Benefits of Antithrombotic Therapy AfterInfrainguinal Bypass Grafting: A Meta-Analysis

Collins TC, Souchek J, Beyth RJ. Am J Med 2004;117:93–9.

Study Question: Investigators performed a meta-analysis toascertain the benefits of antithrombotic therapy for main-taining the patency of vascular grafts following lower ex-tremity bypass operations.Methods: Researchers identified articles studided usingMEDLINE and hand searches of relevant journals for ran-domized clinical trials that compared the use of antithrom-botic therapy with control or placebo therapy. Random-effects analyses were used to determine the risk of graftocclusion following lower extremity bypass operations aswell as the odds of secondary outcomes, such as myocardialinfarction, cerebrovascular accident, all-cause mortalityand bleeding.Results: Sixteen studies met the inclusion criteria of a ran-domized trial of antithrombotic therapy for the patency ofvascular grafts; six were excluded because the analysesinvolved repeat surgeries or lacked a control group. Of the10 studies included in the final analysis, seven comparedantiplatelet agents with placebo or control, and three com-pared anticoagulant agents with placebo or control. The 10studies were homogeneous despite differing durations offollow-up. The odds of graft occlusion in the treated groupwere half that in the placebo or control group. The oddsratio was 0.46 (95% confidence interval [CI]: 0.32–0.66)for the 10 studies that reported outcomes at 12 months orlonger, 0.50 (95% CI: 0.29–0.87) in the five studies with12-month rates, and 0.58 (95% CI: 0.39–0.88) at 24months.Conclusions: The authors conclude that antithrombotic ther-apy decreases the risk of graft occlusion after a vascularoperation by about 50% at 12 months and is still protectiveat 24 months after the operation.Perspective: The study demonstrates that in patients under-going lower extremity bypass operations involving eithersaphenous or prosthetic graft material, the use of anti-thrombotic therapy for at least 10 days and for as long as 10years following the operation can reduce the risk of graftocclusion at 10 days, with the protective effect persisting at24 months after the operation. Patients who undergo lowerextremity bypass operations should be treated for anti-thrombotic therapy for improved graft patency unless con-traindicated. DM

Hypercholesterolemia Is a Risk Factor forBioprosthetic Valve Calcification and Explantation

Farivar RS, Cohn LH. J Thorac Cardiovasc Surg 2003;126:969 –75.

Study Question: Are risk factors for atherosclerosis (andspecifically hyperlipidemia) associated with bioprostheticvalve calcification and dysfunction?Methods: This was a retrospective study of 144 patients whounderwent removal of a bioprosthetic aortic or mitral valveand had available data on serum cholesterol to determinecorrelates of valve calcification. In addition, 66 patientswho underwent bioprosthetic valve explantation werematched for age, valve location and duration after valveimplantation to 66 control patients with bioprostheticvalves not requiring explantation.Results: In the retrospective cohort, univariate predictors ofprosthesis calcification were cholesterol (p�0.035),younger age at implantation (p�0.014) and coronary arterydisease (p�0.017). Only the mean serum cholesterol level(p�0.02) was linked to calcification in multivariate analy-sis. In the case-control analysis, the mean serum cholesterolwas significantly higher in the explanted valve group thanin the group not requiring explantation (189 vs. 163 mg/dL;p�0.0001). A serum cholesterol �200 mg/dL was associ-ated with an odds ratio for valve explantation of 3.9 (95%confidence interval 1.7–8.9).Conclusions: Increased serum cholesterol level may be a riskfactor for bioprosthetic valve calcification requiring explan-tation.Perspective: Growing (albeit retrospective and/or observa-tional) data suggest that high serum cholesterol is associ-ated with both aortic valvular and coronary artery calcifica-tion; data also suggest diminished native aortic valvecalcification is associated with statin use. This report arguesthat lower serum cholesterol may be associated with lessbioprosthetic valve calcification and possibly longer valvedurability. Although prospective, randomized data wouldbe of obvious interest, there might already be a role for theuse of lipid-lowering maneuvers among patients with nativevalve calcification and those having undergone biopros-thetic valve replacement. DB

Abdominal Aortic Aneurysm Expansion: Risk Factorsand Time Intervals for SurveillanceBrady AR, Thompson SG, Fowkes FGR, Greenhalgh RM,Powell JT, on behalf of the UK Small Aneurysm TrialParticipants. Circulation 2004;110:16 –21.

Study Question: Intervention to reduce abdominal aorticaneurysm (AAA) expansion and optimization of screeningintervals would improve current surveillance programs.This study sought to characterize AAA growth in a nationalcohort of patients with AAA both overall and by cardiovas-cular risk factors.

