Chronic Total Occlusion Crossing With the Ocelot System - CONNECT II: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Chronic Total Occlusion Crossing With the Ocelot System - CONNECT II (NCT01537302), a na na study. The primary outcome is Primary Safety Endpoint.

2. Clinical Question

3. Trial Design

CONNECT II is a completed, non-randomized, single-group device study. The registry record identifies the Ocelot System as the intervention and describes its use to cross chronic total occlusions in the superficial femoral and popliteal arteries. The study's stated purpose was to evaluate safety and effectiveness, including OCT-assisted orientation during crossing. The record lists an enrollment of 100.

Because there is one treatment group and no randomized comparator, the design can describe outcomes among participants treated with the system, but it cannot isolate the effect of the device from other influences through a concurrent control comparison. The registry record lists allocation as NA and masking as none. These design features should shape interpretation: an observed event proportion, if reported, would be a description of this treated group, not a randomized estimate of benefit or harm relative to another strategy.

The registry record gives a study start of 2012-02 and a primary completion date of 2012-06, and marks the study completed. The primary endpoint is assessed at Day 30. Two subjects are recorded as having withdrawn before 30-day follow-up. The record does not explain whether those participants contributed any earlier safety information, how missing endpoint information was handled, or whether the endpoint analysis used all enrolled participants or a different analysis population.

Secondary outcomes listed include procedural and technical success, device performance, procedural, fluoroscopic and crossing times, use of assist devices, and contrast or flush volumes. Although the record lists ten outcome measures, it records zero analyses. It does not report detailed statistical methods, outcome estimates for the primary endpoint, or a confidence interval value. Trial registration details therefore describe the planned clinical question and design more fully than the available outcome analysis.

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

Analysis population for the primary outcome, as defined in the registry: Two subjects withdrew prior to 30-day follow-up.

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: All enrolled subjects.

6. Primary Endpoint

The registry lists the primary outcome as Primary Safety Endpoint, measured over Day 30.

The primary safety endpoint is expressed as a percentage of participants and is assessed at Day 30. Its description focuses on the absence of specified safety events after Ocelot System crossing: in-hospital or 30-day major adverse events, clinically significant perforations, clinically significant embolizations, and Grade C or greater dissections, with angiographic confirmation noted. This is a composite-style endpoint because it brings several event types together under one safety question. The registry record does not give the observed percentage or its 95% confidence interval.

Using a prespecified safety endpoint can provide a consistent way to summarize whether important complications were observed over a defined follow-up period. A percentage is intuitive, but its interpretation depends on exactly which events count, how they are assessed, and whether follow-up is complete. Here, the endpoint description identifies the event categories and timing, while the record also notes two withdrawals before 30-day follow-up. It does not report how those withdrawals were treated in the endpoint analysis.

The endpoint is not a measure of comparative safety: no control group is recorded. Nor does a composite percentage, by itself, show the frequency or severity of each component. Component-specific results and a clear account of follow-up would be needed to understand which events contributed to an overall endpoint result. Those details are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Several statistical ideas help clarify what the registry record can and cannot establish. They do not fill in analyses that the record does not report.

What does a participant percentage describe?

A binary outcome classifies each participant into one of two categories for the specified endpoint, such as meeting or not meeting a safety definition. A percentage expresses the share of the analyzed group in a category. For the primary endpoint, the record specifies a percentage of participants and describes an absence-of-events definition. It does not state the observed percentage. The adverse-event summary separately reports participants at risk and participants affected. These figures describe those adverse-event categories; they are not a substitute for the missing primary endpoint result.

Participant-level percentages should be distinguished from event counts. One participant may experience more than one event, depending on the endpoint and reporting rules. The registry record does not explain whether adverse-event terms are mutually exclusive or whether multiple events per participant are counted. Accordingly, terms or event categories should not be combined to create an overall participant total.

What does a confidence interval communicate?

In general, a confidence interval conveys the uncertainty around an estimated quantity under a specified statistical procedure. A narrower interval indicates greater precision for that estimate; a wider interval indicates more uncertainty. Its interpretation depends on the estimate, the method used to calculate the interval, and the assumptions underlying that method. The primary endpoint lists a 95% confidence interval as its dispersion measure, but the interval's numerical limits and the endpoint estimate are not reported in the registry record. Precision therefore cannot be assessed from that listing alone.

Why does a single-group design matter?

A single-group study can report what was observed among participants receiving the intervention. It does not create a concurrent control group. Without random allocation between groups, differences from another population or historical experience may reflect differences in participant selection, clinical practice, follow-up, or other factors, rather than the device itself. General statistical principle: randomization helps balance measured and unmeasured factors on average between assigned groups, while a non-randomized single-group design cannot provide that protection through a treatment contrast. CONNECT II is recorded as non-randomized, single-group, and unmasked, so comparative claims are outside what its design can directly support.

