This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for POWER (Pulse Width Optimized Waveform Evaluation Trial) (NCT00311181), a randomized phase 4 study. The primary outcome is Defibrillation Thresholds (DFTs) (3.5 ms Waveform).
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00311181 |
| Phase | Phase 4 |
| Condition | Sudden Cardiac Death |
| Allocation | Randomized |
| Design model | Single Group |
| Masking | Single |
| Enrollment | 217 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Abbott Medical Devices |
| Results posted | Yes |
2. Clinical Question
Population
The registry record identifies sudden cardiac death as the condition under study and lists enrollment of 217. Eligibility criteria, participant characteristics, and the clinical setting are not reported in the registry record. The record therefore does not establish which enrolled participants were eligible for, or ultimately received, each device or waveform.
Intervention
The intervention is listed as an implantable cardioverter defibrillator (ICD) and cardiac resynchronization therapy defibrillator (CRT-D). The study objective concerns tuned biphasic defibrillation waveforms with membrane time constants of 2.5, 3.5, and 4.5 ms. Details of how a waveform was selected or applied for each participant are not reported in the registry record.
Comparator
The intended comparison is among the 2.5, 3.5, and 4.5 ms waveforms. The record labels the study model single-group and gives one arm description containing all three waveform durations. Separate arm descriptions and arm-specific outcome values are not reported in the registry record.
Primary question
The primary outcome is the defibrillation threshold for the 3.5 ms waveform, measured in volts at implant and expressed as a mean with standard error. The broader study objective also refers to comparing upper limits of vulnerability and defibrillation thresholds across the three waveform durations. Numerical results for the primary outcome and the broader comparison are not reported in the registry record.
3. Trial Design
The registry record identifies POWER as a Phase 4 study with randomized allocation and single masking. It lists the study model as single-group, enrollment of 217, and status as completed. These labels do not, by themselves, explain how randomization was implemented or how the study’s single-group model relates to the intended comparison among waveform settings. Those design details are not reported in the registry record.
The stated objective is to compare upper limits of vulnerability and defibrillation threshold efficacy for biphasic waveforms based on membrane time constants of 2.5, 3.5, and 4.5 ms, with the aim of identifying an optimal time constant for a tuned waveform. The listed device intervention is an implantable cardioverter defibrillator (ICD) and cardiac resynchronization therapy defibrillator (CRT-D). The arm description names the three waveform durations together rather than describing separate groups.
The record gives a start date of 2006-08 and a primary completion date of 2008-04. It does not describe the allocation sequence, masking procedures, treatment assignment, follow-up procedures, or the criteria used to determine completion. The available design labels should therefore be read as registry classifications, not as a complete protocol description. Although the study is described as randomized, the exact comparison structure cannot be reconstructed from the arm information recorded.
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
| Stage | Group 1 |
|---|---|
| STARTED | 217 |
| COMPLETED | 121 |
| NOT COMPLETED | 96 |
Reasons for not completing this period:
| Reason | Group 1 |
|---|---|
| Final DFTs were not obtained | 96 |
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.
| Characteristic | Unit | Group 1 |
|---|---|---|
| Participants analysed | 217 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 88 |
| Age, Categorical: >=65 years | Participants | 129 |
| Age, Continuous | years | 67 (SD 14) |
| Sex: Female, Male: Female | Participants | 57 |
| Sex: Female, Male: Male | Participants | 160 |
| Region of Enrollment: United States | participants | 217 |
6. Primary Endpoint
The registry lists the primary outcome as Defibrillation Thresholds (DFTs) (3.5 ms Waveform), measured over Implant.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Error |
| Unit | Volts |
| Endpoint classification | Continuous Endpoint |
The primary outcome is titled Defibrillation Thresholds (DFTs) (3.5 ms Waveform). It is measured in volts at implant, and its stated summary measure is the mean with standard error. A defibrillation threshold is a measure of the voltage associated with defibrillation under the study’s assessment procedure. In general, such a measure can characterize device waveform performance under specified testing conditions; it is not, by itself, a measure of long-term clinical outcomes.
The registry record does not define the operational method for measuring the threshold, describe how repeated measurements were handled, or give the population included in the endpoint analysis. It also does not report the mean, standard error, confidence interval, or a comparison estimate. As a result, the endpoint’s numerical magnitude and precision cannot be assessed from the registry record.
