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 Safety Study on Stopping Anticoagulation Medication in Patients With a History of Atrial Fibrillation (NCT01650298), a randomized na study. The primary outcome is Total Cumulative Days on Anticoagulation.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01650298 |
| Phase | NA |
| Condition | Atrial Fibrillation |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 64 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Abbott Medical Devices |
| Results posted | Yes |
2. Clinical Question
The study asked whether anticoagulation could be stopped or restarted according to information about atrial tachycardia or atrial fibrillation detected through an implanted device, with the aim of assessing safety and reducing time on anticoagulation. Its posted primary outcome was cumulative days on anticoagulation over one year. The registry record describes the study as a pilot and feasibility study and states that it was not powered to detect thromboembolic events. The primary outcome therefore addresses treatment exposure, rather than establishing a comparative effect on thromboembolic outcomes.
Population
People with a history of atrial fibrillation and an implanted pacemaker or implantable cardioverter defibrillator were the intended population. The registry record reports enrollment of 64 participants. Further eligibility details are not reported in the registry record.
Intervention
In the tailored anticoagulation group, treatment was initiated or discontinued according to atrial tachycardia or atrial fibrillation burden assessed through frequent remote transmissions via Merlin.net. Participants sent biweekly transmissions, and the description also refers to automatic alert-triggered transmissions. The exact alert threshold is not reported in the registry record.
Comparator
The control group followed remote transmission schedules set by each institution’s device-monitoring protocol. Anticoagulation was initiated or discontinued according to standard care or guidelines as prescribed by the doctor. The registry record lists direct thrombin or Factor Xa inhibitors as the drug intervention class.
Primary question
How many cumulative days on anticoagulation were recorded for each group during the one-year timeframe? The registry record gives totals for each arm, but does not report an inferential estimate of the difference between groups or a precision measure for those totals.
3. Trial Design
NCT01650298 is recorded as a randomized, parallel-group study with no masking. The registry lists the phase as NA and the status as terminated. Enrollment was 64. The study began in 2013-01, and primary completion was recorded as 2016-12. The reason for termination is not reported in the registry record.
Participants were assigned to control or tailored anticoagulation. In the control group, the timing of remote transmissions followed each institution’s device-monitoring protocol, and the treating doctor prescribed anticoagulation decisions in line with standard care or guidelines. In the tailored anticoagulation group, decisions to start or stop anticoagulation were based on device-assessed atrial tachycardia or atrial fibrillation burden. The group description refers to biweekly remote transmissions and automatic alert-triggered transmissions through Merlin.net. The remainder of the alert description, including the precise burden threshold, is not reported in the registry record.
All patients completed a 30 day run-in period after enrollment. During that period, anticoagulation could not be stopped, regardless of atrial tachycardia or atrial fibrillation burden. The primary outcome timeframe is one year, and the outcome description reports 14,826 cumulative days of monitoring after the run-in period. That overall monitoring total does not identify monitoring duration separately by arm.
The registry record does not specify the randomization method, whether allocation was concealed, the intended allocation ratio, or the detailed schedule for follow-up beyond the descriptions above. It also does not state why the study was terminated. Those details should not be inferred from the randomized designation or from the observed arm sizes.
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 | Anticoagulation Taken as Prescribed by Doctor | Anticoagulation to be Stopped/Started Per Device Information |
|---|---|---|
| STARTED | 16 | 48 |
| COMPLETED | 11 | 42 |
| NOT COMPLETED | 5 | 6 |
Analysis population for the primary outcome, as defined in the registry: After a 30-day run-in period during which anticoagulation use could not be stopped per study protocol, a total of 14,826 cumulative days of monitoring were completed.
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 | Control | Tailored Anticoagulation | Total |
|---|---|---|---|---|
| Participants analysed | 16 | 48 | 64 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 3 | 12 | 15 |
| Age, Categorical: >=65 years | Participants | 13 | 36 | 49 |
| Age, Continuous | years | 75.0 (SD 11.1) | 71.3 (SD 10.2) | 72.2 (SD 10.4) |
| Sex: Female, Male: Female | Participants | 6 | 17 | 23 |
| Sex: Female, Male: Male | Participants | 10 | 31 | 41 |
| Region of Enrollment: United States | participants | 16 | 48 | 64 |
6. Primary Endpoint
The registry lists the primary outcome as Total Cumulative Days on Anticoagulation, measured over one year.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | days on anticoagulation |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is titled Total Cumulative Days on Anticoagulation. It counts the days participants in each group spent on anticoagulation over the one-year follow-up timeframe. The record says the cumulative total for each group was determined after a 30-day run-in period during which anticoagulation could not be stopped. It also reports 14,826 cumulative days of monitoring after that run-in.
