Evaluation of the Phased Radio Frequency Ablation System: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Evaluation of the Phased Radio Frequency Ablation System (NCT01693120), a na na study. The primary outcome is Number of Participants With Procedure and/or Device Related Stroke.

2. Clinical Question

The study was an IDE, prospective, global, multicenter clinical study, according to its brief summary. Its stated purpose was to evaluate the risk of procedure- and/or device-related strokes among people with persistent or long-standing persistent atrial fibrillation undergoing ablation with the Phased RF System. This is a safety-focused question: the endpoint concerns a serious event temporally associated with the procedure and judged related by an independent clinical events committee. It is not a randomized comparison of the device against another treatment. Accordingly, the design can describe observed events in the treated study group, but the registry record does not establish a comparative effect against another ablation approach.

3. Trial Design

NCT01693120, titled Evaluation of the Phased Radio Frequency Ablation System, is listed as a prospective, global, multicenter, single-arm, unblinded investigational clinical study. The registry record lists the model as single group, allocation as NA, masking as NONE, and phase as NA. It reports enrollment of 199 and identifies Medtronic Cardiac Ablation Solutions as the sponsor. The study began in 2013-11, had primary completion on 2017-02-07, and has status TERMINATED. The reason for termination is not reported in the registry record.

The listed intervention was the Medtronic Phased RF Ablation System, a device, and the arm description is Phased RF ablation. The brief summary calls the study single arm and controlled, but the registry record does not describe a separate control arm or a comparator suitable for a like-for-like comparison. The record also lists no random allocation. Therefore, the design information supports describing outcomes within the study group, not interpreting differences between randomized treatment groups.

The primary outcome is a count of participants with procedure- and/or device-related stroke within 30 days. The listed secondary outcomes are 6-month Post-procedure Effectiveness, acute procedural success, and pulmonary vein stenosis. The registry record lists four outcome measures and four analyses. It does not report the analytic methods, result estimates, uncertainty intervals, or analysis populations for those outcomes. Although the enrollment total is recorded, the number included in each analysis is not reported in the registry record. The registry record also does not report why the study was terminated, the details of any planned comparison, or whether any protocol changes occurred.

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.

Enrollment

Reasons for not completing this period:

Phased RF Study Procedure and Follow-up

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: All subjects with a Phased RF ablation procedure who did not have a non-investigational catheter placed in the left atrium

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: The baseline analysis population is the number of subjects that had an ablation attempt with the Phased RF system.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With Procedure and/or Device Related Stroke, measured over 30 days.

The primary endpoint counts participants with a procedure- and/or device-related stroke. The registry definition requires symptom onset within 30 days of an ablation procedure in which at least one Phased RF ablation catheter was deployed into the left atrium. It further specifies that the independent clinical events committee considered the stroke related to the procedure and/or the investigational device. The population for this endpoint includes subjects with a Phased RF ablation procedure who did not have a non-investigational catheter placed in the left atrium.

This is a binary participant-level outcome: each eligible participant either met the endpoint definition or did not. A participant count can be used to describe how often the defined event occurred in the analyzed group. The endpoint focuses on a serious safety event and uses a defined time window and an independent committee’s relatedness assessment. Those features make the outcome more specific than simply counting any stroke occurring at any time, but the registry record does not provide further detail about adjudication procedures or criteria.

The endpoint’s result is not reported in the registry record. In particular, no observed number of participants with the event, denominator for the primary analysis, or estimate of uncertainty is reported. Enrollment of 199 is not necessarily the primary-endpoint analysis denominator because the endpoint population has additional eligibility conditions; the analyzed population size is not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical information in the registry record is limited. The primary outcome is described as a count of participants with an event, and the study is classified as single-group. The registry record does not report the statistical analysis plan, the method used to estimate the event frequency, or any test or interval for the primary outcome. The explanations below describe general statistical concepts and should not be read as claims about methods actually used in this study.

What does a participant count represent?

For a binary endpoint, each participant is classified according to whether the defined event occurred during the stated period. A count of affected participants is most interpretable alongside its denominator: the number of participants assessed for that endpoint. The ratio of those quantities can be reported as an event proportion, but no such proportion should be inferred without the relevant count and denominator. The registry record gives overall enrollment of 199, but does not report the primary endpoint’s observed count or analysis denominator. Its endpoint definition also sets conditions for inclusion, so overall enrollment and the population evaluated for this outcome need not be identical.

