Comparison of Outcomes of Complex Abdominal Aortic Aneurysm Treatment: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison of Outcomes of Complex Abdominal Aortic Aneurysm Treatment (NCT04773223), a registered phase not stated study. The primary outcome is Aortic Related Reintervention..

2. Clinical Question

The study focuses on complex aneurysm anatomy and compares two repair approaches in a prospective cohort. Its stated aim is to compare short- and long-term clinical outcomes. The primary endpoint is a count of participants who undergo an aortic-related reintervention, with the timeframe described as through study completion and an average of 7 year.

This is not a randomized comparison: the allocation method is not stated in the registry record, and the arms are not a like-for-like control comparison. Patients receiving each approach may differ in their characteristics or clinical circumstances. Those differences can influence outcomes independently of the treatment approach, so a comparison of group counts alone would not establish that the approach caused any difference.

The registry record lists 925 participants enrolled, but it does not report the primary endpoint counts or a comparative estimate. Consequently, the clinical question is clear, but the posted record does not establish the direction or precision of any difference in reintervention between the groups.

3. Trial Design

The registry record describes a prospective cohort study of repair for juxta- and pararenal abdominal aortic aneurysms. It compares an open surgery group with an endovascular group. The endovascular group includes patients undergoing some form of endovascular abdominal aortic aneurysm repair, such as fenestrated or chimney repair; the open group includes patients undergoing open surgery for juxta- or pararenal aneurysm.

The stated aim is to compare short- and long-term clinical outcomes. The methodology describes data collection on demographics, baseline comorbidities, aneurysm parameters, laboratory values, and intraoperative and postoperative data. The summary also refers to follow-up examinations, but the description is incomplete and the follow-up schedule and procedures are not reported in the registry record.

The registry record describes the study as prospective and names Belgrade, Bologna, Milan, Dijklander, Amsterdam, and Helsinki among the participating locations. It describes the centers as high-volume aneurysm repair centers. The sponsor is the Clinical Centre of Serbia. The study start date is 2011-01-01, the primary completion date is 2022-01-01, and the status is COMPLETED. The listed enrollment is 925.

Treatment allocation was not stated. The registry record therefore does not describe random assignment, and the groups should be treated as observational cohorts rather than randomized arms. The record itself cautions that they are not a like-for-like control comparison. The statistical plan, including planned adjustment for differences between groups, is not reported in the registry record.

The primary endpoint concerns participants with an aortic-related reintervention. A secondary outcome listed in the record is 30-day Acute Kidney Injury. Although the record reports adverse-event figures, it does not provide an analysis of the primary endpoint or a comparative estimate for the listed secondary outcome.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Aortic Related Reintervention., measured over through study completion, an average of 7 year.

The primary endpoint is Aortic Related Reintervention, measured as a count of participants. It is intended to capture whether a participant undergoes another procedure related to the aorta after the initial repair. The registry record gives different examples of qualifying events for the two treatment groups: graft infection, graft thrombosis, pseudoaneurysm formation, or secondary aneurysm rupture after open surgery; and endoleak, migration, thrombosis, infection, fracture, or secondary aneurysm rupture after endovascular repair.

Reintervention is a clinically relevant outcome because it records the need for another procedure after the initial repair. However, the listed event definitions are not identical across treatment groups. Some events are specific to a repair type, so the endpoint combines different reasons for reintervention rather than one uniform event. The registry record does not report further adjudication rules or how events with more than one possible cause are classified.

The stated timeframe is through study completion, an average of 7 year. This describes a long-term follow-up window, but the record does not give a participant-level follow-up schedule or explain how time at risk was handled. The primary endpoint result—the number of participants with reintervention in either group—is not reported in the registry record. Nor is a comparative effect estimate or its precision reported. The endpoint definition is available, but the posted data do not allow readers to assess the observed between-group difference.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical interpretation depends on how the endpoint is defined, who is included in each comparison, and what analysis connects the observed data to the study question. The registry record identifies a primary endpoint and describes a prospective cohort, but it does not report an analysis of that endpoint. The concepts below explain how such evidence is ordinarily interpreted; they do not describe undocumented methods as if they were used in this study.

