Stroke Feasibility Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Stroke Feasibility Study (NCT01997905), a na phase 1, phase 2 study. The primary outcome is Number of Serious Adverse Events Within 30 Days Post-Index Procedure.

2. Clinical Question

3. Trial Design

This was a Phase 1/Phase 2, single-group feasibility study of the AtriClip LAA Exclusion Device. The registry reports enrollment of 13 and describes the device as delivered through a minimally invasive surgical procedure. The study was marked completed. The listed start was 2014-01, and the listed primary completion was 2015-07.

The allocation field is listed as not applicable, consistent with the single-group design; masking is listed as none. There is no control group for assessing whether observed outcomes differ from outcomes under another treatment or procedure. The registry’s own note cautions that this is not a randomized comparison and that the arms are not a like-for-like control comparison. In this study, there is only one listed intervention group.

The stated clinical setting was stroke prevention in patients with non-valvular atrial fibrillation who could not take long-term oral anticoagulants. The study’s stated purpose was to assess safety and efficacy of the device when placed by minimally invasive surgical deployment. A feasibility study can describe whether a procedure was undertaken and what outcomes were recorded in its study group, but a single-group design cannot isolate the effect of the device from other influences or establish a comparative treatment effect.

The registry lists a primary safety outcome and secondary outcomes including stroke and non-CNS systemic embolism, serious device- or procedure-related adverse events, overall serious adverse events and overall adverse events. It reports six outcome measures, but numerical results for the primary endpoint and several named outcomes are not reported in the registry record. Detailed eligibility criteria, recruitment procedures, follow-up beyond the stated outcome timeframes and the statistical analysis plan are not reported in the registry record.

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 Number of Serious Adverse Events Within 30 Days Post-Index Procedure, measured over 30 days post-index procedure.

The primary endpoint was the number of participants with specified serious adverse events within 30 days after the index procedure, unless the event definition stated otherwise. An independent physician adjudicator was to assess whether events met the endpoint criteria. The components covered serious injury to cardiac or other body structures deemed related to clip delivery or placement; cardiac-related death, myocardial infarction or ischemic stroke; and major bleeding.

The major-bleeding definition included bleeding requiring re-operation and/or transfusion of > 2 U packed red blood cells within any 24-hour period during the first 2 days after the procedure, or at any time if attributed to the device or index procedure. This endpoint combines clinically serious events that may arise from the procedure or device, rather than measuring a single type of event. It is used to describe short-term safety in the registry’s stated feasibility context. The registry record does not report the primary endpoint result, the component-specific results or an uncertainty interval, so the number of participants meeting this endpoint cannot be established from the posted results.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Methods determine which outcomes are counted, how participants contribute to each analysis and how uncertainty is represented. For this study, the registry identifies a single-group design, a 30-day primary safety endpoint and an adverse-event summary. It does not report a statistical analysis plan or numerical analysis of the primary endpoint. The concepts below explain how such results are ordinarily interpreted; they do not describe unreported procedures from this study.

What does a single-group design allow?

A single-group study describes outcomes among participants who received the intervention. It can document what events were recorded in that group and can contribute feasibility information. Without a concurrent comparator, however, the observed outcomes cannot be separated from background risks, differences in participant characteristics or other aspects of care. A before-and-after comparison would require appropriate measurements and a defined analysis; neither is reported in the registry record. The registry explicitly notes that this is not a randomized comparison.

Randomization is a method for assigning participants to groups so that, on average, baseline factors are less likely to systematically favor one treatment. It is useful for estimating comparative effects when the trial is designed and analyzed appropriately. This study’s allocation is listed as not applicable, and it has no listed control arm. Therefore, methods that rely on a randomized between-group contrast do not provide a treatment comparison for this record.

What does the primary composite count?

The primary safety endpoint combines several kinds of serious event into one outcome: specified injury, cardiac or ischemic events, and major bleeding. A composite can provide a broad summary of whether a participant experienced at least one event meeting the prespecified criteria. Its interpretation depends on the definitions and on the contribution of each component. A composite count does not show which component drove the result, whether some components were more common than others, or whether multiple events occurred in one participant. Component-level and participant-level details are not reported in the registry record.

The endpoint description specifies an adjudicator, which indicates that an independent physician adjudicator was to assess events against the criteria. Adjudication can support consistent classification when event definitions require clinical judgment. It does not, by itself, establish how complete the event capture was, how disagreements were handled or whether the adjudicator was masked; those details are not reported in the registry record.

How should counts and uncertainty be read?

A count of participants with an event is different from a count of event episodes. A participant may experience more than one event, while a participant-level endpoint commonly counts that person once if they meet the endpoint definition. The registry labels the adverse-event summaries as participants with an event, but the primary endpoint result is not reported. The distinction between unique participants and repeated events matters when comparing totals across outcomes; no participant-level event history is reported.

