Introduction:
The human heart is a remarkable organ. It pumps over 6000 liters of blood every day and beats more than 40 million times a year. It is durable, efficient, and ensures a steady blood supply and nutrients to the other organs. Any abnormalities in the heart can lead to devastating consequences. Heart diseases are one of the significant causes of death in developed nations. These diseases can be present at birth (congenital) or acquired during a lifetime. Heart diseases present at birth involve defects of the heart and its blood vessels. Severe forms of these anomalies can cause the death of the fetus inside the uterus. Similarly, the vessels arising from the heart may be defective, leading to inappropriate connections between heart chambers. Congenital defects are also common in the aorta (the largest artery of the human body) and its structures.
What Is the Normal Structure of the Aortic Arch?
Before getting into anomalies of the aorta, it is essential to understand its normal structure. The aorta originates from the heart's left ventricle (the bottom chamber of the heart that pumps oxygenated blood). The aorta arises from the heart (ascending aorta), curves over, and descends (descending aorta) into the chest. The artery also gives rise to several branches that supply blood to the heart and other organs. The aortic arch is the section present between the ascending and descending aorta. The structure of the aortic arch is normal in 75% of individuals, and the rest are likely to develop some changes that are considered normal variations. These variations are commonly seen in the branching of the aortic arch.
What Are Aortic Arch Anomalies?
Aortic arch anomalies are usually congenital (present at birth). These abnormalities occur during the development of the fetus. It can coexist with other structural defects in the heart. Patients can be symptomatic or asymptomatic. The anomalies can be broadly classified based on the structural characteristics:
A. Normal Variations in the Aortic Arch - Bovine arch occurs in 10 to 20 % of the population. The defect lies in branching, where three arteries originate from a single trunk. Other anomalies include variations in the vertebral artery (a major blood vessel in the neck), the presence of aberrant right subclavian artery (arteries below the collar bone), etc.
B. Right Aortic Arch - The aortic arch normally transverses over the left bronchus. This occurs in 0.01 to 0.1 % of the population. In this case, the aortic arch transverses over the right bronchus. It does not cause cardiovascular effects unless it is associated with other heart defects.
C. Double Aortic Arch - The aorta splits into several branches during the aortic arch development. Some of these branches disappear, but sometimes they can be retained. The normal aortic arch is made of one aortic vessel, but here aorta is made of two vessels. Arteries arising from these two aortas go around and compress the windpipe and food pipe. This condition is very rare and affects both males and females equally.
D. Cervical Aortic Arch - A high-lying aortic arch characterizes this anomaly. It is abnormally so high that the aortic arch reaches the level of the collar bones (clavicles). This gives the appearance of a neck mass.
E. Hypoplastic or Interrupted Aortic Arch - The aortic arch is said to be hypoplastic when there is a blockage in the aorta. In this case, a smaller portion of the aorta is constricted, blocking the easy flow of the blood. The constricted site has a smaller diameter compared to the normal aortic arch.
F. Coarctation of the Aortic Arch - This condition is similar to the hypoplastic aortic arch, but a larger portion of the aortic is involved in this case. Constriction or narrowing of the aortic can be observed, and it may cause hemodynamic changes.
G. Persistent Fifth Aortic Arch - It is a rare anomaly usually associated with aortic arch coarctation or interruptions.
What Causes Aortic Arch Anomalies?
The reasons for the occurrence of aortic arch abnormalities can be attributed to the two main factors:
A. Genetic Factors - The role of genetics is demonstrated by the occurrence of aortic arch anomalies in familial forms. It also occurs in several chromosomal abnormalities like Trisomy 13, 15, 18, and 21. Syndromes associated with these chromosomal abnormalities are Down syndrome, DiGeorge syndrome, Turner syndrome, etc.
B. Environmental Factors - Maternal factors like infections during pregnancy, congenital rubella infection, exposure to teratogens (substances that cause fetal abnormalities). But in a majority of cases, the environmental cause is not apparent.
What Are the Symptoms of Aortic Arch Abnormalities?
The anomalies seen as normal variations are considered clinically insignificant. Other major structural defects can be symptomatic or asymptomatic. Symptoms are apparent if the abnormalities are associated with other congenital heart defects. Commonly experienced symptoms include;
2. Chest pain.
3. Difficulty in breathing.
4. Wheezing.
5. Weakness.
How Are Aortic Arch Anomalies Diagnosed?
The diagnosis is made with the help of advanced imaging techniques.
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Ultrasound - It is a reliable method as it does not involve radiation exposure. However, it has a limited ability to view complex anomalies. It also cannot generate 3D images.
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Angiography - It is an imaging technique used to visualize the blood vessels. It can demonstrate the branching and connection of the blood vessels. However, it is invasive and does not provide a 3D view.
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CT (Computed Tomography) Scans - Uses ionizing radiation to produce 3D images. It has a very high resolution.
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MRI (Magnetic Resonance Imaging) - It provides a 3D visualization of the structures. MRI scans are expensive and operator-dependent.
What Is the Treatment for Aortic Arch Anomalies?
A. Surgery - In newborn babies, surgery is performed by a cardiothoracic surgeon to repair the defects. The anomaly is corrected, and a bypass graft is placed.
B. Cardiac Catheterization - This is performed in the case of aortic arch coarctation. It is mainly done in older children and young adults. The surgeon will insert a catheter into the blood vessel, and the narrow area is opened up using a small balloon.
Conclusion:
The aortic arch is the segment between the ascending and descending aorta. Defects can arise during its development due to genetic and environmental factors. Aortic arch anomalies are associated with many chromosomal defects. The common abnormalities include normal branching variations, double aortic arch, right aortic arch, cervical aortic arch, and aortic coarctation. These anomalies are symptomatic as they are associated with other structural heart defects. Diagnosis is made using imaging techniques like ultrasound, CT scan, MRI, and angiography. Aortic arch defects must be surgically treated.
