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 Detect Fluid Early From Intra-thoracic Impedance Monitoring (NCT00916929), a non-randomized na study. The primary outcome is False Positive Rate.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00916929 |
| Phase | NA |
| Condition | Heart Failure |
| Allocation | Non-Randomized |
| Design model | Parallel |
| Masking | Triple |
| Enrollment | 162 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Abbott Medical Devices |
| Results posted | Yes |
2. Clinical Question
Population
People with heart failure who participated in the study and received an eligible cardiac device. The registry reports an enrollment of 162. Its primary-outcome description says that all participating patients were included in the analysis, with 82 patients in each arm. It also describes two patients who moved from the ICD cohort to the CRT-D cohort when their devices were upgraded.
Intervention
The intervention was the Impedance Monitoring Feature in a St Jude Medical cardiac device. The registry describes use of this feature in both an Implantable Cardioverter Defibrillator (ICD) and a Cardiac Resynchronization Therapy (CRT-D) device.
Comparator
The registry lists ICD and CRT-D device groups. This was a non-randomized study, and the registry explicitly cautions that the arms are not a like-for-like control comparison. Device group therefore should not be treated as a randomly assigned intervention-versus-control contrast.
Primary question
The primary endpoint was the number of departures from the device’s programmed threshold that were unrelated to a heart failure event, over a 6-month timeframe. The registry’s stated criterion is that the false-positive rate per patient year of follow-up should be less than 1.5. The numerical rate and its confidence interval are not reported in the registry record, so whether the observed result met that criterion cannot be determined from the posted record.
3. Trial Design
This completed study, NCT00916929, evaluated the Impedance Monitoring Feature in cardiac devices. The registry lists heart failure as the condition, Abbott Medical Devices as the sponsor, and the study intervention as a device feature. The study began in 2009-05, with primary completion in 2011-02. The phase is listed as NA.
The design is described as non-randomized, triple-masked, and parallel. Non-randomized means that the registry does not describe assignment to device groups by random allocation. The record does not explain how participants entered the ICD or CRT-D groups, nor does it give further details about what the triple masking involved. These details are not reported in the registry record.
The two device descriptions are an ICD with the Impedance Monitoring Feature and a CRT-D device with the same feature. The primary-outcome description states that all participating patients were included in the analysis, with 82 patients in each arm. It also states that two patients implanted with ICD were upgraded to CRT-D, censored from the ICD cohort, and included in the CRT-D cohort from the time of upgrade, based on as-treat. The record does not provide further detail about the timing or implementation of this handling.
The registry’s enrollment is 162. The primary-outcome population description and safety groups give their own group counts, but the record does not reconcile these counts with the enrollment figure. The study has a secondary outcome of sensitivity. The eligibility criteria, recruitment procedures, sample-size justification, and detailed protocol 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.
Overall Study
| Stage | Implantable Cardioverter Defibrillator (ICD) Device | Cardiac Resynchronization Therapy (CRT-D) Device |
|---|---|---|
| STARTED | 80 | 82 |
| COMPLETED | 70 | 53 |
| NOT COMPLETED | 10 | 29 |
Reasons for not completing this period:
| Reason | Implantable Cardioverter Defibrillator (ICD) Device | Cardiac Resynchronization Therapy (CRT-D) Device |
|---|---|---|
| Lost to Follow-up | 1 | 3 |
| Death | 5 | 10 |
| Withdrawal by Subject | 1 | 5 |
| Left ventricular epicardial lead | 1 | 2 |
| Transferred to hospice care | 1 | 1 |
| System explant | 1 | 0 |
| Moved to another state | 0 | 1 |
| Device unable to process impedance data | 0 | 7 |
Analysis population for the primary outcome, as defined in the registry: All patients participating in the study were included in the analysis with a total of 82 patients in each arm. Of the 82 patients implanted with ICD, 2 were upgraded to CRT-D. These 2 patients were censored from the ICD cohort and included in the CRT-D cohort at the time of upgrade based on as-treated analysis principle resulting.
