Endovascular repair of abdominal aortic aneurysm

The abdominal aorta is a major blood vessel in the body that carries blood from the heart to the major organs in the chest and abdomen. An abdominal aortic aneurysm (AAA) is a balloon-like bulge (dilation) of the aorta that is greater than 3 cm in diameter. If an AAA ruptures (bursts), this is often fatal. Hence, AAAs that are larger than 5.5 cm are usually treated surgically in order to try to prevent such a rupture. Traditionally, AAAs are treated using an open surgical repair (OSR) technique, in which the abdomen is cut open (referred to as open surgery) and the dilated aorta is repaired using fabric graft material. However, over the past 20 years, a newer, 'key hole' technique has been used, in which the AAA is repaired without the need for open surgery - a thin tube is passed via the blood vessels in the groin to the site of the AAA. Once in the correct position, a sheath is introduced that acts to reline the dilated aorta, acting as an artifical blood vessel through which blood can continue to flow, bypassing the aneurysm. Hence, the risk of further expansion or rupture of the AAA is reduced, This technique is referred to as endovascular aneurysm repair (EVAR). As EVAR is a less invasive technique than OSR, in that there is no need for open surgery, it may have advantages over OSR. In addition, some individuals with other medical illnesses, for whom open surgery may be considered a high-risk procedure and who are not fit for OSR, can be offered EVAR instead.

The review authors identified four randomised controlled trials (RCTs) of good quality that compared OSR with EVAR, involving a combined total of 2790 participants considered fit for surgery, and one RCT of good quality that compared EVAR with no intervention, involving a total of 404 participants considered unfit for OSR.

The pooled analysis of the four trials comparing OSR with EVAR showed that the death rates within 30 days of operation or during admission for surgery were significantly lower in individuals undergoing EVAR than in those undergoing OSR (1.4% versus 4.2%). However, there was no difference in death rates between the groups up to four years after the operation (intermediate follow up) or beyond four years (long-term follow up). Participants undergoing EVAR had a significantly higher incidence of a need for an additional intervention to deal with any complications of the procedure undertaken compared with those receiving OSR. Operative complications, health-related quality of life and sexual dysfunction were generally comparable between the two procedures. However, there was a slightly higher incidence of lung complications in the OSR group than in the EVAR group. The results of the one RCT comparing EVAR with no intervention in individuals considered unfit for OSR showed no difference in overall death rates and complication rates between the groups.

Authors' conclusions: 

In individuals considered fit for conventional surgery, EVAR was associated with lower short-term mortality than OSR. However, this benefit from EVAR did not persist at the intermediate- and long-term follow ups. Individuals undergoing EVAR had a higher reintervention rate than those undergoing OSR. Most of the reinterventions undertaken following EVAR, however, were catheter-based interventions associated with low mortality. Operative complications, health-related quality of life and sexual dysfunction were generally comparable between EVAR and OSR. However, there was a slightly higher incidence of pulmonary complications in the OSR group than in the EVAR group.

In individuals considered unfit for open surgery, the results of a single trial found no overall short- or long-term benefits of EVAR over no intervention with regard to all-cause mortality, but individuals may differ and individual preferences should always be taken into account.

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Background: 

An abnormal dilatation of the abdominal aorta is referred to as an abdominal aortic aneurysm (AAA). Due to the risk of rupture, surgical repair is offered electively to individuals with aneurysms greater than 5.5 cm in size. Traditionally, conventional open surgical repair (OSR) was considered the first choice approach. However, over the past two decades endovascular aneurysm repair (EVAR) has gained popularity as a treatment option. This article intends to review the role of EVAR in the management of elective AAA.

Objectives: 

To assess the effectiveness of EVAR versus conventional OSR in individuals with AAA considered fit for surgery, and EVAR versus best medical care in those considered unfit for surgery. This was determined by the effect on short, intermediate and long-term mortality, endograft related complications, re-intervention rates and major complications.

Search strategy: 

The Cochrane Peripheral Vascular Diseases Group Trials Search Co-ordinator (TSC) searched the Specialised Register (January 2013) and the Cochrane Central Register of Controlled Trials (CENTRAL) (2012, Issue 12). The TSC also searched trial databases for details of ongoing or unpublished studies.

Selection criteria: 

Prospective randomised controlled trials (RCTs) comparing EVAR with OSR in individuals with AAA considered fit for surgery. and comparing EVAR with best medical care in individuals considered unfit for surgery. We excluded studies with inadequate data or using an inadequate randomisation technique.

Data collection and analysis: 

Three reviewers independently evaluated trials for appropriateness for inclusion and extracted data using pro forma designed by the Cochrane PVD Group. We assessed the quality of trials using The Cochrane Collaboration's 'Risk of bias' tool. We entered collected data in to Review Manager (version 5.2.3) for analysis. Where direct comparisons could be made, we determined odds ratios (OR). We tested studies for heterogeneity and, when present, we used a random-effects model; otherwise we used a fixed-effect model. We tabulated data that could not be collated.

Main results: 

Four high-quality trials comparing EVAR with OSR (n = 2790) and one high-quality trial comparing EVAR with no intervention (n = 404) fulfilled the inclusion criteria. In individuals considered fit for surgery, a pooled analysis, including 1362 individuals randomised to EVAR and 1361 randomised to OSR, found short-term mortality (including 30-day or inhospital mortality, excluding deaths prior to intervention) with EVAR to be significantly lower than with OSR (1.4% versus 4.2%, OR 0.33, 95% confidence interval (CI) 0.20 to 0.55; P < 0.0001). Using intention-to-treat analysis (ITT) there was no significant difference in mortality at intermediate follow-up (up to four years from randomisation), with 221 (15.8%) and 237 (17%) deaths in the EVAR (n = 1393) and OSR (n = 1390) groups, respectively (OR 0.92, 95% CI 0.75 to 1.12; P = 0.40). There was also no significant difference in long-term mortality (beyond four years), with 464 (37.3%) deaths in the EVAR and 470 (37.8%) deaths in the OSR group (OR 0.98, 95% CI 0.83 to 1.15; P = 0.78). Similarly, there was no significant difference in aneurysm-related mortality between groups, either at the intermediate- or long-term follow up.

Studies showed that both EVAR and OSR were associated with similar incidences of cardiac deaths (OR 1.14, 95% CI 0.86 to 1.52; P = 0.36) and fatal stroke rate (OR 0.81, 95% CI 0.42 to 1.55; P = 0.52). The long-term reintervention rate was significantly higher in the EVAR group than in the OSR group (OR 1.98, 95% CI 1.12 to 3.51; P = 0.02; I2 = 85%). Results of the reintervention analysis should be interpreted with caution due to significant heterogeneity. Operative complications, health-related quality of life and sexual dysfunction were generally comparable between the EVAR and OSR groups. However, there was a slightly higher incidence of pulmonary complications in the OSR group compared with the EVAR group (OR 0.36, 95% CI 0.17 to 0.75; P = 0.006).

In individuals considered unfit for conventional OSR, the one included trial found no difference between the EVAR and no-intervention groups with regard to all-cause mortality at final follow up, with 21.0 deaths per 100 person-years in the EVAR group and 22.1 deaths per 100 person years in the no-intervention group (adjusted hazard ratio (HR) with EVAR 0.99, 95% CI 0.78 to 1.27; P = 0.97). Aneurysm-related deaths were, however, significantly higher in the no-intervention group than in the EVAR group (adjusted HR 0.53, 95% CI 0.32 to 0.89; P = 0.02). There was no difference in myocardial events (HR 1.07, 95% CI 0.60 to 1.91) between the groups in this study.

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