What is Aortic Valvular Atresia?
Aortic valvular atresia is a birth defect where the flaps of the aortic valve in the heart are stuck together. This defect often occurs in a range of abnormalities of the left ventricular outflow tract (LVOT), a part of the heart that lets blood out from the left section of the heart. The location of the defect determines if it’s labeled subvalvular, valvular, or supravalvular. It commonly shows up as a narrow aortic valve, but in rare instances, it can be completely closed. In such cases, the faulty valve can be in various shapes, and the leaflets of the valve are abnormal or fused, not allowing any blood flow. It may also be associated with another rare heart condition known as hypoplastic left heart syndrome (HLHS), where the left side of the heart and the aortic structures are not properly developed.
In the classic scenario of aortic valve atresia, there is usually a physical connection between the right and left sides of the heart. This connection can be found in various forms including a hole in the wall between the upper heart chambers or a hole in the wall separating the lower heart chambers if the mitral valve works. The right side of the heart is usually larger, whereas the left side is smaller and thick-walled. The mitral valve is often small, and in some situations, the mitral valve can be stuck together too.
There have been no reported cases where the aorta and the main lung artery switch places with this condition, and the main lung artery usually develops correctly from the right side of the heart. Because of the missing aortic valve, the root of the aorta, where the aorta connects to the heart, usually starts at the base of the heart. The arteries that supply blood to the heart start normally from this aorta root, but the Rising and arch aorta are usually underdeveloped. The aorta branches are normal in size and all studied cases have reported a large ductus arteriosus (an artery in a fetus that avoids the routing of blood through the lungs) emptying into the descending aorta, supplying the fetus with mixed-oxygenation blood.
What Causes Aortic Valvular Atresia?
HLHS, or hypoplastic left heart syndrome, often occurs in families and is usually discovered during the screening for a heart valve condition called congenital bicuspid aortic valve. This is typically done using a heart imaging technique called echocardiography.
Studies have shown that HLHS appears in up to 8% of siblings who have a family member already diagnosed with HLHS. Moreover, it can be found in 3.5% of close relatives of these patients. Furthermore, over 20% of these relatives have other types of heart birth defects.
But the abnormalities aren’t limited to the left side of the heart. Reports show that people with congenital left heart disease can also have defects in the large blood vessels that carry blood from the heart, as well as weak spots in the body’s main artery, known as thoracic aortic aneurysms.
A screening study in 2015 found a high rate of other birth defects, such as a bicuspid aortic valve and narrowing of the aorta, in family members of patients with HLHS.
Sometimes, HLHS can also occur in conjunction with Turner syndrome, a genetic condition that’s related to the bicuspid aortic valve and narrowing of the aorta. Other possible associations include dextrocardia (a condition where the heart is on the right side of the chest), mesocardia (the heart is in the middle of the chest), and conditions like DiGeorge syndrome and chromosome 22-q11 deletion.
Risk Factors and Frequency for Aortic Valvular Atresia
Aortic valvular atresia, a heart condition, occurs in about 1% of live births. The condition known as HLHS is found in about 0.163 per 1000 live births as reported by the New England Regional Infant Cardiac Program. It’s worth noting that a solitary aortic valvular atresia mainly affects males, accounting for 73% of cases, and the combination of aortic and mitral stenosis along with HLHS has over 70% male predominance. Sadly, there isn’t a lot of reliable global data on these conditions.
Signs and Symptoms of Aortic Valvular Atresia
Aortic valvular atresia is a heart condition that can be detected quickly after birth. The central initial signs include difficulty in breathing, bluish discoloration of the skin (cyanosis), and rapid advancement of heart failure. Breathing quickly or with difficulty is one of the most common signs of this condition, observed in about 60% of newborns. Cyanosis might not be noticeable at once but becomes evident as a particular artery in the newborn’s heart, known as the ductus arteriosus, closes. This typically happens around two days after birth. The level of oxygen in the blood can change, and in some babies (16%), it can drop slightly when they cry but can be improved to a degree with additional oxygen.
