Thoratec HeartMate II Left Ventricular Assist System (LVAS) for Bridge to Cardiac Transplantation: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Thoratec HeartMate II Left Ventricular Assist System (LVAS) for Bridge to Cardiac Transplantation (NCT00121472), a non-randomized na study. The primary outcome is Survival.

2. Clinical Question

The clinical question focuses on an outcome that combines reaching transplantation with remaining alive on device support under the specified listing conditions. It does not compare the device with another treatment in a randomized design. The registry record describes the intended population as people with end-stage heart failure who were listed for transplant but at imminent risk of dying. It identifies the HeartMate II LVAS as the intervention and records survival as the primary outcome.

The endpoint description sets out two routes to meeting the stated outcome: reaching cardiac transplantation, or continuing LVAS support through 180 days while remaining listed at UNOS status 1A or 1B. The registry record does not give the number of participants who met this endpoint, an estimated event rate, or a statistical comparison. Therefore, the clinical question can be described from the protocol entry, but the posted results do not establish how often the endpoint was achieved.

3. Trial Design

The study is recorded as a completed, non-randomized, single-group device study. The intervention was the Thoratec HeartMate II LVAS. Masking is listed as none, and the allocation is listed as non-randomized. These design details mean the registry record does not describe random assignment or a masked comparison between treatment groups. No comparator arm is identified.

The registry entry lists enrollment as 194. For the primary outcome, it describes the first consecutive 194 patients enrolled under the Pivotal Study Protocol (n=133) and the Continued Access Protocol (CAP, n=61). Those patients were analyzed when the last subject reached the 1 year followup point on September 14, 2007. The primary analysis is described as intent to treat (ITT). The record does not explain how the two protocol cohorts were handled in the analysis beyond identifying them as the primary population.

The study purpose was to assess safety and effectiveness of the LVAS as a bridge to cardiac transplantation in people with end-stage heart failure listed for transplant and at imminent risk of dying. The stated primary outcome was survival to transplantation or 180 days on LVAS support while remaining listed for transplantation at UNOS status 1A or 1B. The record also lists clinical reliability, quality-of-life measures, functional measures, reoperations, and post-transplant survival as secondary outcomes.

The registry record gives start and primary completion dates as 2005-03 and 2006-11, and status as completed. It does not report a randomized comparator, a blinding procedure, or a statistical analysis plan. The study's completed status should not be confused with availability of a complete results report: the primary outcome result and analysis estimates are not reported in the registry record.

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: 194 patients were followed to at least 1 year after implantation of the device, all 133 of the Pivotal Study Cohort patients and 61 of the US CAP patients, results of which are summarized below and in the final FDA-approved labeling for the HeartMate II LVAS. The remaining 292 patients followed for less than 1 year are not included.

Overall Study

Analysis population for the primary outcome, as defined in the registry: The first consecutive 194 patients enrolled under the Pivotal Study Protocol (n=133) and the Continued Access Protocol (CAP, n=61) were analyzed when the last subject reached the 1 year followup point on September 14, 2007. Analysis was Intent To Treat (ITT).

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 Survival, measured over 180 days.

The primary endpoint is labeled survival and measured in participants. Its description specifies survival to cardiac transplantation or 180 days on LVAS support while remaining listed for cardiac transplantation as UNOS status 1A or 1B. Thus, the endpoint reflects a defined clinical status over a specified period, with transplantation or continued qualifying device support serving as the stated outcome condition.

A binary endpoint records whether each participant meets the defined outcome or does not. This can make an outcome easier to interpret than a measure requiring a scale or a change score, but the meaning depends on the exact endpoint definition. Here, the transplant route and the continued-support route are both part of the stated criterion. They should not be treated as interchangeable clinical experiences; the registry description groups them under the primary survival outcome.

In general, a time-bounded survival endpoint can summarize whether participants reach a specified outcome within a follow-up window. That can be useful when the clinical aim concerns maintaining a participant until transplantation or through a stated period of support. Interpretation also depends on how events, follow-up, and the two routes to meeting the criterion are operationalized. The registry record does not provide further details about endpoint adjudication or handling of participants who do not meet the stated condition.

