Since TdP continued and the fetus developed severe hydrops, intravenous magnesium sulfate infusion was administered. Fetal TdP subsequently reduced dramatically, revealing atrioventricular dissociation (Figure 1d). Cesarean section was performed at 35 weeks of gestation and a male infant weighing 2334 g was delivered. Basal fetal electrocardiography showed QTc prolongation of 560 ms. Immediately after birth, magnesium sulfate, mexiletine and propranolol infusions were started, and temporary transvenous pacing wires were placed. Genetic testing revealed a missense p.Ser624Arg mutation in the KCNH2 gene, which is expressed phenotypically as LQTS type 2. Diagnosing LQTS in utero is challenging because fetal ventricular repolarization is impossible to assess on routine ultrasonography. We described previously a case of fetal ventricular tachycardia secondary to LQTS treated successfully with maternal intravenous magnesium1. A previous report compared findings on prenatal Doppler and postnatal electrocardiography in LQTS2, and, similarly, in the current study, we compared real-time prenatal Doppler and prenatal magnetocardiography in LQTS. Although fetal magnetocardiography is used to assess the electromagnetic characteristics of fetal cardiac conduction, it is currently performed in only a few centers worldwide3. Fetal echocardiography is a mechanical, non-electrical, assessment. Simultaneous pulsed-wave Doppler evaluation of superior vena cava (SVC) ascending aorta (aAo) flow is used to examine the sequence and temporal relationship of blood-flow events secondary to atrial and ventricular contractions4. In such Doppler assessment, atrial contraction (retrograde A-wave in the SVC) corresponds to the mechanical consequence of atrial depolarization, whereas the aortic ejection wave (V-wave) corresponds to the mechanical consequence of the QRS complex. Compared with fetal magnetocardiography, a strength of fetal echocardiography is that it can evaluate atrial and ventricular contraction separately. Separate visualization facilitates the diagnosis of dyssynchrony between atrial and ventricular contraction during VT or TdP. Another strength of fetal echocardiography is that it can assess cardiac output in the context of fetal arrhythmia. Although the amplitude of the aortic ejection wave depends on the timing of preceding atrial contraction, it can provide information about ventricular function. During TdP, Doppler recordings of SVC-aAo flow showed irregular aAo Doppler signals of unequal and extremely low amplitude, while regular aAo Doppler signals with relatively uniform and almost normal amplitude were recorded during VT. The fetus rapidly developed severe hydrops due to low cardiac output as TdP continued; thus, magnesium sulfate should be started as soon as TdP is diagnosed5. In summary, serial Doppler recordings are comparable to fetal magnetocardiography in prenatal diagnosis of arrhythmias and allow us to illustrate most of the features encountered in LQTS. In addition, the Doppler approach provides functional assessment, which can help guide management.