EVAS2 IDE Prospective, Multicenter, Single Arm Safety and Effectiveness Confirmatory Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for EVAS2 IDE Prospective, Multicenter, Single Arm Safety and Effectiveness Confirmatory Study (NCT03298477), a na na study. The primary outcome is Safety: Major Adverse Events (MAE).

2. Clinical Question

3. Trial Design

This was a prospective, multicenter, single-arm study of endovascular abdominal aortic aneurysm repair using the Nellix System. The registry describes consecutive enrollment of eligible subjects at each site and reports an enrollment of 98. All participants were assigned to the same study arm; there was no randomized allocation and no masking. The study status is completed.

In a single-arm design, outcomes are described within the treated group. Without a concurrent comparator, differences attributable to the intervention cannot be separated from changes that might have occurred over time, patient selection, care practices, or other influences. The design can document what was observed among enrolled participants, but it does not provide the direct randomized comparison that would support a between-group treatment-effect estimate.

The primary safety endpoint was the incidence of major adverse events at 30 days. The registry lists a set of secondary outcomes, including conversions, death and rupture, device integrity and performance, aneurysm sac diameter, secondary interventions, and renal-function laboratory measures. Although these outcomes are named in the record, their observed values are not reported there. The number of outcome measures is listed as 10, while the number of analyses is listed as 0.

The registry record does not report a sample-size justification, a prespecified statistical analysis plan, the analysis population, or details of follow-up beyond the stated primary endpoint timeframe. It also does not report interim analyses. These omissions do not establish that such plans or procedures were absent; they mean that they are not reported in the registry record.

The record includes planning assumptions for illustrative sample-size calculations: a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the target effect expressed as a stated fraction of an observed effect. These are planning illustrations, not the trial’s design: EVAS2 is a single-arm study, and the registry record does not report a primary-endpoint result from which an observed effect could be read.

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.

1 Month Follow-Up

6 Month Follow-Up

1 Year Follow-Up

2 Year Follow-Up

Analysis population for the primary outcome, as defined in the registry: 98 patients enrolled under the 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.

Population: The baseline analysis population is 97 subjects. A total of 98 subjects were enrolled, with 97/98 subjects implanted with the Nellix System.

6. Primary Endpoint

The registry lists the primary outcome as Safety: Major Adverse Events (MAE), measured over 30 days.

The primary endpoint is the incidence of major adverse events within 30 days. It is defined as a composite of all-cause mortality, bowel ischemia, myocardial infarction, paraplegia, renal failure, respiratory failure, stroke, and procedural blood loss of at least 1,000cc. The registry identifies the population as 98 patients enrolled under the study and describes the endpoint unit as number of events.

A composite endpoint combines several outcomes into one measure. In general, this can capture a broader range of clinically important events than any one component alone, but the overall result depends on which components occur and how often. The composite does not show, by itself, the separate frequency or contribution of each component. Component-level results are therefore useful for understanding what drove an overall composite result, if those results are available.

The registry record defines the endpoint and its 30-day timeframe but does not report an observed count or incidence for it. No conclusion about the frequency of the primary endpoint in this study can be drawn from the endpoint definition alone. The record also does not report details such as an adjudication process or a statistical method for analyzing this endpoint.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record identifies a single-group, nonrandomized study and lists the primary endpoint as a number of events. It reports no analyses. Accordingly, the record does not specify a statistical model, estimation method, confidence-interval method, hypothesis test, or adjustment strategy for the primary endpoint. The endpoint definition and study design can still be explained, but they should not be mistaken for a complete statistical analysis plan.

What does a composite endpoint represent?

General statistical context: a composite endpoint treats the occurrence of one or more defined outcomes as part of a combined measure. This can make the endpoint cover several types of event, but it also means that the combined result may be influenced by components that differ in frequency or importance. Reporting component-specific results helps readers understand the composition of a composite. Here, the registry defines the components but does not report the primary endpoint result or component-specific results.

What can a single-arm design estimate?

General statistical context: a single-arm study can describe outcomes among the participants who received the intervention. It does not directly estimate a contrast against a concurrent control group. A comparison to an external benchmark would require that benchmark and a defensible method for making the groups comparable; neither is reported in the registry record. The absence of a control group does not prevent descriptive summaries, but it limits the causal interpretation of observed outcomes.

How should uncertainty be considered?

General statistical context: a point estimate is a summary of the observed data, and a confidence interval expresses the range of values compatible with the data under the method’s assumptions. A p-value, when used, describes how inconsistent data are with a specified null hypothesis under its assumptions; it is not a measure of clinical importance. The registry record does not provide a primary-endpoint estimate, confidence interval, or p-value. Thus there is no reported inferential result to interpret for the primary endpoint.

