Hypoplastic left heart syndrome with restrictive atrial septum and advanced heart block documented with a novel fetal electrocardiographic monitor

Abstract

Hypoplastic left ventricle with congenital heart block has been reported previously in a fetus with concurrent left atrial isomerism and levo-transposition of the great arteries. We present the unusual case of an infant diagnosed in utero with hypoplastic left heart syndrome, a restrictive atrial septum and advanced heart block but with D-looping of the ventricles and no atrial isomerism. In addition, fetal heart rhythm was documented with the assistance of a new fetal electrocardiographic monitor.

CASE REPORT

A 35-year-old woman, gravida 3 para 2, with a history of gestational diabetes was referred for fetal echocardiography following the detection of abnormal fetal heart structure and rhythm at an outside institution. The pregnancy was conceived naturally. Maternal medications included glyburide and prenatal vitamins and the patient denied exposure to other drugs. Maternal antinuclear antigen, anti-Ro and anti-La antibody screens were negative, fetal karyotype was normal, and there was no family history of heart disease.

A fetal echocardiogram performed at 27 + 5 weeks’ gestation demonstrated hypoplastic left heart syndrome (HLHS) with mitral and aortic atresia and a restricted atrial septum with a pulmonary venous Doppler forward to reverse velocity-time integral ratio of 3.1¹. The fetal heart rhythm indicated second-degree heart block with 2 : 1 atrioventricular (AV) conduction with an atrial rate of 140 beats per minute (bpm) and a ventricular rate of 70 bpm. At 34 weeks fetal echocardiography demonstrated advanced second-degree heart block with ventricular rates ranging from 48 to 66 bpm and intermittent periods of complete AV block.

The final fetal echocardiogram at 37 weeks’ gestation revealed an irregular ventricular rate of 51 bpm with Mobitz II second-degree AV block and inconsistent 3 : 1 AV conduction. The patient consented to an institutional review board-approved study investigating a maternal abdominal fetal electrocardiographic monitor (Monica AN24, Monica Healthcare Ltd, Nottingham, UK). The fetal electrocardiogram demonstrated an atrial rate of 136 bpm and a ventricular rate of 48–60 bpm with intermittent conduction (Figure 1).

Figure 1.

Fetal electrocardiogram obtained at 37 weeks’ gestation over a 4-s interval. (a) Original tracing with both maternal and fetal signals. (b) Fetal tracing following filtering of maternal signal, showing intermittent atrioventricular conduction with a regular atrial rate of 136 beats per min and a variable ventricular rate. *Fetal P-wave. †Fetal QRS complex. ‡Maternal signal artifact related to incomplete filtering of a maternal QRS complex.

During weekly third-trimester monitoring normal fetal movement was reported, biophysical profile remained 8 out of 8, and no signs of hydrops fetalis developed. The severity of the fetal cardiac lesion was discussed at each visit and the family opted for full medical intervention including scheduled Cesarean section at 39 weeks’ gestation to allow for rapid neonatal left atrial decompression in the cardiac catheterization laboratory.

The woman presented in spontaneous labor at 37 + 4 weeks and a 3010-g female infant was born via precipitous vaginal delivery. Apgar scores were 8 and 8 at 1 and 5 min. The initial heart rate was 50 bpm, with a respiratory rate of 42 breaths per minute, and SpO₂ of 77%. Physical examination demonstrated an alert and active cyanotic newborn in no acute distress, with an irregular heart rate and a hyperdynamic precordium with a II/VI systolic ejection murmur.

Prostaglandin-E1 therapy was initiated. Twelve-lead ECG demonstrated an atrial rate of 126 bpm and a variable ventricular rate with a rhythm that represented either intermittent advanced second-degree AV block or complete AV block with occasional premature beats. Echocardiography confirmed the fetal diagnosis of HLHS with mitral and aortic atresia and a posteriorly deviated atrial septum with a restrictive patent foramen ovale and an interatrial mean pulsed-wave Doppler gradient of 9 mmHg.

