FAST (Fluid Accumulation Status Trial): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for FAST (Fluid Accumulation Status Trial) (NCT00289276), a non-randomized na study. The primary outcome is Number of Subjects With at Least 30 Days of Daily Impedance Measurements.

2. Clinical Question

In broad terms, FAST was intended to collect information about fluid build-up in the chest among people with heart failure. Its secondary outcomes concerned changes in thoracic impedance associated with hospitalization or outpatient treatment for worsening heart failure, as well as adverse events. The record lists four outcome measures, but the primary outcome count and results for the secondary outcomes are not reported in the registry record. This leaves the clinical question framed by the monitoring purpose and outcomes, rather than by a posted estimate of how often the primary endpoint was met or how impedance changed around clinical events.

3. Trial Design

FAST (Fluid Accumulation Status Trial) is registered as a completed, non-randomized, double-masked, single-group device study. The registry lists an enrollment of 156 and identifies Medtronic Cardiac Rhythm and Heart Failure as the sponsor. The record gives a start date of 2003-11 and a primary completion date of 2008-04. Its phase is listed as NA.

The intervention is Fluid Status Monitoring (OptiVol™). The registry’s summary describes using very low electrical pulses across the chest cavity to assess resistance, with the resulting thoracic impedance used as an indicator of fluid level in the chest. The stated purpose was to collect information related to fluid build-up in people with heart failure.

Although the study is classified as single-group, the safety results are separated into FAST Pivotal and FAST Expansion. The record does not describe these as randomized groups or specify a control condition. The listed group labels therefore do not establish a comparative treatment design. The study’s non-randomized allocation means that comparisons between those labeled groups, if made, would not have the protection against confounding that random assignment can provide.

The primary outcome concerns the number of participants with at least 30 days of daily impedance measurements, with a timeframe of up to 36 months. The registry description says these measurements were presented graphically over time alongside clinical events. The outcome count itself is not reported in the registry record. There are no posted analysis entries, and the record does not describe the detailed statistical plan, eligibility criteria, or how follow-up and missing measurements were handled.

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: None of the subjects in FAST Pivotal were included in FAST Expansion.

First Part of FAST Study (Pivotal)

Second Part of FAST Study (Expansion)

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Includes all enrolled participants.

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 Subjects With at Least 30 Days of Daily Impedance Measurements, measured over Up to 36 months..

The primary endpoint is titled “Number of Subjects With at Least 30 Days of Daily Impedance Measurements.” It is a count of participants meeting a data-availability and follow-up criterion, rather than a direct measure of heart-failure severity or a comparison of clinical outcomes. The specified timeframe is up to 36 months.

The registry description explains why this endpoint is relevant to the monitoring purpose: impedance measurements were presented over time in relation to clinical events for participants with at least 30 days of follow-up and impedance data collected during follow-up. A record of measurement availability indicates whether the monitoring data were available over a minimum period for that type of temporal description. It does not, by itself, show that the monitoring predicts or changes clinical events.

The population is described as including all enrolled participants. However, the count meeting the endpoint is not reported in the registry record. The record also does not give a numerator and denominator for a proportion, a measure of variation, or an estimate of uncertainty. Consequently, the endpoint’s observed frequency and precision cannot be assessed from the posted registry information. The secondary outcome descriptions refer to changes in impedance associated with heart-failure hospitalization or outpatient treatment, but their results are not reported in the registry record either.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a count: the number of participants who met a stated measurement-duration criterion. Counts answer how many participants experienced or met a defined condition. They are not automatically rates or proportions. To express the count as a proportion, the relevant denominator and its definition must also be available. Although the primary population is described as all enrolled participants, the count meeting the endpoint is not reported in the registry record, so neither the count nor a corresponding proportion can be evaluated.

The endpoint combines follow-up duration with data availability. A participant must have at least 30 days of daily impedance measurements under the endpoint definition. That makes the outcome partly a description of whether sufficient monitoring information was collected, rather than a clinical event outcome. General statistical interpretation: data-availability endpoints can help readers understand whether a study has enough repeated measurements to describe patterns over time. They do not establish that a measurement pattern is clinically predictive, nor that monitoring alters clinical outcomes.

The registry says measurements were presented graphically over time in relation to clinical events. General explanation: repeated measurements can be examined alongside event timing to describe whether values change around events. Such a description is not automatically a causal analysis. Timing, participant characteristics, event definitions, and measurement completeness can all affect an apparent pattern. The record does not report the methods used to estimate changes or associations, or the corresponding numerical results.

Over-dispersion is a general issue for count data when observed variability is greater than a simple count model would expect. If present, it can make standard errors from an overly restrictive model too small and confidence intervals too narrow. The FAST record does not report a count model, an over-dispersion assessment, or a model-based estimate for its primary endpoint. It is therefore not possible to say whether over-dispersion was relevant to the analysis. This general consideration should not be mistaken for a description of a method used in FAST.