For event outcomes, the amount of information depends on the observed event data and the population included in the analysis. General statistical context: sparse events can produce imprecise estimates, and an interval may be wide even when a point estimate appears clear. No event count for the primary endpoint is reported, so the precision of that endpoint cannot be assessed. The listed adverse-event figures do not fill this gap because the record does not specify their relationship to the 30-day composite endpoint.

What do the planning assumptions mean?

The registry record describes a planning illustration using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is framed as a stated fraction of an observed effect. For time-to-event calculations, the record says the illustration concerns the total number of events; other calculations are expressed as participants per arm. These are assumptions for planning illustrations, not reported properties of the EVAS2 design. The actual study had one arm, and the record does not report a sample-size justification or a primary-endpoint effect estimate. The illustrations therefore should not be treated as the trial’s planned design or as observed power.

General statistical context: a sample-size calculation describes how much information a hypothetical design might require under stated assumptions. Its result depends on the chosen outcome, target effect, error rate, allocation, and analysis method. A planning calculation cannot establish that a completed study had adequate power after the fact, and it does not show the probability that a particular finding is true. In this case, the record’s planning assumptions refer to a two-arm setup, whereas the registered study was single-arm. No sample-size justification specific to the single-arm design is reported in the registry record.

Why can over-dispersion matter?

General statistical context: over-dispersion occurs when observed variability in count data exceeds what a chosen statistical model expects. If a model assumes less variability than the data contain, standard errors can be too small and uncertainty can be understated. The registry record does not identify a count model or report a dispersion assessment, so it is not possible to say whether over-dispersion was evaluated or relevant to an analysis in this study.

More generally, a complete interpretation would need the outcome estimates, denominators, analysis populations, missing-data approach, and methods used to quantify uncertainty. Those details are not reported in the registry record. No model-based or recalculated result should be inferred from the endpoint definition or the adverse-event counts alone.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists multiple outcomes: the primary composite safety endpoint and secondary measures covering conversions, death and ruptures, device integrity and performance, aneurysm sac diameter, secondary interventions, and renal laboratory measures. The record lists 10 outcome measures and 0 analyses. It does not report test results for these outcomes or a plan for controlling multiplicity.

General statistical context: when many outcomes or hypotheses are examined, the chance of at least one apparently notable result can increase. A prespecified hierarchy, adjustment method, or clear distinction between confirmatory and exploratory analyses can help readers interpret multiple tests. No such approach is reported in the registry record. Since no analyses are listed, it is not possible to determine whether multiplicity was addressed in another report.

The record does not report how missing observations were handled, whether participants were excluded from any endpoint analysis, or which analysis populations were used. It does not specify whether all enrolled participants were included in each outcome summary or how follow-up completeness was assessed. The enrollment of 98 does not establish that all 98 had complete observations for every endpoint. These details are important because missing outcome data or changing analysis populations can affect both estimates and their interpretation.

General statistical context: a missing-data method should be appropriate to the reason data are missing and should make its assumptions clear. Simply omitting participants with missing outcomes can produce bias if the missingness is related to outcome status. No missing-data assumptions or sensitivity analyses are reported in the registry record, so their use cannot be assessed.

11. 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

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: miscellaneous (19.4%), cardiac (11.2%), pulmonary (8.2%), renal (8.2%), bleeding/anemia (5.1%).

The adverse-event summary lists 98 participants at risk and 49 affected for serious adverse events in the single-arm Nellix group. For other adverse events, it lists 98 at risk and 22 affected. It separately lists 7 deaths. These are registry summary figures; the record does not report their timing, causes, or relationship to the primary 30-day composite endpoint. The counts should not be treated as the primary endpoint result.

The listed serious-event terms and percentages are Miscellaneous, 19.4%; Cardiac, 11.2%; Pulmonary, 8.2%; Renal, 8.2%; Bleeding/Anemia, 5.1%; and Malignancies, 5.1%. The registry record does not explain the denominator for these percentages or whether one participant could contribute to more than one term. As a result, they cannot be read as mutually exclusive categories or combined into an overall percentage.

General statistical context: adverse-event summaries describe events recorded under the study’s collection and coding procedures. The meaning of a count depends on whether it represents participants, event episodes, or another unit, as well as the observation period and attribution rules. Those details are not fully reported in the registry record. The figures describe the posted safety summary, not a causal comparison with another treatment.

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

The record documents a completed prospective, multicenter, single-arm study that enrolled 98 participants and evaluated endovascular aneurysm repair using the Nellix System. It defines a primary safety endpoint: a 30-day composite of major adverse events. It also names secondary outcomes and posts an adverse-event summary, including counts of participants listed as affected and percentages for selected serious-event terms.

