Circ 2005;111:816; Nejm 2003;348:1895; 1993;328:1167

Cause: Thoracic aortic aneurysms result from cystic medial degeneration and are seen in Marfan syndrome (fibrillin-1 gene mutations), familial TAA syndrome, bicuspid aortic valve, syphilis, Turner syndrome, Takayasu’s arteritis (15% ofpts), and giant cell arteritis (18% ofpts). Factors in development of AAA include familial clustering, genetically predisposed and acquired biochemical alterations in the structural matrix of the aortic wall, and hemodynamic mechanical factors. Atherosclerosis may be secondary response to wall injury. Smoking is the strongest independent risk factor for AAA (Lancet 1998;352:1649).

Epidem: Prevalence of AAA is ˜5% in men > 55 yr old, and is 18% in male siblings (age > 60 yr) ofpts with AAA (Ann IM 1999;130:637). Men are 10 times more likely than women to have AAA > 4 cm (J Vasc Surg 1996;23:724). The Mayo Clinic reported an increase in the incidence of detected AAA from 12.2/100,000 to 36.2/100,000 between 1951 and 1980.

Pathophys: Annual expansion rates are 0.2- 0.4 cm/yr. Aneurysms > 5-6 cm in diameter expand more rapidly, but the expansion rate is unpredictable in a givenpt.

Sx: Usually asymptomatic. Aneurysms of ascending aorta may produce AI with murmur. Large thoracic aneurysms may produce cough, wheezing, and dyspnea. Rupture of AAA may be associated with abdominal pain radiating to back and hypotension (may be seen in only 50% ofpts); the sx of rupture are frequently mistaken for renal colic, diverticulitis, or gi hemorrhage.

Si: Pulsatile abdominal mass; abdominal bruit

Crs: The natural h/o of TAA is not well defined. The growth rate is greatest for descending TAA andpts with Marfan syndrome; the annual growth rate is 2% for TAA < 5 cm, 3% for 5-5.9 cm, 7% for TAA > 6 cm diameter (Ann Thorac Surg 2002;73:17). AAAs with diameter < 4 cm have a 0.3% risk of rupture, while 4-4.9 cm AAAs have a 1.5% risk, and 5-5.9 cm AAAs have a 6.5% risk (J Vasc Surg 1996;23:724); 25-41% of aneurysms > 5 cm rupture within 5 yr. Up to 62% ofpts with ruptured aneurysms die before reaching the hospital. Annual rates of rupture for TAA and AA are 3/1000 and 9/1000pts, respectively (Mayo Clin Proc 2004;79:176).

The aneurysm growth rate is not predicted by either size or initial growth rate (Arch IM 1997;157:2064).

Most aneurysms rupture into the retroperitoneum, producing hypovolemic shock but not exsanguination, due to the tamponade effect of the retroperitoneum.

Cmplc: Dissection with TAA; ASHD common inpts with AAA: severe CAD identified in 31%; CAD accounted for 39% of deaths within 5 yr of operation in 1 study, and 37% of early post-op deaths were due to MI.

Lab: Exercise stress testing inpts with AAA seems to be safe and is associated with a low incidence of acute adverse events (Ann IM 1998;129:628).

X-ray: US, contrast CT, and MRI angiography have 100% sensitivity in dx. Ultrasonography is used for aneurysm detection and sequential follow-up. CT is used when ultrasonography is not
possible or precise sizing is required.

Aortography can provide anatomical information useful for aortic reconstruction; it is necessary for suspected suprarenal/juxtarenal aneurysms, renovascular HT, ischemic nephropathy, mesenteric artery stenosis, and iliofemoral arterial occlusive disease. MRI can also provide detailed anatomical data.

Rx: Consider screeningpts at high risk for AAA: age 60-80 with CAD risk factors, HT,pts > 50 yr old with family h/o of AAA (J Vasc Surg 2004;39:267).

β-Blockade and rx to lower systolic BP to 105-120 mm Hg

Aerobic exercise is safe if BP is controlled.

Surveillance: Image aneurysms 3-3.4 cm q 3 yr; 3.5-3.9 cm q 2 yr; 4-4.4 cm q 1 yr; 4.5-4.9 cm q 6 mon

Repair symptomatic aneurysms and asymptomatic TAA > 5.5-6 cm and AAA > 5-5.5 cm diameter in men and 4-4.5 cm in women. Contraindications to elective surgical repair include recent MI, intractable CHF or angina, severe COPD with dyspnea at rest, severe chronic renal insufficiency, incapacitating residual effects from stroke, and life expectancy < 2 yr.

In an unstable pt with suspected ruptured AAA, immediate operation without confirmatory testing or full resuscitation is mandatory.

The reported operative mortality rate for nonruptured ascending TAA is 3-5%; AAA repair, 1.4-6.5%; ruptured aneurysm, 23-69%. Survival after repair is 92% at 1 yr, 67% at 5 yr. Descending TAA has a 5-6% incidence of post-op paraplegia and surgical mortality of 5-14%.

Early complications of AAA after elective surgery include cardiac ischemia, arrhythmia, CHF (15%), pulmonary insufficiency (8%), renal injury (6%), bleeding (4%), distal thromboembolism (3%), and infection (2%). Rare complications include ischemic colitis and stroke/paraplegia. Late (3-5 yr post-op) complications include graft infection, graft occlusion, anastomotic aneurysms, and aortoenteric fistula.

Endovascular stent grafts are an alternative approach to exclude and stabilize both TAA and AAA (Nejm 2004;351: 1607); they may have lower short-term mortality than open repair (Lancet 2004;364:843).