Chronic Total Occlusion Crossing With the Wildcat Catheter: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Chronic Total Occlusion Crossing With the Wildcat Catheter (NCT01174784), a na na study. The primary outcome is Major Adverse Events.

2. Clinical Question

3. Trial Design

The study, titled “Chronic Total Occlusion Crossing With the Wildcat Catheter,” was a prospective, multi-center, non-randomized, single-group device study. Its official title describes use of the Avinger Wildcat to cross femoropopliteal chronic total occlusions. The registry lists 88 participants enrolled and gives the condition as peripheral arterial disease. The study status is completed.

The intervention was the Wildcat catheter, used for crossing a chronic total occlusion. The primary endpoint population is described as patients treated with Wildcat after guidewire failure. The study summary says that safety and efficacy were evaluated during the index procedure through 30-day follow-up. The primary endpoint timeframe is stated as index through 30-day follow-up.

Allocation is listed as not applicable, and masking is listed as none. The study is therefore not a randomized comparison, and its single group cannot serve as a like-for-like control for the device. Observed outcomes describe participants in the study setting; without a concurrent comparator, they do not estimate a comparative treatment effect.

The registry lists the study start as 2010-08 and primary completion as 2011-04. The phase is listed as not applicable. The record does not report the number of participating centers, details of enrollment procedures, or the rationale for the planned enrollment. Those omissions prevent a fuller assessment of recruitment and study planning from the registry information alone.

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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Patients treated with Wildcat post guidewire failure.

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 Major Adverse Events, measured over Index through 30-Day Follow-Up.

The primary safety endpoint is described as absence of in-hospital or 30-day major adverse events, with no evidence of clinically significant perforations, clinically significant embolizations, or Grade C or greater dissections after Wildcat chronic total occlusion crossing confirmed by angiography. It is titled “Major Adverse Events,” and its timeframe runs from the index procedure through 30-day follow-up.

This type of endpoint is used to capture important safety outcomes around a procedure and the subsequent follow-up period. Combining serious events with specified procedure-related complications can make the endpoint relevant to several kinds of potential harm, rather than only one event type. A composite endpoint also requires careful reading: each component may differ in seriousness, frequency, and clinical meaning. A summary count alone would not establish which components occurred or whether the endpoint’s full definition was met.

The endpoint is framed as absence of events, but the registry record does not state the number of participants who met that definition or report a numerical primary-endpoint result. The serious adverse-event listings are not enough to reconstruct the composite result, because the record does not specify how those listings map to every endpoint component or give the endpoint analysis itself. Thus, the posted information identifies what was to be assessed but does not provide a complete estimate of the primary safety endpoint.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record describes a single-group, non-randomized study and lists no analysis records. The statistical methods used to evaluate the primary endpoint, including any model, confidence interval, or hypothesis test, are not reported in the registry record. The concepts below explain how event-count data are generally interpreted; they do not describe an analysis confirmed to have been used in this study.

What does an event count describe?

For a binary outcome, each participant is classified according to whether the defined event occurred during the specified observation period. A count of participants with an event is meaningful only alongside the population included in the calculation and the endpoint definition. Here, the adverse-event listing identifies 84 participants at risk and 4 affected for serious events, and 84 at risk and 0 affected for other events. The registry does not explain the relationship between those safety denominators and the 88 participants enrolled, so the difference should not be assigned a cause.

A percentage is a rescaling of a count relative to a denominator. It can make event frequency easier to read, but it does not add information about participants who were not in the denominator or about how outcomes were collected. The listed 4.8% for clinically significant perforation is a registry entry. The record does not provide a confidence interval for that percentage or additional detail about its calculation.

Why does a confidence interval matter?

In general, a confidence interval expresses statistical uncertainty around an estimated quantity under the assumptions of the method used. It is not a guarantee about an individual outcome, and it does not by itself establish whether a result is clinically important. For an event proportion, the interval can show how much uncertainty remains beyond the observed count. No confidence interval for the primary endpoint or the listed adverse-event proportions is reported in the registry record, so their precision cannot be quantified from the posted information.

A count of zero also needs careful interpretation. It means that no events were recorded in the stated group under the study’s definitions and observation procedures. It does not establish that the true chance of the event is zero. A confidence interval can help convey uncertainty even when no events are observed, but no such interval is reported for the listed 0.0% entries.

What can a single-group design estimate?