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 | ICD Device | CRT-D Device | Total |
|---|---|---|---|---|
| Participants analysed | 80 | 82 | 162 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 44 | 36 | 80 |
| Age, Categorical: >=65 years | Participants | 36 | 46 | 82 |
| Age, Continuous | years | 61 (SD 14) | 66 (SD 13) | 64 (SD 13) |
| Sex: Female, Male: Female | Participants | 32 | 13 | 45 |
| Sex: Female, Male: Male | Participants | 48 | 69 | 117 |
| Region of Enrollment: United States | participants | 80 | 82 | 162 |
6. Primary Endpoint
The registry lists the primary outcome as False Positive Rate, measured over 6-months.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | 95% Confidence Interval |
| Unit | departures from device threshold |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is titled “False Positive Rate.” It is defined as the number of departures from the device’s programmed threshold that are unrelated to a heart failure event. The stated timeframe is 6-months, and the unit is departures from device threshold. The registry describes the intended benchmark as a false-positive rate per patient year of follow-up that should be less than 1.5.
This endpoint addresses how often the monitoring feature generates a threshold departure that is not associated with a heart failure event. Such departures matter when interpreting monitoring because an alert that does not correspond to the event of interest can affect how useful the signal is as an indicator. This is a general explanation of why false-positive measures are used; it does not establish how the study operationalized events beyond the registry’s definition.
The record identifies a 95% confidence interval as the dispersion measure, but does not report the endpoint’s numerical result or interval limits. It also does not give the number of departures, patient-years of follow-up, or the detailed calculation used to obtain a rate per patient year. Consequently, the stated benchmark is a criterion, not evidence that the observed result was above or below it.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry identifies the primary outcome and the criterion against which the false-positive rate was intended to be considered. It does not post the numerical false-positive rate or its 95% confidence interval. Without those values, the posted results do not show the magnitude of the rate, its precision, or whether the stated criterion of less than 1.5 per patient year was met. The endpoint description alone cannot answer those questions.
A confidence interval communicates the range of values reasonably compatible with the observed data under the method used to calculate it. This is a general statistical explanation. A narrower interval generally indicates greater precision than a wider one, but the registry record gives no interval limits to interpret. It also does not state the confidence-interval method or provide the event and follow-up data needed to independently assess the estimate.
The study compares groups defined by device type, but the allocation is non-randomized. The registry cautions that the arms are not a like-for-like control comparison. Differences between the groups, if reported, would therefore not by themselves establish that the device type caused those differences. The record does not report adjusted or causal analyses that would address group differences.
The primary-outcome description says that two patients who began in the ICD cohort were censored from that cohort and included in the CRT-D cohort from the time of upgrade. This is a recorded feature of the analysis population, but the registry does not give enough detail to assess how the approach affected follow-up or the endpoint estimate. The safety groups also list different at-risk counts by device group; those counts should be read as the registry’s safety figures, not substituted for the primary-outcome results.
Sensitivity is listed as a secondary outcome, and the record reports two outcome measures and two analyses. Numerical sensitivity findings, analysis specifications, and any additional outcome results are not reported in the registry record. No conclusion about the feature’s effectiveness, overall performance, or clinical impact can be drawn from the endpoint description and group counts alone. The study’s brief summary states an objective to demonstrate safety and effectiveness, but an objective is not a result.
Any sample-size estimates accompanying the analysis are planning illustrations based on the observed effect, not observed power and not evidence of the study’s findings. The registry record does not report its own sample-size justification. Such illustrations should not be used to fill the gap left by absent endpoint estimates or confidence intervals.
9. Statistical Methods Explained
The central statistical issue is that the primary outcome is a count of threshold departures defined as unrelated to a heart failure event, while the registry states a rate per patient year as the criterion of interest. A count describes how many events occurred; a rate places events in the context of time under observation. This is a general distinction. The record does not provide the actual count, patient-years, or calculation details, so the rate cannot be reconstructed from the registry entry.
