ABDOMINAL AORTIC ANEURYSM


I. Risk factors for abdominal aortic aneurysm (AAA)

  1. Smoking
  2. Advanced age
  3. Male gender
  4. Atherosclerosis elsewhere
  5. Hypercholesterolemia
  6. Hypertension
  7. Family history of AAA

II. Diagnosis and natural history

  1. A diameter of 3cm or greater is generally considered to indicate an aneurysm
  2. In an observational study of 790 men (mean age 69) with AAA's 3.0-3.9cm on screening ultrasound, over mean 3.9y f/u with serial u/s, median rate of expansion was 0.11cm/yr; only 6.7% of AAA's expanded to 5cm or larger (J. Vasc. Surg. 35:666, 2002--JW)
  3. Can be diagnosed by ultrasound or CT
    1. In a cohort study of 334 patients who had undergone endovascular AAA repair who had concurrent ultrasound and CT, diameter of AAA's measured by CT were sig. greater on average than those measured by ultrasound.  In 49% of measurements, the difference was > 1.0cm (J. Vasc. Surg. 38:466, 2003--abst)
  4. The most significant complication is rupture (see below)
III.AAA rupture
  1. May result in rapid death from exsanguination
  2. Survival to hospital discharge in patients with AAA rupture is 10-25% as of 2012
  3. Epidemiology of AAA rupture
    1. Risk for rupture is tightly correlated with AAA diameter-At 5cm or greater, incidence of rupture is about 8%/yr with lifetime risk 25-49% (Eur. J. Vasc. Surg 6:616, 1992; Br. J. Surg 85:1382, 1998)
    2. Other risk factors for rupture in patients with AAA (sources include Ann. Surg. 230:289, 1999--JW):
      1. Diastolic hypertension
      2. COPD
      3. Female gender
      4. Higher mean arterial BP
      5. Smoking
  4. "Classic" clinical presentation is with triad of abdominal or back pain, hypotension, and pulsatile periumbilical mass-Seen only in about 50% of cases, though 82% of patients with ruptured AAA complain of abdominal pain.
  5. Pain may radiate to groin or lower extremity
  6. Syncope occurs in 1/3 of patients
  7. The hemorrhage may be tamponaded by retroperitoneal tissues if the tear is posterior
  8. CT is preferred diagnostic modality
  9. Ruptured AAA is generally treated with open surgical repair or, in some patients, with endovascular repair

IV. Screening for AAA

  1. In a trial of 67,800 men 65-74yo randomized to invitation for abdominal us to r/o AAA vs. no such invitation (with f/u scans periodically if AAA 3-5.4cm and surgery if 5.5cm or greater, increase in diameter 1cm/yr or greater, or sx), over avg. 3.9y f/u, AAA-related mortality (w/intention-to-treat analysis) was 0.19% in u/s group vs. 0.33% in no-u/s group (RR 0.58; sig.).  No subgroup analysis was reported. ("MASS" study, Lancet 360:1531, 2002--abst)
    1. In a f/u report on the "MASS" study, over 7y f/u, AAA-related mortality was still sig. lower in the screened group (HR 0.53) but no sig. diff. in all-cause mortality (Ann. Int. Med. 146:699, 2007--JW)
  2. 41,000 men 65-83yo randomized to a single screening for AAA vs. no screening; over 5y, the age-adjusted rate of AAA-related death was nonsig. lower for those men in the screening group and sig. lower (RR 0.6) for those men in the screening group who actually attended screening (7.5 vs. 18.9 deaths per 100,000 person-years) (BMJ 329:1259, 2004--JW)
  3. In a trial in 12,639 men 64-74yo randomized to invitation for abdominal u/s to screen for AAA (and referral for surgery if 5cm or more diameter) vs. no such invitation; over mean 4.3y, the incidence of AAA-related mortality was sig. lower in the screening group (number needed to screen = 349) (BMJ 330:750, 2005--AFP) 
  4. Current recommendations re: screening

V. Management of AAA

  1. Surgery traditionally recommended for AAA > 5cm (5.5cm in some guidelines) or 1.5-2 times diameter of aorta at renal arteries.
  2. Beta-blockers to slow progression
    1. In a randomized trial of 548 pts with asymptomatic AAA's 3.0cm-5.0cm in diameter randomized to propranolol (titrated to 80-120mg BID) vs. placebo x 2.5y, propranolol group had nonsig. lower risk of elective surgery (20% vs. 26%) in intention-to-treat analysis but sig. less looking just at those who didn't withdraw b/c of adverse effects (RR = 0.63) (J. Vasc. Surg. 35:72, 2002--JW)