In general, a single-group study can describe outcomes among participants who received the study intervention. A randomized comparison can additionally support an estimate of the difference between treatment groups, because random allocation is intended to make groups comparable in expectation. This study has no randomized comparator. Its adverse-event counts therefore describe the study cohort and cannot by themselves estimate a comparative effect or identify the cause of an event.

Even a before-and-after comparison, if one had been reported, would require careful interpretation because changes over time may have explanations other than the intervention. The registry record does not report such a comparison. It also does not report an adjusted analysis, so no adjustment for participant or procedural characteristics can be assessed.

How should the planning illustrations be read?

General sample-size planning asks how many participants might be needed to detect a specified effect under chosen assumptions. The registry record’s planning description says that its illustration uses a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of the observed effect. Such illustrations are not the trial’s original design and are not observed power. They do not change the fact that the study itself is single-group and non-randomized. The record does not report the trial’s own sample-size justification. No particular planning result should be treated as an observed study result.

In general, over-dispersion occurs when variability in data is greater than a model assumes. It can make standard errors too small if the model fails to account for that extra variability. The primary outcome is described as a binary participant count, and the registry record does not identify an over-dispersion model or report a model-based analysis. Accordingly, over-dispersion is a general statistical consideration, not a documented feature of this study’s analysis.

Why does the endpoint definition matter?

The primary safety endpoint is a composite: it includes absence of major adverse events and specified complications, after crossing confirmed by angiography, over the index procedure through 30-day follow-up. In general, a composite can capture several outcomes in one endpoint, but its interpretation depends on its components, their definitions, and how each was observed. The registry gives the endpoint definition but not a numerical primary-endpoint result or a component-by-component primary analysis. The listed adverse-event terms should therefore not be substituted for a full composite analysis.

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("Enrolled/Primary Cohort")
n      <- c(84)
events <- c(4)
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  Enrolled/Primary Cohort  84  4  4.8  1.3  11.7  1.9  11.6  1.9  11.6

11. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures and no analysis records. It does not report whether multiple hypotheses or endpoint comparisons were tested, whether any multiplicity adjustment was planned, or whether interim analyses occurred. These details are not reported in the registry record. Without them, the risk of chance findings across a set of analyses cannot be evaluated.

The primary endpoint population is described as patients treated with Wildcat after guidewire failure, while the overall enrollment is 88 and the adverse-event cohort lists 84 at risk. The record does not explain the difference, give a participant flow, or state how many participants completed the defined follow-up. It does not report missing outcome data, reasons for missingness, or how missing observations were handled. The difference in counts should not be interpreted as a particular form of exclusion or loss to follow-up.

The analysis population is not described in enough detail to determine whether all enrolled participants, all treated participants, or another defined group contributed to the primary endpoint. No analysis population rule or sensitivity analysis is reported. The record also does not describe imputation, censoring, or other approaches to incomplete follow-up.

These omissions affect interpretation because event counts depend on who is included and whether outcomes are available over the stated timeframe. A reader cannot determine from the registry record whether missing observations could have altered the primary endpoint result, nor can a statistical adjustment for multiple analyses be assessed. The registry’s absence of analysis records is distinct from evidence that no analyses were performed; the methods and results are simply not reported there.

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 5% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: clinically significant perforation (4.8%), major adverse event - death (0.0%), major adverse event - unplanned major amputation (0.0%), major adverse event - emergent target vessel revascularization (0.0%), clinically significant embolization (0.0%).

The registry’s Enrolled/Primary Cohort listing reports 4 participants affected by serious adverse events among 84 at risk. For other adverse events, it reports 0 affected among 84 at risk. The serious-event term list reports clinically significant perforation at 4.8%; major adverse event—death, unplanned major amputation, emergent target vessel revascularization, clinically significant embolization, and Grade C dissection are each listed at 0.0%.

These entries are descriptive safety information. They are not a comparison with another treatment, and they do not establish whether an event was caused by the device. The record does not provide event narratives, adjudication methods, or a complete primary-endpoint result. It also leaves the death count blank while listing the death term at 0.0%; both entries should be reported as recorded, without inferring a reason for the blank value.

In general, a zero in an observed event list does not mean the underlying risk is zero. The count reflects events recorded in the stated cohort under the study’s definitions and follow-up. The registry does not report confidence intervals for these safety figures, so their statistical precision is not quantified.

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

The registry record documents a prospective, multi-center study of the Wildcat catheter for crossing a single femoropopliteal chronic total occlusion. It reports 88 participants enrolled and presents safety-event counts for a cohort of 84 at risk. The adverse-event listing includes 4 participants affected by serious adverse events and 0 affected by other adverse events. Clinically significant perforation is listed at 4.8%, while several other named serious-event terms are listed at 0.0%.

