Chapter 5.1: What determines and are the consequences of

needs of each patient is a difficult task. Follow-up examinations are necessary to detect complications and to decide whether a secondary intervention is required. In case of too few control visits complications may not always be detected in time, which may result in a higher mortality rate. Increasing the number of control examinations would raise costs of health care and adds to the burden of exposure to medical management for the patient. In our database, the intensity of follow-up appeared to be confounded by indication, which means that the reason for a more intense follow-up negatively influences the results. Patients with a severe risk profile had a higher chance of receiving a more intensive follow-up policy, which at the same time may worsen the results of treatment in this study group.

In conclusion. Despite more intensive surveillance of patients with greater comorbidity, still more complications occurred in this patient category even after adjustment for patient, demographic, and center- specific characteristics. Further assessment is indicated to evaluate the effectiveness of different frequencies of surveillance visits.

Data quality, advantages and weaknesses of the EUROSTAR registry. Data quality can be described in different dimensions including relevance, accuracy, accessibility, comparability and completeness.

Relevance. The EUROSTAR registry was launched with the objective to include a large number of patients in a reduced time span. It was expected to provide quick answers on clinical questions, while at the same time reflecting existing practice patterns. Furthermore, ongoing analysis of improved or new generation devices provided a constantly updated knowledge. This enabled us as investigators to perform analyses on questions that arised from previous investigations. The multicenter EUROSTAR registry included patients with a large variety of coexisting illnesses and a wide spectrum of disease severities. This makes the registry’s patient population a proper reflection of every day clinical practice. Additional advantages included the possibility to analyse infrequent events, for instance events caused by a breach from accepted indications, anatomic criteria or technique. Due to the large number of included patients, analysis provides greater statistical power. Moreover, assessment of small subgroups, which usually would be too small for a

meaningful analysis can still be performed because of the small confidence intervals.

Accuracy. To prevent selective inclusion into the EUROSTAR- registry, enrolment forms were to be submitted 24h before operation to the data registry center. Inevitably, data collected in a multicenter registry have a relatively large interobserver variation, lower accuracy, and limited data monitoring compared to studies with fewer participants. This situation of non-differential misclassification may lead to an underestimation of differences of variables between comparator categories. At regularly intervals data controls were performed to detect double entry, not-plausible values, and to check on correct data chronology.

Accessibility. Since September 2003 the website ‘www.eurostar- online.org’ (build and maintained by KIKA Medical, Nancy, France) is used for online access to the registry database. Patient data can be entered onlinebasic statistics, such as a comparison of institutional data with the overall database can be performed by each participating physician.

Comparability. In statistical analysis correction for potential confounders can be made. It is important to adjust for differences in risk profile, anatomic and center-related characteristics between study groups, to allow valid comparisons between these stratefied groups and identify independent correlations with the outcome variables.

Completeness. The mean completeness of follow-up data was 70%. Incompleteness of data may distract from generalisability of observed results. Analysis of risk profile, morphologic and center-related characteristics between patients with complete follow-up and patients lost at some period during follow-up revealed that the missing values occurred more frequently in high-risk patients. Patients lost-to-follow-up are more frequently high risk patient reflected by higher incidence of ASA-class ≥

Conclusions

From this thesis we may conclude that different aspects can influence the outcomes after EVAR. Patient-specific, anatomic, device- related and surveillance characteristics have impact on outcomes. These findings emphasize the importance of proper patient selection i.e. patients that meet the accepted clinical and aortoiliac morphology criteria. Most benefit from endovascular aneurysm repair can be obtained in appropriately selected patients. The development of a prognostic model based on preoperative collected measurements is likely to be useful for therapeutically decision making, patient selection for clinical trials, and informing patients and families on the risks and outcome of EVAR.

Proper patient selection, combined with the improved durability of stent-grafts, may also lead to a reduction of costs because of less secondary interventions and in the future perhaps a reduced surveillance schedule after EVAR. These goals are paramount since recent trials suggested that EVAR might not be cost effective compared to open surgery. These assessments were made in patients with an aneurysm larger than 5 cm who were also considered fit for open surgery. The clinical and economic outcomes of EVAR in patients with small aneurysms (<5 cm) are currently assessed in the PIVOTAL and CAESAR trials.54,55

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Section 7