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 Combined Use of BIOTRONIK Home Monitoring and Predefined Anticoagulation to Reduce Stroke Risk (NCT00559988), a randomized phase 4 study. The primary outcome is Composite Primary Endpoint: Kaplan-Meier Estimate of Patients Without a Stroke, Systemic Embolism, or Major Bleed.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00559988 |
| Phase | Phase 4 |
| Condition | Atrial Fibrillation, Atrial Flutter, Stroke |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Single |
| Enrollment | 2718 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Biotronik, Inc. |
| Results posted | Yes |
2. Clinical Question
Population
The trial enrolled patients with implanted dual-chamber defibrillators or cardiac resynchronization therapy devices. Its primary endpoint was specified for an intent-to-treat analysis of all enrolled subjects. The registry record does not report further eligibility details in the information available for this account, so the findings cannot be characterized for narrower clinical subgroups.
Intervention
The intervention combined continuous BIOTRONIK Home Monitoring surveillance with a predefined anticoagulation plan. That plan used the total duration of atrial fibrillation or atrial flutter together with the patient’s CHADS2 score to guide starting, stopping, and restarting anticoagulation. The registry description does not provide the complete operational details of the plan.
Comparator
The comparison group received physician-directed oral anticoagulation. Home Monitoring was active for Safety Net alerts, but remote atrial fibrillation or atrial flutter data were not revealed to the patient or treating physician. The registry characterizes this arm as conventional device evaluation and physician-directed treatment.
Primary question
The primary question was whether the Home Monitoring guided strategy was superior to physician-directed care for the composite of stroke, systemic embolism, or major bleeding. The endpoint was expressed as the Kaplan-Meier estimate of patients without one of these events. The registry record does not report a comparative estimate or a statistical test result, so it does not establish whether the prespecified comparison favored either strategy.
3. Trial Design
The IMPACT study, registered as NCT00559988, was a phase 4, randomized, single-masked, parallel-group trial. The registry lists an enrollment of 2718 and identifies Biotronik, Inc. as sponsor. The study began in 2008-02, had a primary completion date of 2013-06, and is listed as terminated. The reason for termination is not reported in the registry record; the status alone does not explain why the trial ended.
The planned comparison was between Home Monitoring guided oral anticoagulation and physician-directed oral anticoagulation. In the Home Monitoring arm, continuous remote surveillance data were available to investigators, and anticoagulation was governed by a predefined plan linked to atrial fibrillation or atrial flutter duration and CHADS2 score. In the control arm, remote arrhythmia data were withheld from the patient and treating physician, while Safety Net alerts remained active. The registry does not give enough detail to reconstruct every aspect of device evaluation or treatment implementation.
Masking is recorded as single, but the registry record does not identify which trial participants or personnel were masked. Random allocation describes assignment to the study groups; it does not by itself show that treatment delivery, event assessment, or analysis was protected from bias. The methods used to conceal allocation and the procedures for adjudicating endpoint events are not reported in the registry record.
The primary endpoint timeframe ran from enrollment until a primary endpoint event, with follow-up assessed up to study exit. The registry reports a mean treatment duration of 2.0 years. It does not report the distribution of individual follow-up times or the number of participants who completed follow-up. The listed secondary outcomes include mortality, stroke types, major bleeding, arrhythmia burden, quality of life, and ventricular heart rate reduction, but their comparative results 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 | Home Monitoring Guided OAC | Physician-Directed OAC |
|---|---|---|
| STARTED | 1357 | 1361 |
| COMPLETED | 1006 | 1009 |
| NOT COMPLETED | 351 | 352 |
Reasons for not completing this period:
| Reason | Home Monitoring Guided OAC | Physician-Directed OAC |
|---|---|---|
| Death | 147 | 140 |
| Withdrawal by Subject | 152 | 139 |
| Lost to Follow-up | 42 | 56 |
| ICD device explanted | 10 | 17 |
Analysis population for the primary outcome, as defined in the registry: Intent to treat analysis of all enrolled subjects
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.
