This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record.
1. Trial at a Glance
AATAC was a randomized, open-label, parallel-group phase 4 trial evaluating atrial fibrillation ablation versus amiodarone in patients with heart failure and an ICD. The registry lists 203 enrolled participants and one primary endpoint: time to recurrence of atrial fibrillation lasting longer than 15 seconds, measured over 1 year.
| Feature | AATAC |
|---|---|
| Trial acronym | AATAC |
| ClinicalTrials.gov identifier | NCT00729911 |
| Registry title | Ablation vs Amiodarone for Treatment of AFib in Patients With CHF and an ICD |
| Phase | Phase 4 |
| Status | Completed |
| Condition | Heart Failure |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None |
| Primary purpose | Treatment |
| Enrollment | 203 |
| Number of arms | 2 |
| Lead sponsor | Texas Cardiac Arrhythmia Research Foundation |
| Sponsor type | Other |
2. Clinical Question
The central question represented by the registry design is whether atrial fibrillation ablation and amiodarone differ with respect to the time until recurrence of atrial fibrillation lasting longer than 15 seconds over 1 year in patients with heart failure and an ICD.
Population
Patients with heart failure and an ICD enrolled in the AATAC trial.
Intervention
Atrial fibrillation ablation, listed in the registry as a procedure.
Comparator
Amiodarone, listed in the registry as a drug.
Primary question
How does the time to recurrence of atrial fibrillation lasting longer than 15 seconds compare between the two randomized treatment groups over 1 year?
3. Trial Design
Atrial Fibrillation Ablation
- Intervention type: procedure
- Randomized treatment arm
- Primary endpoint assessed over 1 year
Amiodarone
- Intervention type: drug
- Randomized comparator arm
- Primary endpoint assessed over 1 year
The design is explicitly described as randomized and parallel-group, with no masking. Thus, treatment assignment is randomized, but the registry characterizes the trial as open-label rather than blinded.
4. Trial Timeline
Trial start
The registry lists the study start date as 2008-10.
Primary completion
The registry lists the primary completion date as 2014-12.
Registry status
The current registry status posted on ClinicalTrials.gov for the study is COMPLETED.
5. Endpoints
| Endpoint | Registry definition | Time frame |
|---|---|---|
| Primary endpoint | Time to Recurrence of AF lasting longer than 15 seconds | 1 year |
The primary endpoint is a time-to-event endpoint. That distinction is important. The question is not simply whether atrial fibrillation recurred at some point; it is how long it took for a qualifying recurrence to occur.
A participant who has not experienced the qualifying recurrence by the end of observation may contribute information up to the point at which follow-up ends or the participant is otherwise censored, depending on the prespecified analysis rules.
6. Statistical Methodology
Why a time-to-event analysis fits the primary endpoint
The primary endpoint records the time until a qualifying atrial fibrillation recurrence. Two participants could both experience recurrence during the 1-year period but have very different clinical trajectories if one recurs early and the other recurs near the end of follow-up. A binary analysis that simply classifies each participant as "recurrence" or "no recurrence" would discard that timing information.
A survival-analysis framework preserves the ordering of event times and can also accommodate participants whose exact event time is not observed because follow-up ends before recurrence.
Kaplan-Meier estimation
For a primary endpoint of this type, Kaplan-Meier estimation is typically used to describe the event-free probability over time. The resulting curve estimates the probability of remaining free of the qualifying recurrence through successive event times.
Here, di represents the number of events at an event time and ni represents the number of participants at risk immediately before that time.
Between-group comparison
A randomized comparison of two time-to-event curves is commonly performed with a log-rank test. The test evaluates whether the observed event-time experience differs systematically between the randomized groups over follow-up.
Cox proportional-hazards model
A Cox proportional-hazards model is another standard approach for a two-arm time-to-event endpoint. It expresses the treatment comparison through a hazard ratio, which summarizes the relative instantaneous event rate under the model.
The hazard ratio is not a probability, not a percentage of patients who benefit, and not the ratio of median event times. Its interpretation depends on the time-to-event model and its assumptions.
Censoring
Time-to-event analyses can retain participants who remain free of the qualifying recurrence through their last observed follow-up by treating the observation as right-censored. Censoring allows the analysis to use the information accumulated before follow-up ends without treating the participant as if the event had occurred.
