PREVAIL-TA: Placement of Aortic Balloon Expandable Transcatheter Valves Trial (Europe): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for PREVAIL-TA: Placement of Aortic Balloon Expandable Transcatheter Valves Trial (Europe) (NCT01238835), a na na study. The primary outcome is Number of Deaths.

2. Clinical Question

PREVAIL-TA was a confirmatory clinical trial, according to its brief summary. Its single-group structure means the registry describes outcomes after the study procedure, rather than estimating a difference between randomized groups. That distinction matters: an event count in one group cannot by itself establish how outcomes would have differed under an alternative treatment or without the procedure.

The registry also lists stroke as a secondary outcome. It does not report a numeric stroke result in the record. Details such as the full eligibility criteria, the definition of the analysis population, and how participants were followed for each outcome are not reported in the registry record.

3. Trial Design

PREVAIL-TA (NCT01238835) is listed as a completed, single-group, prospective, multicenter, non-randomized confirmatory clinical trial. Its brief summary describes evaluation of the Edwards SAPIEN XT™ transcatheter heart valve, model 9300TFX, the next generation Ascendra™ transapical delivery system, and crimper accessories. The intervention is listed as SAPIEN XT™ transapical aortic valve replacement, with transapical access.

The registry lists an enrollment of 220. The study started in 2009-09, and primary completion was in 2011-02. The phase is recorded as NA. Allocation is recorded as NA, consistent with the single-group design, and masking is listed as NONE. These registry entries describe the design but do not explain additional operational details, such as enrollment procedures or follow-up completeness.

With one group and no randomized comparator, the central descriptive question is what outcomes were recorded among participants who underwent the procedure. The design cannot isolate a treatment contrast from other influences in the way a randomized comparison is intended to do. It also cannot establish what would have happened to the same participants under a different approach.

The registry lists two outcome measures and zero analysis records. The primary measure is death at 30 days from the index procedure; stroke is listed as a secondary outcome. Numeric results for those outcomes are not reported in the registry record. The record does not report the statistical analysis plan, the planned analysis population, the follow-up procedures, or a sample-size justification. The planning assumptions described for an illustration are not evidence of the trial's own design rationale.

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.

Before assignment: Two enrolled subjects did not enter the procedure room.

Overall Study

Reasons for not completing this period:

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: As treated population

6. Primary Endpoint

The registry lists the primary outcome as Number of Deaths, measured over 30 days.

The primary endpoint is the number of participants who died within 30 days of the index procedure. It is a binary participant-level outcome: each participant either experienced the event within the specified timeframe or did not. Reporting the count can describe the observed frequency of this outcome in the study group, provided the relevant denominator and outcome ascertainment are also clear.

A death endpoint is clinically consequential and can be expressed as a count or as a proportion of the participants evaluated. The registry identifies the unit as participants and the timeframe as 30 days. It does not specify a cause-of-death classification in the endpoint description, so the record does not establish that the endpoint is restricted to a particular cause.

The endpoint can support a description of short-term outcomes after the index procedure. It cannot alone show whether the procedure changes the risk of death compared with another treatment, because PREVAIL-TA has no concurrent comparison group. Interpretation also depends on how many participants contributed data, how deaths were ascertained, and how missing follow-up was handled. Those details are not reported in the registry record.

A numeric result for the primary endpoint is not reported in the registry record. The separate safety entry listing deaths does not state that it is the 30-day primary endpoint result, so the two should not be treated as interchangeable.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical interpretation begins with the design and the outcome definition. PREVAIL-TA is a single-group study, so the registry record describes outcomes in participants who received the transapical procedure. There is no randomized control group from which to estimate a between-group treatment contrast. Any statistical summary of the primary endpoint would therefore be a description of the observed group, not a randomized estimate of the difference from another strategy.

What does a binary outcome mean?

A binary outcome classifies each participant according to whether a defined event occurred during a specified period. For this trial, the primary measure counts participants who died within 30 days of the index procedure. A count is easier to interpret when paired with its analysis denominator and a clear account of who had follow-up sufficient to determine the outcome. The registry gives the planned endpoint definition, but a numeric primary result and the denominator used for its analysis are not reported in the registry record.

For a binary endpoint, an analysis may report an event count and the proportion of the evaluated group with the event. A confidence interval expresses the statistical uncertainty around an estimate. In general, a narrower interval indicates greater precision, while a wider interval indicates less precision. The interval does not correct for selection bias, incomplete outcome ascertainment, or lack of a comparator. No primary estimate or confidence interval is reported in the registry record, so precision cannot be assessed for this endpoint.

Why does the single-group design matter?

Random allocation is used in comparative trials to create groups that can be compared while reducing systematic differences in participant characteristics. PREVAIL-TA has no randomized comparison group: allocation is listed as NA, masking as NONE, and the model as SINGLE GROUP. Its results can characterize outcomes recorded in the study group, but they cannot establish the counterfactual outcome that would have occurred under another treatment. A historical or external comparison would require additional assumptions and information, neither of which is reported in the registry record.

