Clinical Evaluation of HW005 Ventricular Assist System for the Treatment of Advanced Heart Failure in Japan: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Clinical Evaluation of HW005 Ventricular Assist System for the Treatment of Advanced Heart Failure in Japan (NCT02091440), a na na study. The primary outcome is Number of Participants Alive on the Implanted HW005 Ventricular Assist System or Transplanted or Explanted for Recovery at 180 Days.

2. Clinical Question

3. Trial Design

The registry record describes a completed, single-group device evaluation of the HW005 Ventricular Assist System for advanced heart failure in Japan. It lists an enrollment of 6 and a study start of 2014-03, with primary completion in 2015-03. The phase is recorded as NA. The sponsor is Medtronic Cardiac Rhythm and Heart Failure.

All participants were in the HW005 Ventricular Assist System group, which is described as receiving an implant of the device. Allocation is recorded as NA, masking as NONE, and the design as SINGLE GROUP. These entries indicate that the registry does not describe random assignment or masking, and it does not identify a concurrent control arm. The posted findings should therefore be read as a description of the enrolled group, rather than as a comparative estimate against another treatment.

The study’s stated purpose was to evaluate safety and effectiveness among people listed for cardiac transplantation with refractory, advanced heart failure and risk of death. The primary endpoint was assessed at 180 days. Secondary outcomes included survival on the implanted system at 180 days; serious adverse events and unanticipated adverse device effects; device failures and malfunctions; and changes in quality of life, functional classification, and walking distance at 6 and 24 months.

The registry lists seven outcome measures and seven analyses, but it does not report the statistical analysis plan, the analysis populations, or the results for the primary endpoint and listed secondary outcomes. Details such as participant eligibility criteria, follow-up completeness, and how outcomes were handled when a participant left the study are not reported in the registry record. The absence of a control group also means that the design cannot separate changes associated with device implantation from changes that might have occurred for other reasons.

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:

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 Participants Alive on the Implanted HW005 Ventricular Assist System or Transplanted or Explanted for Recovery at 180 Days, measured over 180 days.

The primary endpoint counts participants who met a combined success definition at 180 days. Success was defined as being alive on the originally implanted HW005 Ventricular Assist System, having received a transplant, or having the device explanted for recovery and then surviving 60 days after explant. The record therefore treats continued survival with the device, transplantation, and recovery-related explant followed by the specified survival period as qualifying pathways.

This kind of composite endpoint can capture clinically distinct routes through which a participant may reach a favorable status within the assessment period. It is important to read the components as a combined definition: the endpoint is not a count of participants alive on the device alone. Transplantation and explant for recovery are included, with the post-explant survival condition applying to recovery explants. The registry record does not report component-specific counts, so the contribution of each pathway cannot be distinguished.

A fixed assessment time makes the endpoint interpretable as status at 180 days, but a count alone would not describe when events occurred during follow-up. The record does not report the primary endpoint result, an uncertainty interval, or details of how missing status was handled. As a result, the endpoint definition can be described, but the posted registry information does not establish how many participants met it or how precisely that count is estimated.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What can be read from the design? The study is recorded as SINGLE GROUP, with allocation listed as NA and masking as NONE. That describes a study without a randomized comparator in the registry record. The primary outcome is a participant count at 180 days, rather than a continuous measurement such as a score or distance. For a binary outcome, each participant either meets the defined success condition or does not, and the group result can be presented as a count of participants meeting the definition. The registry record does not report that count for the primary endpoint.

Why does the endpoint definition matter? The primary outcome combines several routes to success: being alive on the originally implanted device, transplantation, or recovery-related explant followed by survival for 60 days. A composite can capture different clinically relevant pathways in a single endpoint. Its interpretation depends on the components and their relative contribution. Here, the registry record gives the definition but not component counts, so it is not possible to tell which pathway accounts for any successes. The success condition following recovery explant also means that explant alone is not enough to qualify.

How should a participant count be interpreted? A count is a direct description of how many participants met an outcome in the study group. A proportion can express that count relative to the number assessed, but the registry record does not report the primary success count or the number with complete endpoint assessment. No proportion should be inferred from the enrollment alone. A confidence interval, in general, describes the statistical uncertainty around an estimate under specified assumptions; it does not show the range of outcomes for individual participants, and it does not establish causation. The registry record does not report a confidence interval for the primary outcome.

What does a single-group design allow? It can describe outcomes observed among participants receiving the device. Without a concurrent comparator, it cannot by itself estimate how those outcomes would differ under another treatment or without the device. Changes in a participant’s health over time may reflect multiple influences. General statistical interpretation therefore distinguishes an observed group outcome from a treatment effect established by comparison. No comparative effect is reported in the registry record.

What are the planning illustrations? A separate planning illustration uses a two-sided significance level of 0.05, equal allocation between hypothetical arms, and a normal approximation. It considers effects set as stated fractions of an observed effect. These are assumptions for a planning exercise, not descriptions of this trial’s design: the registry describes a single-group study, not equal allocation between two arms. The illustration should not be read as the trial’s sample-size justification, as an observed power calculation, or as evidence of an effect. The registry record does not report its sample-size justification or the analysis plan behind the study.

