Biology

Coarctation of the aorta is a congenital anomaly wherein a portion or a long segment of the aorta is narrowed or constricted. It can occur proximal or distal of the ductus arteriosus however, at present studies revealed that the coarctation is juxtaductal. The cause of this condition is still unknown however, there are two hypotheses that attempts to explain the etiology, namely ectopic ductal tissue theory and hemodynamic theory. Physical exam findings include diminished and delayed femoral pulses, blowing systolic murmur on the posterior left interscapular areas. The 3 sign in the chest x-ray is almost pathognomonic and a rib notching is usually observed. These physical exam findings are also found in the patient. The treatment of this condition is surgical where 3 techniques are used and modified according to the patients anatomy. After successful surgical operation, a number of patients report to be asymptomatic for an average of 20 years however most of the operated patients have a higher risk of developing cardiovascular disease.

1. What is this lesion
The patient was diagnosed with coarctation of the aorta. This condition is the narrowing or constriction of the lumen of a portion of the aorta. This constriction can occur in any part of the aorta however, it is most common in the distal portion of the left subclavian artery near the ligamentum arteriosum. This is most common among males but this could also affect the females. It occurs in approximately 7 of patients with congenital heart disease.

The aorta is the main arterial trunk that delivers oxygenated blood from the left ventricle of the heart to the different tissues of the body this includes the lower extremities. This is divided into four parts, for the purpose of description, namely, ascending aorta, arch of the aorta, descending thoracic aorta and abdominal aorta. In delivering the blood from the left ventricle to the lower extremities, the blood first passes to the ascending aorta then to the arch of the aorta and goes down to the descending thoracic aorta which continues with the abdominal aorta after the diaphragm. The abdominal aorta then bifurcates into common iliac arteries and this divides into internal and external iliac arteries. The external arteries continue to the thigh as femoral arteries. Thus, when a coarctation of the aorta exists, there is a decrease in blood pressure to the lower extremities due to a diminished blood flow. The blood is also pooled in the upper body thus there is a marked upper body hypertension.

Coarctation of the aorta usually only involves a short segment, however, there are also cases that there is a narrowing of a long segment of the aorta. The constricted segment involves some infolding of the medial and superimposed neointimal tissue of the blood vessel.

At present, most result of a closer look on the coarctation of the aorta reveals that the constrictions are juxtaductal. However, in the past, this condition was classified into preductal (or infantile) and postductal (or adult) type.

There are two theories that attempt to explain the etiology of this condition. These two theories are ectopic ductal tissue theory and hemodynamic theory. In ectopic ductal tissue theory, there is an extension of ductal tissue into the aorta that exists abnormally and this has been believed to have created the coarctation shelf. After the ductus arteriosus closes, thus the development of aortic obstruction. On the other hand, the hemodynamic theory hypothesized tat there is an abnormal preductal flow due to an abnormal angle between the aorta and the ductus. This deformity increases the right-to-left ductal flow of the blood. The decrease in isthmic flow results to the development of the coarctation. After delivery, the ductus arteriosus spontaneously closes thus, completing the development of the aortic obstruction.

2. Is there a difference in the findings of such a lesion as an adult or as a child
The postductal type of coarctation of aorta is also called the adult type. This type of coarctation of the aorta is located just distal to the ligamentum arteriosum, wherein 7 of these patients have an open ductus. On the other hand, the infantile or preductal coarctation of the aorta is a more serious condition than the postductal type. The lesion of the preductal type is located proximal to the ductus arteriosus. Majority of patients with preductal type develops congestive heart failure at infancy and the correct diagnosis is usually done at autopsy.

3. What were the diagnostic clinical features of the case
In the coarctation of the aorta, the physical findings are diagnostic. It is usually found out on physical exam diminished and delayed femoral pulses and a systolic gradient between the extremities. There is also a blowing systolic murmur heard on the posterior left interscapular areas. To confirm diagnosis, a chest x-ray and transesophageal echocardiogram should be done (Fauci, 2008).

In adults, this condition is best diagnosed clinically by simultaneously palpating the brachial and femoral pulses. The blood pressure of one leg and both arms should be determined also. Thus, a pressure difference of greater than 20 mmHg may be considered as one of the evidence of the condition.

In relation to the case, the patient had cool lower extremities with an absence of distal pulses and diminished femoral pulses. This may be due to a decrease in blood supply which is evidenced by a blood pressure in the lower extremities of 4010 mmHg. The blood pressure difference in the upper and lower extremities is greater than 20 mmHg, which is also an evidence of the coarctation of the aorta. Also, there was a systolic murmur heard over the 5th intercostal space radiating to the interscapular region. This finding is also concurrent to the physical findings of a patient with coarctation of the aorta.

4. What single diagnostic finding was found on the chest X-ray
As discussed, as one of the confirmatory laboratory exams, a chest x-ray should be performed. In patients with coarctation of the aorta, there is usually a dilatation of the left subclavian artery on the left mediastinal border and a dilated ascending aorta is also visible. The 3 sign of this condition is almost pathognomonic. It is the indentation of the aorta at the site of coarctation and poststenotic and prestenotic dilatation, thus forming a 3 sign on the left paramediastinal shadow. Also, there is usually a notching of the 3rd to 9th ribs due to the inferior rib erosion by the dilated collateral vessels and this is an important radiological finding.

In relation to the case, a rib notching was noted along with a visible dilation of the aorta in the region of the aortic knob. The dilatation of the aorta was a significant evidence of the condition. This was supported by also a very important sign, the rib nothching.

5. Can you explain why a postductal (inferior) lesion is more compatible with long term survival versus a preductal lesion

In a postductal lesion, the lesion occurs distal to the ductus arteriosus. In the intrauterine life of a fetus with this condition, a collateral circulation develops and this will develop further postnatal. Thus, more or less, there is a better circulation in an infant with a postductal type than a preductal type. In the latter type, the lesion is distal to the ductus arteriosus and in this condition, the ductus almost always remains open postnatal. The preductal lesion is accompanied by serious complications because this may lead to congestive heart failure early in life.

6. What are the treatment options for a patient with this type of lesion
The first line of treatment is surgery in most patients. However, patients with hypertension andor congestive heart failure are contraindicated to undergo surgery. There are several techniques that can be used to correct the coarctation and these techniques are sometimes modified to fit the patients anatomy. For example, there are times that a reverse left subclavian flap aortoplasty is used. The left subclavian artery is patched back toward the patients left carotid artery. This is done to enlarge a portion of the transverse arch hypoplasia. The exact technique still depends on the patients age during the time of operation and the size of the coarctation and also if there is any associated abnormalities in the aorta. The anatomy of the aortic arch should also be considered. The said techniques are patch aortoplasty, resection and end-to-end anastomoses, tubular bypass grafts and left subclavian flap aortoplasty. Other non-surgical options are aortic stents and balloon angioplasty. A left posterolateral thoracotomy in the 4th intercostal space may also be used. In doing this technique, the mediastinal pleura are incised and the vagus nerve is retracted medially. The aortic arch proximal to the left subclavian artery, distal aorta and the ligamentum arteriosum are serially mobilized. The intercostal arteries are isolated and preserved. The proximal aorta, distal aorta and left subclavian artery are all occluded during surgical repair operation.

7. What surgical complications would cause the greatest amount of concern
There are many patients who report as asymptomatic in a mean of 20 years after operation but studies show that patients are at increased risk of developing cardiovascular disease. Other possible complications after surgery, which can also occur before or during surgery, are aortic dissection, aortic aneurism, bleeding in the brain, infective endocarditis, heart failure, impaired kidney function, coronary artery disease, stroke and severe hypertension.