Why can over-dispersion matter?

General explanation: a statistical model may assume that observations vary according to a particular distribution. Over-dispersion occurs when the data vary more than that model expects. If ignored, uncertainty estimates may be too small, making confidence intervals appear more precise than warranted and tests potentially too optimistic. This issue can arise in some count or clustered-data settings, but the registry record does not report a model for the primary endpoint or indicate that over-dispersion was assessed. It would be inappropriate to claim that this was or was not a concern in the trial's analysis.

What can planning calculations tell a reader?

Sample-size planning calculations use assumptions about a future study and a target effect to illustrate the number of participants that might be needed under those assumptions. They are not observed results and do not show the probability that a completed study has established an effect. The registry record's stated planning assumptions refer to a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a fraction of the observed effect. These are planning conventions, not evidence that CONNECT II itself had two randomized arms; its recorded design is single-group. A planning illustration based on an observed effect also depends on the estimate used, and the primary endpoint estimate is not reported.

More broadly, statistical interpretation requires separating the protocol's question from the analysis actually documented. The registry identifies a Day 30 endpoint and a 95% confidence interval as the intended summary, but records zero analyses. It does not give a model, an interval-calculation method, a hypothesis test, or a detailed definition of the analysis population. Such details cannot be inferred from the endpoint label or from the design description.

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("Ocelot System")
n      <- c(98)
events <- c(2)
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  Ocelot System  98  2  2.0  0.2  7.2  0.6  7.1  0.6  7.1

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists a primary safety endpoint alongside secondary outcomes covering procedural success, technical success, device performance, procedure and fluoroscopy times, crossing time, assist-device use, and contrast or flush volumes. When a study examines multiple endpoints, the chance of obtaining at least one seemingly notable result can increase if each is tested separately without accounting for multiplicity. General statistical practice may address this through a hierarchy, adjusted testing, or emphasis on estimation and prespecified primary outcomes. The registry record does not report a multiplicity strategy, adjustment method, testing hierarchy, or analysis of the listed secondary outcomes; it records zero analyses.

Missing data also matter because the primary assessment occurs at Day 30 and the record states that two subjects withdrew before 30-day follow-up. It does not say whether those participants had partial follow-up, whether their status for each component was known, or how their endpoint status was assigned. General principle: excluding participants with missing follow-up can bias an estimate if missingness is related to outcome, while treating missing outcomes as events or non-events requires an explicit rationale. No such handling method is reported in the registry record.

The record also does not specify whether the primary analysis included all enrolled participants, only participants who received the device, or another defined group. It gives no analysis-population definition and no account of deviations or incomplete records. These omissions make it difficult to assess how the reported adverse-event figures relate to the primary endpoint population. They also limit reproducibility: the endpoint definition alone is not enough to reconstruct an analysis without rules for eligibility, follow-up, missingness, and event adjudication.

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

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: vessel dissection, grade a or b (3.0%), bruising or hemorrhage at procedural access site (3.0%), thrombosis (3.0%), pain, new or worsening (3.0%), infection (3.0%).

The serious adverse-event summary lists the Ocelot System group with 100 participants at risk and 26 affected. For other adverse events, it lists 100 at risk and 25 affected. The record also lists zero deaths. These are separate adverse-event summaries and should not be interpreted as the primary endpoint result, whose percentage and confidence interval are not reported.

The top serious-event terms are Vessel Dissection, Grade A or B; bruising or hemorrhage at procedural access site; thrombosis; new or worsening pain; infection; and pseudoaneurysm. Each is listed at 3.0%. The registry record does not give term-specific participant counts in the registry record reported, nor does it state whether a participant could appear under more than one term. The percentages therefore should not be added, and they should not be assumed to represent distinct people or mutually exclusive events.

These figures are descriptive. With no control group, they cannot establish whether event frequency was higher or lower than it would have been under another approach. The registry record does not report a detailed event-analysis method, the relationship between these summaries and the primary endpoint definition, or how withdrawals before 30-day follow-up affected safety ascertainment.

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

The registry record describes a device study with a clear clinical focus: crossing chronic total occlusions in femoropopliteal arteries using the Ocelot System, with safety assessed at Day 30. It also reports group-level serious and other adverse-event figures and lists common serious-event terms. These details establish what the study set out to evaluate and provide some descriptive safety information.

However, the primary endpoint result itself is not reported in the registry record. The endpoint definition and the mention of a 95% confidence interval do not reveal the observed percentage or its precision. The record therefore cannot support a quantitative statement about the primary safety endpoint's frequency. The withdrawals before Day 30 also make the missing-data approach relevant, but that approach is not reported.

