Abdominal aortic aneurysm is a disease of the elderly. With the aging of the US population, it would be expected that the volume of AAA repair as well as AAA related mortality would increase. Our current study shows that after the introduction of EVAR there has been an increase in elective repairs and a decrease in ruptured AAA as well as a decrease in procedure related mortality for both intact and ruptured AAA. This has led to a decrease in overall AAA related deaths despite an unchanged mortality for elective open repair.
Heller et al. examined trends in AAA related mortality from the National Hospital Discharge Survey and found no improvement in the number of aneurysm repair deaths from 1979–1997. They also found an unchanged incidence of ruptured aneurysms and ruptured aneurysm repair.15
Cowan et al. found stable rates of repair using NIS data up to 2003.16
This background, along with the current finding that open repair mortality remains the same, suggests that the decrease in annual AAA-related deaths of 38% seen in this study is not a continuing effect of medical advancement in general, but a result of the new technique of repair.
The increased age of those repaired in the post-EVAR era (as well as EVAR vs open) suggests the expansion to an older and perhaps sicker patient population that may not have been considered for open surgery but were still at risk for rupture. The shift of repair to EVAR has driven an increase in intact aneurysm repair volume and a subsequent reduction in the number of ruptures overall. In this NIS population, EVAR volume was slightly greater than open repair volume in 2004 and accounted for 56% of repairs by 2005. In the Medicare population, EVAR volume overtook open repair volume by 2003.2
This difference is likely due to the age difference of the datasets given that EVAR patients (and Medicare patients) are typically older. Although EVAR now is more common than open repair, with its low elective mortality, its contribution to elective deaths was only 27% in 2005.
We previously have reported that, even when patient populations are matched closely to control for confounders, EVAR has a lower in-hospital mortality rate in the US Medicare population than open repair (1.2% vs 4.8%). This difference is still significant, 1.3% vs 4.6%, when comparing the entire (unadjusted) Medicare population even though EVAR patients are older with more comorbidities.2
The outcome of this lower mortality as we see here is an overall decrease in population deaths as EVAR becomes the favored repair.
As with intact AAA repair, we see a lower mortality with EVAR for ruptured aneurysms compared to open repair (32% vs 43%). Less can be concluded from this finding in a retrospective study as there is the potential for selection bias that cannot be assessed with this administrative database. With proper utilization, however, it is believable that the method could lead to overall improved outcomes. Our finding that mortality within the US population has decreased to just under 40% for ruptured repair shows progress compared to prior studies for the past 5 decades.17
Institutional ‘EVAR first’ programs have been promising with lower mortality using EVAR for ruptured aneurysm repair.11,18,19
Mehta et al. reported the results of a hospital- wide initiative to facilitate EVAR for ruptured AAA. Their program resulted in an 18% mortality after EVAR with 47% of patients receiving an endovascular graft rather than open repair when presenting with ruptured aneurysms.11
Cowan et al. found that mortality associated with repair of ruptured aneurysms decreased from 1993 to 2003 for open repair (46.5% to 40.7%).16
Dillavou et al. reported outcomes from the same time period using a 5% inpatient sample from the Medicare population. They reported an unchanged mortality for ruptured repair overall (male average 44.2%, female average 52.8%).20
With the inclusion of more recent years of data, we show that ruptured repair mortality has decreased from an annual average of 44.3% prior to EVAR to 39.9% for all repairs and to 40.8% for open repair. The decrease in open repair mortality over this time indicates that EVAR is not entirely responsible for the decreased mortality of ruptured aneurysm repair, however there is a contribution that could be expected to increase as volume continues to rise.
Another of the promising findings of this study is that hospital admission for the diagnosis of a ruptured AAA has decreased since EVAR. In the Medicare population, Dillavou et al. found ruptured aneurysms to decline from 7300 in 1994 to 5640 in 2003 (23%).20
We report a 30% decrease within our time frame with a rate of decrease that was more rapid after the introduction of EVAR. Given that rupture repair deaths are the larger contributor to overall aneurysm repair deaths, the population benefit is substantial.
Overall mortality associated with a diagnosis of ruptured AAA without repair was lower than expected, raising questions about the accuracy of the diagnosis. This highlights a limitation of the database in that it is reliant upon accurate coding of conditions in order identify cases. Pairing concomitant procedures within the hospitalization increases the accuracy of the diagnosis. It is likely that some patients are admitted with an initial diagnosis of ruptured AAA and an alternative diagnosis is ultimately determined. In this database, the admitting diagnosis is retained as well as any subsequent final diagnoses. This should not impact rupture repair rate and mortality calculations, nor should it impact intact repair. We allowed ruptured AAA diagnosis without repair as an endpoint due to the fact that the observed trends in diagnoses and related deaths mirrored those seen in ruptured AAA with repairs () and there was no identifiable reason why coding accuracy would change over time.
The limitations of the current study include the data source along with its retrospective design. The NIS is designed to analyze heathcare trends and outcomes and as such, it is ideal for a study of this nature, however the database is reliant upon accurate and uniform coding and relies upon sampling weights to derive total population estimates. The weights are designed to control for sampling bias and are based upon hospital region and patient characteristics. Analysis of only actual NIS cases without the utilization of the sampling weights resulted in the same outcome. The NIS has undergone multiple changes since its introduction that include changes in state participation as well as data element inclusion. We used the published supplemental trend file weights to discount any effect these changes may have in comparisons across years.14
Additionally, administrative data do not include anatomic data such as AAA diameter or extent (infrarenal vs pararenal), so stratification along those criteria is not possible.
The inclusion of the peripheral stent code in combination with a primary diagnosis of AAA was made in order to capture some of the EVARs performed before the introduction of the specific procedure code. We believe that this still underestimates the true number of EVARs performed in the transition period however, and thus those years were excluded for the comparative analyses in order for more accurate conclusions to be reached.
There are other factors that may have an effect on aneurysm repair and ruptures in the US today including health care patterns and risk factor prevalence. Increased patient and physician awareness of AAAs as a result of screening programs may have an impact upon the number of patients presenting with rupture.21
In 2004 the Society for Vascular Surgery Consensus Statement recommended ultrasound screening for patients greater than 50 years with a family history of AAA, or for men age 60 to 85 years and women 60 to 85 years with cardiovascular risk factors.22
Screening for AAA did not become a benefit offered by Medicare until January of 2007, and then only for male smokers or patients with a family history of aneurysm at the time of their welcome to Medicare visit.
Risk factors including smoking and hypertension have been associated with the diagnosis or rupture of AAA.23,24
Smoking has decreased in the US population over the past four decades by 50% and from 1993–2005 the rates have decreased from 25% to 21%.25
This may account for some of the observed decrease in ruptures and may decrease the prevalence of AAA over time. Hypertension was shown to have an unchanged prevalence from 1999 to 2006 (28–30%). In the year 2005–2006, 68% of hypertensive adults in the US used antihypertensive medication, however only 64% of those achieved an adequate blood pressure goal.26,27
Less than half of patients entering a large multicenter trial for infrainguinal bypass were using beta-blockers or lipid-lowering therapy.28
With new technology the threshold for repair may be lowered to include older, sicker patients who were not candidates for open repair yet were still at risk for rupture. Additionally, the threshold may be lowered for smaller diameter aneurysms although these data cannot confirm any potential benefit in these subgroups.