Population: All enrolled subjects
| Characteristic | Unit | Home Monitoring Guided OAC | Physician-Directed OAC | Total |
|---|---|---|---|---|
| Participants analysed | 1357 | 1361 | 2718 | |
| Age, Continuous | years | 64.7 (SD 10.8) | 64.2 (SD 11.5) | 64.4 (SD 11.2) |
| Sex: Female, Male: Female | Participants | 347 | 368 | 715 |
| Sex: Female, Male: Male | Participants | 1010 | 993 | 2003 |
6. Primary Endpoint
The registry lists the primary outcome as Composite Primary Endpoint: Kaplan-Meier Estimate of Patients Without a Stroke, Systemic Embolism, or Major Bleed, measured over From date of enrollment until date of primary endpoint event, assessed up to study exit, with a mean treatment duration of 2.0 years.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | percentage of participants-Kaplan Meier |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint combined stroke, systemic embolism, and major bleeding. It was reported as a Kaplan-Meier estimate of patients remaining free of these events, rather than as a simple count of people with an event at a single fixed assessment. This form of endpoint accounts for time until an event and can incorporate follow-up that ends before an event occurs, provided the required censoring assumptions are reasonable.
A composite can capture several clinically important outcomes within one endpoint and may represent a broader balance of potential benefits and harms than any component alone. But its interpretation depends on the component definitions and on how often each component occurs. A composite result cannot show, by itself, whether the overall pattern was driven by stroke, systemic embolism, or major bleeding. The registry record does not report component-specific primary endpoint estimates or definitions for the event criteria.
The endpoint description says the comparison was intended to test superiority of Home Monitoring guided anticoagulation over physician-directed care. The record identifies the intent-to-treat population as all enrolled subjects. It does not report the Kaplan-Meier estimates, their uncertainty, a hazard ratio, or a test result. Thus, the endpoint is defined, but its comparative result and precision cannot be assessed from the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record establishes the trial question and the outcome framework, but it does not provide the primary endpoint result. It names the composite of stroke, systemic embolism, and major bleeding and specifies a Kaplan-Meier estimate of patients without an event. It does not report the estimate for either arm, the difference between arms, a relative effect, a confidence interval, or a p-value. Consequently, neither the direction nor the precision of the primary comparison can be described from the registry record.
The absence of a reported estimate is not evidence that the groups had the same outcome. It also does not establish that one strategy was superior or inferior. A conclusion about statistical evidence would require the actual result and its uncertainty, along with enough information about the analysis to understand how follow-up and censoring were handled. Those elements are not reported in the registry record.
The primary endpoint is a composite. Even if an overall composite estimate were available, interpretation would require attention to its separate components. A composite can combine outcomes that differ in clinical importance and frequency; a result driven mainly by one component can obscure a different pattern in another. Component-specific primary results are not reported in the registry record. The listed secondary outcomes include different stroke categories and major bleeding, but their results are also not reported in the registry record.
The safety information describes event counts and selected serious-event terms, not a comparative analysis of the primary endpoint. Serious adverse events were reported for 372 of 1357 at risk in the Home Monitoring Guided OAC group and 374 of 1361 at risk in the Physician-Directed OAC group. Other adverse-event figures were 135 of 1357 and 139 of 1361, respectively. These summaries should not be treated as a substitute for the primary time-to-event analysis; they have different outcome definitions and the registry does not report an adjusted or unadjusted treatment comparison for them.
The sample-size illustrations use the observed effect as a planning input and specify assumptions including a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such illustrations are not observed power and do not supply missing evidence about the actual primary endpoint. The record does not report the trial’s own sample-size justification, statistical analysis plan, or interim analyses. Accordingly, the most defensible reading is that the registry describes a randomized comparison with a prespecified clinical question, while leaving the primary comparative result and its uncertainty unavailable.
9. Statistical Methods Explained
Statistical interpretation begins by distinguishing the trial question from the result. The registry defines a randomized parallel-group comparison and identifies a time-to-event composite endpoint. However, it does not report the arm-specific primary estimates or a treatment-effect estimate. General statistical concepts can clarify what such results would mean, but they cannot fill in the missing analysis.
What does a Kaplan-Meier estimate represent?
In general, a Kaplan-Meier estimate describes the probability of remaining free of an event over follow-up while accounting for participants whose observation ends before the event is recorded. Such participants are commonly treated as censored at the end of their observed follow-up. This method relies on assumptions about censoring: broadly, that the reasons follow-up ends do not make the remaining event risk systematically different in a way that invalidates the estimate. The registry gives the endpoint timeframe as enrollment until a primary event, assessed up to study exit, but does not report the censoring rules, numbers censored, or follow-up distribution.
The registry calls the outcome a Kaplan-Meier estimate of patients without stroke, systemic embolism, or major bleeding. It does not clarify whether all component events were analyzed using a single time-to-first-event approach, nor does it provide event counts for the primary composite. Therefore, the exact implementation cannot be reconstructed from the record. The mean treatment duration of 2.0 years gives a summary of exposure duration, but it does not describe how long each participant was followed or how much follow-up was available at different times.
