Comparison of endovascular aneurysm repair with open repair in patients with abdominal aortic aneurysm (EVAR trial 1), 30-day operative mortality results: randomised controlled trial

BACKGROUND

Endovascular aneurysm repair (EVAR) is a new technology to treat patients with abdominal aortic aneurysm (AAA) when the anatomy is suitable. Uncertainty exists about how endovascular repair compares with conventional open surgery. EVAR trial 1 was instigated to compare these treatments in patients judged fit for open AAA repair.

METHODS

Between 1999 and 2003, 1082 elective (non-emergency) patients were randomised to receive either EVAR (n=543) or open AAA repair (n=539). Patients aged at least 60 years with aneurysms of diameter 5.5 cm or more, who were fit enough for open surgical repair (anaesthetically and medically well enough for the procedure), were recruited for the study at 41 British hospitals proficient in the EVAR technique. The primary outcome measure is all-cause mortality and these results will be released in 2005. The primary analysis presented here is operative mortality by intention to treat and a secondary analysis was done in per-protocol patients.

FINDINGS

Patients (983 men, 99 women) had a mean age of 74 years (SD 6) and mean AAA diameter of 6.5 cm (SD 1). 1047 (97%) patients underwent AAA repair and 1008 (93%) received their allocated treatment. 30-day mortality in the EVAR group was 1.7% (9/531) versus 4.7% (24/516) in the open repair group (odds ratio 0.35 [95% CI 0.16-0.77], p=0.009). By per-protocol analysis, 30-day mortality for EVAR was 1.6% (8/512) versus 4.6% (23/496) for open repair (0.33 [0.15-0.74], p=0.007). Secondary interventions were more common in patients allocated EVAR (9.8% vs 5.8%, p=0.02).

INTERPRETATION

In patients with large AAAs, treatment by EVAR reduced the 30-day operative mortality by two-thirds compared with open repair. Any change in clinical practice should await durability and longer term results.

Inflammation and matrix metalloproteinases in the enlarging abdominal aortic aneurysm

The risk of rupture of an abdominal aortic aneurysm increases with aortic diameter. To obtain insight into the pathological processes associated with the vascular remodeling that accompanies aortic dilatation, we compared the histological features and the activity of matrix metalloproteinases (MMPs) in biopsies from 21 small (4.0 to 5.5 cm in diameter) and 45 larger abdominal aortic aneurysms. The histological feature most clearly associated with enlarging aneurysm diameter was a higher density of inflammatory cells in the adventitia, P = .018. This inflammation was nonspecific, principally macrophages and B lymphocytes. Fibrosis of the adventitia provided compensatory thickening of the aortic wall as the aneurysm diameter increased. A combination of zymography and immunoblotting identified gelatinase A (MMP-2) as the principal metallogelatinase in small aneurysms, whereas zymography indicated an increasing activity of gelatinase B (MMP-9) in large aneurysms. Homogenates prepared from both small and large aneurysms had similar total activity against gelatin or type IV collagen. However, the concentration of gelatinase A, determined by immunoassay, was highest for small aneurysms: median concentrations, 385, 244, and 166 ng/mg protein for small aneurysms, large aneurysms, and atherosclerotic aorta, respectively. Immunolocalization studies indicated that gelatinase A was concentrated along fibrous tissue of both the acellular media and the atherosclerotic plaque. The recruitment of inflammatory cells into the adventitia, with subsequent elaboration of metalloproteinases, including gelatinase B, may contribute to the rapid growth and rupture of larger aneurysms.

Risk factors for aneurysm rupture in patients kept under ultrasound surveillance. UK Small Aneurysm Trial Participants

OBJECTIVE

To investigate risk factors associated with aneurysm rupture using patients randomized into the U.K. Small Aneurysm Trial (n = 1090) or monitored for aneurysm growth in the associated study (n = 1167).

SUMMARY BACKGROUND DATA

The U.K. Small Aneurysm Trial has shown that ultrasound surveillance is a safe management option for patients with small abdominal aortic aneurysms (4.0 to 5.5 cm in diameter), with an annual rupture rate of 1%.

METHODS

In the cohort of 2257 patients (79% male), aged 59 to 77 years, 103 instances of abdominal aortic aneurysm rupture were identified during the 7-year period of follow-up (1991-1998). Almost all patients (98%) had initial aneurysm diameters in the range of 3 to 6 cm, and the majority of ruptures (76%) occurred in patients with aneurysms > or =5 cm in diameter. Kaplan-Meier survival and Cox regression analysis were used to identify baseline risk factors associated with aneurysm rupture.