This endpoint is used to describe treatment exposure: it indicates how much time the groups collectively spent receiving anticoagulation under their assigned management approach. That is relevant to the stated aim of assessing whether device-informed decisions could reduce time on treatment. It does not, by itself, measure whether thromboembolic events occurred, whether bleeding occurred, or the balance between clinical benefits and harms. The registry explicitly describes the study as a pilot or feasibility study not powered to detect thromboembolic events.
The posted arm totals are 5840.0 days for control and 3763.0 days for tailored anticoagulation. The corresponding arm sizes are 16 and 48. These are cumulative totals, not average days per participant. The record does not report a dispersion measure, confidence interval, or statistical test for this endpoint. Nor does it provide a numerical two-arm effect estimate that accounts for the unequal arm sizes. The totals therefore describe the recorded exposure but do not establish the precision or statistical significance of a group contrast.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted primary outcome is a descriptive count of cumulative anticoagulation days in each randomized group. Control had 5840.0 cumulative days and tailored anticoagulation had 3763.0. The registry reports 16 participants in control and 48 in tailored anticoagulation. Because the endpoint values are group totals and the arm sizes differ, the totals alone do not express a participant-level average or a directly adjusted comparison. No such derived comparison should be inferred from the posted totals.
The registry record reports one outcome measure and no posted analyses. It provides no confidence interval, p-value, or other inferential result for the primary outcome, and the record identifies the two-arm comparison as missing or not estimable for this count outcome. Accordingly, the numerical totals can be described, but there is no posted estimate of the uncertainty around a between-group effect. The absence of an inferential result is not evidence that the groups were equivalent or that there was no difference.
The endpoint concerns treatment exposure, not clinical events. The study description says the pilot was not powered to detect thromboembolic events. The primary outcome totals therefore cannot establish whether either strategy changed thromboembolic risk. Safety-event counts are reported separately, but the record does not provide an adjusted comparative safety analysis or a precision estimate for those counts. The design and posted results support a feasibility-oriented description, not a definitive safety conclusion.
Interpretation also depends on the protocol context. Anticoagulation could not be stopped during the 30 day run-in period, regardless of device-detected burden. The outcome description states that 14,826 cumulative days of monitoring were completed after that period, but does not break this total down by arm. The endpoint thus reflects exposure within the study’s stated run-in and monitoring framework; it should not be treated as a direct measure of time off treatment for a typical participant.
The trial was randomized and parallel-group, but the registry record does not give details of the randomization procedure, allocation concealment, or a statistical analysis plan. The status is terminated, and the reason for termination is not reported in the registry record. These omissions limit assessment of how the study was conducted and why the reported results have the form they do. They do not change the narrow description of the posted primary outcome: cumulative days on anticoagulation were recorded for each group, without a posted inferential comparison.
9. Statistical Methods Explained
Statistical interpretation begins with the type of outcome. The primary measure is a cumulative count of days on anticoagulation for each group. It is not a time-to-event endpoint, a proportion of participants with an event, or a mean with a reported standard deviation. The posted values are group totals: 5840.0 days for control and 3763.0 days for tailored anticoagulation. The record also gives arm sizes of 16 and 48. The distinction between a total and a participant-level summary matters: a total can depend both on how long participants were observed and on how many participants were in the group.
What does a confidence interval add?
In general, a confidence interval expresses the uncertainty around an estimated quantity under the assumptions of a statistical method. It helps readers distinguish a point estimate from the range of values that remain compatible with the data and analysis. The registry record does not report a confidence interval for the primary outcome or for a between-group contrast. Thus, the precision of a comparative effect cannot be assessed from the posted results. A confidence interval should not be reconstructed from the group totals alone without the necessary participant-level information and a justified model.
Why does the outcome’s distribution matter?
