Thoracic Aortic Aneurysms

Author :

Dr Gabriele Di Luozzo Mount Sinai Medical Center New York

2010-03-27

Patients with thoracic aortic aneurysms represent clinical challenges that typically involve both complex anatomical issues and considerable associated comorbidities. While in years past surgical repair was considered "high-risk" surgery, recent refinements in technique coupled with effective means of brain and spinal cord protection have made most elective operations safe. Aortic disease should be managed by refenece centers in the United States who can provide a multi-disciplinary approach and provide treatment safley. Lastly, aortic surveillance with serial imaging is very important to prevent life-threatening complications.

Descending Thoracic Aortic Aneurysm

Overview of Thoracic Aortic Aneurysms

Each year in the United States, some 45,000 people die from diseases of the aorta and its branches. Acute aortic dissection, a life-threatening event due to a tear in the aortic wall, affects 5 to 10 patients per million population each year, most often men between the ages of 50 and 70; of those that occur in woman younger than 40, nearly half arise during pregnancy. The majority of these deaths occur as a result of complications of thoracic aneurysmal disease. The diagnosis of thoracic aortic aneurysm usually involves patients in the 6th and 7th decades of life. Aneurysms in patients younger than 40 usually involve the ascending aorta due to a weakening of the aortic wall associated with connective tissue disorders like the Marfan and Ehler-Danlos syndromes or congenital bicuspid aortic valve. Younger patients may develop aortic aneurysms of the thoracoabdominal aorta after an aortic dissection. Atherosclerosis is the principal cause of descending aortic aneurysms, while aneurysms of the aortic arch may be due to dissection, atherosclerosis or inflammation. Hypertension and cigarette smoking are the most important risk factors, though the importance of genetic factors has been increasingly recognized. Approximatlely 10% of patients may have other family memebers who have aortic aneurysms. The principal causes of death due to thoracic aneurysmal disease are dissection and rupture. Once rupture occurs, the mortality rate is 50-80%, and most deaths in patients with the Marfan syndrome are the result of aortic disease.
Numerous therapeutic interventions are available to prevent these catastrophic events, but the key to success is early diagnosis. In most cases, the diagnosis is made incidentally when an imaging procedure – X-rays, computerized tomography or magnetic resonance imaging of the chest or an echocardiogram-- reveals aortic enlargement. In the majorit of pateitns there are no symptoms. However, in a small group of patients, if questioned carfeully, will report a dull, vague pain in their chest. In other patients, the aneurysms may present with symptoms related to the expansion of the aneurysm and its compression of surrounding organs. For an example, a patient may present with a hoarse voice due to the stretching of the nerve that controls the vocal cords that wraps around the aortic arch. In asymptomatic patients with thoracic aortic aneurysms, annual expansion and complication rates depend on several factors, including the initial size (diameter), location (chest or abdomen), and presence or absence of dissection (aortic tear). Dissection doubles the rate of an eurysm expansion as well as the risk of rupture and other complications. In studies that examined the natural history of thoracic aortic aneurysms, a measurement of 6.0 cm for ascending and 7.0 cm for descending aortic aneurysms was found to be associated with increased risk for rupture or dissection, but some patients suffer complications at smaller diameters. These results help set the guidleines for elective surgery to repair the aneurysms at diameters smaller than the diameter that was associated with an increase risk of complication. In another study that investigated the behavior of aneurysms which did not initially meet criteria for elective surgery the predictors of rupture were aneurysm-related chest pain, aneurysm size, patient age, and history of chronic obstructive lung disease (i.e. emphysema). An equation derived from these clinical features can be used to calculate the probability of rupture within one year and, when combined with institution-specific surgical outcomes, allows generation of reasonable criteria for elective intervention.

