C-Pulse IDE Feasibility Study- A Heart Assist System: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for C-Pulse IDE Feasibility Study- A Heart Assist System (NCT00815880), a na na study. The primary outcome is Number of Surviving Participants That Completed the Study.

2. Clinical Question

This is a feasibility question rather than a randomized comparison of C-Pulse with another treatment or with no device. The study description frames its objectives as assessing safety and performance, alongside measures of heart function and whether quality of life improved after implantation. The registry lists NYHA Classification as a secondary outcome. However, the posted information does not include a result for that measure, a result for the primary outcome, or estimates of change in quality of life or heart function. Consequently, the clinical question can be described from the stated objectives and outcome definitions, but the recorded information does not establish the observed degree of completion or change in the secondary measures.

3. Trial Design

The C-Pulse IDE Feasibility Study is listed as a completed, single-group device study in people with heart failure. Its intervention is C-Pulse™ (Implantable Counterpulsation Therapy). The registry gives an enrollment of 21 and identifies Nuwellis, Inc. as the sponsor. The start date is 2008-09-10, and the primary completion date is 2018-05-07. The listed phase and allocation are NA, and masking is none.

The single-group structure is central to interpretation. Participants eligible for the study were to enter the treatment arm, as described in the registry. There is no independent control group against which to estimate what would have happened without the device or with another intervention. The record therefore does not support a randomized treatment-effect comparison. The listed enrollment is 21; it should not be treated as the number who completed the five-year outcome period, because a completion result is not posted in the information summarized for the study.

The arm description says the primary study population would include 20 patients enrolled and implanted, and that an expansion protocol would allow up to 40 patients to be enrolled and implanted. These are statements about the described study design, not evidence that those numbers were ultimately implanted. The registry's recorded enrollment is 21. The posted information does not clarify the number actually implanted, the eligibility criteria, or the timing and decision process for any expansion.

The brief summary describes follow-up visits after implantation to assess how participants were doing and monitor safety concerns. It does not give a detailed visit schedule or a protocol for outcome assessment. The record does not report a statistical analysis plan, an analysis population definition, or planned interim analyses. The study status is completed, but that status alone does not supply the numerical results needed to assess the primary question.

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 Surviving Participants That Completed the Study, measured over 5 Years.

The primary outcome is titled “Number of Surviving Participants That Completed the Study.” Its unit is participants, and its stated timeframe is 5 Years. The description defines the count as participants who did not exit the study for reasons including worsening heart failure resulting in hospitalization, LVAD implantation, study withdrawal, or death. This combines survival and study completion into a count rather than reporting a comparative treatment effect.

A completion count can describe how many enrolled participants met a defined follow-up criterion, which is relevant in a feasibility study. It can also make clear that death, withdrawal, or other specified events affect whether a participant is counted as completing the study. The registry record does not include a numerical primary outcome result, so the number who completed or the number who did not meet the completion definition is not reported in the registry record.

The endpoint is not described as a rate, a time-to-event estimate, or a comparison between groups. The record does not report how the endpoint was analyzed, how participants with incomplete follow-up were classified, or whether a particular analysis population was used. Those details matter because a raw count is most interpretable when its denominator, follow-up completeness, and outcome rules are clear. The stated enrollment of 21 does not by itself reveal how many participants completed the study.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Study structure and estimand

The study is listed as single-group, with no allocation and no masking. These design features determine what can be learned statistically. With one treatment group, a result can describe the participants observed after implantation, but there is no concurrent control group for estimating a between-group contrast. The registry does not report a target estimand, meaning a fully specified description of the treatment effect the study intended to estimate, including the population, outcome, handling of events after implantation, and summary measure.

The primary measure is a participant count: the number of surviving participants who completed the study. A count is directly interpretable only alongside its definition, denominator, and observed value. The definition gives examples of reasons for not completing, including death, withdrawal, worsening heart failure resulting in hospitalization, and LVAD implantation. The record does not specify whether these reasons were handled as mutually exclusive categories or how other forms of incomplete follow-up were classified. Most importantly, it does not post the observed count.

What can a single-group count show?

In general, a count can describe how many participants met a prespecified outcome definition in the observed group. It does not, by itself, establish what would have happened to those same participants under another intervention. A rate or proportion would require a clearly defined denominator and an appropriate analysis; neither should be reconstructed when a result is not posted. Likewise, a count over a stated follow-up period is not the same as a time-to-event analysis, which uses information about when events occur and how long participants are followed.

How should uncertainty be described?