A confidence interval is a statistical range expressing uncertainty around an estimate under the assumptions of the method used. A narrow interval generally indicates more precise estimation than a wide interval, while neither width nor location alone establishes clinical importance. No confidence interval for the primary endpoint or secondary outcome results is reported in the registry record. Without an estimate and an interval, the precision of those outcomes cannot be assessed.

The registry classifies the study as non-randomized and single-group. General explanation: random allocation is used to make comparison groups more similar, on average, with respect to measured and unmeasured characteristics. In a non-randomized study, differences between groups can reflect differences in who entered each group, their care, or their follow-up, as well as any intervention-related effects. Here the labeled FAST Pivotal and FAST Expansion groups do not create a randomized control comparison. Their safety counts should therefore be interpreted descriptively.

The planning illustration described in the record is separate from the study’s observed outcomes and from its original design justification. It is based on an observed effect and specifies a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation; the effect to detect is a stated fraction of the observed effect. The record does not report the trial’s own sample-size justification or enough outcome information to evaluate a recalculation. Any such planning values are illustrations for future planning, not observed power and not evidence of an effect in FAST.

For time-to-event planning, the stated illustration uses the total number of events under the Schoenfeld approach. For other outcome types, it gives participants per arm. General explanation: time-to-event planning is often driven by the number of outcome events because events supply information about the contrast of interest; the number of participants needed also depends on design assumptions and follow-up. These are general principles, not additional descriptions of FAST’s analysis. The registry does not report a statistical analysis plan, interim analysis methods, adjusted estimates, or the procedures used to handle repeated measurements.

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("FAST Pivotal", "FAST Expansion")
n      <- c(47, 109)
events <- c(47, 106)
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  FAST Pivotal  47  47  100.0  92.5  100.0  92.4  100.0  92.6  99.9
ARM  FAST Expansion  109  106  97.2  92.2  99.4  92.2  99.1  92.2  99.0

11. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary outcome and secondary outcomes concerning impedance changes associated with hospitalization or outpatient treatment for a heart-failure exacerbation, along with adverse events. When a study examines multiple outcomes, the chance of at least one apparently notable result can increase if each is tested separately without accounting for the multiplicity. General approaches can include specifying a hierarchy of outcomes, adjusting inference, or treating secondary analyses as exploratory. The registry record does not report whether any such approach was planned or used.

The record lists 0 analyses. This indicates that no analysis entries are posted in the registry, but it does not establish that analyses were not performed. No methods for repeated measurements, covariate adjustment, subgroup analyses, or handling of multiple testing are reported in the registry record. There is no posted statistical plan from which to assess whether analyses followed a prespecified hierarchy.

The primary endpoint requires at least 30 days of daily impedance measurements. Participants who do not meet that criterion may differ in follow-up or measurement availability, but the record does not report how such cases were handled in outcome analyses. It does not give missing-measurement counts, reasons for missingness, imputation methods, or sensitivity analyses. General explanation: missing data can affect estimates when the likelihood of missingness is related to participant characteristics or outcomes. Without details on completeness and handling, readers cannot determine whether the observed measurement data represent the intended population.

The primary population is described as all enrolled participants, but the endpoint is restricted by its measurement criterion. The record does not further explain the analysis population for secondary outcomes or safety summaries. It also does not report whether participants contributed data for the full stated timeframe. These omissions limit assessment of the analysis population and the potential influence of incomplete follow-up.

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

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: other: marquis battery field action (29.8%), other: battery at elective replacement indicator (26.6%), heart failure decompensation (25.7%), premature battery failure (10.6%), renal failure (9.2%).

The safety record reports serious adverse event figures for two labeled groups. FAST Pivotal lists 47 participants at risk and 33 affected by a serious adverse event. FAST Expansion lists 109 at risk and 76 affected. These figures describe participants with an event in each group as recorded; they do not indicate event rates over a specified person-time period, and the registry does not provide a comparative statistical analysis.

The record also lists percentages for selected serious adverse event terms: Other: Marquis Battery Field Action, 29.8%; Other: Battery at Elective Replacement Indicator, 26.6%; Heart Failure Decompensation, 25.7%; Premature Battery Failure, 10.6%; Renal Failure, 9.2%; and Chest Pain/Angina Pectoris, 5.5%. The denominators and calculation methods for these percentages are not reported in the registry record. The percentages should not be treated as risks without that information.

The group labels do not make the figures a randomized comparison. The record does not report whether the groups had comparable follow-up or participant characteristics, and it gives no deaths value. These descriptive safety figures do not establish that the device caused an event or that the groups differed because of the monitoring intervention.

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

FAST’s registry record is informative about the study’s purpose and how its primary outcome was defined. It describes a device-based method for monitoring thoracic impedance as an indicator of fluid level in the chest, and it sets the primary endpoint around the availability of daily measurements for at least 30 days. The record also identifies clinical events around which impedance changes were of interest.