General statistical principle: a confidence interval gives a range of values compatible with the observed data under a stated method and assumptions. It communicates uncertainty, rather than guaranteeing that the true value lies in a particular range. Small studies commonly yield imprecise estimates, especially for uncommon outcomes, but the precision for this study cannot be quantified without reported estimates and intervals. No confidence interval or p-value for the primary endpoint is reported in the registry record.

General statistical principle: p-values assess how compatible data are with a specified null model, under the assumptions of the analysis. They do not measure the probability that a treatment works, nor do they describe the size or clinical importance of an effect. No p-value or inferential analysis is listed in the registry record. A statistical conclusion therefore cannot be reconstructed from the endpoint definition or adverse-event counts.

What do planning calculations represent?

Sample-size calculations are planning tools. The registry’s stated illustration assumes a two-sided significance level of 0.05, equal allocation between two arms and a normal approximation, with the effect to detect defined as a stated fraction of an observed effect. For non-time-to-event outcomes, such illustrations are expressed as participants per arm for a specified power; time-to-event illustrations use a total event count. These assumptions describe planning illustrations, not the design of this single-group study and not observed power.

Observed power is not a substitute for an uncertainty interval around a result. A planning calculation asks what sample size would be needed under specified assumptions; it does not describe the probability that this completed study detected an effect. Since the primary endpoint result is not reported in the registry record, a planning illustration based on its observed effect cannot be interpreted from the information available. No planning value should be mistaken for an observed trial result.

Why does over-dispersion matter in general?

General statistical principle: over-dispersion occurs when the variability in count data exceeds what a chosen probability model expects. If a model assumes less variation than the data contain, standard errors may be too small and confidence intervals may be too narrow. Analysts may use methods that allow for extra variability when the data and design justify them. The registry record does not report a count model, an over-dispersion assessment or an adjustment for it. The primary endpoint is described as a number of participants, but that description alone does not establish which model, if any, was used.

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("AtriClip LAA Exclusion Device")
n      <- c(10)
events <- c(0)
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  AtriClip LAA Exclusion Device  10  0  0.0  0.0  30.8  0.0  27.8  0.2  28.5

11. Multiplicity, Missing Data and Analysis Populations

The registry lists six outcome measures, including the primary safety endpoint and named secondary outcomes. When a study evaluates multiple outcomes, multiplicity can arise because repeated statistical tests increase the chance of at least one apparently unusual finding under a null model. General statistical principle: investigators may prespecify a primary outcome, a hierarchy, or an adjustment strategy to control how multiple tests are interpreted. The statistical plan and any multiplicity strategy are not reported in the registry record. The record lists no analyses, so it does not report a set of inferential results to assess for multiplicity.

Missing data and analysis populations also affect interpretation. The enrollment is 13, while the adverse-event summary lists 10 at risk for serious adverse events and 10 at risk for other adverse events. The reason those at-risk counts differ from enrollment is not reported in the registry record. The record does not state whether anyone was excluded from an analysis, whether outcomes were unavailable, or how missing observations were handled. It also does not identify an intention-to-treat, per-protocol or other analysis population for the primary endpoint.

These omissions do not show that data were missing or that a particular analysis population was used. They mean the record does not explain the relationship between enrollment and the adverse-event denominators, or how participants with incomplete follow-up would have been handled. Without those details and the primary endpoint result, the completeness and robustness of the safety analysis cannot be evaluated from the registry record.

12. Safety Results

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

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: atrial fibrillation (20.0%), pnemonia (10.0%), respiratory tract infection (10.0%), sepsis (10.0%), sick sinus syndrome (10.0%).

The adverse-event summary lists 5 participants with serious adverse events among 10 at risk and 8 participants with other adverse events among 10 at risk in the AtriClip group. These entries describe the registry’s adverse-event categories; they are not a like-for-like comparison with another group. The serious adverse-event listing also names atrial fibrillation at 20.0%, and Pnemonia, respiratory tract infection, sepsis, sick sinus syndrome and chest pain at 10.0% each.

Those adverse-event entries should be distinguished from the primary endpoint. The primary endpoint was a specific adjudicated composite within 30 days after the index procedure, with an exception for events whose definitions specify another timing. The adverse-event summary does not establish which listed events met that composite definition, and the primary endpoint result is not reported in the registry record. The record also does not explain the at-risk denominator or give participant-level details showing whether event terms overlapped. Therefore, the adverse-event counts and terms describe posted safety information but do not supply a complete accounting of the primary endpoint.

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

The registry establishes that a single-group feasibility study of the AtriClip LAA Exclusion Device was conducted in the stated clinical context and marked completed. It defines a short-term primary safety endpoint and lists secondary outcomes relevant to stroke, systemic embolism and adverse events. The adverse-event summary contains participant counts and named event terms. These details can describe what the registry records, but they are not enough to establish a comparative treatment effect.