In general, a confidence interval expresses the statistical uncertainty around an estimate under the assumptions of the analysis. A narrow interval indicates greater precision than a wide interval, while neither interval width nor statistical significance establishes clinical importance. No confidence interval or other uncertainty estimate for the primary outcome is reported in the registry record. The outcome count itself is also not posted, so its precision cannot be evaluated from the available information.

The record lists five outcome measures and zero analyses. That means the summarized registry information does not include posted analyses from which to assess model choice, adjustment, hypothesis testing, or uncertainty. It does not establish whether analyses were conducted outside the registry. The statistical analysis plan and any prespecified approach to the outcome measures are not reported in the registry record.

What do the sample-size assumptions represent?

The record describes planning illustrations based on an observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It says that the effect to detect is a stated fraction of the observed effect. For time-to-event illustrations, the stated quantity is total events; for other illustrations, it is participants per arm. These are planning assumptions, not a description of the actual single-group study design. The numerical planning results are not included in the information summarized for the study, and a sample-size illustration is not observed power or evidence that the study could detect a particular effect.

In general, over-dispersion matters when counts vary more than a chosen statistical model expects: a model that understates that variation can give overly narrow uncertainty intervals. This is a general concept only; the registry does not report a count model or an over-dispersion assessment for this study. Likewise, no adjustment method or approach to repeated measurements is reported, despite the summary's mention of several follow-up visits and multiple measures of heart function and quality of life.

These limitations mean the design and posted information support an account of the study's stated objectives and recorded safety summaries, but not a detailed reanalysis of its primary endpoint. No statistical test, adjusted estimate, effect size, or comparative estimate should be inferred where the registry does not report one.

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("Implantable Counterpulsation Therapy")
n      <- c(21)
events <- c(3)
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  Implantable Counterpulsation Therapy  21  3  14.3  3.0  36.3  5.0  34.6  5.2  34.9

11. Multiplicity, Missing Data and Analysis Populations

The registry lists five outcome measures and identifies NYHA Classification as a secondary outcome. It reports zero analyses in the summarized record. It does not identify a hierarchy among the outcomes, state which measures were confirmatory, or report a method for controlling the chance of false-positive findings when multiple outcomes are examined. A multiplicity adjustment or analysis plan is not reported in the registry record.

The record also does not describe missing-data procedures. In particular, it does not say how missed visits, loss to follow-up, withdrawal, or incomplete assessments were handled for the primary or secondary outcomes. The primary endpoint description includes study withdrawal among reasons for not completing, but the record does not state how incomplete observations were incorporated into any analysis. The reasons for missing outcome data, if any, are not reported in the registry record.

The analysis populations are not defined in the summarized information. It is therefore unclear whether any intended analysis was based on all enrolled participants, only implanted participants, participants with available follow-up, or another group. The arm description refers to patients enrolled and implanted, but the posted enrollment of 21 does not establish the number implanted or the denominator used for outcome analyses.

These omissions limit the ability to assess whether outcome reporting followed a prespecified plan or how robust any findings would be to missing information. Because results for the primary and secondary outcomes are not posted in the information summarized for this study, multiplicity and missing-data methods cannot be evaluated from outcome estimates.

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

Serious events with the highest arm-level rate: major infection (71.4%), cardiac arrhythmias (38.1%), worsening left heart failure (23.8%).

The adverse-event summary lists 21 participants at risk and 21 affected by serious adverse events. For the other adverse-event category, it lists 21 at risk and 0 affected. The record also lists 7 deaths. These are distinct summary figures: the number affected by serious events is not the same measure as the death count, and the record does not explain the overlap between those groups.

The most frequently listed serious-event terms are Major Infection (71.4%), Cardiac Arrhythmias (38.1%), and Worsening Left Heart Failure (23.8%). These are reported percentages for event terms. The registry information does not state whether an individual could contribute to more than one term, nor does it provide event counts, timing, severity gradations, or duration. The percentages should not be added together or treated as proportions of mutually exclusive categories.

The summary does not report whether events were judged related to the device or procedure, when they occurred relative to implantation, or whether they led to study exit. The count of deaths does not identify causes or timing. Accordingly, these figures describe the adverse-event information recorded in the registry; on their own, they do not establish causation or allow comparison with another treatment group.

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

The record establishes that this was a completed, single-group feasibility study of C-Pulse implantable counterpulsation therapy in people with heart failure, with 21 participants enrolled. It identifies a primary outcome focused on surviving participants completing the study over 5 Years and includes a summary of serious adverse events. These details describe the study's scope and the types of information the registry records.