The prospective, multicenter description indicates that the trial followed a planned forward-looking study structure across multiple centers. It does not, on its own, specify how centers were selected, how outcomes were adjudicated, or whether follow-up was complete. Those details are not reported in the registry record. Likewise, the term confirmatory is part of the trial description; the registry record does not report a statistical analysis plan that would explain what was being confirmed or how success was to be judged.

What can a planning illustration tell readers?

The planning illustration is described as using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It is based on fractions of an observed effect. These assumptions describe a hypothetical two-arm planning exercise, not the observed design of this single-group trial. The assumptions therefore do not supply a valid randomized comparator for PREVAIL-TA or make the trial's primary endpoint result available.

Such planning calculations are generally sensitivity illustrations: they show how a hypothetical future study's participant requirements may vary with the effect it aims to detect and the statistical assumptions used. A planning sample size is not an observed outcome, and it is not observed power. Observed power should not be inferred from a trial's results; the estimate and its uncertainty are more informative. No numerical planning outputs are stated in the registry record, and its own sample-size justification is not reported.

Over-dispersion is a general concern when outcome variation is greater than a model assumes. If a statistical model underestimates variation, its standard errors can be too small and its intervals or tests may be misleading. The registry record does not report a model for the primary endpoint, evidence of over-dispersion, or any adjustment for it. For a simple participant-level binary outcome, a different set of assumptions is relevant, including a well-defined population and reliable outcome classification.

How should multiple outcomes and analyses be considered?

The registry lists two outcome measures: death as the primary endpoint and stroke as a secondary outcome. When researchers assess multiple outcomes or make multiple statistical tests, the chance of at least one apparently unusual result can increase unless the analysis plan accounts for multiplicity. The registry record does not report a multiplicity procedure, a hierarchy of tests, or whether any interim analyses were planned or conducted. The presence of a primary and secondary outcome alone does not reveal how multiplicity was handled.

The registry lists zero analysis records. It does not report a test statistic, model specification, adjustment strategy, confidence interval, or missing-data method for the primary outcome. Without those details and a numeric result, readers cannot independently assess the statistical evidence for the endpoint. Nor can they determine whether analysis choices were prespecified or made after results were known.

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("TAVR-TA")
n      <- c(218)
events <- c(16)
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  TAVR-TA  218  16  7.3  4.3  11.6  4.6  11.6  4.6  11.6

11. Multiplicity, Missing Data and Analysis Populations

The registry lists death within 30 days as the primary outcome and stroke as a secondary outcome. Considering more than one outcome can raise multiplicity concerns: when several hypotheses are tested, the likelihood of at least one apparently notable result may increase. A prespecified hierarchy or adjustment method can help govern interpretation. The registry record does not report whether such a method was planned or used, and it does not report interim analyses.

The record lists zero analysis records and provides no numeric primary or secondary outcome result. It also does not report an analysis population, such as whether all enrolled participants, all participants who received the intervention, or only participants with available outcome data were included. The relationship between the enrollment of 220 and the safety entry's 218 participants at risk is not explained; the registry record does not report why those counts differ.

Missing outcome data can affect an estimate if participants without recorded outcomes differ from those with complete follow-up. General approaches include describing the amount and pattern of missingness, using defensible assumptions about unobserved outcomes, and checking whether conclusions change under alternative assumptions. The registry record does not report missingness, follow-up completeness, imputation, sensitivity analyses, or how participants with unknown endpoint status were handled. These omissions prevent assessment of how missing data may have affected the primary result.

The registry also does not report whether outcomes were analyzed according to a prespecified plan or whether any analysis populations differed across outcomes. Without a numeric estimate, denominator, and account of missing data, the precision and representativeness of the reported endpoint cannot be evaluated.

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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: other (30.7%), infection / inflammation (28.4%), heart failure (26.6%), coagulopathy / hematological disorder (24.3%), conduction defects with permanent pacemaker (14.7%).

The safety record lists the TAVR-TA group with 218 participants at risk for serious adverse events and 201 affected. For other adverse events, it lists 218 at risk and 212 affected. These are participant counts in the safety entry. The record also lists 124 deaths, but does not state that this count uses the primary endpoint's 30-day timeframe. It should not be interpreted as the 30-day endpoint result without that link being reported.

The serious adverse event terms are listed with percentages: Other at 30.7%, Infection / Inflammation at 28.4%, Heart Failure at 26.6%, Coagulopathy / Hematological Disorder at 24.3%, Conduction Defects with Permanent Pacemaker at 14.7%, and Gastro-Intestinal Event at 13.3%. The registry record does not specify the denominator for these percentages or whether an individual participant could contribute to more than one term. The categories therefore should not be summed or treated as mutually exclusive.

Adverse-event counts describe what was recorded in the study group. Without a comparator and fuller information on ascertainment, timing, and event definitions, they do not estimate a comparative excess or establish cause. The registry record does not report those additional details.

