Heart | Hypoplastic left heart syndrome with intact atrial septum

The heart is made up of four important chambers (two ventricles and two atria), as well as a wall called the “atrioventricular septum” that separates the left and right sides of the heart, four important valves, critical arteries and veins that all work together to pump blood from the heart to the lungs and to the rest of the body. Serious health risks may result from the abnormal development of any of these structures.

Essential Information

  • The septum refers to the wall that separates the left side of the heart (the left ventricle and left atrium) from the right side of the heart (the right ventricle and the right atrium). Sometimes, there is a small opening in the septum, called an atrial septal defect (ASD) or a ventricular septal defect (VSD). If there is no opening, or only a very small opening, in the septum separating the left atrium from the right atrium, this is referred to as an intact or restrictive atrial septum.
  • Hypoplastic left heart syndrome (HLHS) occurs when the left side of the heart is severely underdeveloped, and therefore unable to pump blood to the rest of the body. When HLHS occurs in combination with an intact or restrictive atrial septum, the condition is especially severe.
  • In certain cases of HLHS with an intact or restrictive atrial septum, a small hole may be created in the atrial septum while the baby is still inside the womb in order to help improve baby’s stability after birth.

Overview

Hypoplastic left heart syndrome (HLHS) occurs when the left side of the heart is severely underdeveloped, and therefore unable to pump blood to the rest of the body. This is a very severe cardiac condition, which, if not corrected soon after baby is born, can be fatal.

In most cases of HLHS, there is also a small hole in the wall that separates the right and left atria, referred to as an atrial septal defect. If there is no hole in the atrial septum (an intact atrial septum, or if the hole is very narrow (a restrictive atrial septum), the outcomes for HLHS are especially poor.

HLHS is typically detected on ultrasound between 18-22 weeks’ GA. This diagnosis is then confirmed by a targeted assessment of the baby’s heart structure and function, called a fetal echocardiogram. Occasionally, additional imaging in the form of a fetal cardiac MRI may be required.

 

Treatment

Atrial septum shunting

Because the outcomes of babies with HLHS with an intact or restrictive atrial septum are poor, a procedure to create a hole, or a shunt in the atrial septum may be offered while the baby is still in the womb. This procedure is done under ultrasound-guidance using a catheter, called a stent, and a small balloon.

Though emergency surgery will still be required after birth, in-utero intervention may reduce the severity of the damage to the heart and the lungs and improve the survival rates for affected babies.

 

Referral Information (for physicians)

Procedures are typically performed as soon as the diagnosis is confirmed to allow for maximal in-utero growth. Echocardiography will be organized at The Hospital for Sick Children (SickKids). Patients should prepare for 2-3 days admission as surgical feasibility is highly dependent on fetal position. Postoperatively, out-of-province patients will be referred back to a local centre with experience in managing these high-risk cardiac conditions for further antenatal care and delivery. Local patients will have ongoing follow-up at Mount Sinai Hospital and SickKids.