What Is a Pulmonary Artery?
It is a blood vessel that carries impure (deoxygenated) blood from the right side of the heart to the lungs for purification. The term is a bit of a misnomer because arteries typically carry pure (oxygenated) blood from the heart to the entire body.
The pulmonary artery arises from the right ventricle of the heart. The heart has four chambers-
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Right Atrium- Deoxygenated blood from the entire body returns to the right atrium through the superior vena cava (the largest vein that drains into the heart).
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Right Ventricle- From the right atrium, the deoxygenated blood enters the right ventricle, which then pumps it to the lungs through the pulmonary artery.
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Left Atrium- Once the blood is oxygenated in the lungs, it returns to the left atrium through the pulmonary vein.
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Left Ventricle- The oxygenated blood enters the left ventricle through the left atrium and pumps blood to the entire body through the aorta (the largest artery that distributes the oxygenated blood).
The main pulmonary artery (also known as the pulmonary trunk) arises from the right ventricle; it then splits into the right pulmonary artery (RPA) and left pulmonary artery (LPA), which provide blood flow to their respective lungs.
What Is Ascending Aorta?
The aorta is the largest blood vessel in the entire body. It arises from the left ventricle, then instead of descending downwards, it ascends, arches to the left, and then descends down to the chest, abdomen, and pelvis.
The portion of the aorta that ascends is known as the ascending aorta; the portion that arches are the aortic arch, and the rest of the vessel that descends is known as the descending aorta.
This ascending aorta is around two to three inches long, and before arching, it gives off two branches-
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The right coronary artery supplies the right side of the heart.
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The left coronary artery supplies the left side of the heart.
It is important to note that the heart is a muscle that needs oxygen-rich blood to function.
What Is AOPA?
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Also known as hemitruncus arteriosus (HA), it is a congenital anomaly when one of the branches of the pulmonary artery arises from the ascending aorta while the other normally arises from the pulmonary trunk.
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When the RPA arises from the ascending aorta, it is known as the right hemitruncus arteriosus (RHA), also known as the anomalous origin of the right pulmonary artery (AORPA).
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When the LPA arises from the ascending aorta, it is known as left hemitruncus arteriosus (LHA), also known as the anomalous origin of the left pulmonary artery (AOLPA).
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LHA is more frequently associated with other cardiac anomalies; on the other hand, RHA has a frequent occurrence when compared to LHA.
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Patients present with respiratory distress, congestive heart failure, and failure to thrive within the first few days or months of life. Early diagnosis and surgical repair are mandatory in order to prevent cardiac failure and pulmonary hypertension. Treatment involves different implants of the anomalous right pulmonary branch to the main pulmonary artery.
What Causes RHA?
Although the exact pathogenesis is unknown, an association has been observed between 22q11.2 deletion syndrome and RHA. In patients with 22q11.2 deletion syndrome, a small part of chromosome 22 is missing; this leads to poor and abnormal development of several body systems. A few of the anomalies are RHA, tetralogy of Fallot, absence of pulmonary valve, aortopulmonary window, anomalous subclavian arteries, etc.
What Are the Symptoms of Right Hemitruncus Arteriosus?
This anomaly will create two separate blood circuits in each lung; they are-
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Circuit 1- This is the normal one; the right ventricle will receive deoxygenated blood which will transfer to the pulmonary trunk. After reaching the pulmonary trunk, only the LPA will carry the deoxygenated blood to the left lung. This results in the left lung receiving the complete systemic volume flow of the deoxygenated blood.
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Circuit 2- This is the abnormal one, the left ventricle, which will receive the oxygenated blood from the left pulmonary vein and will transfer it to the ascending aorta. Here, the anomalous RPA that arises from the ascending aorta will receive some of the oxygenated blood, which will carry it to the right lung (at systemic pressure).
In patients with LHA, these circuits are reversed. Although the right lung is receiving oxygenated blood, which does not require further purification, it is receiving the blood at a higher pressure than it is supposed to, which will cause right pulmonary hypertension (a type of blood pressure).
The left lung, on the other hand, is bearing the load of purifying the entire blood, which will also increase pulmonary hypertension.
If early intervention is not performed, the above conditions will cause the following symptoms-
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Respiratory distress.
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Recurrent respiratory infection.
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Moderate to severe pulmonary hypertension.
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Cyanosis (a condition characterized by a bluish-purple hue of the skin that occurs due to inadequate oxygenation of the arterial blood).
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Chest pain.
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Congestive heart failure.
How Is RHA Diagnosed?
Initial diagnosis is made with 2D echocardiography. This helps in defining the morphology and detection of the systemic pressures in the right ventricle. Diagnosis is confirmed with catheterization, angiocardiography, magnetic resonance imaging (MRI), and CT (computed tomography) angiography. The same imaging techniques can be used for the diagnosis of LHA.
How Is RHA Treated?
The only available treatment is surgery. The underlying principle is to resect and implant the anomalous pulmonary artery into the main pulmonary artery; depending on the type of abnormality, different techniques are used for repair.
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For RHA, the first step in surgery will involve an autologous vein graft, also known as an autoplastic graft (a graft taken from another area of the patient's own body). This is done to lengthen the right pulmonary artery.
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The following steps are end-to-end anastomosis with a synthetic graft, homograft patch, and an “aortic ring” flap.
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Except for the first step, the rest of the procedure is the same for LHA.
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After the procedure, the surgeon will conduct a postoperative echocardiographic study to detect the presence of stenosis (narrowing of pulmonary valve).
Conclusion:
Patients with HA will have good short and long-term outcomes if treated early on. If left untreated, the anomaly will lead to congestive heart failure and pulmonary hypertension, causing death within three months. HA is a preventable death in newborns that can be achieved with the help of early diagnosis, genetic counseling, and an efficient interdisciplinary team.