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

The record establishes that PREVAIL-TA was a completed, prospective, multicenter, non-randomized, single-group trial of transapical SAPIEN XT™ transcatheter aortic valve replacement. It lists an enrollment of 220 and a primary endpoint of death within 30 days of the index procedure. It also records safety counts for the TAVR-TA group and lists stroke as a secondary outcome. These registry entries describe the study and the outcomes it set out to assess.

The record does not report a numeric result for the primary endpoint or stroke. It therefore does not support a numerical statement about the observed 30-day death count, the rate of death, or the precision of that estimate. The safety count of 124 deaths is not identified as the primary endpoint result and does not have the primary endpoint's stated timeframe attached to it in the registry record. Those entries should remain distinct.

Because there is no randomized comparator, the trial cannot estimate a randomized treatment difference. Outcomes recorded in a single group may be influenced by participant characteristics, clinical context, and other factors, as well as the procedure. Statistical adjustment can sometimes address measured differences in comparative studies, but the registry record does not report such an analysis, and adjustment cannot replace an unobserved comparison group in a single-arm design.

The designation confirmatory is part of the trial summary, but the registry record does not report the statistical plan, a success criterion, or the primary endpoint result. That information is needed to evaluate whether the intended confirmatory question was answered. The record's safety listings can be read as reported event information, but they do not by themselves establish a causal relationship or comparative safety profile.

The most defensible interpretation is limited: the registry documents the trial design, endpoint definitions, and selected safety figures, while leaving the primary outcome's numerical result and key analysis details unreported. No conclusion about treatment benefit or lack of benefit follows from that absence.

14. Why This Trial Matters Statistically

PREVAIL-TA illustrates why study design and outcome reporting must be read together. The registry describes a prospective, multicenter confirmatory trial, but it is also explicitly single group and non-randomized. The first description indicates the trial's stated purpose and organization; the second defines the limits of what its outcomes can establish. A careful statistical reading avoids treating a single-group event count as if it were a randomized treatment comparison.

The trial's primary endpoint is clearly tied to death within 30 days of the index procedure. A defined timeframe matters because outcomes can differ depending on the observation window. Yet a definition alone is not an estimate: the record does not report the numeric primary result, its denominator, or its uncertainty. The distinction between an endpoint being named and a result being available is fundamental to evidence interpretation.

The safety entry is another useful statistical lesson. It reports participants at risk and affected, along with term percentages, but the registry record does not explain whether event terms overlap or what denominators underlie those percentages. A list of adverse event categories is not necessarily a partition of participants. Reading categories as independent, exclusive groups without that information can misstate what the record says.

Finally, hypothetical sample-size planning assumptions should not be mistaken for evidence that the trial had a particular power or that the primary question was answered. The planning description uses assumptions for a two-arm illustration, while PREVAIL-TA is single group. The trial underscores the value of transparent outcome results, analysis methods, denominators, and missing-data reporting alongside an explicit design description.

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 trial-specific limitation is the absence of a reported numeric result for the primary endpoint. Although the registry defines death within 30 days of the index procedure as the primary outcome, it does not provide the count, analysis denominator, estimate, or uncertainty interval. A numeric result for the secondary stroke outcome is also not reported.

The single-group, non-randomized design is a further limitation for comparative interpretation. No concurrent randomized comparator is described, so the record cannot estimate a randomized difference between the procedure and another approach. Masking is listed as NONE, but the registry record does not explain how outcome assessment was conducted or whether any independent adjudication was used.

Several details that would support appraisal are not reported in the registry record: the full eligibility criteria, participant characteristics, analysis populations, follow-up completeness, missing-data handling, and the statistical analysis plan. The record does not state how the enrollment of 220 relates to the 218 participants at risk in the safety entry. It also does not report the timing or definitions for the safety death count in relation to the primary endpoint.

The adverse-event term percentages are listed without an explanation of their denominators or whether a participant could be represented in more than one category. The registry record also does not report an approach to multiplicity or interim analyses. These omissions constrain interpretation of both outcome evidence and safety listings. They should not be filled in by assumptions about standard practice or about what the trial may have done.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: PREVAIL-TA: Placement of Aortic Balloon Expandable Transcatheter Valves Trial (Europe) — NCT01238835.
• Registry record last updated 2020-11-02; status last verified 2020-10.
• Results first posted 2020-11-02.
• 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

PREVAIL-TA (NCT01238835) is listed as a completed, prospective, multicenter, non-randomized, single-group confirmatory trial of transapical SAPIEN XT™ aortic valve replacement. The registry lists an enrollment of 220, a start date of 2009-09, and primary completion in 2011-02. The primary endpoint is the number of deaths within 30 days of the index procedure; stroke is listed as a secondary outcome.

The registry record does not report a numeric result for either outcome or a statistical analysis plan. The safety entry lists 218 participants at risk and 201 affected for serious adverse events, 218 at risk and 212 affected for other adverse events, and 124 deaths. The safety death count is not identified as the 30-day primary endpoint result. The record's single-group design does not provide a randomized comparator, and key details about analysis populations, missing data, and safety-event denominators are not reported.