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Heart | Critical aortic / pulmonary stenosis

The heart is made up of four chambers (two ventricles and two atria, separated by a wall called the septum) and four valves. The foramen ovale is an opening in the septum connecting the right and left atria. The right side of the heart pumps blood to the lungs and the left side pumps blood to the brain and body. Serious health risks may result from the abnormal development of any of these structures.

Essential Information

  • Aortic stenosis is caused by a narrowed aortic valve, creating an obstruction of blood flow between the left ventricle and the aorta, the largest artery in the body.
  • Pulmonary stenosis is caused by a narrowed pulmonary valve, creating an obstruction of the blood flow between the right ventricle and the pulmonary artery supplying the lungs.
  • Fetal surgical intervention may be required to help unblock or stretch these narrowed connections.

Overview

Aortic stenosis is caused by narrowed aortic valve, creating an obstruction of blood flow between the left ventricle and the aorta, the largest artery in the body. The heart then has to work much harder to pump blood out to the body, and as a result, the heart muscle may become thickened and/or damaged, and the left ventricle may become enlarged or function poorly.

Pulmonary stenosis is caused by a narrowed pulmonary valve, creating an obstruction of the blood flow between the right ventricle and the pulmonary artery supplying the lungs. The right-side of the heart must work much harder and, again, may become damaged and function poorly.

Left untreated, critical aortic or pulmonary stenosis will impact the health and function of the fetal heart.  Without treatment, the affected side may become underdeveloped over time during pregnancy and lead to hypoplastic left or right heart syndrome respectively – these are severe heart conditions which will significantly affect baby’s health after birth.

The diagnosis of aortic or pulmonary stenosis is most often be made by ultrasound, and confirmed by a targeted assessment of fetal heart structure and function – a fetal echocardiogram.

Fetal Therapy

Critical aortic or pulmonary stenosis in the fetus may, in some cases, be amenable to treatment by a fetal balloon valvuloplasty. During this procedure, under ultrasound-guidance, a small needle is passed into the fetal heart through the mother’s abdomen and uterus, and a tiny catheter containing a balloon is introduced through the needle into the ventricle of the heart. It is advanced through the narrowed passageway and inflated, to relieve the obstruction and allow blood to flow more easily and under less pressure. The balloon is then deflated and everything is removed.

The baby will still require monitoring and possible intervention after birth, but this procedure can allow the heart to grow more normally whilst still inside the womb, and, as a result, the newborn’s work-up and treatment can be organized in a much calmer and less urgent manner.

Delivery

Vaginal delivery is usually appropriate for most babies with critical aortic stenosis or pulmonary stenosis, unless there are other obstetric indications for Caesarean section.

Referral Information (for physicians)

Procedures are typically performed in carefully selected cases at a gestation which will allow optimal growth of the heart in-utero. Fetal echocardiography will be organized at the Hospital for Sick Children (SickKids). Procedures are done in the Fetal Medicine Unit at Mount Sinai Hospital and patients should prepare for 1-2 days admission as the feasibility of the procedure is critically dependent on fetal position. Post-operatively, out-of-province patients will be referred back to their local center for ongoing antenatal care and delivery. Local patients will have ongoing follow-up at Mount Sinai and SickKids hospitals.

Please refer patients via the Fetal Cardiac Program at SickKids