However, the primary outcome count is not reported in the registry record. Nor are numerical results for the secondary impedance outcomes. As a result, the posted information does not quantify whether the measurement criterion was met, what changes in impedance were observed, or how precisely any association with clinical events was estimated. A completed study status is not a substitute for outcome data.

The safety figures provide descriptive counts in the FAST Pivotal and FAST Expansion groups and percentages for selected event terms. Since allocation was non-randomized and no like-for-like control comparison is described, these summaries cannot isolate a causal effect. The posted figures also lack details about follow-up and the denominators for the listed term percentages. They should be interpreted as registry summaries rather than comparative estimates.

General statistical interpretation: a monitoring measure may be useful to study because it can be collected repeatedly and related to clinical events. Establishing whether it predicts events or changes outcomes requires appropriate outcome definitions, complete data, and analyses that account for the study design and uncertainty. The registry record does not provide those results or enough methods detail to evaluate them. The appropriate conclusion is therefore limited: FAST studied thoracic impedance monitoring and defined relevant outcomes, but the posted record does not establish the magnitude or precision of the primary or secondary results.

14. Why This Trial Matters Statistically

FAST is statistically notable because its main endpoint concerns measurement availability in a device-monitoring study. Before interpreting repeated measurements in relation to clinical events, it matters whether participants have enough follow-up and impedance data to describe those patterns. The endpoint’s minimum of 30 days makes this aspect explicit, while the stated timeframe extends up to 36 months.

The record also illustrates why a stated outcome and a reported result are not interchangeable. The primary endpoint is clearly named, and the description explains how measurements were intended to relate to clinical events, yet the endpoint count is absent. Without the count and an uncertainty estimate, readers cannot assess how often the criterion was met or how precisely it was estimated. The secondary outcome descriptions similarly indicate questions of interest without supplying their numerical answers.

The non-randomized, single-group classification is important for interpreting the separate FAST Pivotal and FAST Expansion safety summaries. Group labels and counts can describe what the registry records, but they do not create an unbiased comparative design. General statistical reasoning cautions against attributing a difference between non-randomized groups to an intervention without accounting for group composition, follow-up, and other potential explanations.

Finally, the record separates the idea of future sample-size planning from evidence about the completed study. Planning illustrations based on an observed effect and specified assumptions are not observed power and cannot replace outcome estimates. Taken together, the study highlights the importance of reporting outcome values, uncertainty, analysis methods, and missing-data handling alongside a clearly stated monitoring question.

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 direct limitation of the registry record is that it does not report the primary endpoint count. The outcome is defined as the number of participants with at least 30 days of daily impedance measurements, but the observed value and its uncertainty are absent. Results for the described secondary impedance outcomes are also not reported in the registry record. This prevents quantitative assessment of the study’s main monitoring question.

The study is classified as non-randomized and single-group. The record does not describe a randomized control group, and the FAST Pivotal and FAST Expansion safety labels should not be treated as evidence of randomized allocation. Any comparison across these labels would be vulnerable to differences in participant characteristics, follow-up, and other factors not accounted for in a like-for-like design.

The registry gives limited information about the outcome analyses. It lists 0 analyses, but does not say whether analyses were performed outside the registry. The record does not report model specifications, uncertainty estimates, adjustments, handling of repeated measurements, or procedures for multiple outcomes. It also does not describe missingness in daily impedance measurements or how incomplete follow-up was addressed.

The safety summaries lack further context about event ascertainment and follow-up duration. The denominator and calculation method for the listed serious adverse event term percentages are not reported in the registry record, and no deaths value is listed. The primary population is described as all enrolled participants, but details about the populations contributing to each secondary outcome are not reported. These limitations constrain both the interpretation of the safety summaries and the assessment of how representative the reported information is.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: FAST (Fluid Accumulation Status Trial) — NCT00289276.
• Registry record last updated 2010-10-13; status last verified 2010-10.
• Results first posted 2010-09-28.
• 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

FAST is a completed, non-randomized, double-masked, single-group device study sponsored by Medtronic Cardiac Rhythm and Heart Failure. The registry lists enrollment of 156, a start date of 2003-11, and a primary completion date of 2008-04. The intervention was Fluid Status Monitoring (OptiVol™), intended to collect information about fluid build-up in the chest among people with heart failure.

The primary endpoint was the number of participants with at least 30 days of daily impedance measurements, with a timeframe of up to 36 months. The endpoint count and numerical results for the described secondary outcomes are not reported in the registry record. Safety summaries are listed for FAST Pivotal and FAST Expansion, but the groups do not constitute a randomized comparison. The registry lists 0 analyses and does not report a detailed statistical plan, missing-data methods, or uncertainty estimates.