Diseases Of The Aorta II: Dissecting Aneurysm Of The Aorta

Acute aortic dissection is one of the most lethal disorders affecting the aorta.

Causes

1. Hypertension: More than 90% of the patients suffer from chronic hypertension.
2. Conditions that cause cystic medial necrosis, e.g, Marfan’s syndrome, Ehler’s-Danlos syndrome, pregnancy.
3. Other structural disorders of the aorta: Coarctation of the aorta, aortic hypoplasia, aortic stenosis, tricuspid aortic valve, syphilitic aortitis, giant cell arteritis.
4. Trauma: Blunt trauma to the chest in automobile accidents eg, steering wheel injury, iatrogenic causes such as femoral artery cannulation.

Men are affected twice as common as women.

Pathology

The intima is disrupted at the areas of greatest stress such as ascending aorta and descending aorta just beyond the left subclavian artery. This leads to entry of blood into the aortic wall in between the intima and media, creating a false lumen between these layers. When fully developed, the aorta resembles a double-barrel tube. The blood in the false lumen may re-enter the true lumen at a variable point down stream, and in such cases further dissection of the aortic wall does not take place. On the other hand, the dissection may proceed proximally to rupture at the root of the aorta into the pericardium giving rise to severe fatal hemopericardium. The hematoma and thrombus in the layers of the aortic wall may occlude any major branch of the aorta and produce ischemia in its area of supply. Three types have been described.

Type 1: There is complete dissection of aorta starting with a tear in the aortic root.

Type II: Tear is situated in the ascending aorta, with the formation of a localized aneurysm.

Type III: Dissection is distal to left subclavian artery.

Cardinal clinical features

The symptoms start with severe pain in the chest, interscapular region, neck, mid-back, abdomen, sacral region, and lower limbs. The pain may be mistaken for myocardial infarction. Unlike the pain of acute myocardial infarction, the chest pain produced by aortic dissection is usually abrupt in onset, very severe from the start and unremitting. Several other manifestation may develop. These include syncope, blindness, dyspnea, nausea, vomiting, hematemesis, melena, oliguria, hematuria and paresis or paralysis of lower extremities.

Physical examination

The blood pressure may be elevated, or the patient may be in shock. Arterial occlusion leads to absence of pulses in the major arteries. Aortic regurgitation may develop giving rise to the characteristic early diastolic murmur. The jugular vein may be engorged unilaterally. Other features include left-sided hemothorac, cardiac tamponade, silent abdomen due to paresis of intestines, presence of arterial bruits and variable neurological deficit.

Diagnosis

Aortic dissection should be suspected in all cases of intense chest pain associated with signs of shock, especially if the clinical features and ECG do not suggest myocardial infarction, X-ray chest may show widening of mediastinal shadow. Two-dimensional echocardiography, CT scan and aortography are useful diagnostic investigations.

Course and prognosis

In extensive dissection, death occurs due to shock or rupture into the pericardium and pericardial tamponade.

Treatment

Supportive care includes careful monitoring of blood pressure, maintenance of fluid intake and output and control of the blood pressure with a negative inotropic agent such as trimethaphan or a combination of sodium nitroprusside and propranolol. Drugs like hydralazine which increase the velocity of ventricular ejection, favour progression of dissection and therefore, these should be avoided. Once the medical condition is stabilized, surgery (resection and prosthetic reconstruction of the aorta) is undertaken, but moretality remains high. If medical treatment fails to arrest progression, emergency surgery may be required.