The objective mentions both upper limit of vulnerability and defibrillation threshold, while the named primary outcome specifically identifies the DFT for the 3.5 ms waveform. The record does not explain how the broader objective relates to this primary measure. No conclusions about differences among waveform settings can be drawn from the endpoint title alone.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record establishes the study’s stated comparison and identifies a primary outcome, but it does not report numerical primary outcome results. It names the mean DFT for the 3.5 ms waveform, in volts, at implant, with standard error as the dispersion measure. Without the mean or its uncertainty, the magnitude and precision of that result cannot be evaluated. Numerical comparisons between the 2.5, 3.5, and 4.5 ms waveforms are also not reported in the registry record.
The record labels allocation as randomized, but the model is listed as single-group and the arm description combines all three waveform durations. There are no separate arm-level outcome values in the registry information described. Therefore, the intended comparison should not be mistaken for a reported randomized contrast. The actual allocation structure, analysis population, and statistical model are not reported in the registry record.
In general, an estimate describes the observed magnitude of an outcome, while an uncertainty measure indicates how precisely that estimate has been determined. A standard error describes uncertainty around an estimated mean under a statistical model; it is not the spread of individual measurements. A confidence interval, if reported, would give a range of values compatible with the data and assumptions. No standard error value or confidence interval is reported for this primary endpoint, so precision cannot be judged.
The registry record gives enrollment of 217, but that figure does not establish how many participants contributed data to the primary endpoint or to any particular analysis. The analysis population and endpoint-specific denominators are not reported in the registry record. The outcome record lists three outcome measures, while the available information does not give numerical results for the primary endpoint. The record also indicates zero analyses. These omissions limit assessment of the study’s findings, rather than demonstrating that a particular result was absent in the underlying study.
The record’s completed status and its listed primary completion date of 2008-04 describe the registry’s administrative information. They do not supply an effect estimate or determine whether the waveform comparison favored one setting. Statistical interpretation must therefore remain limited to the design description, outcome definition, and safety counts that are actually recorded.
9. Statistical Methods Explained
The primary outcome is a continuous measure summarized by a mean. In general, a mean describes the central value of measurements on a numerical scale. Here the stated unit is volts and the measurement is the defibrillation threshold for the 3.5 ms waveform at implant. The registry record does not provide the observed mean, so its value cannot be interpreted or compared with any other waveform setting.
What does the standard error describe?
In general, the standard error describes the statistical uncertainty of an estimated quantity, such as a sample mean. It is different from the standard deviation, which describes variability among individual observations. A small standard error can indicate a more precise estimate under the assumptions used, but it does not establish that the estimate is clinically important or free from bias. The registry record specifies standard error as the dispersion measure but gives no numerical standard error for the primary outcome.
In general, confidence intervals combine an estimate and its uncertainty to show a range of values compatible with the data under specified assumptions. A confidence interval can help readers assess both precision and which effect sizes remain plausible. No confidence interval or confidence level for the primary endpoint is reported in the registry record. Without an estimate and its uncertainty, the strength of evidence for a difference cannot be assessed.
What can be inferred about comparisons?
The study objective describes a comparison among the 2.5, 3.5, and 4.5 ms waveform durations. A statistical comparison requires a clearly specified contrast and outcome data for the relevant groups or conditions. The record labels allocation randomized, but it labels the model single-group and gives one arm description containing the three waveform durations. Separate group estimates, contrast estimates, and a statistical model are not reported in the registry record. Consequently, a reader cannot reconstruct a comparison or independently evaluate its uncertainty.
In general, randomization can reduce systematic differences between groups when assignment is properly implemented and analyzed. The randomized label alone does not disclose the allocation procedure, whether assignment was concealed, or how any within-participant measurements were handled. Those details are not reported in the registry record. It would be inappropriate to infer the analysis structure from the label alone.
What do planning assumptions mean?
The registry record describes sample-size calculations as planning illustrations based on an observed effect, not as the trial’s own design. It states assumptions of a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. These assumptions describe an illustrative planning framework, not evidence that the trial used those choices when it was designed or analyzed.