Most importantly, the record gives the endpoint definition but not its observed result. It does not report how many participants met the criterion, the proportion meeting it, or an uncertainty interval. The endpoint therefore describes what the study set out to assess, not the degree to which the outcome was observed.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a single-group, non-randomized design, with no masking. These terms define how to read the evidence. In a randomized study, allocation by chance is intended to make comparison groups similar on average with respect to measured and unmeasured characteristics. This registry record does not describe that kind of allocation. With a single group, the outcome data describe participants receiving the HeartMate II LVAS; they do not constitute a randomized comparison against another group.

What does a single-group design show?

In general, a single-group study can document the outcomes observed during use of an intervention in a specified study population. It can also describe safety events and performance measures. Without a concurrent randomized comparator, however, it cannot isolate the effect of the intervention from the influence of participant prognosis, clinical decisions, background care, or other changes over time. This is a design limitation, not a reason to disregard the observations. It means the interpretation must stay within the scope of the data recorded.

The study's allocation is listed as non-randomized, and its model as single-group. The record does not identify a comparator or a masked assessment process. It does not report the protocol's statistical plan, including any model choice, covariate adjustment, hypothesis-testing approach, or planned interim analysis. Those details should not be inferred from the study's endpoint or status.

How should the primary endpoint be understood?

The primary outcome is a binary participant-level endpoint: survival to cardiac transplantation or reaching 180 days on LVAS support while remaining listed for transplantation at UNOS status 1A or 1B. For a binary endpoint, a participant is classified according to whether the stated criterion is met. A count of participants with the event and the corresponding denominator can describe the observed frequency. A confidence interval, when reported, communicates statistical uncertainty around an estimated frequency or contrast. The registry record does not report the primary event count, estimate, or interval, so none can be interpreted from this entry.

The endpoint combines two routes: transplantation and continued qualifying LVAS support. In general, composite endpoints can increase the range of events captured by a single outcome, but the components may differ in clinical meaning and frequency. Component-level results can therefore help readers understand what contributes to a composite result. The registry record does not report component counts or explain whether separate component analyses were performed.

What does ITT indicate?

The primary population is described as analyzed by intent to treat. In general, ITT analysis retains participants in the group to which they were originally assigned, regardless of treatment changes, and can preserve comparability created by randomization. This study is not randomized, so that usual protection from random allocation does not apply. The registry record does not explain how ITT was operationalized for this device study, how treatment discontinuation was handled, or how participants with incomplete follow-up were classified. The label should be reported as the registry states it, without assuming details that are not documented.

The population description identifies the first consecutive 194 patients enrolled under the Pivotal Study Protocol (n=133) and CAP (n=61), analyzed when the last subject reached the 1 year followup point on September 14, 2007. The entry does not report separate outcome estimates by protocol or explain whether enrollment into the two protocols involved different eligibility or follow-up procedures. The dates and cohort labels provide context, but do not supply an outcome estimate.

How should uncertainty and significance be read?

In general, a confidence interval expresses uncertainty about an estimated quantity under specified statistical assumptions. A narrower interval indicates greater precision than a wider interval, while the interval's location describes the values compatible with the data and method. A p-value, when reported, measures how surprising data at least as extreme would be under a specified null model; it is not the probability that a treatment works or that the null hypothesis is true. Neither a confidence interval nor a p-value for the primary outcome is reported in the registry record. There is no posted inferential result to interpret.

Statistical significance and clinical importance are distinct concepts. A statistically detectable difference may be small in clinical terms, while an estimate that is imprecise may leave substantial uncertainty. In this record, a treatment contrast is not available because no comparator is identified, and the primary outcome estimate itself is not reported. General discussion of inference cannot fill that information gap.

What is missing from the methods record?