RESULTS

After 3 years, the annual rate of aneurysm rupture was 2.2% (95% confidence interval 1.7 to 2.8). The risk of rupture was independently and significantly associated with female sex (p < 0.001), larger initial aneurysm diameter (p < 0.001), lower FEV1 (p = 0.004), current smoking (p = 0.01), and higher mean blood pressure (p = 0.01). Age, body mass index, serum cholesterol concentration, and ankle/brachial pressure index were not associated with an increased risk of aneurysm rupture.

CONCLUSIONS

Within this cohort of patients, women had a threefold higher risk of aneurysm rupture than men. Effective control of blood pressure and cessation of smoking are likely to diminish the risk of rupture.

Long-term outcomes of immediate repair compared with surveillance of small abdominal aortic aneurysms

BACKGROUND

Two clinical trials, one British and one American, have shown that early, prophylactic elective surgery does not improve five-year survival among patients with small abdominal aortic aneurysms. We report long-term outcomes in the United Kingdom Small Aneurysm Trial.

METHODS

We randomly assigned 1090 patients, 60 to 76 years of age, with small abdominal aortic aneurysms (diameter, 4.0 to 5.5 cm) to one of two groups: 563 were assigned to undergo early elective surgery, and 527 were assigned to undergo surveillance by ultrasonography. Patients were followed in the trial until June 1998 and thereafter until August 2001; the mean duration of follow-up was 8 years (range, 6 to 10).

RESULTS

The mean duration of survival was 6.5 years among patients in the surveillance group, as compared with 6.7 years among patients in the early-surgery group (P=0.29). The adjusted hazard ratio for death from any cause in the early-surgery group as compared with the surveillance group was 0.83 (95 percent confidence interval, 0.69 to 1.00; P=0.05). The 30-day operative mortality in the early-surgery group (5.5 percent) led to an early disadvantage in terms of survival. The survival curves crossed at three years, and at eight years, mortality in the early-surgery group was 7.2 percentage points lower than that in the surveillance group (P=0.03). There was no evidence that age, sex, or the initial size of the aneurysm modified the hazard ratio or that delayed surgery in the surveillance group increased 30-day postoperative mortality. Death was attributable to a ruptured aneurysm in 19 of the 411 men who died (5 percent) and in 12 of the 85 women who died (14 percent) (P=0.001). The rate of early cessation of smoking was higher in the early-surgery group than in the surveillance group.

CONCLUSIONS

Among patients with a small abdominal aortic aneurysm, we found no long-term difference in mean survival between the early-surgery and surveillance groups, although after eight years, total mortality was lower in the early-surgery group. This difference may be attributed in part to beneficial changes in lifestyle adopted by members of the early-surgery group.

Vitamin D and cardiovascular disease

Vitamin D plays a classical hormonal role in skeletal health by regulating calcium and phosphorus metabolism. Vitamin D metabolites also have physiological functions in nonskeletal tissues, where local synthesis influences regulatory pathways via paracrine and autocrine mechanisms. The active metabolite of vitamin D, 1α,25-dihydroxyvitamin D, binds to the vitamin D receptor that regulates numerous genes involved in fundamental processes of potential relevance to cardiovascular disease, including cell proliferation and differentiation, apoptosis, oxidative stress, membrane transport, matrix homeostasis, and cell adhesion. Vitamin D receptors have been found in all the major cardiovascular cell types including cardiomyocytes, arterial wall cells, and immune cells. Experimental studies have established a role for vitamin D metabolites in pathways that are integral to cardiovascular function and disease, including inflammation, thrombosis, and the renin-angiotensin system. Clinical studies have generally demonstrated an independent association between vitamin D deficiency and various manifestations of degenerative cardiovascular disease including vascular calcification. However, the role of vitamin D supplementation in the management of cardiovascular disease remains to be established. This review summarizes the clinical studies showing associations between vitamin D status and cardiovascular disease and the experimental studies that explore the mechanistic basis for these associations.

Meta-analysis of individual patient data to examine factors affecting growth and rupture of small abdominal aortic aneurysms

Background

Surveillance is a common management strategy for small abdominal aortic aneurysm (AAA) (3·0–5·4 cm in diameter). Individual characteristics, other than diameter, may influence aneurysm growth or rupture rates.