VI. Trials of elective repair of small aneurysms

  1. Traditionally, surgery done if diameter is 5.5cm or greater
  2. 1090 pts 60-76yo with asymptomatic AAA 4.0-5.5cm randomized to surveillance vs. elective repair; over avg 4.6y f/u, mortality was 7.0% in early-surgery group and 7.4% in surveillance group (nonsig.) (Lancet 352:1649, 1998--JW)
  3. 8944 people aged 65-80yo were screened with u/s for AAA over 8y. 356 had AAA 3cm or greater. Followed those pts with Q3mo serial u/s. Used criteria for repair if
  1. Diameter reached 6cm
  2. Expanded > 1cm/yr
  3. Caused sx

124 pts met criteria. Only one death from AAA (0.4% of the 356 with AAA) in a pt who didn't meet criteria; this occurred 5d post-op for a colon Ca. Authors assert that risk for elective AAA surgery is 1-8% and thus greater than risk of no surgery in pts with AAA not meeting criteria. An accompanying editorial (p. 1377) urges caution in switching old guidelines (above) for these new ones given small # (28) of aneurysms 5-5.9cm in this study (Lancet 342:1395, 1993)

  1. UK Small Aneurysm Trial (Lancet 352:1649, 1998--AFP)
    1. 1,090 pts 60-75yo with AAA < 5.5cm randomized to early surgical intervention vs. surveillance
    2. Surveillance group periodic u/s to monitor growth (Q6mo if 4.0-4.9cm, Q3mo if > 4.9cm) & electively repaired if:
    1. Diameter reached 5.5cm
    2. Expanded > 1cm/yr
    3. Caused sx or tenderness
    1. No diff. in mortality over 6y f/u, including after adjustment for age, sex, or initial aneurysm size
  2. 1136 patients (age range, 50 to 79; 99% male) with AAAs 4.0 cm to 5.4 cm diameter randomized to immediate open repair or vs. surveillance with Q6mos u/s or CT. Surveillance pts underwent surgery if AAA's found to be > 5.5 cm, expanded by 0.7 cm within 6 months (or by 1.0 cm within 1 year), or became symptomatic. Over mean 5y f/u, no sig. diff. in total mortality (NEJM 346:1437, 2002)

VII. Endovascular stent-graft for AAA repair

  1. Risks include internal leaks and thrombosis, stenosis, or migration of stent-graft (J. Vasc. Surg 29:292, 1999--JW)
  2. Associated with shorter hospital stays and similar perioperative mortality as open repair (Ann. Surg. 230:298, 1999; Arch. Surg. 134:947, 1999--JW)
  3. Endovascular vs. open repair associated with sig. lower 30-day all-cause mortality (1.7% vs. 4.7%) in a randomized study in 1082 pts with AAAs > 5.4cm in diameter ("EVAR Trial 1"; Lancet 364:843, 2004--JW)
    1. In a follow-up study of the same cohort of patients, after median 2.9y, there was no sig. diff. in all-cause mortality,  but endovascular group had sig. lower (RR about 0.5 per summary) incidence of aneurysm-related death; also had sig. lower incidence of reintervention (9% vs. 41%) (Lancet 365:2179, 2005--JW)
  4. In a randomized trial in 345 pts with AAAs 5cm diameter or greater, endovascular vs. open repair was ass'd with no sig. diff. in 30d incidence of (death or mod-severe complications) ("DREAM" Trial; NEJM 351:1607, 2004--JW)
    1. In a follow-up study of the same cohort of patients, going up to 2y after randomization, there was no sig. diff. in the two groups in survival, but the endovascular group had sig. higher incidence of reintervention during f/u (13% vs. 3%) (NEJM 352:2398, 2005--JW)
    2. In a randomized trial in 881 pts > 49yo randomized to endovascular vs. open AAA repair, over mean 1.8y f/u, endovascular repair was associated with sig. lower 30d mortality (0.5% vs. 3.0%) but no sig. diff. in 2y mortlality (JAMA 302:1535, 2009-abst)
(Sources include Core Content Review of Family Medicine, 2012)