The registry record lists no analysis rows. It does not report the statistical plan, sample-size justification, model specification, handling of missing data, censoring rules, or endpoint adjudication procedures. It also does not state whether subgroup analyses or interim analyses were planned or conducted. These omissions should be treated as missing reporting rather than evidence that a particular method was or was not used. The available methods information supports a clear account of the design and endpoint, but not reconstruction of the analysis.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists survival as the primary outcome and lists secondary outcomes covering clinical reliability, KCCQ, NYHA classification, MLWHF, the six-minute walk test, reoperations, and post-transplant survival. It does not report analysis rows or a statistical analysis plan. The record therefore does not explain which outcomes were tested inferentially, whether a hierarchy was prespecified, or how multiplicity across outcomes was addressed.

In general, testing multiple outcomes can increase the chance of at least one apparently notable result arising by chance if each test is interpreted without accounting for the broader testing context. Methods such as prespecified outcome hierarchies or multiplicity adjustments can address particular forms of this issue. No such method is reported, so it would be inappropriate to assume one was used or to characterize the secondary outcomes as confirmatory.

The primary population is described as an ITT analysis of the first consecutive 194 participants across the Pivotal Study Protocol and CAP. The record does not describe missing-data handling, loss to follow-up, withdrawal, censoring, or how incomplete outcome information was treated. It also does not state whether every participant contributed complete information for every secondary measure. Those are important details because incomplete follow-up can affect both the denominator and interpretation of an observed outcome.

The registry does not report subgroup analyses, protocol-specific outcome estimates, or sensitivity analyses. Their absence from the record does not establish whether such work occurred outside the posted entry. The result is a limited account of analysis populations and missing-data methods: the ITT label and population description are available, but the implementation and robustness of the analysis are not reported in the registry record.

11. 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

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: bleeding (60.3%), cardiac arrhythmias (42.3%), bleeding requiring surgery (28.9%), respiratory failure (27.3%), local infection (23.2%).

The adverse-event entry identifies an HMII group with 194 participants at risk for serious adverse events and 194 participants affected. For other adverse events, it lists 194 at risk and 36 affected. The record describes these figures as counts of participants with an event. It does not provide an analysis comparing these counts with a control group.

The listed serious adverse event terms and percentages are Bleeding, 60.3%; Cardiac arrhythmias, 42.3%; Bleeding requiring surgery, 28.9%; Respiratory failure, 27.3%; Local infection, 23.2%; and Right heart failure, 18.6%. The registry record does not explain the denominator for each percentage or whether participants could be included under more than one term. The categories should not be added together or interpreted as mutually exclusive.

The record does not report a death count in the adverse-event entry. It also does not provide event timing, severity criteria, relatedness assessment, duration, or a comparator rate. The listed counts and terms describe what is recorded, but do not establish that the device caused an event or permit a comparative safety estimate. In general, safety interpretation depends on definitions, follow-up, ascertainment, and the population at risk; several of those details are not reported in the registry record.

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

The record establishes that the study evaluated the HeartMate II LVAS in a non-randomized, single-group setting, with a stated aim of assessing safety and effectiveness as a bridge to cardiac transplantation. It identifies a clinically defined population, a primary survival endpoint, and a primary analysis population described as ITT. It also lists secondary clinical, functional, and quality-of-life outcomes, as well as serious adverse event terms.

The record does not report the observed primary endpoint result. It gives no count of participants meeting the endpoint, no estimated frequency, and no confidence interval or other measure of precision. The entry therefore cannot support a quantitative statement about how often participants survived to transplantation or remained on LVAS support for 180 days while listed at the specified status. A description of the endpoint is not evidence of its observed frequency.

The single-group design also limits what can be concluded about comparative effects. Even if an outcome estimate were available, the design as recorded would not provide a randomized control contrast. The posted information does not show what outcomes would have occurred in a comparable group receiving another approach. It therefore cannot establish that outcomes were better or worse than under an alternative.

Safety counts and percentages identify reported events, but they do not by themselves establish causation or comparative risk. The entry does not explain the percentage denominators, overlap among terms, event timing, or the approach to determining device relatedness. This makes the safety information descriptive rather than a basis for a complete risk comparison.

In general, a clinical study's meaning depends on its design, endpoint definition, analysis, completeness of follow-up, and precision of results. The registry record provides some design and population details, but lacks the primary result and important analysis details. Its contribution is therefore chiefly to document the study question, endpoint, and recorded safety information, while leaving the magnitude and uncertainty of the primary outcome unavailable.