On physical examination, there can be a noticeable bulge in the chest region over the heart (precordial bulge), but it’s not always a reliable sign. More than 50% of these patients have a specific type of heart murmur that can be graded between 1 to 3 in intensity and is clearest along the left side of the breastbone. The child’s doctor may also notice a single or very closely split second heart sound at the base of the heart. Rapid heart failure can develop in about 60% of these patients, typically around 2.5 days after birth, and is often linked with an enlarged liver. An added heart sound (S3), chest sounds indicating fluid in the lungs, swelling, and enlarged spleen can also sometimes be seen. The baby’s blood pressure might be lower than average, around 65/45 mmHg, with a narrow difference between the systolic and diastolic pressure. There’s usually no significant pressure difference between measurements taken from the baby’s upper and lower limbs.
Testing for Aortic Valvular Atresia
Evaluations for potential heart issues can start even before a child is born. Doctors often use a tool called color Doppler during a sonogram (or ultrasound) to look at the heart. If there appears to be no blood flow through the aortic valve, the child may be at a higher risk for a condition called aortic valvular atresia. This can also put the child at risk of developing a more severe condition known as Hypoplastic Left Heart Syndrome (HLHS), even if the left side of their heart looks normal or only slightly larger than usual.
Once the child is born, an X-ray of the chest can provide more information. The heart may look rounded or show a pattern that’s also seen in another condition called truncus arteriosus. This includes a narrowing at the base of the heart, a rounded peak, and a sort of ‘shoulder’ on the left side of the heart. Sometimes there might be a ‘bulge’ because of the pulmonary artery, but this only occurs in a small number of cases. This type of X-ray can also show fluid in the lungs and, in some cases, a partial collapse of the upper or middle part of the lungs.
An electrocardiogram (EKG) is another test that can give important clues. It might show a shift to the right side, signs of the right side of the heart being larger than normal, and an enlarged right atrium (the upper chamber of the heart). However, in some cases, the pattern might look normal for the child’s age. Some unusual findings on the EKG could include a shift to the left side, signs of the left side of the heart being larger than normal, and issues with the electrical signals that control the heart’s rhythm. Sometimes, an EKG might show a pattern called the Wolff-Parkinson-White pattern or a right bundle branch block. One small but noteworthy detail is the lack of a type of wave (known as a Q wave) in a specific lead (or connection) on the EKG. Although this could suggest issues with the aortic valve, it’s not exclusive to aortic valvular atresia and, therefore, isn’t a sure sign of the condition.
Treatment Options for Aortic Valvular Atresia
When it comes to repairing aortic valve abnormalities in infants, the appropriate surgical approach depends on the specifics of the baby’s heart. These conditions can range from hypoplastic left heart syndrome (HLHS), a severely underdeveloped left side of the heart, to ventricular septal defect (VSD), which is a hole in the wall separating the heart’s lower chambers.
If the left ventricle (the heart’s primary pumping chamber) is underdeveloped, doctors may opt for a three-step surgery involving the Norwood, Bidirectional-Glenn, and Fontan procedures. This series of surgeries essentially redirects blood flow around the underdeveloped part of the heart.
If the baby has a VSD and the potential for using both ventricles, another operation, called the Yasui procedure, could be utilized soon after birth. This technique involves making a tunnel from the left ventricle to the lung artery using the existing hole (VSD). The lung artery is then split, with one part connected to the aorta and the other attached to the right ventricle using a tube. While this surgery is high-risk, it can initially permit the use of both heart chambers for blood flow and offer complete correction.
An alternative approach involves using the Norwood operation initially, allowing the baby to function with single ventricle physiology for several months. This is then followed by the Rastelli operation which restructures the aorta, the heart’s main artery, and repairs the hole in the heart and the connection to the lung artery. This two-segment repair strategy was first introduced by Dr. William Norwood in 1981.