Ascending Aortic Aneurysm

Medical therapy involves careful blood pressure and heart rate monitoring, smoking cessation and a modest exercise program. Blood pressure monitoring should be under supervision of a cardiologist. Heart rate control with beta-adrenergic antagonist may have some effect on aortic expansion. Experimental animal studies suggest a role for the angiotensin-II receptor antagonist, losartan, in decreasing the expansion of thoracic aortic aneurysms and reduce the risk of rupture. Mount Sinai Medical Center in New York has a renowned Aortic Program which provides stringent surveillance for patients with thoracic aortic aneurysms, including a large database of clinical features and aneurysm measurements. Imaging is carried out at regular intervals, and intervention is recommended based on changes observed over time. In general, CT scans are performed every six months for patients with large aneurysms and annually for those with small aneurysms. A 3-dimensional reconstruction of the aorta created from these images provides comparative measurements of diameter, volume and changes in tortuosity over time. An increase in aortic volume over 10% is a relatively rapid change that typically prompts surgical evaluation, and intervention is recommended when the probability of rupture in the next year exceeds the risk of the operation.

Indications for Repair of Thoracic Aortic Aneurysms

Aortic Arch Aneurysm

The timing of corrective surgery is based on aneurysm size, symptoms, other medical conditions, and the anticipated risk of intervention. In general, the indications for surgical intervention may change from one patient to another or various circumstances. These are general guidelines: Type A (ascending) aortic dissection (emergency surgery) Ascending aortic diameter ≥4.5-5 cm in those with the Marfan syndrome Ascending aortic diameter ≥5.5 cm in patients without the Marfan syndrome Earlier surgery may be indicated in patients with aneurysms of the aortic root associated with incompetence of the aortic valve, in whom combined repair procedures are employed. Descending and thoraco-abdominal atherosclerotic aortic aneurysm diameter ≥6 cm Type B aortic dissection complicated by impaired distal perfusion, rupture, or rapid expansion Dissecting descending thoracic aortic aneurysm diameter ≥5.0 cm Symptomatic (pain or symptoms due to compromised blood flow to major arterial branches) aortic aneurysms should be operated regardless of diameter Expansion at a rate ≥1 cm/year.

Open Surgical Repair

The last two decades have seen advances in diagnostic imaging, surgical technology, anesthesia and critical care that have dramatically improved the outcomes of surgery for patients with thoracic aortic diseases. In high volume reference centers the risk associated with complex thoracic aortic surgery should be in the low single digit range and with a parapegia rate less than 4%. A very important aspect of modern-day aortic operations is proper neurologic monitioring (spinal cord and brain) in the operating room and a dedicated team of doctors and nurse who care for aneurysm patients in the operating room and the intensive care unit. The operation for an aortic aneurysm requires replacing the diseased aorta with a synthetic tube which functions as the aorta. Open surgical procedures provide very durable results with a long track record.

Endovascular Repair of Thoracic Aortic Aneurysms

The potential advantages of an endovascular approach include reduced blood loss, faster recovery, and the ability to perform the repair under local or regional anesthesia. The endovascular stents approved by the FDA are for patients who have mutiple medical conditions that prohibit open surgical repair. Clinical studies are on-going to evaluate the role of endovascular stents in acute aortic dissections. The long-term durability of TEVAR is unknown. There are many limitations to endovascular stents such as the location of the aneurysms, the presence of dissection, large delivery systems, available stent sizes and the size of the arteries necessary to deliver the stents. Another option for high-risk patients is a hybrid procedure with includes open surgery and endovascular stents to handle complex thoracoabdominal aortic aneurysms.

Summary

Patients with thoracic aortic aneurysms represent clinical challenges that typically involve both complex anatomical issues and considerable associated comorbidities. While in years past surgical repair was considered "high-risk" surgery, recent refinements in technique coupled with effective means of brain and spinal cord protection have made most elective operations safe. Aortic disease should be managed by refenece centers in the United States who can provide a multi-disciplinary approach and provide treatment safely. Lastly, aortic surveillance with serial imaging is very important to prevent life-threatening complications.

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