Methods

Individual data were collated from 15 475 people under follow-up for a small aneurysm in 18 studies. The influence of co-variables (including demographics, medical and drug history) on aneurysm growth and rupture rates (analysed using longitudinal random-effects modelling and survival analysis with adjustment for aneurysm diameter) were summarized in an individual patient meta-analysis.

Results

The mean aneurysm growth rate of 2·21 mm/year was independent of age and sex. Growth rate was increased in smokers (by 0·35 mm/year) and decreased in patients with diabetes (by 0·51 mm/year). Mean arterial pressure had no effect and antihypertensive or other cardioprotective medications had only small, non-significant effects on aneurysm growth, consistent with the observation that calendar year of enrolment was not associated with growth rate. Rupture rates were almost fourfold higher in women than men (P &lt; 0·001), were double in current smokers (P = 0·001) and increased with higher blood pressure (P = 0·001).

Conclusion

Follow-up schedules for individuals with a small AAA may need to consider diabetes and smoking, in addition to aneurysm diameter. The differing risk factors for growth and rupture suggest that a lower threshold for surgical intervention in women may be justified. No single drug used for cardiovascular risk reduction had a major effect on the growth or rupture of small aneurysms.

Interleukin-6 (IL-6) and the prognosis of abdominal aortic aneurysms

BACKGROUND

Abdominal aortic aneurysm is a multifactorial disorder in which inflammation is an important pathophysiological feature. In explant culture, aneurysm biopsies secrete large amounts of interleukin-6 (IL-6), and among aneurysm patients, the circulating concentration of IL-6 appears to be increased.

METHODS AND RESULTS

We investigated, in 19 patients, whether aneurysm wall was an important source of circulating IL-6. We also tested the hypotheses, in 466 patients with a small aneurysm, that (1) high concentrations of circulating IL-6 signaled rapid aneurysm growth and (2) the -174 G-->C polymorphism in the IL-6 promoter predicted survival. For 19 patients with large or inflammatory aneurysms, the concentration of IL-6 was higher in the iliac arteries than the brachial arteries (median difference 26.5 pg/mL, this difference increasing with aneurysm diameter, P=0.01). In 466 patients with small aneurysms, the frequency of the -174 C allele (0.40) was similar to that in a normal healthy population. Patients of GG genotype had lower plasma concentrations of IL-6 than patients of GC and CC genotypes (medians 1.9, 4.8, and 15.6 pg/mL, respectively, Kruskal-Wallis P=0.047). Cardiovascular and all-cause mortalities were lower for patients of GG genotype than for patients of GC and CC genotype: hazard ratios 0.32 (95% CI 0.12 to 0.93), P=0.036, and 0.51 (95% CI 0.25 to 1.00), P=0.05, respectively. There was no association between plasma IL-6 or IL-6 genotype and aneurysm growth.

CONCLUSIONS

Aortic aneurysms appear to be an important source of circulating IL-6, the concentration being influenced by genotype. For patients with small aneurysms, the -174 G-->C IL-6 genotype predicts future cardiovascular mortality.

Elastin degradation in abdominal aortic aneurysms

Histological sections through the walls of abdominal aortic aneurysms showed scarce and disrupted elastic tissue. The elastin content of the aneurysmal aortic media was only 8.1 +/- 3.2% dry defatted weight (n = 11). The elastin content of grossly normal age and anatomically matched aortic media was 35.0 +/- 3.2% dry weight (n = 4) and the elastin content of severely atherosclerotic, stenosed infrarenal aortic media was 22.0 +/- 7.2% dry weight (n = 6). There was an inverse correlation of elastin content with the elastinolytic activity of aortic media homogenates, r = -0.78. Elastase activity, measured by the hydrolysis of [3H]elastin, was highest in aneurysmal aortic homogenates, 92.1 +/- 43.7 U/mg protein (n = 18), falling to 46.9 +/- 13.3 U/mg protein (n = 13) in severely stenosed atherosclerotic aortic homogenates and 35.5 +/- 11.9 U/mg (n = 6) in grossly normal aortic homogenates. The elastinolytic activity of stenotic aorta contained leukocyte elastase as an important component. In aneurysmal homogenates leukocyte elastase was also found but the increased elastase activity resulted from a protease(s) (Mr 95,000) extracted in 2 M urea, having minimal specificity for alanyl bonds and no immunological cross-reactivity with leukocyte elastase.

Final 12-year follow-up of Surgery versus Surveillance in the UK Small Aneurysm Trial

Background

The aim was to determine whether early open surgical repair would benefit patients with small abdominal aortic aneurysm compared with surveillance on long-term follow-up.