What does a confidence interval add?
The registry lists a 95% confidence interval for the primary endpoint. In general, a confidence interval expresses uncertainty around an estimate: it indicates which values are compatible with the data and the calculation method under the stated confidence procedure. It is not a guarantee that the true value lies within the reported limits, and it does not by itself establish that a criterion was met. Here, the numerical estimate and interval bounds are not reported in the registry record. The method used to form the interval is also not reported, so its assumptions and suitability cannot be evaluated.
Why does follow-up time matter for a rate?
When event counts are expressed per patient year, the amount of observed time contributes to the denominator. Participants may contribute different amounts of follow-up, particularly when observation ends or a cohort assignment changes. This is a general explanation of rate analysis, not a claim about the individual follow-up durations in this study. The registry gives a 6-month timeframe for the outcome but does not report participant-level follow-up, total patient-years, or how follow-up was accumulated for the calculation.
What does non-randomized allocation imply?
Random allocation is one way to make comparison groups similar, on average, with respect to characteristics that can influence an outcome. In a non-randomized study, groups may differ for reasons other than the device group itself. This is a general statistical consideration. The registry explicitly says the arms are not a like-for-like control comparison. It does not describe group assignment, adjustment variables, or an analysis designed to address confounding. Accordingly, a group contrast should not be interpreted as a randomized treatment effect.
How should the device upgrade be understood?
The registry says that two patients implanted with ICD were censored from the ICD cohort and included in the CRT-D cohort at the time of upgrade, based on as-treat. This describes how those participants were handled in the primary-outcome population. In general, censoring means that a participant’s contribution to an analysis is treated as ending at a specified point; the consequences depend on the endpoint and analysis method. The record does not provide enough detail to assess the assumptions behind the censoring or the effect of the upgrade on the estimated outcome.
What can planning calculations tell readers?
The sample-size assumptions describe planning illustrations computed from the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. For non-time-to-event outcomes, the illustrations are expressed as participants per arm for a stated power; time-to-event illustrations are described as total event counts. These are planning illustrations, not observed power and not proof that the study was adequately or inadequately powered. The registry’s own sample-size justification is not reported. The numerical planning results and the fractions used are not included in the registry record.
A normal approximation is a general method that uses an approximate distribution to make statistical calculations. Its adequacy depends on the outcome and data conditions. The registry does not report diagnostic checks or details that would allow readers to assess whether this approximation was suitable for the endpoint. Equal allocation is an assumption for the planning illustration; it should not be confused with evidence that the observed study groups were assigned randomly or had equal analyzed populations.
What is not specified about the analyses?
The record lists two analyses and two outcome measures, but does not describe the analysis methods, model form, covariates, missing-data approach, or any interim analyses. It also does not say whether the posted endpoint estimate was adjusted, how departures were classified, or whether repeat departures were handled in a particular way. These details are not reported in the registry record. Without them, readers cannot independently reproduce the analysis or judge all of its assumptions.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists a primary outcome of false-positive rate and a secondary outcome of sensitivity. It also reports two outcome measures and two analyses. The record does not describe how the analyses correspond to the outcomes, whether additional comparisons were planned, or whether any adjustment was made for multiple testing. Multiplicity procedures and the statistical analysis plan are not reported in the registry record.
When several outcomes or comparisons are examined, the chance of obtaining a notable result by chance can increase. This is a general statistical consideration, not a statement about a result in this study. Without a reported multiplicity plan and the numerical results, the consequences for interpretation cannot be assessed.
The primary-outcome population description says that all participating patients were included and gives 82 patients in each arm. It also describes two ICD patients who were censored from that cohort and included in the CRT-D cohort from the time of upgrade, based on as-treat. This does not fully explain the analysis population or follow-up rules. The registry does not report missing-data counts, reasons for missingness, imputation methods, or sensitivity analyses for missing data.