In general, count data can have a distribution that differs from the assumptions of methods designed for continuous, normally distributed measurements. Counts may be influenced by differing time at risk or observation, and their variability can exceed what a simple count model expects. Over-dispersion refers generally to variability greater than a model’s assumed level; when present, it can make conventional uncertainty estimates too narrow if the model does not account for it. The registry record does not report a model, an over-dispersion assessment, or a dispersion measure for this endpoint. It is therefore not possible to say which count-data assumptions were considered or whether a specific model was used.
Exposure duration is especially relevant to cumulative totals. The record gives an overall monitoring total of 14,826 days after the run-in period, but does not report monitoring totals separately by arm. Without arm-specific exposure information and an analysis method, the posted cumulative counts cannot be interpreted as rates per unit of monitoring time. No rate calculation is reported in the registry record, and a rate should not be inferred from the overall monitoring total.
What can randomization establish?
Generally, random assignment is intended to make treatment groups comparable in expectation, reducing confounding by factors measured or unmeasured at baseline. Randomization does not ensure that groups are identical in a particular trial, and it does not remove the need to report how the allocation was generated, how participants were analyzed, or how missing outcome data were handled. The record identifies this study as randomized, but the method of generating or concealing the allocation is not reported in the registry record. The observed arm sizes are 16 and 48; the reason for that allocation pattern is not reported.
Masking is listed as none. In general, lack of masking can matter when treatment decisions, outcome assessment, or reporting may be influenced by knowledge of group assignment. The primary outcome is a count of days on anticoagulation, and the intervention itself changes treatment decisions using device information. The registry record does not describe blinded outcome assessment or procedures to limit bias in recording or adjudicating outcomes. It is not possible to determine from the record whether such safeguards were used.
Why is there no inferential comparison?
The registry lists zero analyses and indicates that values are missing or not estimable for a two-arm comparison of this count outcome. This means the posted record supports description of the arm totals, but not a reported test of a group contrast. Statistical significance cannot be determined from the totals alone. A numerical difference between the totals would also be an incomplete comparison because the arms have different sizes, and calculating a normalized measure would require selecting a method and assumptions not stated in the record.
In general, an analysis plan should identify the estimand, the population to be analyzed, the model, handling of missing data, and methods for uncertainty and multiplicity. The registry record does not report those details. No sample-size justification or planned interim analysis is reported in the registry record. The absence of these details does not prove that no such planning occurred; it means they cannot be evaluated from the record. Any sample-size illustration based on an observed effect is a planning exercise and not observed power, and the registry does not report an inferential estimate from which to assess a trial-specific effect with precision.
10. Multiplicity, Missing Data and Analysis Populations
The registry record lists one outcome measure and zero secondary outcomes. It reports zero analyses. There is no posted statistical analysis plan describing a hierarchy of outcomes, a multiplicity adjustment, or a strategy for selecting among analyses. With no reported inferential analyses, the record does not support an assessment of whether or how multiple testing was addressed. The number of listed outcomes alone does not establish what analyses may have been planned or performed outside the posted record.
Missing-data handling is not reported in the registry record. The record does not describe the amount of missing endpoint information, the reasons for missingness, any imputation method, or sensitivity analyses. It also does not specify an analysis population, such as an intention-to-treat population or a population defined by treatment received. These omissions matter because the interpretation of a randomized comparison can depend on who was included and how incomplete follow-up was handled.
The registry provides arm sizes and cumulative endpoint totals, but does not report participant-level data, arm-specific monitoring time, or a statistical comparison. It does not state whether every randomized participant contributed complete endpoint information. The 14,826 monitoring days are reported for the study overall after the run-in, not separately by group. Therefore, the completeness and comparability of follow-up cannot be assessed from the posted totals.
These are limits of what the registry record reports, not evidence that data were necessarily missing or that an analysis was necessarily omitted from all study materials. The record does not give enough detail to evaluate the handling of multiplicity, missingness, or analysis populations.