Methods

The 1090 patients who were enrolled into the UK Small Aneurysm Trial between 1991 and 1995 were followed up for aneurysm repair and mortality until November 2005.

Results

By November 2005, 714 patients (65·5 per cent) had died, 929 (85·2 per cent) had undergone aneurysm repair, 150 (13·8 per cent) had died without aneurysm repair and 11 (1·0 per cent) remained alive without aneurysm repair. After 12 years, mortality in the surgery and surveillance groups was 63·9 and 67·3 per cent respectively, unadjusted hazard ratio 0·90 (P = 0·139). Three-quarters of the surveillance group eventually had aneurysm repair, with a 30-day elective mortality of 6·3 per cent (versus 5·0 per cent in the early surgery group, P = 0·366). Estimates suggested that the cost of treatment was 17 per cent higher in the early surgery group, with a mean difference of £1326. The death rate in these patients was about twice that in the population matched for age and sex.

Conclusion

There was no long-term survival benefit of early elective open repair of small abdominal aortic aneurysms. Even after successful aneurysm repair, the mortality among these patients was higher than in the general population.

Perioperative β-blockade (Pobble) for patients undergoing infrarenal vascular surgery: Results of a randomized double-blind controlled trial

OBJECTIVE

To assess whether a pragmatic policy of perioperative beta-blockade, with metoprolol, reduced the 30-day cardiovascular morbidity and mortality and reduced the length of hospital stay in average patients undergoing infrarenal vascular surgery.

METHODS

This was a double-blind randomized placebo-controlled trial that occurred in vascular surgical units in four UK hospitals. Participants were 103 patients without previous myocardial infarction who had infrarenal vascular surgery between July 2001 and March 2004. Interventions were oral metoprolol (50 mg twice daily, supplemented by intravenous doses when necessary) or placebo from admission until 7 days after surgery. Holter monitors were kept in place for 72 hours after surgery.

RESULTS

Eighty men and 23 women (median age, 73 years) were randomized, 55 to metoprolol and 48 to placebo, and 97 (94%) underwent surgery during the trial. The most common operations were aortic aneurysm repair (38%) and distal bypass (29%). Intraoperative inotropic support was required in 64% and 92% of patients in the placebo and metoprolol groups, respectively. Within 30 days, cardiovascular events occurred in 32 patients, including myocardial infarction (8%), unstable angina (9%), ventricular tachycardia (19%), and stroke (1%). Four (4%) deaths were reported. Cardiovascular events occurred in 15 (34%) and 17 (32%) patients in the placebo and metoprolol groups, respectively (unadjusted relative risk, 0.94; 95% confidence interval, 0.53-1.66; adjusted [for age, sex, statin use, and aortic cross-clamping] relative risk, 0.87; 95% confidence interval, 0.48-1.55). Time from operation to discharge was reduced from a median of 12 days (95% confidence interval, 9-19 days) in the placebo group to 10 days (95% confidence interval, 8-12 days) in the metoprolol group (adjusted hazard ratio, 1.71; 95% confidence interval, 1.09-2.66; P < .02).

CONCLUSIONS

Myocardial ischemia was evident in a high proportion (one third) of the patients after surgery. A pragmatic regimen of perioperative beta-blockade with metoprolol did not seem to reduce 30-day cardiovascular events, but it did decrease the time from surgery to discharge.

On the accumulation of D-aspartate in elastin and other proteins of the ageing aorta

Ageing and degenerative changes of the human aorta are associated with medial thinning and a reduced dry weight content of elastin. The metabolic stability of cross-linked elastin was investigated by measuring the accumulation of D-aspartate with ageing in insoluble elastin isolated from human aorta. D-Aspartate accumulation in elastin was compared with D-aspartate accumulation in aortic collagen and an elastin bound glycoprotein fraction. The D-aspartate content of elastin, purified from infrarenal aorta; increased linearly with age from 3% of the total aspartate in youth to 13% in the mid 80s. In contrast the D-aspartate content of aortic collagen remained invariant (3-5% of the total aspartate) from youth to old age. The apparent first order rate constant for the racemization of L-aspartate in elastin was 1.14 x 10(-3). The D-aspartate content of the elastin bound glycoproteins increased by only a small amount, from 3% in the mid 30s to 6% in the mid 80s. These results argue for the metabolic stability of aortic elastin as compared with the fibrillar collagens of the human aorta. Both the rate of racemization and the specific accumulation of D-aspartate in elastin, but not collagen, indicates that mature cross-linked elastin is not synthesized in the adult aorta.