13. Why This Trial Matters Statistically

This study illustrates why design features matter when interpreting device evidence. The registry labels the study non-randomized and single-group, and identifies no comparator. That means any outcome description would concern participants in the study rather than a randomized contrast between treatment strategies. Readers need to distinguish documenting outcomes during device use from estimating what difference the device makes relative to an alternative.

The endpoint also makes clear that outcome definition is part of statistical interpretation. Survival is described through two routes: reaching cardiac transplantation, or remaining on LVAS support for 180 days while listed at UNOS status 1A or 1B. A reader needs the definition to understand what a reported event count would represent. Component results and follow-up details would further clarify how participants met or failed to meet the criterion, but those results are not reported in the registry record.

The entry also demonstrates that a completed study record can still leave major quantitative questions unanswered. Although the registry describes the primary population and the outcome, it does not report the primary endpoint result or its precision. Without those, readers cannot judge the observed outcome frequency from this record. The ITT label alone does not substitute for a result or resolve uncertainty about missing data and analysis implementation.

Finally, safety summaries require careful reading. The record lists participants affected and percentages for serious adverse event terms, yet does not explain the term-specific denominators or category overlap. Those details matter for interpreting whether percentages represent distinct people, repeated events, or overlapping event types. This trial is statistically instructive because it shows how design, endpoint construction, reporting completeness, and safety definitions jointly determine what readers can conclude.

14. 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 primary limitation for interpreting efficacy is that the registry record does not report the primary outcome result. No count, estimated frequency, confidence interval, or test result is available. As a result, the endpoint can be described, but its observed level and precision cannot be assessed from this record.

The non-randomized, single-group design has no identified comparator. It does not support a direct randomized estimate of the difference between the device and another treatment. The registry record also does not report adjustment methods or baseline characteristics that might help describe the enrolled population in more detail. No causal comparison should be inferred from the design information alone.

The primary population includes participants from the Pivotal Study Protocol and CAP, but the entry does not describe protocol-specific outcome results or explain how any differences between cohorts were addressed. Although analysis is labeled ITT, the record does not provide operational details about treatment changes, withdrawals, or incomplete observations. Missing-data methods, follow-up completeness, and censoring rules are not reported.

The endpoint combines transplantation and continued support under specified listing conditions. The record does not provide component-specific counts, adjudication procedures, or further detail on how changes in listing status were handled. These omissions limit assessment of endpoint implementation and of the contribution of each route to the composite definition.

Safety reporting is also incomplete for comparative interpretation. The entry lists affected-participant counts and percentages for serious adverse event terms, but does not specify term-specific denominators, overlap, event timing, relatedness, or a control rate. A death count is not reported in the adverse-event entry. The registry record does not report a statistical analysis plan, sample-size justification, multiplicity approach, or interim-analysis procedures. These limitations concern what is documented in the registry record and should not be taken as proof that a procedure was absent from other study materials.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Thoratec HeartMate II Left Ventricular Assist System (LVAS) for Bridge to Cardiac Transplantation — NCT00121472.
• Registry record last updated 2022-06-27; status last verified 2022-06.
• Results first posted 2013-03-19.
• 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.

18. Record Summary

The record describes a completed, non-randomized, single-group study of the Thoratec HeartMate II LVAS as a bridge to cardiac transplantation. Enrollment is listed as 194, and the primary population is described as the first consecutive 194 participants enrolled under the Pivotal Study Protocol (n=133) and CAP (n=61), analyzed by ITT.

The primary outcome is survival to cardiac transplantation or 180 days on LVAS support while remaining listed for transplantation at UNOS status 1A or 1B. The registry record does not report the primary outcome result, its precision, or analysis details such as missing-data methods. It lists secondary measures involving clinical reliability, quality of life, functional status, reoperations, and post-transplant survival.

Safety information includes participant counts and percentages for serious adverse event terms, but key details about denominators, overlap, and comparative risk are not reported. The design and endpoint are documented; the primary quantitative result is not reported in the registry record.