Prenatal diagnosis of long QT syndrome with the superior vena cava–aorta Doppler approach

We describe a fetus at 36 weeks with long QT syndrome presenting with variable types of atrioventricular blocks, ventricular premature beats, and torsades de pointes. All these diagnoses were made with the superior vena cava–aorta Doppler approach and confirmed with postnatal electrocardiography.

Congenital long QT syndrome (LQTS) is a heterogeneous inherited disorder with an increased risk of lethal ventricular arrhythmia. Severe forms of LQTS have been described in fetuses, characterized by bradycardia, arrhythmia, and eventual fetal demise. However, as fetal ventricular repolarization is impossible to assess with routine ultrasonography, prenatal LQTS remains a difficult diagnosis. Simultaneous recording of the aorta (Ao) and superior vena cava (SVC) Doppler waveforms has been shown to allow identification of the chronology of atrial and ventricular contractions in various forms of fetal arrhythmia. We report the case of fetus at 36 weeks with LQTS, presenting several types of atrioventricular (AV) block associated with ventricular arrhythmia investigated with the SVC-Ao Doppler approach. Postnatal electrocardiography (ECG) helped determine the potentials and limits of ultrasound in the prenatal diagnosis of this challenging syndrome.

Case Report

A 31-year-old woman, gravida 2, para 1, was referred to our fetal cardiology unit at 36 weeks-1 day of gestation for fetal arrhythmia. Neither she nor her family had any medical history of arrhythmia or sudden death. Doppler studies were done on Philips Sonos 4500 (Philips Healthcare, Andover, MA) using a 6-MHz probe.

The diagnosis of rhythm disturbances was done with the SVC-Ao Doppler approach. From a vertical 4-chamber view of the heart, a 90-degree rotation of the probe gives a sagittal view of the SVC and the ascending Ao closely related to each other ( Figure 1 ). The sample volume is then widened to simultaneously record blood flow in both vessels. The retrograde A wave in the SVC corresponds to atrial contraction and the Ao ejection to the ventricular contraction.

Doppler recordings of SVC-Ao flows showed a basal heart rhythm of 120 bpm with first-degree AV block (AV delay >95th percentile) and variable AV intervals ( Figure 2 , A). Ventricular premature contractions were also suspected ( Figure 3 ). Episodes of tachycardia at 300 bpm were observed during which an irregular and fluctuating Doppler signal in the ascending Ao was recorded ( Figure 4 , A). The morphologic cardiac evaluation revealed normal findings, as did biventricular systolic function (left ventricular shortening fraction of 33% by M mode). Two days later, prolonged periods of bradycardia were noted, as low as 60 bpm, due to a high-degree AV block ( Figure 5 ), including 2:1 AV block ( Figure 6 ). The cardiac systolic function was then decreased (left ventricular shortening fraction of 25%) with appearance of cardiomegaly. Due to these signs of fetal compromise, the patient was delivered by cesarean section. Apgar score of the female neonate was 9 at 5 minutes and her birthweight was 3600 g. Her basal ECG showed a sinus rhythm with a QTc prolongation of 671 milliseconds using Bazett correction ( Figure 2 , B). Initial echocardiography revealed a moderately depressed biventricular function (left ventricular shortening fraction of 27%). Immediately after birth, she experienced sustained recurrent torsades de pointes ( Figure 4 , B) alternating with severe bradycardia, requiring esmolol and isoproterenol infusion to maintain a sinus heart rhythm at the rate of 110 bpm until an epicardial double-chamber pacemaker (Medtronic, Minneapolis, MN) was implanted. After pacemaker implantation, she was in 2:1 AV block with permanent ventricular pacing. Ventricular function normalized. She was discharged home on propranolol and mexiletine and after 9-month follow-up she did not experience any ventricular arrhythmia. Mexiletine was then withdrawn since no mutation in SCN5 encoding for the alpha subunit of the sodium channel was identified. Genetic testing revealed a heterozygous mutation for Gly628Ser in the KCNH2 gene, encoding for the pore-forming subunit of the potassium channel and phenotypically expressed as LQT2 syndrome.