Vascular damage from smoking: disease mechanisms at the arterial wall

The products of tobacco combustion are absorbed into the systemic circulation. Absorbed nicotine stimulates the release of catecholamines, whilst other products (perhaps including nicotine) injure the arterial endothelium and promote atherogenesis. Free radicals and aromatic compounds diminish the endothelial synthesis of nitric oxide, causing impaired endothelium-dependent relaxation of arteries, the earliest clinical sign of endothelial dysfunction. Smoking alters the shear forces and rheology at the endothelial surface and these changes enhance the effects of products of tobacco combustion to upregulate leucocyte adhesion molecules on the endothelial surface. The increased oxidation of low density lipoprotein (LDL) in smokers has synergistic effects to promote monocyte adhesion and monocyte migration into the subintimal space. Continued stimulation of intimal cells by oxidized LDL leads to the development of atherosclerosis. Many of these effects are ameliorated by high concentrations of vitamin C. Smoking also potentiates thrombosis at the dysfunctional endothelium by increasing the concentration of plasma fibrinogen and altering the activity of platelets. All these proatherogenic effects of smoking to injure the endothelium also are observed, albeit to lesser extent, in passive smokers.

Metalloproteinases in degenerative aortic disease

1. Atherosclerosis and aneurysm of the abdominal aorta are associated with thinning of the medial connective tissue. We have investigated the presence of the connective-tissue-degrading metalloproteinases in homogenates prepared from atherosclerotic, aneurysmal and control aortic media. 2. Gelatinase activity was much increased in homogenates from atherosclerotic and aneurysmal aorta [10.9 +/- 1.8 and 13.3 +/- 3.3 micrograms of gelatin hydrolysed h-1 (mg of protein)-1 respectively]. This gelatinase activity was highest at the luminal aspect of the aortic media, where the activity increased three- to five-fold after the destruction of alpha 2-macroglobulin. Zymograms demonstrated the principal gelatinase in atherosclerotic aorta to have a molecular mass of about 92 kDa, whereas in aneurysmal aorta there was a spectrum of gelatinase activity from 92 to 55 kDa. 3. Collagenase and stromelysin (proteoglycanase) could be detected by immunoblotting in homogenates of aneurysmal aorta, but rarely in atherosclerotic aorta and never in control aorta. Collagenase and stromelysin activities were low, but increased two- to three-fold after the destruction of tissue inhibitor of metalloproteinases. Collagenase and stromelysin activities were highest at the adventitial aspect of aneurysmal media. 4. The secretion of gelatinase by inflammatory cells at the intima of diseased aorta could have a pathological role in establishing atherosclerotic plaques and medial thinning. Secretion of collagenase, gelatinase and stromelysin from the adventitia could accelerate connective tissue degradation in the media of aneurysmal aorta.

Inhibition of prostaglandin E2 synthesis in abdominal aortic aneurysms: implications for smooth muscle cell viability, inflammatory processes, and the expansion of abdominal aortic aneurysms

BACKGROUND

There is no treatment proven to limit the growth of abdominal aortic aneurysms, in which the histological hallmarks include inflammation and medial atrophy, with apoptosis of smooth muscle cells and destruction of elastin.

METHODS AND RESULTS

Aneurysm biopsies were used for explant cultures, the preparation of smooth muscle cell cultures, and isolation of macrophages. Tissue macrophages stained strongly for cyclooxygenase 2. Prostaglandin E2 (PGE2) concentrations in aneurysm tissue homogenates, conditioned medium from explants, and isolated macrophages were 49+/-22 ng/g, 319+/-38 ng/mL, and 22+/-21 ng/mL, respectively. PGE2 inhibited DNA synthesis and proliferation in normal aortic smooth muscle cells (IC50, 23.2+/-3.8 and 23.6+/-4.5 ng/mL, respectively). In smooth muscle cells derived from aneurysmal aorta, PGE2 also caused cell death, with generation of oligonucleosomes. Conditioned medium from the mixed smooth muscle and monocyte cultures derived from explants also had potent growth-inhibitory effects, and fractionation of this medium showed that the growth-inhibitory molecule(s) coeluted with PGE2. In explants, indomethacin 10 micromol/L or mefenamic acid 10 micromol/L abolished PGE2 secretion and significantly reduced IL-1beta and IL-6 secretion. In a separate case-control study, the expansion of abdominal aortic aneurysms was compared in 15 patients taking nonsteroidal anti-inflammatory drugs and 63 control subjects; median growth rates were 1.5 and 3.2 mm/y, respectively, P=0.001.