In general, a planning calculation estimates the amount of information that might be needed to detect a specified effect under stated assumptions. Its result depends on those assumptions and on the effect used as the planning target. It is not a measure of the probability that an already completed trial found a true effect. Such calculations should not be described as observed power. The record notes a skip because the primary outcome has fewer than two arms. No numerical planning results are reported in the registry record, so no sample-size illustration can be evaluated from the recorded information.
Why can measurement structure matter?
In general, repeated measurements or measurements taken under more than one condition on the same participant may be statistically related. Analyses need to account for that dependence; treating related observations as independent can make uncertainty estimates misleading. The registry record does not explain whether waveform measurements were repeated within participants or how dependence was modeled. This is a methodological question, not evidence that the analysis was conducted incorrectly.
In general, continuous outcomes can also have skewed distributions, outlying values, or unequal variability across conditions. A mean-based analysis may require assumptions about the distribution and the structure of variability. The registry record does not describe diagnostic checks, transformations, robust methods, or other distributional decisions. No claims about those aspects of the analysis can be made without the analysis plan or numerical results.
10. Confidence Intervals for Each Arm
No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.
| Arm | Participants | Mean | Standard deviation | 95% CI for the mean |
|---|---|---|---|---|
| Group 1 | 121 | 427.000 | 121.000 | 405.221 to 448.779 |
R code and output
arm <- c("Group 1")
n <- c(121)
m <- c(427)
sp <- c(11)
sd <- sp * sqrt(n) # standard errors converted to SDs
for (i in seq_along(n)) {
se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}
CARM Group 1 121 427.000 121.000 405.221 448.77911. Multiplicity, Missing Data and Analysis Populations
The study objective refers to comparisons across three waveform durations, and the registry record lists three outcome measures. When a study evaluates multiple outcomes or multiple contrasts, the chance of a misleading finding can increase if each is tested without an appropriate strategy. In general, multiplicity methods specify how the analysis will address that issue, for example by prioritizing an outcome or adjusting inference across comparisons. The multiplicity strategy is not reported in the registry record.
The record identifies one primary endpoint, the DFT for the 3.5 ms waveform, but does not describe the statistical hierarchy among the stated objective, the primary outcome, and the other outcome measures. It does not report which contrasts were planned, whether the three waveform settings were compared pairwise, or how any additional analyses were treated. The number of analyses is recorded as zero. The registry record therefore does not allow assessment of the analysis plan or the handling of multiple comparisons.
Missing-data procedures and analysis populations are also not reported in the registry record. The enrollment figure does not reveal how many participants had an endpoint measurement, whether any measurements were excluded, or how missing observations were handled. In general, missing-data methods matter because conclusions can depend on why data are missing and on the assumptions used to address them. No such assumptions or procedures are described in the available record. These omissions do not establish that data were missing; they mean that the registry record does not document how this issue was managed.
12. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Group 1 | 0 | 217 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Group 1 | 0 of 217 |
The safety entries list Group 1 with 217 at risk and 0 affected for serious events. The other-event entry also lists 217 at risk and 0 affected. No serious adverse event terms are listed. Deaths are not reported in the registry record.
These entries describe the counts recorded in the registry; they do not establish that no event occurred outside the recorded categories or observation period. The registry record does not provide event definitions, the safety observation period, methods for collecting events, or information about how the at-risk counts were determined. It also does not report whether participants had different exposure to the waveform settings or devices.
In general, a zero count in a registry entry means that no affected participants were recorded for that entry. It does not prove that an event is impossible or that the safety profile is fully characterized. Interpretation depends on the completeness of reporting, the definitions used, and the amount and duration of observation. The available safety counts should therefore be read narrowly, without inferring broader safety conclusions.
13. What the Result Does, and Does Not, Mean
The registry record gives a clinical and statistical outline of a Phase 4 study intended to compare waveform settings based on membrane time constants of 2.5, 3.5, and 4.5 ms. It identifies a primary outcome: mean defibrillation threshold for the 3.5 ms waveform, in volts, at implant. It also records randomized allocation, single masking, a single-group model, and enrollment of 217. Those details describe the registered study, but they do not provide its outcome findings.
Most importantly, the numerical primary endpoint result and the estimates for comparisons among waveform settings are not reported in the registry record. There is no reported mean, standard error, confidence interval, or statistical test for the primary outcome. Accordingly, the recorded information does not show the size, direction, or precision of a waveform difference. It cannot support a conclusion that one setting performed better or worse than another.