Analysis population
The registry information identifies randomized allocation but does not provide a detailed statistical analysis population definition. For a randomized primary efficacy analysis, an intention-to-treat framework is commonly used because it preserves the randomized treatment comparison. The exact population and censoring rules used for AATAC are not reported in the ClinicalTrials.gov record.
7. Planned Analysis
The registry identifies one primary endpoint: Time to Recurrence of AF lasting longer than 15 seconds, with a time frame of 1 year. Because this is a time-to-event endpoint, an appropriate statistical analysis would ordinarily estimate the recurrence-free experience over time and compare the randomized treatment groups using survival-analysis methods.
Primary estimand
The clinically relevant quantity is the difference in time-to-recurrence experience between atrial fibrillation ablation and amiodarone.
Time-to-event framework
Kaplan-Meier methods can describe recurrence-free probability, while a log-rank test can compare the groups and a Cox model can estimate a hazard ratio.
What the endpoint preserves
Unlike a simple proportion, time-to-event analysis retains information about when the qualifying recurrence occurs.
Registry reporting
No formal statistical analyses are posted in the ClinicalTrials.gov record for the primary endpoint.
For this endpoint, the most informative presentation would ordinarily include the estimated recurrence-free curves, an appropriate between-group test, an effect estimate such as a hazard ratio with its confidence interval, and the prespecified analysis population and censoring rules. The registry information available here does not report those statistical results.
8. How to Interpret a Future Hazard Ratio
If a formal analysis reports a hazard ratio for recurrence, the direction of the estimate determines which group has the lower modeled instantaneous recurrence rate. The interpretation must always identify the reference group.
A hazard ratio below 1 would indicate a lower estimated instantaneous rate of qualifying AF recurrence in the numerator treatment group relative to the reference group, under the Cox model. It would not mean that the same percentage of participants were protected from recurrence throughout the entire year.
A confidence interval quantifies statistical uncertainty around the estimated treatment effect. A narrow interval indicates greater precision than a wide interval, all else being equal. It does not describe the range of individual patient responses.
A p-value addresses compatibility of the observed data with a specified null hypothesis under the statistical model. It does not tell the reader how large or clinically important a treatment difference is. Effect size, confidence interval, event-free probabilities, and the timing of events provide complementary information.
9. Statistical Methods Explained
Why is this a survival-analysis problem?
Because the primary endpoint is explicitly defined as time to recurrence. The timing of recurrence contains information that would be lost if the analysis reduced every participant to a simple yes/no outcome at 1 year.
Why might Kaplan-Meier curves be useful?
Kaplan-Meier estimation provides a visual and numerical description of the probability of remaining free of the qualifying recurrence over time. It can accommodate right-censored observations, which are common when participants reach the end of observation without experiencing the event.
What does a log-rank test compare?
A log-rank test compares the observed event experience between groups over follow-up. It is designed for time-to-event data and uses information from the sequence of event times rather than only the final proportion of participants with recurrence.
What does a Cox hazard ratio measure?
A Cox hazard ratio compares the modeled instantaneous event rates between treatment groups. An estimate below 1 means a lower modeled instantaneous recurrence rate for the numerator group relative to the reference group; an estimate above 1 means a higher rate.
Why does censoring matter?
If a participant reaches the end of observed follow-up without a qualifying recurrence, the analysis generally should not treat that participant as though recurrence occurred at the end of follow-up. Right-censoring allows the information available up to the last observation to contribute without asserting an unobserved event.
Why does the 15-second threshold matter statistically?
The primary endpoint is not recurrence of AF in an unrestricted sense. It specifies recurrence of AF lasting longer than 15 seconds. The threshold defines which observed episodes count as primary endpoint events and therefore determines the event classification used in the time-to-event analysis.
10. Interpretation of the 1-Year Time Frame
The registry specifies a 1-year time frame for the primary endpoint. This means the primary endpoint is framed around recurrence experience during that period rather than an unspecified lifetime outcome.
| Feature | Statistical implication |
|---|---|
| Time horizon | 1 year |
| Event definition | Recurrence of AF lasting longer than 15 seconds |
| Data type | Time-to-event |
| Randomized comparison | Atrial fibrillation ablation versus amiodarone |
| Masking | None |
A one-year endpoint can be clinically informative while still requiring careful interpretation of longer-term recurrence patterns. The ClinicalTrials.gov record identifies the primary time frame but does not report additional endpoint estimates outside that frame.