CONCLUSIONS

The adverse effects of PGE2 on aortic smooth muscle cell viability and cytokine secretion in vitro and the apparent effect of anti-inflammatory drugs to lower aneurysm growth rates suggest that selective inhibition of PGE2 synthesis could be an effective treatment to curtail aneurysm expansion.

Systematic review and meta-analysis of the growth and rupture rates of small abdominal aortic aneurysms: implications for surveillance intervals and their cost-effectiveness

BACKGROUND

Small abdominal aortic aneurysms (AAAs; 3.0-5.4 cm in diameter) are usually asymptomatic and managed by regular ultrasound surveillance until they grow to a diameter threshold (commonly 5.5 cm) at which surgical intervention is considered. The choice of appropriate surveillance intervals is governed by the growth and rupture rates of small AAAs, as well as their relative cost-effectiveness.

OBJECTIVES

The aim of this series of studies was to inform the evidence base for small AAA surveillance strategies. This was achieved by literature review, collation and analysis of individual patient data, a focus group and health economic modelling.

DATA SOURCES

We undertook systematic literature reviews of growth rates and rupture rates of small AAAs. The databases MEDLINE, EMBASE on OvidSP, Cochrane Central Register of Controlled Trials 2009 Issue 4, ClinicalTrials.gov, and controlled-trials.com were searched from inception up until the end of 2009. We also obtained individual data on 15,475 patients from 18 surveillance studies.

REVIEW METHODS

Systematic reviews of publications identified 15 studies providing small AAA growth rates, and 14 studies with small AAA rupture rates, up to December 2009 (later updated to September 2012). We developed statistical methods to analyse individual surveillance data, including the effects of patient characteristics, to inform the choice of surveillance intervals and provide inputs for health economic modelling. We updated an existing health economic model of AAA screening to address the cost-effectiveness of different surveillance intervals.

RESULTS

In the literature reviews, the mean growth rate was 2.3 mm/year and the reported rupture rates varied between 0 and 1.6 ruptures per 100 person-years. Growth rates increased markedly with aneurysm diameter, but insufficient detail was available to guide surveillance intervals. Based on individual surveillance data, for each 0.5-cm increase in AAA diameter, growth rates increased by about 0.5 mm/year and rupture rates doubled. To control the risk of exceeding 5.5 cm to below 10% in men, on average a 7-year surveillance interval is sufficient for a 3.0-cm aneurysm, whereas an 8-month interval is necessary for a 5.0-cm aneurysm. To control the risk of rupture to below 1%, the corresponding estimated surveillance intervals are 9 years and 17 months. Average growth rates were higher in smokers (by 0.35 mm/year) and lower in patients with diabetes (by 0.51 mm/year). Rupture rates were almost fourfold higher in women than men, doubled in current smokers and increased with higher blood pressure. Increasing the surveillance interval from 1 to 2 years for the smallest aneurysms (3.0-4.4 cm) decreased costs and led to a positive net benefit. For the larger aneurysms (4.5-5.4 cm), increasing surveillance intervals from 3 to 6 months led to equivalent cost-effectiveness.

LIMITATIONS

There were no clear reasons why the growth rates varied substantially between studies. Uniform diagnostic criteria for rupture were not available. The long-term cost-effectiveness results may be susceptible to the modelling assumptions made.

CONCLUSIONS

Surveillance intervals of several years are clinically acceptable for men with AAAs in the range 3.0-4.0 cm. Intervals of around 1 year are suitable for 4.0-4.9-cm AAAs, whereas intervals of 6 months would be acceptable for 5.0-5.4-cm AAAs. These intervals are longer than those currently employed in the UK AAA screening programmes. Lengthening surveillance intervals for the smallest aneurysms was also shown to be cost-effective. Future work should focus on optimising surveillance intervals for women, studying whether or not the threshold for surgery should depend on patient characteristics, evaluating the usefulness of surveillance for those with aortic diameters of 2.5-2.9 cm, and developing interventions that may reduce the growth or rupture rates of small AAAs.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Risk factors for postoperative death following elective surgical repair of abdominal aortic aneurysm: results from the UK Small Aneurysm Trial. On behalf of the UK Small Aneurysm Trial participants

BACKGROUND

In regional and population studies, the mortality rate within 30 days of elective surgical repair of abdominal aortic aneurysm is approximately 8 per cent. Identification of preoperative factors associated with this mortality risk is important for informing surgical policy and may suggest suitable preoperative interventions.