The decision regarding the surgical approach is complex and continues to be debated among medical professionals. Repairing the heart to use both chambers, whether done all at once or in stages, is seeing consistently improved outcomes and is thought to stack up well against single chamber repairs. However, post-surgical interventions remain common due to issues associated with the tubes connecting the heart chambers, even as techniques and materials improve.
What else can Aortic Valvular Atresia be?
If a baby might have a heart condition, doctors need to consider other possible diagnoses related to the heart’s structure. When using a 2-D echo test during pregnancy, it can sometimes be difficult to make an accurate diagnosis right away. Symptoms such as difficulty in breathing and a bluish color of the skin, lips, or nailbeds (cyanosis) might not be visible at birth but can appear in many other heart conditions that the baby is born with. These include:
- Narrowing of the main artery that carries blood from the heart to the rest of the body (Coarctation of the aorta)
- A combination of four heart defects present at birth (Tetralogy of Fallot)
- A condition where there is only one large artery in the heart instead of two (Truncus arteriosus)
- A rare heart defect that’s present at birth where the valve that controls blood flow from the right atrium to the right ventricle doesn’t work properly (Ebstein anomaly)
- A condition where the tricuspid valve doesn’t develop, preventing blood flow from the right atrium to the right ventricle (Tricuspid valve atresia)
- A heart defect where the pulmonic valve doesn’t develop properly, affecting blood flow to the lungs (Pulmonic valve atresia)
- A condition were the two main blood vessels leaving the heart are swapped (Transposition of the great arteries)
- A rare heart defect where the left side of the heart is critically underdeveloped (HLHS)
- A heart defect where the blood vessels that take blood from the lungs to the heart aren’t connected correctly (Anomalous pulmonary venous return)
It is crucial for doctors to consider these other conditions when making their diagnosis. They must conduct proper tests to ensure they get the correct diagnosis.
What to expect with Aortic Valvular Atresia
Aortic valvular atresia, if left unattended, can lead to fatal consequences. It’s responsible for 25% of heart-related deaths in newborns. When suspected after birth, it’s crucial to swiftly start treatment with a drug called prostaglandin E1 to prevent the closure of a crucial blood vessel called the patent ductus arteriosus (PDA).
Studies indicate that mortality rates significantly drop following intervention, irrespective of whether it’s a single or staged operation. A review of 27 patients from 1990 to 2013, tracked for 23 years, revealed a re-treatment rate of roughly 50%. Notably, there were no deaths between different stages of a common surgical process, the Norwood procedure.
Further studies show that the rate of freedom from re-operation at the 5-year mark averages between 14% and 29%. Meanwhile, the overall survival rate at 10 years is almost 90%.
Possible Complications When Diagnosed with Aortic Valvular Atresia
Surgery complications can happen. The death rate during surgery is about 7%, often due to problems with machines used to help patients breathe, as reported in a particular study. The decision to perform a follow-up surgery depends on various factors. Sometimes, replacements of a tube that carries blood from the heart to the rest of the body, repairs to the passage from the heart’s main pumping chamber to the aorta, and repairs to the aorta itself might be necessary. It’s also possible that remaining holes in the heart’s wall need to be mended.
Like all heart surgeries for children, there could be risks for conditions like a type of bronchitis that produces a lot of mucus, a disease where too much protein is lost from the digestive tract, and malformed blood vessels in the lungs. The cause of these malformed blood vessels is not fully understood.
Common risks and complications may include:
- Death during surgery
- Follow-up surgeries
- Tube replacements
- Repairs to sections of the heart and aorta
- Mending holes in the heart’s wall
- A bronchitis variant
- Excessive protein loss from the digestive tract
- Malformed blood vessels in the lungs
Preventing Aortic Valvular Atresia
Currently, there’s no proven way to prevent this kind of birth defect. It’s advisable for pregnant women to keep up with all their regular pregnancy check-ups and continue taking any necessary vitamins. Interestingly, genetic factors, including changes in a gene known as NOTCH1, might play a role in increasing the risk of this condition. However, more research is needed to fully understand this connection.