The design further narrows what can be concluded. CONNECT II is recorded as non-randomized and single-group, with no masking. The group-level event figures do not constitute a comparison with another intervention, and they cannot establish that the Ocelot System caused an event or prevented one. No alternative-treatment group is available in the record for a direct contrast.

General statistical interpretation distinguishes descriptive evidence from comparative evidence. Descriptive data characterize what was recorded in a study group; comparative evidence needs a suitable comparison and analysis. The adverse-event summary offers descriptive figures, while the missing primary estimate prevents full assessment of the stated primary question. The record also does not report component-specific primary endpoint outcomes, the analysis population, or details of how follow-up and missing values were handled.

Thus the findings that can be read from the record are limited: the study design and endpoint are described, certain adverse-event summaries are listed, and a primary result is absent. The absence of a reported estimate should not be mistaken for evidence that no endpoint events occurred. It means the registry record does not provide the result needed to characterize that endpoint.

14. Why This Trial Matters Statistically

CONNECT II illustrates why registry entries need to be read in layers. The study description identifies the clinical task and intervention, while the design tells readers whether outcomes can be compared causally. A non-randomized single-group study can contribute descriptive experience about device use, but it does not supply a randomized control contrast. That distinction remains important even when a registry specifies a safety endpoint and a follow-up time.

The endpoint also shows why definitions and estimates are both necessary. The record describes a composite safety question involving major adverse events, perforations, embolizations, and dissections through Day 30. But without the observed percentage and confidence interval, readers cannot assess the endpoint's frequency or precision. A detailed endpoint definition cannot replace its reported result.

The adverse-event summaries offer another statistical lesson: participant counts, event terms, and endpoint components are not automatically interchangeable. The record reports affected participants and lists event terms, but does not explain overlap among terms or their relation to the primary endpoint. Careful interpretation avoids summing categories or treating them as independent without supporting information.

Finally, the two withdrawals before follow-up underscore the importance of transparent analysis populations and missing-data methods. Knowing that follow-up was incomplete is useful, but it does not show how incomplete observations were handled. Clear reporting of these choices, alongside endpoint estimates and uncertainty, is needed for readers to judge how well a result represents the enrolled group. The record's limitations are therefore not merely administrative: they constrain the statistical conclusions that can be drawn.

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.

Several limitations are specific to the information recorded for this trial. First, the primary safety endpoint is defined but its observed percentage and 95% confidence interval are not reported. The most central outcome therefore cannot be assessed for magnitude or precision from the registry record.

Second, the design is single-group and non-randomized, with no control arm. Outcomes in the Ocelot System group cannot be directly contrasted with outcomes under another device or procedure. The absence of masking is also recorded, but the registry does not describe how outcome assessment or event adjudication was conducted.

Third, the record notes two withdrawals before 30-day follow-up without specifying the amount of follow-up available for those participants or how their endpoint status was handled. It does not define the analysis population, explain missing-data methods, or state whether all participants at risk were included in each endpoint analysis.

Fourth, although secondary outcomes are listed, the record gives no analysis entries. It does not report endpoint-specific estimates, uncertainty intervals, testing procedures, multiplicity handling, or a detailed statistical analysis plan. Consequently, the listed outcomes should not be mistaken for reported findings.

Finally, the adverse-event summary does not clarify whether event terms overlap, how terms map to the primary endpoint, or how events were assessed. These gaps limit interpretation of the relationship between the serious-event figures and the primary safety question. They also make it inappropriate to draw broader comparative or causal conclusions from the listed adverse-event data.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Chronic Total Occlusion Crossing With the Ocelot System - CONNECT II — NCT01537302.
• Registry record last updated 2021-03-22; status last verified 2021-03.
• Results first posted 2015-03-18.
• 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

CONNECT II is recorded as a completed, non-randomized, single-group device study of the Ocelot System for crossing chronic total occlusions in femoropopliteal arteries. The registry lists enrollment of 100, a start of 2012-02, and primary completion in 2012-06. The primary safety endpoint is a participant percentage assessed at Day 30 and defined around the absence of specified adverse events. Two subjects withdrew before 30-day follow-up.

The registry record lists serious adverse events for 26 participants at risk of 100, other adverse events for 25 participants at risk of 100, and zero deaths. Six top serious-event terms are each listed at 3.0%. However, the primary endpoint estimate and confidence interval are not reported in the registry record. The record lists secondary outcomes but records zero analyses, and does not describe missing-data handling, analysis populations, or multiplicity procedures. The single-group design does not provide a randomized comparison.