The record does not state whether participants were analyzed according to an intention-to-treat principle, nor does it provide a complete analysis-population definition beyond the primary-outcome description. The protocol’s planned handling of missing data, deviations, or interim analyses is not reported in the registry record. These omissions limit assessment of whether the reported analysis, if numerical results were available, followed a prespecified plan.
11. 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 |
|---|---|---|---|
| CRT-D Device | 2 | 82 | 2.4% |
| ICD Device | 3 | 80 | 3.8% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 1% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| CRT-D Device | 6 of 82 |
| ICD Device | 8 of 80 |
Most frequent serious adverse event terms
| Event term | Organ system | CRT-D Device | ICD Device |
|---|---|---|---|
| Infection (system related) | Cardiac disorders | 0 of 82 | 2 of 80 |
| Device Migration | Cardiac disorders | 1 of 82 | 0 of 80 |
| Loss of Capture (LV lead related) | Cardiac disorders | 1 of 82 | 0 of 80 |
| Lead dislodgement / migration (RV lead related) | Cardiac disorders | 0 of 82 | 1 of 80 |
Most frequent non-serious adverse event terms
| Event term | Organ system | CRT-D Device | ICD Device |
|---|---|---|---|
| Therapy for Non Ventricular Rhythm | Cardiac disorders | 3 of 82 | 6 of 80 |
| Elevated Pacing Threshold (LV lead related) | Cardiac disorders | 1 of 82 | 0 of 80 |
| Phrenic Nerve / Diaphragmatic Stimulation (LV lead related) | Cardiac disorders | 1 of 82 | 0 of 80 |
| Twiddler Syndrome | Cardiac disorders | 1 of 82 | 0 of 80 |
| Bleeding / Hematoma | Cardiac disorders | 0 of 82 | 1 of 80 |
| Unable to Turn Impedance Data Collection on | Cardiac disorders | 0 of 82 | 1 of 80 |
Serious events with the highest arm-level rate: infection (system related) (2.5%), lead dislodgement / migration (rv lead related) (1.2%), device migration (1.2%), loss of capture (lv lead related) (1.2%).
The safety record lists separate groups for CRT-D Device and ICD Device. For the CRT-D group, 82 participants are listed as at risk, 2 as affected by serious adverse events, and 6 as affected by other adverse events. For the ICD group, 80 are listed as at risk, 3 as affected by serious adverse events, and 8 as affected by other adverse events. These are the registry’s group counts and should be read separately from the primary endpoint.
The record lists the most frequent serious adverse-event terms with percentages: Infection (system related), 2.5%; Lead dislodgement / migration (RV lead related), 1.2%; Device Migration, 1.2%; and Loss of Capture (LV lead related), 1.2%. The registry does not provide additional detail alongside these terms about event timing, duration, recurrence, or severity beyond the serious-adverse-event classification.
These figures do not establish that one device group is safer than the other. The study was non-randomized, and the registry cautions that the arms are not a like-for-like control comparison. The record does not report deaths in these groups. It also does not provide enough detail to determine how the listed event-term percentages were calculated or whether participants could contribute to more than one term.
12. What the Result Does, and Does Not, Mean
The registry record establishes that a non-randomized, triple-masked, parallel study evaluated an impedance monitoring feature in ICD and CRT-D devices, with a primary endpoint defined as departures from the programmed threshold unrelated to a heart failure event. It also states the intended criterion: a false-positive rate per patient year of follow-up should be less than 1.5.
The posted record does not include the numerical primary-outcome result or its confidence interval. It therefore does not show whether the observed rate was below the stated criterion, how far it may have been from that criterion, or how precisely it was estimated. The endpoint definition and objective cannot substitute for the missing result. Sensitivity is listed as a secondary outcome, but its numerical result is not reported in the registry record.
The device groups are not randomized, and the registry warns that they are not a like-for-like control comparison. Consequently, the record does not support attributing any observed difference between groups to the monitoring feature or device type. The safety counts describe adverse events recorded in each group but do not, on their own, establish comparative safety.