What does a count of participants measure?

A count of participants with an event records how many people experienced the defined outcome during the specified observation period. It is not the same as an event rate per unit of follow-up, a time-to-event estimate, or a comparison adjusted for participant characteristics. A participant can contribute an event only if the event definition is met and the participant's outcome is observed. The primary endpoint counts participants with aortic-related reintervention through study completion, with an average follow-up duration stated as 7 year.

For this endpoint, the registry record gives examples of qualifying reinterventions that differ by treatment group. This makes the clinical interpretation dependent on those group-specific definitions. It also means that the count combines multiple event types. The record does not report how endpoint events were confirmed, whether they were adjudicated, or how recurrent procedures were treated in the participant count.

Why does the cohort design matter?

In a randomized study, random assignment is intended to make treatment groups comparable at baseline, on average. In an observational cohort, treatment is not assigned randomly; choices or clinical circumstances can influence which treatment a participant receives. If those circumstances also predict the outcome, a crude group comparison can mix the association with treatment and the effects of those underlying differences. This is confounding.

Adjustment methods can sometimes address measured differences, for example by including baseline variables in a model or constructing a matched comparison. Such methods cannot automatically account for differences that were not measured or were not included appropriately. The registry record does not state an adjustment strategy, model, or matching procedure. It also explicitly cautions that the arms are not a like-for-like control comparison. Therefore, no adjusted interpretation should be attributed to the posted record.

What would an estimate and confidence interval add?

A comparative effect estimate expresses the observed contrast between groups using a chosen scale. A confidence interval describes the statistical uncertainty around that estimate under the analysis assumptions. A narrower interval indicates greater precision, while a wider interval indicates less precision. A confidence interval does not remove confounding or repair differences in endpoint definition; it addresses uncertainty under the statistical model, not every source of bias.

No primary endpoint estimate or confidence interval is reported in the registry record. A numerical comparison, its uncertainty, and a judgment about whether it is compatible with materially different outcomes therefore cannot be drawn from the posted record. A p-value, even if available, would not substitute for an estimate and interval: it would not communicate the magnitude or precision of the observed contrast on its own.

How should the planning illustrations be read?

The accompanying planning illustrations are described as calculations based on an observed effect, with a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. They consider effects that are stated fractions of the observed effect. For time-to-event outcomes, the illustrations count total events; for other outcomes, they express participants per arm for a specified power.

These are planning illustrations, not observed study results and not observed power. A sample-size calculation asks how much information might be required under stated assumptions; it does not show that the study achieved that information or that an effect was demonstrated. The record does not report the primary endpoint result needed to assess what observed effect anchors such an illustration, nor does it report the trial's own sample-size justification. The posted illustration should not be mistaken for the study's design rationale or a retrospective measure of success.

What is not documented?

The registry record lists zero analyses. It does not describe the statistical analysis plan, model specification, covariate selection, handling of center effects, or whether estimates were intended to be adjusted. It does not report an interim analysis plan. These are not details that can be inferred from the fact that data collection included demographics, comorbidities, aneurysm parameters, laboratory values, and operative data. Collecting a variable does not establish that it was used in an analysis.

The primary endpoint is a count of participants, but the record does not state whether any analysis accounted for different follow-up durations or censoring. General statistical practice distinguishes a simple count from time-to-event analysis when observation time varies; the registry record does not identify which approach was intended or used. The average follow-up description alone does not supply participant-level observation times or an analysis method.