In general, a sample-size calculation asks how many participants might be needed under specified assumptions to detect a target effect with a chosen error rate and power. Such a calculation is prospective: it depends on assumptions about the effect, variability or event frequency, and analysis method. It does not tell whether a completed study found an effect, and it does not remedy limitations such as the absence of a comparison group. The registry record does not report a protocol rationale for the enrollment of 6. The planning illustration is distinct from that unreported rationale.

Why does event frequency matter for safety interpretation? The outcome type is binary, and the record reports affected-participant counts for safety. When a group is small, counts can change noticeably with the experience of an individual participant. General statistical reasoning therefore calls for attention to both the count and its uncertainty, rather than treating a percentage as a stable estimate. The registry record does not report uncertainty intervals for the safety counts. The percentages attached to event terms describe the reported categories, but the record does not give sufficient event-level information to determine whether categories overlap or to reconstruct a complete incidence analysis.

What about over-dispersion? Over-dispersion is a general concern when count data vary more than an assumed statistical model allows. It can make standard errors too small if a model treats observations as less variable than they are. That issue is relevant to some count-data analyses, but the primary endpoint is described as a participant count meeting a binary definition, and no model or dispersion estimate is reported. It would therefore be inappropriate to claim that an over-dispersion adjustment was used or was needed in this study.

What analysis details remain unknown? The registry record lists seven analyses and seven outcome measures, but does not describe the statistical tests, adjustment methods, confidence interval methods, or analysis populations. It also does not report whether the analyses were prespecified, whether there were interim analyses, or how missing observations were treated. Those omissions prevent a full appraisal of the statistical methods. They should be understood as unreported details, not as evidence that a particular method was or was not 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("HW005 Ventricular Assist System")
n      <- c(6)
events <- c(6)
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  HW005 Ventricular Assist System  6  6  100.0  54.1  100.0  61.0  100.0  59.0  99.6

11. Multiplicity, Missing Data and Analysis Populations

The registry lists seven outcome measures and seven analyses. The primary endpoint is a composite assessed at 180 days; the listed secondary outcomes cover survival on the implanted system, serious adverse events and unanticipated adverse device effects, device failures and malfunctions, and changes in quality of life and functional measures at 6 and 24 months. When a study examines multiple outcomes, the chance of finding at least one apparently notable result can depend on how many comparisons are made and whether the analysis accounts for that multiplicity. The registry record does not report a multiplicity strategy, a hierarchy among outcomes, or whether secondary analyses were considered confirmatory or exploratory.

Missing data can affect both counts and changes from baseline. If follow-up measurements are unavailable, the number assessed may differ from the number enrolled, and the interpretation depends on why observations are missing and how the analysis handles them. The registry record does not report missingness by outcome, follow-up completeness, imputation methods, or sensitivity analyses. It is therefore not possible to determine from this record whether the reported safety figures or any unreported effectiveness results use all enrolled participants.

Analysis populations also matter: an analysis might include participants according to enrollment, treatment received, or availability of outcome data, depending on its prespecified definition. The registry record does not report the analysis populations or the rules used to assign participants to them. These details are especially important for a composite outcome that can be reached through different clinical pathways and for outcomes measured at distinct follow-up times. Without the statistical plan and participant-level disposition, the impact of missingness and analysis choices cannot be assessed.

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: other (50.0%), bleeding requiring re-hospitalization (33.3%), bleeding requiring re-operation (33.3%), ventricular cardiac arrhythmia (33.3%), supraventricular cardiac arrhythmia (33.3%).

For the HW005 Ventricular Assist System group, the registry reports serious adverse events affecting 5 participants among 6 at risk. It reports other adverse events affecting 6 among 6 at risk, and 2 deaths. These are participant counts in the study group, not estimates of comparative risk. The record does not establish that the device caused the events or deaths, and the absence of a concurrent control group limits interpretation of whether the counts differ from what might occur under another treatment or care setting.

The listed serious-event terms are “Other” at 50.0%, bleeding requiring re-hospitalization at 33.3%, bleeding requiring re-operation at 33.3%, ventricular cardiac arrhythmia at 33.3%, supraventricular cardiac arrhythmia at 33.3%, and pericardial fluid collection at 33.3%. These percentages should be read as category summaries, not added together to create a total: the registry record does not state that categories are mutually exclusive. It also does not provide event timing, recurrence, severity detail beyond the serious-event designation, or participant-level overlap.

The registry lists outcomes concerning serious adverse events and unanticipated adverse device effects, as well as device failures and malfunctions. The available record does not provide separate results for every listed outcome. The figures above therefore give a limited safety description rather than a complete account of all device-related events or their clinical course.

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

The registry record documents an evaluation of the HW005 Ventricular Assist System among participants with refractory, advanced heart failure who were listed for cardiac transplantation. It defines a 180-day primary endpoint that includes being alive on the originally implanted system, transplantation, or recovery-related explant followed by survival for 60 days. It also reports selected adverse-event counts and event categories. These details describe the questions the study set out to address and some safety observations in the enrolled group.