These entries do not provide the observed primary-endpoint result. The frequency of the composite, its component-specific results, and estimates of uncertainty are not reported in the registry record. The secondary outcome names likewise do not establish what was observed for those outcomes. The adverse-event summary can be described on its own terms, but its entries should not be substituted for the primary endpoint or treated as a comparative effect estimate.

General statistical context: an observed outcome in a treated group is descriptive. Without a concurrent comparison group, it does not show what would have happened to comparable participants under another treatment or no treatment. Outcomes can also be affected by participant selection, clinical practice, follow-up, and other factors. A single-arm design cannot isolate these influences through a randomized between-group contrast.

The registry record also does not report the statistical analysis plan, confidence intervals, missing-data procedures, analysis populations, or multiplicity methods. Their absence from the record limits assessment of precision and robustness; it does not prove that they were never specified or performed elsewhere. The responsible interpretation is therefore narrow: the design, endpoint definition, enrollment, and listed safety-summary figures can be described, while the primary outcome result and comparative effectiveness cannot be determined from the registry record.

No conclusion about clinical benefit or lack of benefit follows from these entries alone. The registry record supplies neither a reported primary-endpoint estimate nor a control-group comparison on which to base such a conclusion.

13. Why This Trial Matters Statistically

This study is statistically notable because its registered primary question is a safety question in a single-arm design. The design can describe outcomes within the treated group, while the absence of a control group means there is no randomized internal comparison. That distinction matters when interpreting any safety or effectiveness claim: a within-group event summary is not the same as an estimate of difference between treatments.

The primary endpoint is also a composite. It includes events spanning mortality, organ complications, neurologic outcomes, and procedural blood loss. General statistical context: a composite can broaden the scope of an endpoint, but an overall summary can conceal variation among its components. Component-level results and the composite result together are useful for understanding the outcome. The registry record defines the composite but does not report either its observed result or component-level results.

The adverse-event summary illustrates another statistical issue: counts, event categories, and percentages require clear denominators and definitions. The record lists participants at risk and affected, deaths, and percentages for serious-event terms, but does not report enough detail to establish overlap, timing, or the denominator for those term percentages. Those distinctions matter for comparing categories and understanding what a summary represents.

Finally, the record names many secondary outcomes but reports no analyses. General statistical context: multiple outcomes raise questions about which analyses are confirmatory, how uncertainty is quantified, and whether multiplicity is addressed. Missing analysis details also limit interpretation of precision and completeness. The record is therefore informative about the design and registered outcome definitions, but it leaves key elements needed for inferential interpretation unreported.

14. 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 central limitation for interpreting results is that the registry record does not report the primary-endpoint result. It defines the 30-day major adverse event composite and identifies 98 enrolled participants, but gives no observed count, estimate, or measure of uncertainty for that endpoint. Secondary outcomes are named but their results are not reported in the registry record.

The study has one arm and no randomized comparator. Its design can describe outcomes in the enrolled group but cannot, by itself, estimate a treatment contrast against another intervention or no intervention. The record does not report an external comparator or a method for using one.

The adverse-event summary has interpretive limits. Although it lists participants at risk and affected, deaths, and percentages for selected serious-event terms, the record does not specify the timing and attribution of deaths, the denominator for the term percentages, or whether event categories overlap. It also does not clarify how these summary entries relate to the primary composite endpoint.

Important analysis details are not reported in the registry record, including the statistical analysis plan, analysis populations, missing-data handling, multiplicity strategy, and methods for estimating uncertainty. The record does not provide enough information to assess follow-up completeness or whether all enrolled participants contributed to every outcome. The planning assumptions describe a hypothetical two-arm illustration and do not constitute a sample-size justification for this single-arm study. These limitations constrain what can be inferred from the registry entries; they do not establish that unreported procedures were not conducted elsewhere.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: EVAS2 IDE Prospective, Multicenter, Single Arm Safety and Effectiveness Confirmatory Study — NCT03298477.
• Registry record last updated 2026-05-19; status last verified 2026-04.
• Results first posted 2025-03-19.
• 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.

18. Record Summary

EVAS2 was a prospective, multicenter, single-arm safety and effectiveness confirmatory study of endovascular abdominal aortic aneurysm repair using the Nellix System. The registry reports 98 enrolled patients with abdominal aortic aneurysm without rupture and a completed study status.

The primary endpoint was the incidence of major adverse events at 30 days, defined as a composite of all-cause mortality, bowel ischemia, myocardial infarction, paraplegia, renal failure, respiratory failure, stroke, and procedural blood loss of at least 1,000cc. The registry record does not report the primary-endpoint result. It lists secondary outcome topics and adverse-event summary figures, but does not report analyses, statistical methods, missing-data handling, or analysis populations.