Why is the composite important?
As a general principle, composite endpoints can increase the number of events contributing to an analysis and can reflect more than one important outcome. They also require care in interpretation. If the components occur at different frequencies or have different consequences, an overall treatment effect can be difficult to explain without component-specific estimates. The composite in this trial joins stroke, systemic embolism, and major bleeding. The registry does not report separate primary-endpoint results for these components, so no claim about which component accounts for the overall pattern is possible.
Time-to-event methods can also be affected by competing events. For example, an event that prevents a later event from being observed may require particular handling depending on the estimand and analysis plan. The record does not describe a competing-risk method or explain how death was handled in the primary analysis. General considerations about competing risks therefore identify questions for interpretation, not evidence that a particular method was used.
What does randomization contribute?
In general, random assignment aims to make treatment groups comparable at the start of a trial with respect to both measured and unmeasured prognostic factors. It supports a causal comparison when allocation is implemented appropriately, follow-up and outcome assessment are sufficiently complete, and the analysis matches the randomized assignment and the question of interest. The registry labels the trial randomized and states that the primary analysis population was all enrolled subjects on an intent-to-treat basis. It does not report the allocation sequence, concealment procedures, baseline characteristics, or detailed analysis population rules.
Intent-to-treat analysis generally compares participants according to their assigned group, regardless of later treatment changes. This can preserve the advantages of randomization and estimate the effect of assignment to a strategy. The record identifies the intended population but does not provide a primary analysis, the handling of participants with missing outcomes, or information about adherence and crossover. Thus, it is not possible to verify from the registry record how the stated population was implemented in the analysis.
How should uncertainty be judged?
In general, a confidence interval communicates the range of effect estimates compatible with the data under a specified model and repeated-sampling procedure. A narrow interval indicates greater statistical precision than a wide interval, but precision is not the same as clinical importance. A p-value addresses compatibility with a null hypothesis under the analysis assumptions; it does not show the probability that a treatment works or that the null hypothesis is true. No confidence interval, p-value, or primary treatment-effect estimate is reported in the registry record, so neither significance nor precision can be evaluated.
The sample-size assumptions describe planning illustrations based on the observed effect, with a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. For time-to-event calculations, the stated convention is to report total events using the Schoenfeld approach; other calculations are expressed as participants per arm. These assumptions explain how planning illustrations are framed, not how the trial itself was designed. The registry does not report the original sample-size justification, target effect, or full statistical plan. A planning illustration is not evidence of observed power, and it does not replace the missing confidence interval or endpoint estimate.
Why can event rates differ from time-to-event results?
General event counts do not necessarily correspond to a Kaplan-Meier estimate. Counts may ignore when events occurred, how long participants were observed, or whether follow-up ended before an event. Time-to-event estimates use event timing and censoring information, while a simple proportion is tied to a specified observation period and denominator. The registry’s serious adverse-event summaries are counts among those at risk; they do not provide the timing information or analysis needed to derive the primary endpoint estimate. No new primary estimate can be recovered from those summaries.
These method distinctions help define what can and cannot be inferred. The record supports describing the study design, endpoint, and selected safety counts. It does not support reconstructing the primary comparison, its uncertainty, the specific time-to-event model, or the effects of missing data and protocol deviations.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists several secondary outcomes, including all-cause mortality, ischemic and hemorrhagic stroke, fatal or disabling and non-disabling stroke, major bleeding, atrial fibrillation or atrial flutter burden, cardioembolic and non-cardioembolic stroke, quality of life, and ventricular heart rate reduction. Testing multiple outcomes can increase the chance of at least one apparently unusual result when each is assessed separately. In general, a prespecified strategy for controlling or interpreting multiplicity helps readers distinguish confirmatory findings from exploratory ones.
The registry record does not report a multiplicity adjustment, testing hierarchy, alpha allocation, or other strategy for interpreting multiple outcomes. It also does not provide the results for the listed secondary outcomes. Therefore, no claim about whether these outcomes were adjusted for, or how any secondary finding should be interpreted relative to the primary endpoint, can be made from the record.
The primary population is described as an intent-to-treat analysis of all enrolled subjects. That statement identifies the intended analysis population, but it does not explain the handling of missing endpoint data, withdrawal, loss to follow-up, treatment discontinuation, or crossover. The amount and pattern of missing data, imputation procedures, sensitivity analyses, and reasons for missingness are not reported in the registry record.
