What is Aortopulmonary Septal Defect?
An aortopulmonary (AP) window, also called an AP septal defect, is a very rare kind of congenital heart defect. It makes up less than half a percent of all congenital heart diseases. This problem can exist on its own, or it can be present along with other kinds of congenital heart diseases. These might include a hole in the wall between the heart’s lower chambers, an interrupted aortic arch, a group of four related heart defects known as tetralogy of Fallot, or, infrequently, abnormalities in the coronary arteries.
By definition, an AP window is characterized by a physical connection between the main artery carrying blood from the heart to the body (the ascending aorta) and the main artery carrying blood from the heart to the lungs (the main pulmonary artery). This connection happens “side by side.” However, the aortic valve forms normally, as does the pathway for blood outflow from the right lower chamber of the heart. These characteristics differentiate an AP window from truncus arteriosus, another type of congenital heart defect. Embryologically, an AP window forms when the large arteries do not fully divide during fetal development.
What Causes Aortopulmonary Septal Defect?
Aortopulmonary window defects make up much less than 0.5% of all heart defects present at birth, known as congenital heart defects. These defects often show up alongside other congenital heart problems about half of the time. Some of these other issues can include defects like tetralogy of Fallot, interrupted aortic arch, D-transposition of the great arteries, narrowing of the aorta, ventricular septal defect, abnormalities of the coronary arteries, and issues with the tricuspid valve.
Despite these defects seeming to belong to the same family of irregularities as others found in the same region of the heart, it is not commonly found in conjunction with DiGeorge syndrome. This indicates that this defect may not be connected to issues with the cardiac neural crest, a group of cells that play a significant role in the development of the heart during the embryonic stage.
Risk Factors and Frequency for Aortopulmonary Septal Defect
An AP window is a rare birth defect of the heart that occurs in less than 0.5% of all heart defects present at birth. Some genetic connections, like VACTERL and Bohring-Opitz, are known, but no specific causes related to the mother’s environment have been identified so far.
Signs and Symptoms of Aortopulmonary Septal Defect
An AP window, or aortopulmonary window, is a heart condition that can be diagnosed when a baby is still in the womb or shortly after they are born. Signs of an AP window typically present when the baby’s pulmonary blood flow increases in the first few weeks of life. This condition can cause several symptoms:
- Sweating, especially during feeding
- Rapid breathing
- Rapid heart rate
- Difficulty gaining weight
- Increased breathing problems during a viral infection
Additionally, the baby’s chest may appear unusually active, a sign known as a hyperdynamic precordium. The baby might also have extremely strong pulses because the pressure in their blood vessels decreases due to reverse blood flow from their aorta. Sometimes, a continuous murmur, or an abnormal sound heard during a heartbeat, may be detected as this usually indicates a significant connection between the aorta and pulmonary artery.
An AP window can sometimes be linked to other heart defects, which can change the way the condition presents. For instance, in the case of the tetralogy of Fallot, you might hear a sound indicating a restriction in blood flow through the pulmonary valve. If an AP window occurs with an interrupted aortic arch, the neonate can suddenly develop shock as the ductus arteriosus constricts. In less serious circumstances, a continuous heart murmur could be noted. It’s also possible for an AP window diagnosis not to be made until much later in life, potentially presenting symptoms related to Eisenmenger syndrome, which includes bluish skin color (cyanosis) and abnormal nail shape (clubbing). Nevertheless, a late diagnosis of the AP window still necessitates a thorough evaluation of how the blood flows in the heart, to assess if the patient is still a candidate for repair surgeries.
Testing for Aortopulmonary Septal Defect
In kids with an Aortopulmonary (AP) window, a chest X-ray will often show a larger than normal heart and increased markings in the lungs. An electrocardiogram, or EKG, will reveal a faster than normal heart rate, and higher voltages from both the right and left side of the heart. After suspecting that there is an excessive flow from left to right in the heart, the diagnosis of an AP window is typically confirmed by an echocardiogram. Because the connection between two major blood vessels, aorta and pulmonary artery, is generally unobstructed, colour Doppler echocardiography usually cannot detect a high-speed coloured jet of blood flow. If the doctor strongly suspects an AP window and the echocardiogram gives good quality 2D images, it will typically be enough to measure the AP window communication. In some cases, where echocardiogram results are not clear enough, a CT scan could help show the AP window.