11. Randomization and Open-Label Design
AATAC is registered as randomized, with a parallel design and no masking. These characteristics address different statistical and operational questions.
Randomized
Treatment assignment is randomized, providing the foundation for a comparative treatment-effect analysis.
Parallel
Participants are assigned to one of the two treatment arms rather than being assigned sequentially to both treatments as part of a crossover design.
No masking
The registry describes the study as unmasked. Knowledge of treatment assignment can affect aspects of participant and investigator behavior and should be considered when interpreting outcomes.
Treatment purpose
The primary purpose is listed as TREATMENT, consistent with a trial evaluating interventions rather than an observational registry.
Randomization and masking are not interchangeable. Randomization primarily addresses allocation and confounding, whereas masking concerns knowledge of treatment assignment after allocation.
12. Sample Size and Statistical Precision
The registry lists 203 participants across 2 arms. The total sample size is important for interpreting the precision of any eventual time-to-event estimate because the amount of information depends not only on the number randomized but also on the number and timing of qualifying events.
Information comes from events as well as participants
Total enrolled participants
A time-to-event comparison is informed by the number and timing of qualifying AF recurrences, not simply by the number of participants enrolled.
This distinction is particularly important when interpreting a hazard ratio or confidence interval. Two trials with the same enrollment can produce different statistical precision if their event patterns differ.
13. What Is and Is Not Specified in the Registry
| Design or analysis feature | Registry information available here |
|---|---|
| Randomization | Yes — randomized allocation |
| Parallel design | Yes |
| Masking | None |
| Primary endpoint | Yes |
| Primary endpoint time frame | 1 year |
| Formal posted statistical analyses | No |
| Primary endpoint effect estimate | Not reported in the registry information provided |
| Primary endpoint confidence interval | Not reported in the registry information provided |
| Primary endpoint p-value | Not reported in the registry information provided |
| Detailed analysis population | Not reported in the registry information provided |
| Detailed censoring rules | Not reported in the registry information provided |
| Interim analysis plan | Not reported in the registry information provided |
| Multiplicity procedure | Not reported in the registry information provided |
| Bayesian methods | Not reported in the registry information provided |
| Missing-data or imputation method | Not reported in the registry information provided |
This distinction is central to statistical interpretation. A registry can establish the prespecified endpoint and design structure without providing the complete statistical analysis plan or numerical results needed to reproduce a formal treatment-effect estimate.
14. Limitations
- No posted statistical results: the ClinicalTrials.gov record contains no posted statistical analyses for the primary endpoint, so numerical treatment-effect estimates, confidence intervals, and p-values are not available from the registry information used here.
- Open-label design: the study is registered as having no masking, so knowledge of treatment assignment is part of the trial context.
- Endpoint-specific interpretation: the primary endpoint is specifically recurrence of AF lasting longer than 15 seconds; broader descriptions of atrial fibrillation recurrence should not silently substitute a different event definition.
- Time horizon: the registered primary endpoint has a 1-year time frame, so conclusions about other follow-up periods would require additional reported evidence.
- Event-driven precision: the statistical information in a time-to-event comparison depends on the number and timing of qualifying events as well as the number enrolled.
- Incomplete statistical specification: the registry information provided does not identify detailed censoring rules, analysis populations, multiplicity procedures, interim analyses, or missing-data methods.
- Unreported baseline detail: detailed baseline characteristics and subgroup results are not reported in the ClinicalTrials.gov record.
15. Why This Trial Matters Statistically
AATAC is a useful teaching example because its primary question naturally illustrates the difference between a binary endpoint and a time-to-event endpoint. The registry specifies not merely whether AF recurs, but the time to recurrence of an episode meeting a defined duration threshold.
| Statistical concept | How it appears in AATAC |
|---|---|
| Randomization | Participants were randomized between two treatment arms. |
| Parallel-group design | The study is registered as a parallel trial. |
| Time-to-event analysis | The primary endpoint is time to recurrence. |
| Event definition | The qualifying recurrence must last longer than 15 seconds. |
| Time horizon | The registered primary endpoint is evaluated over 1 year. |
| Open-label treatment | The registry lists masking as none. |
| Survival-function estimation | Kaplan-Meier estimation is a natural framework for describing recurrence-free probability over time. |
| Between-group testing | A log-rank framework is a standard method for comparing two time-to-event distributions. |
| Hazard-ratio modeling | A Cox model can summarize the relative instantaneous recurrence rate between groups. |
| Censoring | Time-to-event methods can incorporate participants whose event status is not observed through the complete time horizon. |
16. Statistical Interpretation vs Clinical Interpretation
Statistical interpretation
The registered primary endpoint is a randomized comparison of time to a precisely defined AF recurrence event over 1 year. A time-to-event framework preserves information about when recurrence occurs.