Overall, the design and endpoint can be described, and the planning assumptions can be explained as assumptions. The registry record does not provide the estimates, analysis methods, or supporting details needed to evaluate the comparative primary outcome statistically.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Open Surgery Group", "Endovascular Group")
n      <- c(600, 234)
events <- c(44, 63)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Open Surgery Group  600  44  7.3  5.4  9.7  5.5  9.7  5.5  9.7
ARM  Endovascular Group  234  63  26.9  21.4  33.1  21.6  32.9  21.6  33.0

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists a primary outcome and a secondary outcome, 30-day Acute Kidney Injury. It also describes short- and long-term clinical outcomes in the study aim and includes adverse-event information. However, it does not report which outcomes were included in a formal analysis, how many comparisons were planned, or whether any approach to multiplicity was specified. When several outcomes or comparisons are examined, the chance of at least one apparently notable result can increase; methods for addressing that issue depend on the analysis plan. No such plan is reported in the registry record.

Missing outcome data can affect both the number of participants included and the interpretation of a group comparison. The record does not report the number of participants with missing primary endpoint data, reasons for missingness, follow-up losses, or any method for handling missing observations. It also does not state whether participants were analyzed according to initial treatment, treatment received, or another population definition. The analysis population for the primary endpoint is therefore not reported in the registry record.

The overall enrollment is listed as 925, while the adverse-event entries use group denominators of 600 and 234. The registry record does not explain the difference between these figures or provide corresponding primary endpoint denominators. It is not possible to determine from the record whether the same participants contributed to each outcome or whether the analysis populations differed.

These omissions do not prove that missing data or multiplicity affected the results. They mean that the reader cannot evaluate their handling or potential influence from the registry record. No primary endpoint analysis is reported, so the effects of these issues on a comparative estimate cannot be assessed.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: srugical bleeding (6.3%), spinal cord ischemia (3.4%), acute lower limb ischemia (3.4%), acute coronary syndrome (2.7%), wound infection (2.6%).

The registry record lists serious adverse events for 133 participants among 600 at risk in the open surgery group and 51 participants among 234 at risk in the endovascular group. It lists 256 deaths in the open surgery group and 91 in the endovascular group. The record does not explain the relationship between these denominators and the overall enrollment of 925, or provide a comparative analysis of the entries.

The listed serious-event terms and percentages are surgical bleeding, 6.3%; spinal cord ischemia, 3.4%; acute lower limb ischemia, 3.4%; acute coronary syndrome, 2.7%; wound infection, 2.6%; and prolonged intubation, 2.3%. These descriptions identify entries in the registry's adverse-event record. They should not be read as estimates comparing treatment groups: group-specific percentages for each term, event timing, follow-up duration, and uncertainty are not reported in the registry record.

Counts alone do not show whether groups had comparable observation time or baseline risk. The record does not give causes or timing for the deaths, nor does it explain how adverse events were collected. Consequently, these entries describe what is recorded, but do not establish a causal safety difference between approaches.

13. What the Result Does, and Does Not, Mean

The registry record establishes that a prospective cohort was intended to compare endovascular and open repair for juxta- and pararenal abdominal aortic aneurysms. It identifies a primary endpoint—participants with aortic-related reintervention—and a stated follow-up period through study completion, with an average of 7 year. It also reports enrollment, study status, group descriptions, and adverse-event entries.

It does not report the primary endpoint counts or a comparative estimate. Without those results, readers cannot determine from the registry record whether the observed reintervention experience differed between groups, how large any difference was, or how precisely it was estimated. No conclusion about the primary comparison should be inferred from the endpoint definition, study completion status, or adverse-event entries.

The safety figures are descriptive counts in groups with different listed denominators. They do not establish that one approach caused more or fewer serious events or deaths. Differences in treatment selection, patient characteristics, follow-up, and other factors could affect these figures. The registry record does not report an analysis addressing such differences.

Statistical significance and clinical importance are distinct concepts. A statistical estimate, if reported, would need to be read alongside its uncertainty and the scale of the endpoint. Even a precise association in this cohort would not by itself establish a causal treatment effect, because allocation was not stated and the record cautions that the arms are not like-for-like. Conversely, the absence of an analysis in the registry record does not demonstrate that the treatments have equal outcomes.