These results describe the recorded experience, not a comparative effect. There was no randomized control group, and no analysis records are listed. The registry does not report a numerical result for the primary endpoint, its confidence interval, or the statistical method used to assess it. The adverse-event entries therefore cannot establish the complete primary endpoint result or how precisely that result was estimated.

In general, an observed event count does not establish that an intervention caused or prevented an event. That question requires an appropriate comparison and a clearly described analysis. This study’s design does not provide a like-for-like control comparison, so the counts should not be interpreted as proof that the catheter improves outcomes, causes no harm, or is equivalent to another approach.

The scope is also limited by the population and timeframe described in the record: patients treated after guidewire failure, with safety and efficacy evaluated from the index procedure through 30-day follow-up. The record does not provide sufficient detail to judge outcomes beyond that period or in populations outside the study description. The responsible interpretation is therefore narrow: these are registry-reported safety entries from a single-group study, with important uncertainty about the primary endpoint result, participant accounting, and statistical precision.

14. Why This Trial Matters Statistically

This study illustrates a basic distinction in clinical statistics: describing outcomes in a treated group is not the same as estimating what treatment changed. The registry reports counts after use of the Wildcat catheter, but allocation is not randomized and there is no comparator group. The data can describe the recorded cohort; they cannot establish a counterfactual outcome under another approach.

It also illustrates why the endpoint definition and the reported result must be considered separately. The record defines a composite primary safety endpoint that includes specified events and a particular timeframe. Yet the registry does not report the numerical result for that endpoint. Separate adverse-event entries do not necessarily reconstruct a composite endpoint, particularly when the analysis population and event handling are not fully described.

Denominators matter as much as counts. The registry lists 88 participants enrolled but gives 84 at risk in the adverse-event cohort. Without participant-flow information, readers cannot determine why those counts differ or how this affects interpretation. A denominator should not be silently assumed to include everyone enrolled.

Finally, a zero count is not a precise statement that an event cannot occur. Uncertainty intervals and transparent analysis methods help readers understand what an observed count can support. Their absence limits statistical interpretation, even when the registry records percentages and event counts. These are broadly useful lessons for reading single-group device studies and other clinical safety reports.

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 principal limitation is the single-group, non-randomized design. Without a comparator, the registry-reported events cannot be interpreted as a relative treatment effect, and differences from outcomes under another approach cannot be estimated from these data alone. The absence of masking is also recorded; the registry does not describe safeguards for outcome assessment.

The study population is narrowly described as patients with a single femoropopliteal chronic total occlusion, with the primary endpoint population specified as patients treated with Wildcat after guidewire failure. The record does not report participant characteristics or detailed eligibility criteria, limiting assessment of how well the cohort represents other clinical settings. Although the study is described as multi-center, the number of centers is not reported.

Follow-up is described through 30 days, so the registry information does not establish longer-term outcomes. The primary endpoint result and its statistical uncertainty are not reported. The record also does not explain the difference between 88 participants enrolled and 84 at risk in the adverse-event listing, or provide enough information to evaluate completeness of follow-up and the analysis population.

Event definitions are stated, but event adjudication, collection procedures, and handling of missing outcomes are not described. The registry lists no analysis records and does not report a statistical analysis plan or the study’s sample-size justification. These gaps prevent assessment of the planned inferential approach, precision, and robustness of the reported safety entries.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Chronic Total Occlusion Crossing With the Wildcat Catheter — NCT01174784.
• Registry record last updated 2020-07-17; status last verified 2020-02.
• Results first posted 2013-09-27.
• 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

NCT01174784 is a completed, prospective, multi-center, non-randomized, single-group device study of the Wildcat catheter for femoropopliteal chronic total occlusion crossing. The registry lists 88 participants enrolled, a study start of 2010-08, and primary completion in 2011-04. Safety and efficacy were to be evaluated during the index procedure through 30-day follow-up.

The primary safety endpoint concerns absence of in-hospital or 30-day major adverse events and specified complications after crossing confirmed by angiography. The registry does not report a numerical primary-endpoint result or analysis records. Its adverse-event listing reports 4 serious-event participants among 84 at risk and 0 other-event participants among 84 at risk; clinically significant perforation is listed at 4.8%, and several other serious-event terms at 0.0%. The single-group design, unexplained cohort-count difference, and absent precision estimates limit interpretation.