Alberto Pochettino, M.D., Cardiovascular Surgery, Mayo Clinic: I’m Dr. Alberto Pochettino, a cardiovascular surgeon specializing in the treatment of aortic disease at the Mayo Clinic in Rochester, Minnesota. The easiest way for me to describe some of the surgical procedures I perform is to first look at the aorta itself. The aorta is a large vessel that carries blood from the heart to the entire body. At the simplest level, the aorta can be divided into four parts–the ascending aorta, the aortic arch, the descending thoracic aorta and the abdominal aorta. The ascending aorta starts at the heart with the aortic root containing the aortic valve and the origin of the coronary arteries. The tubular ascending aorta is next and travels to the base of the neck. There the aorta arches back to the spine. Along the aortic arch, three branch vessels come off, carrying blood to the brain and the arms. From the aortic arch, the descending thoracic aorta travels downward along the spine. When it crosses the diaphragm, the muscle that divides the chest from the abdomen, the name changes to abdominal aorta. At the pelvis, the aorta divides and becomes the iliac arteries.
The main disease that I see is aortic aneurysm. An aneurysm is an enlargement of the aorta and as the aorta enlarges, it becomes thinner. The thinner it is, the more likely it is to rupture, which is much like an over inflated balloon that is at high risk of popping. Another aortic disease, which often occurs in the presence of aortic aneurysms, is called aortic dissection. The aorta has three layers–a thin inside layer, which prevents blood from clotting; a muscular middle layer, which provides the structural integrity of the vessel; and a tough fibrous outside layer, which holds everything in place. Dissection is a process where the inner layer of the aorta tears. Blood is forced inside the middle muscular layer which is torn apart. This forms a new channel called the false lumen as opposed to the true lumen, which is the passage to which the aorta should be carrying blood. As blood continues to flow into the false lumen, the false lumen grows until it reaches a branch vessel. At which point, the tissue may tear, connecting the true and false lumen or the false lumen may compress the branch vessel cutting off blood flow through that vessel. The implication of compromised blood flow take on a high degree of urgency when you consider that the vessel branching for the aorta can feed organs such as the heart, the brain, kidneys, liver and intestine. Compromise to these vessels can lead to heart attacks, strokes and organ failure. Finally, if the aortic valve is compromised by the dissection, it results in acute heart failure. The nature of the aortic dissection alone weakens the aortic wall putting it at risk for rupture. Thus, a dissection, which involves the ascending aorta, referred to as Type A dissection, always requires emergency surgery.
Now why do these things happen? There are three players in the aortic disease game. The first is structural genetic abnormality. Basically, the aorta is built wrong. The classic genetic disease that lead to aortic aneurysm and dissection is Marfan syndrome. However, the most common genetic abnormality associated with a standing aortic aneurysm is bicuspid aortic valve. The second player is accelerated atherosclerotic injury. This can also be a genetic problem, but it just as often stems from sustained high blood pressure compounded by high cholesterol, smoking, obesity and sometimes diabetes. The least common player is inflammatory disease such as vasculitis or even infection.
Now, how can a person prevent a catastrophic event like a dissection from occurring? If you have a family history of aortic disease or high blood pressure or if you have a heart murmur, a good starting point is an echocardiogram, which is an ultrasound to the heart and the ascending aorta. If the echocardiogram suggests any aortic disease, it should be followed by a CT scan. Once an aneurysm has been identified, a decision must be made regarding when it is time for surgical intervention. An ascending aortic aneurysm greater than 5.5 centimeters requires surgery for all patients. In the presence of bicuspid aortic valve, the criteria for surgery is five centimeters. In the presence of genetic abnormalities, such as Marfan, an aneurysm of 4.5 centimeters would indicate surgery. An aneurysm in an aorta is replaced by Dacron graft. At the level of the root, a normal aortic valve can be saved inside a Dacron conduit. This operation is called a valve-spearing root replacement. If the valve is abnormal, it can be replaced at the same time as the aorta. We need a biologic or a mechanical valve. A portion of the aortic arch often need to be replaced during ascending replacement. The aortic arch is particularly important because of the branch vessel that supply blood to the brain. Therefore, techniques to replace the aorta in this area must protect brain function. Moving to the descending thoracic aorta, the size indication for surgical replacement is between 5.5 and 6 centimeters. Replacement of the descending thoracic aorta can often be done with endovascular techniques with good results. Endovascular aneurysm repair involves placement of the Dacron graft which is advanced through a peripheral artery and held in place by a metal stent. Access to the peripheral artery is obtained through a small incision without needing to open the chest or the abdomen. The last and most complex aneurysms are those of the thoracic and abdominal aorta. They are called thoracoabdominal aortic aneurysms. The majority of these require open surgery where both the chest and the abdomen are entered to make the repair. The same size criteria of 5.5 to 6 centimeters apply. Techniques are employed to minimize the risk of paraplegia which can result from the thoracic or thoracoabdominal aortic repair. Technology is in development to allow more of this complex aneurysm to be repaired in an endovascular fashion.
In summary, techniques to repair all segments of the aorta in either open or endovascular fashion are available at the Mayo Clinic. A patient can be evaluated by a multidisciplinary team and any diseased portion of the aorta can be repaired.