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 |
|---|---|---|---|
| Anticoagulation Taken as Prescribed by Doctor | 3 | 16 | 18.8% |
| Anticoagulation to be Stopped/Started Per Device Information | 8 | 48 | 16.7% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Anticoagulation Taken as Prescribed by Doctor | 0 of 16 |
| Anticoagulation to be Stopped/Started Per Device Information | 2 of 48 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Anticoagulation Taken as Prescribed by Doctor | 5 of 16 |
| Anticoagulation to be Stopped/Started Per Device Information | 9 of 48 |
Most frequent serious adverse event terms
| Event term | Organ system | Anticoagulation Taken as Prescribed by Doctor | Anticoagulation to be Stopped/Started Per Device Information |
|---|---|---|---|
| ATRIAL ARRHYTHMIA | Cardiac disorders | 1 of 16 | 6 of 48 |
| Hemorrahagic event | Gastrointestinal disorders | 1 of 16 | 0 of 48 |
| DECOMPENSATED HF | Cardiac disorders | 1 of 16 | 0 of 48 |
| HEMORRHAGIC EVENT | Nervous system disorders | 0 of 16 | 1 of 48 |
| INFECTION | Infections and infestations | 0 of 16 | 1 of 48 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Anticoagulation Taken as Prescribed by Doctor | Anticoagulation to be Stopped/Started Per Device Information |
|---|---|---|---|
| ATRIAL ARRHYTHMIA | Cardiac disorders | 1 of 16 | 2 of 48 |
| HEMORRHAGIC EVENT | Vascular disorders | 2 of 16 | 0 of 48 |
| HEMORRHAGIC EVENT | Gastrointestinal disorders | 0 of 16 | 2 of 48 |
| HEMORRHAGIC EVENT | General disorders | 1 of 16 | 0 of 48 |
| LV Thrombus | Cardiac disorders | 1 of 16 | 0 of 48 |
| RIB FRACTURE | Injury, poisoning and procedural complications | 1 of 16 | 0 of 48 |
| PNEUMONIA | Infections and infestations | 0 of 16 | 1 of 48 |
| DIVERTICULITIS | Gastrointestinal disorders | 0 of 16 | 1 of 48 |
| SYNCOPE | General disorders | 0 of 16 | 1 of 48 |
| CORONARY ARTERY DISEASE | Cardiac disorders | 0 of 16 | 1 of 48 |
Serious events with the highest arm-level rate: atrial arrhythmia (12.5%), hemorrahagic event (6.2%), decompensated hf (6.2%), hemorrhagic event (2.1%), infection (2.1%).
The registry reports serious adverse events and other adverse events separately for the two groups. In control, 3 of 16 participants are listed as affected by serious adverse events and 5 of 16 by other adverse events; deaths are listed as 0. In tailored anticoagulation, 8 of 48 are listed as affected by serious adverse events and 9 of 48 by other adverse events; deaths are listed as 2. These are reported counts, not estimates adjusted for follow-up duration or other factors.
The record lists serious-event terms including ATRIAL ARRHYTHMIA at 12.5%, Hemorrahagic event at 6.2%, DECOMPENSATED HF at 6.2%, HEMORRHAGIC EVENT at 2.1%, and INFECTION at 2.1%. The registry uses different capitalization for hemorrhagic-event labels, and one entry is spelled Hemorrahagic event. The listed terms and percentages should be read as registry labels rather than assumed to be a complete clinical classification.
These safety figures do not by themselves establish that an event was caused by the assigned strategy. The record does not provide event timing, a comparative statistical analysis, or precision estimates for the safety counts. The study is described as a pilot not powered to detect thromboembolic events, so the counts should be interpreted descriptively and not as a definitive safety comparison.
12. What the Result Does, and Does Not, Mean
The posted results establish that the registry recorded cumulative anticoagulation totals of 5840.0 days in control and 3763.0 days in tailored anticoagulation, with 16 and 48 participants in those groups, respectively. They also establish that the study completed 14,826 cumulative days of monitoring after the 30 day run-in period. These registry entries describe the trial record and its reported endpoint; they do not provide an inferential estimate of the effect of assignment to one strategy rather than the other.
The results do not show whether a difference between groups is statistically distinguishable from chance, because no comparative estimate, confidence interval, or p-value is posted. The totals should not be converted into a participant-level average or a monitoring-time rate without further information and an explicit analysis method. Nor does a treatment-exposure outcome directly establish whether participants experienced thromboembolic events or other clinical outcomes.
The registry explicitly says that the study was designed as a pilot or feasibility study and was not powered to detect thromboembolic events. The safety counts should therefore be read as descriptive observations, not definitive evidence for or against the safety of either approach. The record does not provide the statistical precision needed to compare serious adverse events reliably, and it does not report whether events were judged related to the intervention.
