Aortic Dissections

Aortic dissections are divided into two types: A and B, depending on the location of the tear. In a type A dissection, the tear is in the ascending aorta and progresses throughout the vessel, often extending as far as the arteries in the leg. In a type B dissection, the tear is just past the left subclavian artery. The distinction between the two is important, as it guides the management of the disease.

Type A dissections are a surgical emergencies, with a mortality rate of 1% per hour after onset. They often present as a "tearing" or "crushing" pain between the shoulder blades or behind the sternum. The onset is sudden and severe. The patient cannot find a comfortable position, and is often profoundly hypertensive at presentation. Often, patients who are experiencing an aortic dissection, feel as if they are having a heart attack.

The first steps are control of blood pressure and pain control, while simultaneously mobilizing the operating room personnel. Prompt diagnosis is essential and is made by CT scan of the chest and/or transesophageal echocardiography (TEE). In patients in whom the diagnosis is strongly suspected, the patient is transported directly from an outside hospital or our own emergency room, to the operating room for diagnosis via TEE. In those found to be positive, surgical repair is immediately begun.

A type B dissection is a medical emergency, with surgery reserved for complications of the disease. The tear is just after the takeoff of the left subclavian artery and may progress long the entire length of the thoracic and abdominal aorta. The initial treatment is control of hypertension. Often these patients will not require surgical correction.

Complications

With type A dissection there are a myriad of acute and chronic complications. The reason for emergent intervention is to prevent death from acute complications. The most lethal acute complications are:

1. Aortic rupture causing exsanguinating hemorrhage
2. Aortic valve incompetence leading to rapid heart failure
3. Dissection of the coronary artery causing myocardial infarction
4. Cardiac tamponade due to rupture of blood into the pericardial sac
5. Dissection of the carotid arteries causing acute stroke

The mechanism of disease—blood flowing in the wall rather than through the vessel—may also prevent blood from reaching the intended destination. This process is known as malperfusion syndrome, and may result from type A or B dissection. The clinical manifestation of this complication is end-organ failure. The organs most frequently involved in this complication include the kidneys and intestines. The result may be temporary or permanent renal failure and dead bowel, necessitating extensive bowel resection.