In addition to this, the echocardiogram should also give a full picture of the rest of the heart structures, and check for other heart diseases such as Tetralogy of Fallot, interruption of the aortic arch. It is also important to locate and identify the coronary arteries. Cardiac catheterization, which is a test to check the heart’s function and structures, usually doesn’t provide much additional diagnostic information if the diagnosis is made early or can be made with less invasive methods. However, in cases where the diagnosis is made late, or in adults, especially if they have a bluish or purplish skin color indicating less oxygen in the blood, catheterization might be used to check the resistance to blood flow in the lungs, as Eisenmenger syndrome might develop. If there is any lung blood vessel disease, then reactivity testing should be carried out during catheterization to determine whether it is advisable to close the AP window.
Treatment Options for Aortopulmonary Septal Defect
The treatment for a large ‘AP window’, a type of heart defect, is typically a surgical procedure where a patch is used to close the opening. This surgery tends to produce good results when performed early in a baby’s life. Smaller defects can be closed directly by tying or stitching it closed. Performing surgery becomes more challenging if the baby also has other heart abnormalities and this can also lead to worse outcomes.
There are certain cases where closure devices, usually used in the treatment of other heart defects, can be used to close an AP window. This typically applies to defects that are smaller and allow for closure later in childhood.
Medications such as diuretics (for example, furosemide and chlorothiazide) and digoxin can be used to temporarily relieve symptoms. However, these do not have a significant impact on the progression of the disease. ACE inhibitor therapy can also be considered to reduce the stress on the heart. However, these medical treatments should be used with caution, considering potential issues like abnormal kidney blood flow. Surgery is usually recommended upon diagnosis as there’s a risk of developing irreversible lung hypertension over time. The AP window defect does not lessen or become less harmful over time. The general surgical procedure separates the two main arteries in the heart and then stitches or patches the aorta and pulmonary artery. The risk of death from the surgery is low.
If the defect is small enough, a device can be inserted via catheterization to close it without causing stenosis, a narrowing of the arteries, or causing issues with the valves in the heart. If other heart defects are present, these should be addressed in the same surgery. After the operation, there is a slight chance of narrowing occurring in the aorta and pulmonary artery. If this narrowing becomes a real issue, further procedures, such as expanding the artery with a balloon or inserting a stent, can be performed. Moreover, in cases of ‘interrupted aortic arch repair’, extra procedures might be necessary to fix any residual obstruction in the arch of the aorta.
What else can Aortopulmonary Septal Defect be?
The medical conditions often mistaken for an Aortopulmonary window include:
- Truncus Arteriosus: This condition shares a lot of similarities with an Aortopulmonary window, but the key difference is that it features a single ‘truncal’ valve instead of two crescent-shaped valves.
- Patent Ductus Arteriosus (PDA): This has a lot in common with an Aortopulmonary window in terms of their workings. A ‘window’ type PDA refers to a linking spot between the beginning of the descending aorta (the big artery from the heart) and the left lung artery near where it splits. However, the Aortopulmonary window is a junction between the rising section of the aorta and the main lung artery.
- A Large Ventricular Septal Defect: This also works similarly but should be easily distinguishable from an Aortopulmonary window.
In these cases, the heart’s structure and functions play a major role in identifying the exact condition.
What to expect with Aortopulmonary Septal Defect
The outlook for a single Aortopulmonary (AP) window tends to be positive if it’s treated early with surgical closure and when the development of lung-related vascular disease is prevented. However, a late diagnosis could lead to the development of high blood pressure in the lungs or Eisenmenger syndrome, both of which have a negative outlook. If an AP window occurs alongside other birth defects of the heart, this can make the surgery more complex.
Possible Complications When Diagnosed with Aortopulmonary Septal Defect
If a diagnosis is missed, complications can arise, such as the development of a condition called Eisenmenger syndrome. There can also be lingering issues after the repair, such as the narrowing of arteries in the lungs or a remaining opening in the heart (referred to as an aorticopulmonary window) that may need addressing down the line. In particular, doctors need to be careful when performing balloon angioplasty as it can potentially lead to the reopening of this window. Another possible complication is injury to the recurrent laryngeal nerve, which can be indicated by symptoms like hoarseness or choking during feeding after the repair.
Potential complications are:
- Development of Eisenmenger syndrome
- Residual defects like artery narrowing or remaining AP window
- Aorticopulmonary window reopening after aggressive balloon angioplasty
- Injury to the recurrent laryngeal nerve leading to hoarseness or choking during feeding