The posted results do not report the primary endpoint count, so the record does not show how many participants met the defined success condition. It also does not report component-specific primary outcome results or results for the listed quality-of-life and functional outcomes. As a result, the information available cannot quantify the endpoint result or describe the full pattern of outcomes over follow-up.

The reported safety counts should not be interpreted as proof that the device caused an event, nor do they establish that an event was unrelated to the device. A single-group study has no concurrent control group for separating outcomes associated with device use from outcomes that might occur because of the underlying condition or other influences. The registry record does not provide a causal analysis.

The enrollment of 6 also means the study describes a small group. That limits how confidently its results can characterize outcomes in a broader population, especially when uncertainty intervals and participant-level details are not reported. The record does not provide enough information to assess generalizability, missing follow-up, or the robustness of the statistical analysis.

In short, the registry record establishes the study design, endpoint definition, and selected adverse-event counts. It does not provide the primary endpoint result or enough comparative and statistical detail to determine effectiveness, estimate a treatment effect, or make a definitive assessment of the balance of benefits and harms. The study’s completed status does not fill in these missing results.

14. Why This Trial Matters Statistically

This trial is statistically notable because it makes the limits of descriptive evidence clear. The registry identifies a clinically serious population and a device intervention, but records a single-group design with no concurrent comparator. Such a design can describe what happened among participants who received the device; it cannot by itself distinguish the device’s effect from other influences on health outcomes.

The primary endpoint is a composite rather than a single event type. Its definition combines survival with the device, transplantation, and recovery-related explant followed by the specified survival period. Composite endpoints can be useful when participants may reach a meaningful outcome through different pathways, but the overall count is more informative when component counts are also available. Those component results are not reported in the registry record.

The record also illustrates why outcome definitions and outcome results must be distinguished. A detailed definition at 180 days does not tell the reader how many participants met it. Similarly, listing secondary outcomes does not establish what those outcomes showed. The missing primary result prevents a direct statistical summary of the endpoint the study was designed to evaluate.

Safety counts remain important descriptive information, particularly in a small device evaluation, but they require careful interpretation. The group-level counts and event categories do not identify causation, provide a controlled comparison, or describe uncertainty. The registry record also leaves analysis methods, missing-data handling, and analysis populations unreported.

For clinical researchers and biostatisticians, this study underscores the value of complete results reporting: endpoint counts, component results, denominators, uncertainty estimates, analysis methods, and participant follow-up are needed to assess precision and interpretability. The registry record supplies a clear design and endpoint framework, while leaving key results and analytic details unresolved.

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 most consequential limitation in the registry record is that the primary endpoint result is not reported. The endpoint definition is detailed, but no count of participants meeting it, component breakdown, or uncertainty estimate is available. This prevents a direct assessment of the study’s main stated outcome.

The single-group design has no concurrent control arm, and allocation is recorded as NA. Masking is recorded as NONE. Accordingly, the study record does not support a randomized or masked comparison. Any changes over time or safety events cannot be contrasted within the study against outcomes under a different treatment.

The enrollment was 6, which limits the amount of outcome information available for describing this group. The registry record does not report participant characteristics beyond the stated population, follow-up completeness, event timing, or individual outcome histories. It is not possible to assess how representative the participants were or whether follow-up differed across outcomes.

Several methodological details are also not reported in the registry record: the sample-size justification, statistical analysis plan, analysis populations, interim analyses, multiplicity approach, and missing-data methods. The record lists seven outcome measures and seven analyses, but does not clarify how the analyses relate to each measure or which results were prespecified. The listed secondary outcome results are not reported in the record.

Safety information is limited to selected participant counts and event terms. The record does not provide a full event-level account, causal attribution, or separate results for every listed safety outcome. The percentages for event terms cannot be treated as mutually exclusive without further detail. Together, these limitations mean the available registry information supports a restricted descriptive account, not a complete statistical evaluation of effectiveness or safety.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Clinical Evaluation of HW005 Ventricular Assist System for the Treatment of Advanced Heart Failure in Japan — NCT02091440.
• Registry record last updated 2019-09-09; status last verified 2019-07.
• Results first posted 2019-09-09.
• 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, single-group evaluation of the HW005 Ventricular Assist System for advanced heart failure in Japan. Enrollment was 6; the study began in 2014-03 and reached primary completion in 2015-03. Allocation is listed as NA, masking as NONE, and phase as NA.

The primary endpoint counts participants meeting a composite success definition at 180 days. The primary endpoint result and results for the listed secondary outcomes are not reported in the registry record. Safety summaries report serious adverse events affecting 5 participants among 6 at risk, other adverse events affecting 6 among 6 at risk, and 2 deaths. The record does not establish causation or provide a concurrent comparison group.

The registry record does not report the statistical analysis plan, missing-data methods, analysis populations, or sample-size justification. The available information therefore supports a description of the design, endpoint, and selected safety findings, but not a comparative estimate of effectiveness.