The primary endpoint’s numerical result is not reported in the registry record. Numerical results for stroke and non-CNS systemic embolism are also not reported in the registry record. Consequently, the posted information cannot establish how often the primary composite occurred, the precision of that estimate, or whether any stroke-prevention outcome differed from what would have occurred under another approach. The stated goal of evaluating stroke prevention is not itself evidence of an observed stroke-prevention effect.

The serious and other adverse-event counts should be read as descriptive observations in the listed group. They do not prove that an event was caused by the device or procedure. The primary endpoint specifies attribution for certain components, but the adverse-event listing does not provide enough detail to determine which entries were adjudicated as related. Nor does the single-group design provide a control group for judging whether the observed counts were higher or lower than expected under a different strategy.

General statistical principle: an observed count is most informative when read with its outcome definition, analysis denominator, follow-up completeness and measure of uncertainty. Here, the primary result, uncertainty intervals, detailed analysis populations and missing-data handling are not reported in the registry record. The findings should therefore be interpreted as limited registry information about a feasibility study, not as a definitive estimate of comparative safety or efficacy.

14. Why This Trial Matters Statistically

Feasibility studies address a different statistical task from trials designed to estimate a precise comparative effect. They can document whether a procedure was undertaken in a defined study setting and can identify outcomes that warrant careful monitoring. This study’s registry record describes minimally invasive surgical deployment of an AtriClip device in patients with non-valvular atrial fibrillation who could not take long-term oral anticoagulants. Its single-group design and listed enrollment of 13 are essential context for reading the posted results.

Statistically, the distinction between a defined endpoint and a reported endpoint result is important. The registry gives a detailed definition of a 30-day serious-adverse-event composite, including adjudication and event criteria, but does not report its numerical result. A well-specified endpoint helps readers understand what should be counted; it cannot replace the observed count, denominator or uncertainty estimate needed to assess the result.

The record also illustrates why adverse-event summaries need careful interpretation. The serious-event and other-event counts are descriptive, while the record does not explain the at-risk denominator or show how those summaries relate to the primary composite. A single-group study cannot provide a randomized comparator, so counts alone do not estimate a difference between strategies. General statistical principle: comparisons require a clearly defined contrast and an analysis that accounts for the study design.

For biostatisticians and clinical researchers, the central lesson is to separate study purpose, endpoint definition, observed results and causal interpretation. The purpose concerns feasibility and safety in a particular clinical setting. The endpoint definition states what was intended to be measured. The registry’s missing primary result and analysis details constrain what can be concluded. Recognizing those distinctions prevents a study rationale or event listing from being mistaken for an effect estimate.

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 main limitation for interpreting this trial-specific record is that the primary endpoint’s numerical result is not reported in the registry record. The registry defines the endpoint but does not give the number of participants who met it, its components or an uncertainty interval. Numerical results for the named stroke and non-CNS systemic embolism outcome are also not reported in the registry record, limiting assessment of the study’s stated stroke-prevention purpose.

The study is single-group, with no randomized comparator. The registry itself notes that this is not a randomized comparison. As a result, the adverse-event counts cannot be used to estimate a comparative effect against another intervention or no intervention. The registry lists enrollment of 13, but the adverse-event summary lists 10 at risk for each of its two categories; why those denominators differ from enrollment is not reported in the registry record.

Other design and analysis details that would help interpret results are absent. Eligibility criteria beyond the broad clinical description, participant characteristics, missing-data handling, analysis populations, statistical methods and multiplicity strategy are not reported in the registry record. The posted adverse-event terms do not provide participant-level event histories or establish how they map to the adjudicated primary composite. Follow-up for the primary endpoint is specified, but the completeness of follow-up is not reported in the registry record.

These limitations restrict both precision assessment and causal interpretation. They do not establish that the study had missing data, that events were misclassified or that the intervention caused any listed event. They identify what cannot be resolved from the registry information.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Stroke Feasibility Study — NCT01997905.
• Registry record last updated 2016-12-14; status last verified 2016-10.
• Results first posted 2016-10-21.
• 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 describes a completed Phase 1/Phase 2, single-group feasibility study of the AtriClip LAA Exclusion Device, delivered through a minimally invasive surgical procedure. The stated setting was patients with non-valvular atrial fibrillation who were unable to take long-term oral anticoagulants. Enrollment was 13; the listed start was 2014-01 and primary completion was 2015-07. Masking was listed as none.

The primary outcome was the number of participants with specified serious adverse events within 30 days after the index procedure, with event adjudication and defined components. The registry lists six outcome measures and no analyses. The adverse-event summary reports 5 participants with serious adverse events among 10 at risk and 8 with other adverse events among 10 at risk. The primary endpoint result and numerical stroke or systemic embolism results are not reported in the registry record. The single-group design does not provide a randomized comparison.