The appropriate interpretation is therefore limited: the study question and endpoint are described, but the comparative primary result is not reported in the registry record. The available counts provide context about enrollment and recorded adverse events, not a complete statistical assessment of comparative effectiveness or safety.

14. Why This Trial Matters Statistically

This study addresses a comparison where both the clinical setting and the treatment groups are complex. Juxta- and pararenal aneurysms are the stated conditions, and the endovascular group includes different forms of repair. The endpoint also combines several reasons for repeat intervention, with examples that vary between open and endovascular repair. These features make careful outcome definition and interpretation especially important.

From a statistical perspective, the prospective cohort design raises the question of treatment selection and confounding. Patients receiving open or endovascular repair may differ in ways that also relate to outcomes. The registry record describes collecting baseline and aneurysm information, but does not report an adjustment strategy or comparative analysis. The design label alone cannot establish whether the comparison adequately addresses those differences.

Long-term outcomes add another interpretive issue: participants may have different amounts of follow-up. A participant count over a stated period and a time-to-event analysis answer related but distinct questions. The record gives an average follow-up description, but does not report participant-level observation time or the analysis method. Understanding how follow-up was handled would be important for interpreting a long-term reintervention comparison.

The record also illustrates why reporting estimates, uncertainty, and analysis details matters. Enrollment and adverse-event counts do not substitute for the primary endpoint result. Without an effect estimate, confidence interval, analysis population, or explanation of missing data, readers cannot judge the magnitude or precision of the comparison or assess its robustness.

The study's question is relevant to comparative outcomes, but the registry record's missing primary analysis limits what can be learned statistically from it. A transparent report of the endpoint data and methods would be needed to evaluate the comparison, its uncertainty, and the extent to which differences between treatment groups were addressed.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The most important limitation for interpretation is that the primary endpoint result is not reported in the registry record. There are no group-specific reintervention counts, comparative estimates, confidence intervals, or tests reported. The stated primary question therefore cannot be answered from the posted record.

The study is described as a prospective cohort, with allocation not stated. The record explicitly cautions that the arms are not a like-for-like control comparison. Without a reported analysis strategy, it is not possible to assess whether baseline differences were addressed. Although the methodology lists demographics, comorbidities, aneurysm parameters, laboratory values, and operative data as collected, the record does not state how these data were used.

The primary endpoint includes different event types in the two groups. The record gives examples of qualifying events, but does not report event adjudication procedures, detailed classification rules, or how repeat events were handled. This makes it difficult to assess the consistency of endpoint ascertainment across treatment approaches.

The timeframe is described as through study completion, an average of 7 year, but the follow-up schedule, participant-level follow-up, and handling of censoring are not reported in the registry record. The record also does not report missing-data counts, analysis populations, multiplicity handling, or the statistical analysis plan. The adverse-event denominators differ from the overall enrollment, and their relationship is not explained. These limitations restrict assessment of both the primary outcome and the safety entries.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Comparison of Outcomes of Complex Abdominal Aortic Aneurysm Treatment — NCT04773223.
• Registry record last updated 2024-07-22; status last verified 2024-02.
• Results first posted 2024-07-22.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

The registry record describes a completed prospective cohort comparing open surgery with endovascular repair for juxta- and pararenal abdominal aortic aneurysms. It lists 925 participants enrolled, a study start date of 2011-01-01, a primary completion date of 2022-01-01, and the Clinical Centre of Serbia as sponsor.

The primary endpoint is the count of participants with aortic-related reintervention through study completion, with an average of 7 year stated. The record also lists 30-day Acute Kidney Injury as a secondary outcome. It reports adverse-event entries, but does not report a primary endpoint result or comparative analysis.

Allocation was not stated, and the record cautions that the arms are not a like-for-like control comparison. Details about the statistical plan, missing data, analysis populations, and adjustment methods are not reported in the registry record. The clinical question is identifiable, but the posted record does not provide the results needed to interpret the primary comparison.