Interim analyses and stopping boundaries are not reported in the registry record. Nor is a full statistical analysis plan reported. Since the study status is terminated, the reason for termination and any relationship between termination and the planned analysis are not reported in the registry record. These gaps limit assessment of selective outcome reporting, the robustness of the primary analysis, and the impact of incomplete follow-up.
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 |
|---|---|---|---|
| Home Monitoring Guided OAC | 372 | 1357 | 27.4% |
| Physician-Directed OAC | 374 | 1361 | 27.5% |
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 |
|---|---|
| Home Monitoring Guided OAC | 135 of 1357 |
| Physician-Directed OAC | 139 of 1361 |
Most frequent serious adverse event terms
| Event term | Organ system | Home Monitoring Guided OAC | Physician-Directed OAC |
|---|---|---|---|
| Congestive heart failure | Cardiac disorders | 136 of 1357 | 127 of 1361 |
| Arrhythmia | Cardiac disorders | 64 of 1357 | 63 of 1361 |
| Angina | Cardiac disorders | 42 of 1357 | 53 of 1361 |
| Myocardial infaction | Cardiac disorders | 26 of 1357 | 35 of 1361 |
| Stroke | Nervous system disorders | 22 of 1357 | 30 of 1361 |
| Cardiac arrest | Cardiac disorders | 23 of 1357 | 27 of 1361 |
| Coronary artery disease | Cardiac disorders | 28 of 1357 | 18 of 1361 |
| Dyspnea | Cardiac disorders | 17 of 1357 | 26 of 1361 |
| Upgrade to CRT-D device | Surgical and medical procedures | 25 of 1357 | 18 of 1361 |
| Gastrointestianal bleeding | Vascular disorders | 23 of 1357 | 18 of 1361 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Home Monitoring Guided OAC | Physician-Directed OAC |
|---|---|---|---|
| Arrhythmia | Cardiac disorders | 52 of 1357 | 53 of 1361 |
| Angina | Cardiac disorders | 32 of 1357 | 34 of 1361 |
| Device replacement | Surgical and medical procedures | 29 of 1357 | 35 of 1361 |
| Congestive Heart Failure | Cardiac disorders | 22 of 1357 | 25 of 1361 |
| Dyspnea | Cardiac disorders | 19 of 1357 | 18 of 1361 |
Serious events with the highest arm-level rate: congestive heart failure (10.0%), arrhythmia (4.7%), angina (3.9%), myocardial infaction (2.6%), stroke (2.2%).
The registry reports serious adverse events separately by treatment group. In the Home Monitoring Guided OAC group, 372 participants were affected among 1357 at risk. In the Physician-Directed OAC group, 374 were affected among 1361 at risk. The registry also gives other adverse-event figures of 135 among 1357 at risk and 139 among 1361 at risk, respectively. These are descriptive safety summaries; the registry does not report a statistical comparison, uncertainty interval, or adjustment for differences in follow-up.
Selected serious-event terms are listed with percentages: congestive heart failure, 10.0%; arrhythmia, 4.7%; angina, 3.9%; myocardial infaction, 2.6%; stroke, 2.2%; and coronary artery disease, 2.1%. The registry record does not specify the denominator or provide group-specific percentages for these terms. The listed terms should therefore be read as reported safety information, not as evidence that the trial strategy caused or prevented any particular event.
Death counts are not reported in the adverse-event summary. These safety figures do not establish the primary endpoint result, which concerns time to stroke, systemic embolism, or major bleeding. Nor do they show whether an event was related to treatment. Attribution rules and detailed event definitions are not reported in the registry record.
12. What the Result Does, and Does Not, Mean
The registry record shows that IMPACT was designed to compare a monitoring-guided anticoagulation strategy with physician-directed anticoagulation in patients with implanted cardiac devices. It defines a primary composite endpoint and reports selected adverse-event summaries. It does not report the primary endpoint estimates or a treatment comparison. The central question—whether the two strategies differed on the composite—therefore remains unanswered by the result information in the record.
This absence should not be interpreted as evidence of no effect. A finding of no statistically significant difference would require reported data and an analysis; the registry record does not provide either for the primary endpoint. Likewise, it would be unjustified to say that the Home Monitoring strategy reduced or increased stroke, systemic embolism, or major bleeding. Those outcomes are named in the endpoint, but their comparative results are not reported.
Even a reported composite result would need to be considered alongside its components, the amount of follow-up, and the uncertainty around the estimate. A combined endpoint can be useful for evaluating an overall strategy, but it can mask variation between components. The registry does not report the component-specific primary results or the confidence interval for the composite. Readers therefore cannot assess whether any apparent overall effect would be precise, clinically important, or driven by a particular event type.