In general, a defibrillation threshold is a measure of device-related performance under the study’s measurement procedure. It is not automatically equivalent to a long-term clinical outcome. The registry record does not define the measurement procedure in enough detail to evaluate that link, nor does it report clinical outcomes that would permit one. The study’s stated objective should therefore be distinguished from evidence about clinical benefit.
The serious and other event entries each record zero affected participants, with 217 at risk; deaths are not reported. These entries do not resolve the missing efficacy results and do not establish a complete safety profile. The registry record supports description of the research question, design labels, endpoint definition, and recorded event counts. It does not support a treatment recommendation or a conclusion about comparative efficacy.
14. Why This Trial Matters Statistically
This trial is statistically notable because its registry record combines an intended comparison among three waveform durations with a single-group model and a single arm description. That combination makes it important to distinguish the research objective from the analysis structure actually documented. Randomized allocation is recorded, but the record does not explain how randomization maps onto the waveform comparison or how measurements were analyzed.
The endpoint also highlights the importance of reporting both an estimate and its uncertainty. Naming a mean DFT and its standard error identifies the intended summary, but without numerical values, readers cannot assess the effect size or its precision. In general, uncertainty is essential to interpreting a continuous outcome; a point estimate alone would not show how much the estimate may vary across plausible samples.
The registry record additionally illustrates the limits of interpreting a study from administrative and outcome labels alone. Completed status and enrollment are not substitutes for results, and a zero recorded event count is not a complete safety assessment. The record’s planning note distinguishes illustrative sample-size calculations from the original trial design, a useful distinction because hypothetical planning scenarios should not be mistaken for the study’s observed evidence.
For statisticians and clinical researchers, the main lesson is to examine whether the intended contrast, endpoint, analysis population, uncertainty estimates, and multiplicity strategy are all reported. Several of these details are not reported in the registry record. That absence limits independent statistical appraisal, even though the clinical question and primary outcome are identifiable.
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 available registry information has substantial limitations for evaluating the trial’s findings. Numerical results for the primary endpoint are not reported in the registry record. The record also does not report separate estimates for the 2.5, 3.5, and 4.5 ms waveform settings, or an estimate of the difference between them. Without these values and their uncertainty, the magnitude and precision of any comparison cannot be assessed.
The design description is not sufficiently detailed to reconstruct the analysis. Randomized allocation is recorded, while the model is listed as single-group and the sole arm description names all three waveform durations. The allocation procedure, waveform assignment, measurement sequence, and handling of repeated or related measurements are not reported in the registry record. Participant eligibility and baseline characteristics are also not reported.
The primary outcome is identified as a mean DFT for the 3.5 ms waveform at implant, with standard error as the dispersion measure. The measurement procedure, endpoint-specific analysis population, denominator, missing-data handling, and statistical model are not reported. The registry record lists three outcome measures but does not describe a multiplicity strategy or provide numerical results for the other measures.
Safety reporting is limited to the recorded event counts and does not include event definitions, observation duration, or death counts. The planning assumptions are described as illustrations rather than the trial’s design, and no numerical planning results are reported in the registry record. These reporting limitations prevent a full assessment of efficacy, precision, analysis choices, and safety; they should not be taken as proof that the underlying study lacked such information.
16. Related Tutorials
17. Related Statistical Calculators
18. Sources
- ClinicalTrials.gov: POWER (Pulse Width Optimized Waveform Evaluation Trial) — NCT00311181.
- Registry record last updated 2019-02-20; status last verified 2019-02.
- Results first posted 2012-08-30.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
19. Record Summary
POWER is recorded as a completed Phase 4 study with randomized allocation and single masking. Its model is listed as single-group, enrollment is 217, and the stated objective is to compare biphasic defibrillation waveforms based on membrane time constants of 2.5, 3.5, and 4.5 ms. The registry record lists an implantable cardioverter defibrillator and cardiac resynchronization therapy defibrillator as the device intervention.
The primary outcome is mean defibrillation threshold for the 3.5 ms waveform, measured in volts at implant, with standard error as the dispersion measure. Numerical primary results and waveform comparison estimates are not reported in the registry record. The serious-event and other-event entries each record 0 affected participants and 217 at risk; deaths are not reported. The record does not describe the analysis population, missing-data approach, or multiplicity strategy.