METHODS

In the UK Small Aneurysm Trial, 820 patients aged 60-80 years underwent elective open surgical repair of an abdominal aortic aneurysm. The relationship between 30-day mortality rate and 13 prespecified potential prognostic factors was investigated. The value of a published clinical prediction rule was also evaluated.

RESULTS

The postoperative mortality rate was 5.6 per cent overall (46 deaths in 820 patients). Postoperative mortality risk was significantly associated with older age (P = 0. 03), higher serum creatinine level (P = 0.002) and lower forced expiratory volume in 1 s (FEV1) (P = 0.003) in univariate analyses. Evidence of a relationship between age and postoperative death was weakened (P = 0.08) after adjustment for creatinine level and FEV1. The predicted postoperative mortality risk ranged from 2.7 per cent in younger patients with below average creatinine levels and above average FEV1, to 7.8 per cent in older patients with above average creatinine levels and below average FEV1. The published clinical prediction rule did not validate well on these data; observed risk did not correlate with predicted risk except for a small group of high-risk patients.

CONCLUSION

Poor preoperative lung and renal function was strongly associated with postoperative death. Age was less important once these two important prognostic factors had been taken into account. The potential for preoperative improvement in lung and renal function to reduce postoperative mortality rates should be addressed in future studies.

Pathogenesis of abdominal aortic aneurysm

The pathogenesis of abdominal aortic aneurysm involves many factors acting over time. However, destruction of elastin in the aortic wall is a key event that shifts the load produced by blood pressure on to collagen. This is exacerbated in the presence of hypertension. Smoking and age are further important factors, as is the site; elastic lamellae are relatively less common in the abdominal aorta. Once the shielding effect of elastin is lost, further dilatation and rupture of the aorta depend on the physical properties of the collagen present.

Smoking and growth rate of small abdominal aortic aneurysms

Smoking is an important risk factor for abdominal aortic aneurysm. Limiting the growth rate of small aneurysms has the potential to prevent them reaching a size at which surgical repair is considered. In 43 patients, with small aneurysms, growth rates were studied by serial ultrasound over 3 years. The median expansion rate of these small aneurysms was 0.13 cm per year. Growth rates were higher in those who continued to smoke (0.16 vs 0.09 cm per year in those who no longer smoked, p = 0.038). Higher growth rates were significantly correlated with the concentration of serum cotinine. Stopping smoking could reduce the growth rate of small abdominal aortic aneurysms.

Influence of smoking and plasma factors on patency of femoropopliteal vein grafts

OBJECTIVE

To determine the effects of smoking, plasma lipids, lipoproteins, apolipoproteins, and fibrinogen on the patency of saphenous vein femoropopliteal bypass grafts at one year.

DESIGN

Prospective study of patients with saphenous vein femoropopliteal bypass grafts entered into a multicentre trial.

SETTING

Surgical wards, outpatient clinics, and home visits coordinated by two tertiary referral centres in London and Birmingham.

PATIENTS

157 Patients (mean age 66.6 (SD 8.2) years), 113 with patent grafts and 44 with occluded grafts one year after bypass.

MAIN OUTCOME MEASURE

Cumulative percentage patency at one year.

RESULTS

Markers for smoking (blood carboxyhaemoglobin concentration (p less than 0.05) and plasma thiocyanate concentration (p less than 0.01) and plasma concentrations of fibrinogen (p less than 0.001) and apolipoproteins AI (p less than 0.04) and (a) (p less than 0.05) were significantly higher in patients with occluded grafts. Serum cholesterol concentrations were significantly higher in patients with grafts that remained patent one year after bypass (p less than 0.005). Analysis of the smoking markers indicated that a quarter of patients (40) were untruthful in their claims to have stopped smoking. Based on smoking markers, patency of grafts in smokers was significantly lower at one year by life table analysis than in non-smokers (63% v 84%, p less than 0.02). Patency was significantly higher by life table analysis in patients with a plasma fibrinogen concentration below the median than in those with a concentration above (90% v 57%, p less than 0.0002). Surprisingly, increased plasma low density lipoprotein cholesterol concentration was significantly associated with improved patency at one year (85%) at values above the median compared with patency (only 68%) at values in the lower half of the range (p less than 0.02).