The record does not include the numerical result for the primary endpoint or results for the secondary outcome of NYHA Classification. It therefore cannot establish how many participants completed the study, how functional classification changed, or how the other listed outcome measures changed. It also does not provide estimates of precision for those outcomes. A completed registry status should not be read as a positive primary endpoint result.

Because there is no control group, the study does not provide a direct comparison with another treatment. Even if a before-and-after change were available, change within one group would not by itself isolate the effect of the device from other influences. The posted information includes no comparative effect estimate, and none should be inferred from the enrollment or safety summaries.

The serious adverse event figures warrant a careful descriptive reading. They record 21 participants affected by serious adverse events and 7 deaths, but the available summary does not establish the causes, timing, or attribution of those events. The information does not permit a complete assessment of safety across time or a comparison of risk against a control group.

Overall, the registry supports a description of study design, enrollment, stated outcomes, and selected safety figures. It does not support a conclusion about whether the device changed clinical outcomes or about the magnitude or precision of any such change. Missing results and analysis details should be treated as unavailable information, not as evidence of no effect or of a particular effect.

14. Why This Trial Matters Statistically

This study illustrates why design and reporting details matter when interpreting clinical evidence. A feasibility study can collect information about device use, follow-up, participant outcomes, and safety. Yet the ability to draw conclusions depends on the results being reported with clear outcome definitions, denominators, and uncertainty. Here, the registry identifies a five-year completion outcome and provides adverse-event summaries, but the numerical primary outcome result is not reported in the registry record.

The single-group design also highlights the distinction between describing outcomes and estimating comparative effects. Counts from a treated group may be useful as a record of what occurred among those participants, but they cannot show how outcomes would have differed under an alternative. Without a comparator, the statistical question is narrower than a randomized treatment comparison, and conclusions must remain descriptive.

The adverse-event figures show another important reporting issue: event summaries need context. Counts and percentages can identify recorded event categories, but interpretation also depends on timing, exposure, attribution, repeated events, and whether participants contribute to multiple categories. Those details are not available in the information summarized for this study.

Finally, planning calculations should not be confused with evidence observed in the trial. The registry describes assumptions for sample-size illustrations, including two-arm equal allocation, whereas this study is listed as single-group. Such illustrations do not replace a stated protocol justification, an analysis plan, or posted outcome results. The study therefore matters statistically as a reminder that feasibility, safety description, and causal effectiveness are different questions, each requiring appropriate design and transparent reporting.

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 study. The study is single-group, with no allocation and no masking, and no comparator is listed. Consequently, the record does not support a direct comparison with another treatment. The registry describes an enrollment of 21, while the arm description refers to an initial primary population of 20 and a possible expansion up to 40. It does not clarify how many participants were actually implanted or how the recorded enrollment relates to the implanted population.

The primary outcome is described, but its result is not included in the information summarized for the study. The record also does not provide results for the listed secondary outcome or the other outcome measures. It does not report confidence intervals, analysis methods, participant-level follow-up, missing-data handling, or analysis populations. The study's completed status does not resolve these gaps.

The safety information is limited to summary figures and selected serious-event terms. The record does not provide timing, event duration, causes of death, attribution to the device, or a description of overlap between event categories and deaths. These omissions prevent a detailed assessment of the safety profile or comparison of event risk.

The brief summary mentions repeated follow-up visits and assessments of heart function and quality of life, but the detailed schedule, instruments, and analysis approach are not reported in the registry record. The sample-size planning assumptions are described as illustrations and do not amount to a reported protocol justification for the single-group design. These limitations apply to interpretation of the registry information; they do not establish that additional information was not collected or analyzed elsewhere.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: C-Pulse IDE Feasibility Study- A Heart Assist System — NCT00815880.
• Registry record last updated 2023-08-24; status last verified 2023-08.
• Results first posted 2023-08-24.
• 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 C-Pulse IDE Feasibility Study is listed as a completed, single-group device study in people with heart failure. The intervention is C-Pulse™ (Implantable Counterpulsation Therapy), and the registry records an enrollment of 21. Nuwellis, Inc. is listed as sponsor. The study began on 2008-09-10, with primary completion on 2018-05-07.

The primary outcome is the number of surviving participants who completed the study over 5 Years. NYHA Classification is listed as a secondary outcome, and the record identifies five outcome measures. The summarized information does not include primary or secondary outcome results and lists zero analyses.

The adverse-event summary lists 21 participants affected by serious adverse events, 0 affected in the other adverse-event category, and 7 deaths. Selected serious-event terms and percentages are also recorded. The registry does not report a control group, a statistical analysis plan, or details needed to interpret event timing and attribution. The available information supports a description of the study design and posted safety figures, but not an estimate of comparative treatment effect.