The adverse-event summaries offer descriptive information, but they do not resolve the efficacy question or establish causality. Counts among those at risk do not provide the same information as the time-to-event endpoint, and the record does not give an inferential comparison for these safety summaries. The trial’s terminated status is also not, by itself, an explanation for the missing results or evidence about the direction of an effect; the reason for termination is not reported in the registry record.
The appropriate conclusion is limited: the registry records the study design, treatment strategies, planned primary outcome, and some safety data, while leaving the primary comparative finding unavailable. No treatment recommendation follows from this record alone.
13. Why This Trial Matters Statistically
Statistically, IMPACT illustrates the distinction between a clearly described research question and a reportable treatment-effect estimate. The trial was randomized and parallel, and its primary endpoint was a time-to-event composite intended to compare two anticoagulation strategies. Yet without arm-specific endpoint estimates and uncertainty, the design cannot be translated into a conclusion about the observed comparative effect.
The composite endpoint also makes the reporting of components important. Stroke, systemic embolism, and major bleeding are combined in the primary question, but they may contribute differently to an overall estimate. Component-specific results would help readers understand the pattern, while uncertainty estimates would show how much precision the data support. Neither is reported in the registry record.
The case also shows why safety counts and efficacy analyses should not be treated as interchangeable. Serious adverse-event summaries describe the number affected in each group, whereas the primary endpoint is defined using Kaplan-Meier estimates over follow-up. The summaries answer different statistical questions and have different requirements for interpretation. A registry reader needs the endpoint analysis, follow-up information, and uncertainty—not just event counts—to evaluate the primary comparison.
Finally, the record makes planning assumptions visible without reporting the trial’s own sample-size justification or full analysis plan. Planning illustrations can clarify the consequences of chosen assumptions, but they are not observed power and do not substitute for trial results. The statistical importance of IMPACT in this record is therefore less a conclusion about treatment effect than a reminder that design features, outcome definitions, analysis details, and transparent result reporting are all needed for a complete interpretation.
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 this trial from the registry record is the absence of the primary comparative result. Arm-specific Kaplan-Meier estimates, a treatment-effect estimate, confidence interval, and p-value are not reported. The primary composite is defined, but the record does not provide the component-specific primary results or event counts needed to understand its composition.
Important analysis details are also not reported. These include the censoring approach, follow-up distribution, missing-data procedures, endpoint adjudication, handling of death, and sensitivity analyses. The record identifies the intent-to-treat population but does not give enough information to verify the analysis population or assess the effects of withdrawal, treatment changes, or incomplete follow-up. The reason for the terminated status is not reported.
The registry describes the trial as single-masked without identifying who was masked. It does not report allocation concealment procedures or baseline characteristics. The intervention descriptions do not give the complete operational protocol for the predefined anticoagulation plan. These omissions make it difficult to assess implementation and the potential for bias.
The adverse-event information is limited to group counts and selected serious-event terms. The record does not report death counts, a treatment comparison for safety, event attribution, or the denominator for the listed term percentages. The listed secondary outcomes also lack reported results. Finally, the registry does not report the trial’s own sample-size justification, interim analyses, multiplicity strategy, or complete statistical plan. Together, these gaps prevent a full appraisal of efficacy, precision, safety comparisons, and robustness.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Combined Use of BIOTRONIK Home Monitoring and Predefined Anticoagulation to Reduce Stroke Risk — NCT00559988.
- Registry record last updated 2017-12-05; status last verified 2017-11.
- Results first posted 2014-06-23.
- 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
NCT00559988, titled Combined Use of BIOTRONIK Home Monitoring and Predefined Anticoagulation to Reduce Stroke Risk, is listed as a phase 4 randomized, single-masked, parallel-group trial sponsored by Biotronik, Inc. The registry reports enrollment of 2718, a start date of 2008-02, primary completion in 2013-06, and terminated status.
The study compared Home Monitoring guided oral anticoagulation with physician-directed oral anticoagulation in patients with implanted dual-chamber defibrillators or cardiac resynchronization therapy devices. Its primary endpoint was a Kaplan-Meier estimate of patients without stroke, systemic embolism, or major bleeding, assessed from enrollment through study exit; mean treatment duration was 2.0 years.
The registry record does not report the comparative primary endpoint result, its uncertainty, or the reason for termination. It includes selected adverse-event summaries and lists secondary outcomes, but does not report their comparative results.