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Cardiovascular SurgeryAbstracts

Methods: Patients with AAA referred to vascular surgeons at93 UK hospitals were entered into the UK Small AneurysmTrial. For this study, 1743 patients were monitored forchanges in AAA diameter by ultrasonography over a meanfollow-up of 1.9 years.Results: Mean initial AAA diameter and growth rates were43 mm (range 28 to 85 mm) and 2.6 mm/year (95% range,�1.0 to 6.1 mm/year), respectively. Baseline diameter wasstrongly associated with growth, suggesting that AAAgrowth accelerates as the aneurysm enlarges. The AAAgrowth rate was lower in those with low ankle/brachialpressure index and diabetes but higher for current smokers(all p�0.001). No other factor (including lipids and bloodpressure) was associated with AAA growth. Intervals of 36,24, 12 and 3 months for aneurysms of 35, 40, 45 and 50mm, respectively, would restrict the probability of breach-ing the 55-mm limit at rescreening to below 1%.Conclusions: The authors concluded that annual, or lessfrequent, surveillance intervals are safe for all AAAs �45mm in diameter. Smoking increases AAA growth, but ath-erosclerosis appears to play a minor role.Perspective: Evidence from several clinical trials indicatethat medical surveillance is a safe, cost-effective manage-ment of small AAAs. A strategy to reduce cardiovascular riskfactors of those enrolled in surveillance programs appearsreasonably likely to improve patient survival, but this studydemonstrates that, with the exception of smoking cessation,such a strategy is unlikely to slow AAA growth. Smokingcessation must be aggressively targeted, because smokingappears to be the only modifiable factor associated withAAA expansion. The authors also provide a rational basisfor determining appropriate rescreening intervals for thoseenrolled in surveillance programs. DM

Gender-Related Differences in Acute AorticDissectionNienaber CA, Fattori R, Mehta R, et al. Circulation 2004;109:3014 –21.

Study Question: To investigate gender-related differences inpresentation and outcome in acute aortic dissection (AoD).Methods: This is a substudy from the International Registryof Acute Aortic Dissection (IRAD) in which presentingsymptoms, diagnostic imaging and hospital outcomes wereanalyzed based on gender.Results: The IRAD Registry contained 1078 patients, 346 ofwhom were female (32%). Broken down by age, the per-centage of females was 20%, 23%, 36% and 51% for ages�50, 50–65, 66–76 and �75 yrs. Type A dissection wasseen in 61% of male and 65.9% of females; females weremore likely to have a history of hypertension. Dissectionwas noted during pregnancy only in two patients. Therewas a trend (p�0.2) to a longer duration from onset topresentation for women compared to men (21.5�51.4 h vs.16.8�43.6 h). Female patients were less likely to have

abrupt onset of pain than were males (p�0.004); other-wise, presenting symptoms were similar. Pulse deficits weremore common in males than in females (31.7% vs. 19.2%;p�0.001), whereas altered mental status was more com-mon in females (13% vs. 9%; p�0.05). A widened medias-tinum was more common in males (62.7% vs. 55.1%;p�0.02). Considering type A AoD, more males than fe-males were referred for surgical repair (86.8% vs. 70.6%;p�0.001). Hospital complications were similar in the twogroups, with a trend toward a greater incidence of mentalstatus changes and coma (8.7% vs. 5.4%; p�0.06), hypo-tension (34.1% vs. 23.9%; p�0.001) and cardiac tampon-ade (16.5% vs. 10.5%; p�0.007) in women. Limb ischemiawas more prominent in males (11.8% vs. 7.4%; p�0.04).Overall mortality was higher in females (30.1% vs. 21%;p�0.001), which was predominantly due to excess mortal-ity in Type A dissection (38.2% vs. 26.2%; p�0.002).When analyzed by age, the excess mortality seen in femaleswas exclusively attributed to the age group 66–75 yrswhere mortality was 36% vs. 16% for males.Conclusions: There are subtle gender-related differences inpresenting symptoms for patients who have AoD, as well asdifferences in outcome, with a higher overall mortality infemales than in males.Perspective: This substudy from IRAD sheds further light onthe clinical presentation of patients with acute AoD. As withother forms of cardiovascular disease, including acute isch-emic syndromes, gender-based differences in presentingsymptoms and complication rates were noted. Of impor-tance, there was an “insignificant” increase in the time fromonset of symptoms to presentation noted in female patients(4.7 h), which, although not statistically significant, mayhave clinical relevance in an entity with a high early mor-tality such as AoD. WA

Comparison of Aortic Dissection in Patients Withand Without Marfan’s Syndrome (Results From theInternational Registry of Aortic Dissection)Januzzi JL, Marayati F, Mehta RH, et al. Am J Cardiol 2004;94:400 –2.

Study Question: Investigators assessed the prevalence ofMarfan syndrome (MS) among a large contemporary cohortof patients with aortic dissection (AD) and systematicallycompared the clinical characteristics of patients who hadAD with and without MS.Methods: All patients enrolled in IRAD from January 1,1996, to December 31, 2000, were included for the pur-pose of this analysis. Acute type A AD was defined as anydissection that involved the ascending aorta with presenta-tion within 14 days of symptom onset. Type B AD wasdefined as any in which the dissection did not involve theascending aorta. Variables of interest included demograph-ics, history, physical examination, imaging results, manage-ment strategies and outcomes. Patients were then divided

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