Isoproterenol infusion was initiated for bradycardia and the patient was taken to the cardiac catheterization laboratory, where a radiofrequency perforation of the atrial septum was performed and the interatrial pressure gradient decreased from 20 to 3 mmHg. An electrophysiologic study was attempted but a His deflection could not be identified, precluding assessment of the level of AV block.

Owing to increasing lactic acidosis, atrial and ventricular epicardial temporary pacemaker wires were surgically placed and DDD pacing was initiated on the second day following delivery. The following day, the infant underwent a modified Norwood procedure with a 6-mm right ventricle-to-pulmonary artery shunt. Despite sequential AV pacing, multiple attempts to wean the patient off bypass failed due to persistent hypoxemia and hypotension. After discussion with the family, support was withdrawn and the patient expired in the operating room.

DISCUSSION

We present an unusual case of an infant diagnosed in utero with HLHS, a restrictive atrial septum and advanced heart block. In addition, fetal heart rhythm was documented with the assistance of a new fetal electrocardiographic monitor. In the English language literature, hypoplastic left ventricle with congenital heart block has only been reported in a fetus with concurrent left atrial isomerism (LAI) and levo-transposition of the great arteries (L-TGA)². The infant in this case report was unique, as she did not have either of these concurrent lesions that are more commonly associated with heart block.

Congenital complete AV block (CAVB) is associated with structural heart disease in roughly 50% of cases, most commonly LAI and L-TGA³. It is thought that in L-TGA an anteriorly malpositioned, elongated AV node can lead to AV block⁴. The abnormal atrial development associated with LAI may lead to defective formation of the tract distal to the AV node or destruction of a previously formed AV bundle, thereby causing heart block⁵. In isolated heart block, 70–90% of cases are attributable to maternal anti-Ro and anti-La antibodies, which cross the placenta and lead to fibrosis of the AV node^6–7. Genetic defects, such as mutations in the SCN5A gene, also may cause AV block⁸.

In the present case, maternal auto-antibody titers were negative. It is possible that the fetus developed heart block related to the structural heart disease, although hypoplastic left ventricle with CAVB has only been described in combination with L-TGA and LAI. Another possibility is that there was a separate genetic basis for the AV block. Intraoperatively, the surgeon noted a thickened and unusual appearance of the atrial septum, but the family did not consent to an autopsy, preventing further investigation.

Survival of neonates with prenatally diagnosed isolated CAVB may be as high as 85%, but is significantly lower in patients with concurrent congenital heart disease⁹. Survival with an in-utero diagnosis of HLHS with a highly restrictive atrial septum and advanced AV block was presumed to be very low, and in prenatal counseling the fetus described was given less than a 10% chance of survival.

Fetal echocardiography is the current modality of choice for the assessment of fetal heart rhythm, but it relies on indirect measurement of mechanical events using M-mode and pulsed-wave Doppler modalities. Magnetocardiography provides direct assessment of the fetal cardiac electrical signal, but its prohibitive expense limits its use. Fetal electrocardiography holds promise as an alternative to these modalities. Historically, fetal electrocardiography has been unreliable owing to interference from maternal signals. However, recent improvements in signal acquisition and filtering have led to several reports of antenatal diagnosis of fetal arrhythmia, including prolonged QT interval and premature atrial contractions^10–11. A recent study has shown fetal electrocardiography to be more accurate than fetal echocardiography in the diagnosis of first-degree AV block¹².

The recording performed on this infant is the first reported fetal electrocardiographic diagnosis of advanced second-degree AV block using a contemporary monitor. The monitor used in this report can be applied with limited training and is less expensive than fetal echocardiography. The ability of this monitor to reliably detect fetal arrhythmias is currently under investigation.

In conclusion, we report an unusual case of fetal HLHS and advanced AV block managed prenatally with the assistance of a fetal electrocardiographic monitor.