Clinical interpretation
The trial compares two different treatment approaches in patients with heart failure and an ICD. The clinical meaning of any treatment difference depends on the magnitude, timing, precision, and context of the observed recurrence difference.
These two perspectives should remain distinct. Statistical significance, if reported, would address evidence against a specified null hypothesis; clinical interpretation would additionally consider the size and timing of the treatment difference and the context in which it occurred.
17. Understanding Recurrence-Free Time
For a time-to-recurrence endpoint, a useful conceptual quantity is the probability that a participant remains free of the qualifying recurrence through a particular time point.
This is different from the probability of never experiencing AF recurrence. It is tied to the specified event definition and time horizon.
The distinction becomes important because the registered endpoint includes a duration threshold. An AF episode that does not satisfy the specified duration would not be equivalent, for purposes of the primary endpoint, to a recurrence lasting longer than 15 seconds.
18. Hazard Ratio, Risk, and Probability Are Different Quantities
| Measure | What it describes |
|---|---|
| Hazard ratio | Relative instantaneous event rate under a time-to-event model. |
| Risk or cumulative incidence by a time point | Probability of experiencing the event by that specified time, under the relevant event framework. |
| Recurrence-free probability | Probability of remaining free of the qualifying event through a specified time. |
| Median time to event | The time at which the estimated event-free probability reaches 50%, when that point is estimable. |
These quantities should not be substituted for one another. A hazard ratio is a relative model-based measure, whereas a one-year recurrence probability is an absolute time-specific measure.
19. Primary Endpoint Reporting Framework
For an educational statistical report of AATAC, a complete primary-endpoint presentation would ideally bring together the event definition, time horizon, recurrence-free estimates, treatment-effect estimate, confidence interval, and hypothesis-test result.
| Component | Role in interpretation |
|---|---|
| Event definition | Determines exactly what counts as a primary endpoint event. |
| Time horizon | Defines the period over which recurrence is evaluated. |
| Kaplan-Meier estimate | Describes recurrence-free probability over time. |
| Hazard ratio | Summarizes the relative instantaneous recurrence rate under the Cox model. |
| 95% confidence interval | Describes statistical uncertainty around the effect estimate. |
| p-value | Addresses compatibility with the specified null hypothesis under the test framework. |
The registry currently identifies the first two components but does not post the numerical statistical analyses for the remaining components.
20. What the Registry Establishes
The registry establishes a clear high-level statistical structure: 203 participants, randomized allocation, two parallel treatment arms, no masking, a treatment purpose, and a single registered primary endpoint concerning time to recurrence of AF lasting longer than 15 seconds over 1 year.
That structure is enough to identify the appropriate class of statistical methods. It is not enough, by itself, to reconstruct a numerical treatment effect. Numerical inference requires the underlying event-time information or a formally reported analysis containing the relevant estimates and uncertainty measures.
21. Sources
- ClinicalTrials.gov: AATAC — NCT00729911.
- PubMed: PubMed record associated with AATAC.
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22. Record Summary
AATAC is a randomized, parallel-group phase 4 trial with 203 enrolled participants, comparing atrial fibrillation ablation with amiodarone in patients with heart failure and an ICD. Its registered primary endpoint is time to recurrence of AF lasting longer than 15 seconds, with a 1-year time frame.
Statistically, the trial is centered on a time-to-event question. The appropriate analytical framework preserves the timing of recurrence and can accommodate right-censored observations. Kaplan-Meier estimation can describe recurrence-free probability, the log-rank test can compare the randomized groups, and a Cox proportional-hazards model can express the relative instantaneous recurrence rate through a hazard ratio.
The ClinicalTrials.gov record does not post formal statistical analyses for the primary endpoint. Consequently, the key numerical quantities that would ordinarily complete the statistical story—such as an effect estimate, confidence interval, and p-value—are not reported in the registry information available here. The most important statistical lesson is therefore the structure of the endpoint itself: time to a precisely defined recurrence event rather than a simple yes/no outcome.