The stated planning calculations are illustrations based on the observed effect, rather than observed power. They do not resolve the absence of the endpoint estimate or provide a conclusion about the study’s findings. The registry’s sample-size justification, detailed analysis plan, and approach to missing data are not reported.
In practical statistical terms, the record provides information about the study’s purpose, design, endpoint definition, and some safety counts, but not enough numerical efficacy-related outcome information to assess the primary endpoint. This is a statement about what the registry record reports, not a conclusion about the device’s clinical performance.
13. Why This Trial Matters Statistically
This study raises a useful measurement question: how often does an impedance-monitoring threshold departure occur without a related heart failure event? The distinction between a signal and the event it is intended to indicate is statistically important. A false-positive measure can describe one aspect of monitoring performance, but it must be interpreted alongside its definition, observation time, and uncertainty.
The registry’s use of a rate per patient year highlights the role of follow-up exposure. A count alone and a rate answer different questions, and the latter depends on how time under observation is handled. The record identifies a 6-month timeframe and a 95% confidence interval, but does not post the rate, interval bounds, or patient-years. This illustrates why endpoint definitions and numerical results both matter for interpretation.
The non-randomized design is also central to the statistical reading. The registry explicitly cautions that the device groups are not a like-for-like control comparison. Group counts may describe the participants analyzed, but they cannot establish that group differences are caused by the device type. This distinction is important whenever researchers compare naturally occurring or otherwise non-randomized groups.
Finally, the record notes that some participants changed device cohort after an upgrade. That makes clear why analysis-population rules and follow-up handling should be described precisely. The entry gives a brief account of the approach but does not report enough detail to evaluate its implications. The trial therefore illustrates the value of transparent reporting of estimates, uncertainty, group assignment, and analysis methods—not only the stated objective.
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 principal limitation for interpreting the primary endpoint is that the registry does not report its numerical estimate or 95% confidence interval. The stated benchmark is available, but the observed rate cannot be compared with it from the registry record. Event counts, patient-years, and the calculation method are also not reported.
The allocation is non-randomized, and the registry explicitly says the arms are not a like-for-like control comparison. The record does not explain how participants entered each device group, report adjustment methods, or provide information sufficient to interpret group differences causally. The device upgrade handling is described briefly, but the analysis assumptions and effect on follow-up cannot be evaluated.
Several design and analysis details are absent, including eligibility criteria, the detailed protocol, sample-size justification, statistical analysis plan, missing-data procedures, and interim analyses. The record lists sensitivity as a secondary outcome but does not report its numerical results. It also does not give the methods used for the confidence interval or detailed definitions for classifying departures.
Safety figures are reported as group counts and serious-event terms, but the record does not supply further detail on event timing, recurrence, or the calculation of the listed percentages. These limitations concern the completeness of the registry information; they do not establish that the underlying study lacked these procedures or data.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Detect Fluid Early From Intra-thoracic Impedance Monitoring — NCT00916929.
- Registry record last updated 2019-02-19; status last verified 2019-02.
- Results first posted 2013-06-24.
- Data retrieved from ClinicalTrials.gov on 2026-11-09.
- Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.
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18. Record Summary
NCT00916929 is a completed, non-randomized, triple-masked, parallel study sponsored by Abbott Medical Devices. It evaluated the Impedance Monitoring Feature in ICD and CRT-D devices among participants with heart failure. The registry lists enrollment of 162, a start of 2009-05, and primary completion in 2011-02.
The primary endpoint was the number of threshold departures unrelated to a heart failure event, with a 6-month timeframe and a stated false-positive-rate criterion of less than 1.5 per patient year. A 95% confidence interval is identified, but the numerical endpoint result and interval are not reported in the registry record. Sensitivity is listed as a secondary outcome, without a numerical result.
The record gives serious and other adverse-event counts by device group and names the most frequent serious-event terms. Because the arms were not randomized and are not described as like-for-like controls, group comparisons should be interpreted cautiously. Detailed analysis methods, missing-data handling, and the study’s own sample-size justification are not reported.