CONCLUSIONS

Plasma fibrinogen concentration was the most important variable predicting graft occlusion, followed by smoking markers. A more forceful approach is needed to stop patients smoking; therapeutic measures to improve patency of vein grafts should focus on decreasing plasma fibrinogen concentration rather than serum cholesterol concentration.

Observations from the IMPROVE trial concerning the clinical care of patients with ruptured abdominal aortic aneurysm

BACKGROUND

Single-centre series of the management of patients with ruptured abdominal aortic aneurysm (AAA) are usually too small to identify clinical factors that could improve patient outcomes.

METHODS

IMPROVE is a pragmatic, multicentre randomized clinical trial in which eligible patients with a clinical diagnosis of ruptured aneurysm were allocated to a strategy of endovascular aneurysm repair (EVAR) or to open repair. The influences of time and manner of hospital presentation, fluid volume status, type of anaesthesia, type of endovascular repair and time to aneurysm repair on 30-day mortality were investigated according to a prespecified plan, for the subgroup of patients with a proven diagnosis of ruptured or symptomatic AAA. Adjustment was made for potential confounding factors.

RESULTS

Some 558 of 613 randomized patients had a symptomatic or ruptured aneurysm: diagnostic accuracy was 91·0 per cent. Patients randomized outside routine working hours had higher operative mortality (adjusted odds ratio (OR) 1·47, 95 per cent confidence interval 1·00 to 2·17). Mortality rates after primary and secondary presentation were similar. Lowest systolic blood pressure was strongly and independently associated with 30-day mortality (51 per cent among those with pressure below 70 mmHg). Patients who received EVAR under local anaesthesia alone had greatly reduced 30-day mortality compared with those who had general anaesthesia (adjusted OR 0·27, 0·10 to 0·70).

CONCLUSION

These findings suggest that the outcome of ruptured AAA might be improved by wider use of local anaesthesia for EVAR and that a minimum blood pressure of 70 mmHg is too low a threshold for permissive hypotension.

Limitations of ultrasonography in surveillance of small abdominal aortic aneurysms

The repeatability, observer bias and instrument bias of aortic diameter measurement by ultrasonography, were investigated in ten patients with small (3-6 cm by computed tomography) infrarenal abdominal aortic aneurysm. The repeatability of maximum aortic diameter measurement by ultrasonography was much better for anterior-posterior than transverse diameter, with coefficients of repeatability 3.0-7.5 mm and 10-15 mm respectively. The repeatability of suprarenal aortic diameter measurement was poor. Surprisingly, maximum diameter using ultrasonography was larger than that using computed tomography, the difference being least for anterior-posterior measurements. At best a single, experienced observer, using the same instrument may provide aortic diameters using ultrasonography accurate to within 5 mm, but more commonly such aortic diameter is only accurate to within 8 mm.

Explaining the decrease in mortality from abdominal aortic aneurysm rupture

BACKGROUND

A steady rise in mortality from abdominal aortic aneurysm (AAA) was reported in the 1980s and 1990 s, although this is now declining rapidly. Reasons for the recent decline in mortality from AAA rupture are investigated here.

METHODS

Routine statistics for mortality, hospital admissions and procedures in England and Wales were investigated. All data were age-standardized. Trends in smoking, hypertension and treatment for hypercholesterolaemia (statins), together with regression coefficients for mortality, were available from public sources for those aged at least 65 years. Deaths from ruptured AAA avoided in this age group were estimated by using the IMPACT equation: deaths avoided = (deaths in index year) × (risk factor decline) × β-coefficient.

RESULTS

From 1997, deaths from ruptured AAA have decreased sharply, almost twofold in men. Hospital admissions for elective AAA repair have increased modestly (from 40 to 45 per 100,000 population), attributable entirely to more procedures in those aged 75 years and over (P < 0.001). Admissions for ruptured AAA have declined from 18.6 to 13.5 per 100,000 population, across all ages, with the proportion offered and surviving emergency repair unchanged. From 1997, mortality from ruptured aneurysm in those aged at least 65 years has fallen from 65.9 to 44.6 per 100,000 population. An estimated 8-11 deaths per 100,000 population were avoided by a reduced prevalence of smoking and a similar number from an increase in the number of elective AAA repairs. Estimates for the effects of blood pressure and lipid control are uncertain.

CONCLUSION

The reduction in incidence of ruptured AAA since 1997 is attributable largely to changes in smoking prevalence and increases in elective AAA repair in those aged 75 years and over.