Randomization is a useful design feature for reducing confounding in expectation, but the registry record does not describe the allocation procedure, missing-data approach, analysis population, or statistical plan. The status is terminated, and the reason is not reported. These limitations leave important questions about trial conduct and analysis unanswered. The most defensible interpretation remains narrow: the record reports group-level cumulative exposure totals and adverse-event counts, but does not report an inferential comparison or establish clinical safety or efficacy.
13. Why This Trial Matters Statistically
This study raises a statistical distinction that is easy to miss: reducing treatment exposure and changing clinical risk are different questions. Cumulative days on anticoagulation directly describes time receiving treatment, while thromboembolic events and other safety outcomes describe clinical events. A result on exposure cannot substitute for an analysis of those events. The registry itself identifies the study as a pilot and says it was not powered to detect thromboembolic events.
The design also illustrates why group totals need context. The reported arm sizes differ, and the primary outcome is a total number of days rather than a participant-level summary or a rate adjusted for observation time. The record gives overall monitoring time after the run-in but not a group-specific breakdown. A clear statistical report would explain how the outcome was summarized and how unequal group sizes and follow-up were handled; those details are not reported in the registry record.
Finally, randomized design does not replace transparent reporting of the analysis. The registry identifies randomization and no masking, but reports no analysis results for the primary comparison. The statistical analysis plan, missing-data handling, allocation procedure, and analysis population are also not reported in the registry record. Without those elements, readers can describe the observed totals but cannot assess precision, test a comparative claim, or judge how robust an estimate would be.
The study therefore matters statistically as an example of the boundary between feasibility information and confirmatory evidence. Its posted outcome captures treatment exposure under a device-guided strategy, while its design description explicitly limits claims about thromboembolic outcomes. Keeping those questions separate helps prevent descriptive counts from being mistaken for proof of a clinical effect.
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 posted primary outcome is a group-level cumulative total, and no dispersion measure, confidence interval, or comparative test is reported. Arm sizes are 16 in control and 48 in tailored anticoagulation. The record does not provide a participant-level summary or arm-specific monitoring duration, so the totals cannot be interpreted as adjusted rates or directly compared as participant averages from the information reported.
The registry describes a 30 day run-in period when anticoagulation could not be stopped, regardless of device-detected burden. It reports 14,826 cumulative days of monitoring after the run-in, but does not show how those days were distributed between arms. The exact threshold for alert-triggered transmissions is not reported, and the detailed operational rules for device-informed treatment decisions are incomplete in the registry description.
The study is marked terminated, but the reason for termination is not reported in the registry record. Although the record identifies randomization, it does not explain the randomization method or allocation concealment. Masking is listed as none, but procedures for outcome assessment are not described. The record also does not specify the analysis population, missing-data handling, statistical analysis plan, sample-size justification, or interim analyses.
The study was described as a pilot or feasibility study and was not powered to detect thromboembolic events. The registry reports adverse-event counts but no comparative analysis, event timing, or precision estimates. These limits restrict conclusions to the posted descriptive exposure and safety information; they preclude a definitive comparative assessment of clinical outcomes.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Safety Study on Stopping Anticoagulation Medication in Patients With a History of Atrial Fibrillation — NCT01650298.
- Registry record last updated 2020-08-13; status last verified 2020-08.
- Results first posted 2020-08-13.
- 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
NCT01650298, titled Safety Study on Stopping Anticoagulation Medication in Patients With a History of Atrial Fibrillation, is listed as a randomized, unmasked, parallel-group pilot study. Its official title is Pilot Study: Tailored Anticoagulation for Noncontinuous AF. The registry lists enrollment of 64, status as terminated, start in 2013-01, and primary completion in 2016-12. The reason for termination is not reported in the registry record.
The primary outcome is Total Cumulative Days on Anticoagulation over one year. The posted totals are 5840.0 days for control and 3763.0 days for tailored anticoagulation. The outcome description reports 14,826 cumulative monitoring days after a 30 day run-in, during which anticoagulation could not be stopped. No inferential comparison is posted, and the record reports zero analyses.
The study description states that it was a pilot or feasibility study and was not powered to detect thromboembolic events. Serious and other adverse-event counts are reported by group, but no comparative safety analysis or precision estimate is posted. The registry record does not report a statistical analysis plan, missing-data approach, or analysis population.