The outcome definition includes a 30-day window, a specified procedure context, and a relatedness judgment by an independent clinical events committee. In general, a prespecified definition helps make outcome classification more consistent. A committee’s assessment can distinguish events considered related from events that are not, but the registry record does not report the committee’s detailed criteria, procedures for resolving disagreement, or whether adjudicators were blinded.

What does a confidence interval add?

In general, a confidence interval expresses statistical uncertainty around an estimated quantity. It reflects how much the estimate might vary because of sampling under the chosen model and assumptions. It does not automatically account for selection, measurement problems, incomplete follow-up, or other sources of bias. A point estimate without an interval gives less information about precision; an interval without a clear denominator and analysis method is also difficult to interpret. No estimate or confidence interval for the primary endpoint is reported in the registry record.

For a single-group event outcome, an interval can help communicate uncertainty about the event proportion. Its width depends in part on the number of participants contributing data and the number of observed events, as well as the interval method. Those inputs are not reported for the primary endpoint. Therefore, no inference about precision is possible from the endpoint description alone. General statistical uncertainty should also be kept separate from clinical meaning: a precise estimate can still be affected by limitations in design or event ascertainment.

What can a single-group design establish?

In general, a single-group study can describe outcomes observed among participants who received the study intervention. Without an appropriate comparison group, it cannot by itself distinguish the effect of the intervention from other explanations, such as participant characteristics, the procedure context, or background event risk. This is why a within-group count should not be presented as a comparative treatment effect. The registry record labels this study single-group and reports no randomized allocation. Although its brief summary calls it controlled, it does not describe a comparator or a comparative analysis.

Unblinded status means the registry does not report masking of participants or study personnel. In general, lack of masking can matter for outcomes that involve judgment, behavior, or follow-up, although an independent clinical events committee is specified for the primary outcome. The record does not say whether committee members were masked to treatment or other study information, so that aspect cannot be characterized further.

How should the planning illustrations be understood?

The registry-related material includes sample-size planning illustrations based on the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The stated effect to detect is a fraction of the observed effect. These are planning illustrations, not the trial’s own design justification or observed power. The study itself is registered as single-group, so the equal-allocation assumption in the illustrations does not describe the listed trial design. The registry record does not report the trial’s sample-size justification or a protocol-based calculation.

In general, sample-size planning asks how many participants would be needed under specified assumptions to detect a target effect with a chosen probability and type I error rate. Such planning depends on the assumed effect, outcome variability or event frequency, analysis method, and allocation. If an observed effect is used as the planning basis, the resulting illustration is conditional on that observed effect and should not be mistaken for an independent design target. A planning calculation also does not show that a study actually achieved a particular probability of detecting an effect. The numerical planning results and the observed primary endpoint result are not reported in the registry record.

The stated method description distinguishes time-to-event outcomes, for which illustrations give a total event count, from other outcomes, for which they give participants per arm. That convention concerns the planning illustrations rather than evidence that this single-group study used a two-arm analysis. The registry record does not report a time-to-event analysis for the primary endpoint; the endpoint is described as a participant count within a 30-day period.

Why can over-dispersion matter?

In general, over-dispersion occurs when outcome variability exceeds what a statistical model assumes. When present and ignored, standard errors and confidence intervals can be too small, making results appear more precise than warranted. This concept is relevant to some count-data models, but the primary endpoint is defined as participants with an event, and no model or variance estimate is reported. The registry record does not indicate that over-dispersion was assessed or that a count model was used. It would therefore be inappropriate to claim that this issue affected the study analysis.

For any outcome, interpretation also depends on how missing observations and analysis populations are handled. The registry record does not report missing-data methods, exclusions from the primary analysis, or sensitivity analyses. Those omissions prevent a complete assessment of the assumptions underlying any statistical estimate, especially if participants had incomplete follow-up.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Ablation")
n      <- c(127)
events <- c(2)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Ablation  127  2  1.6  0.2  5.6  0.4  5.6  0.5  5.5

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists a primary outcome and three secondary outcomes: 6-month post-procedure effectiveness, acute procedural success, and pulmonary vein stenosis. It also lists four outcome measures and four analyses. It does not report whether these outcomes were assigned a testing hierarchy, whether the analyses were considered confirmatory or exploratory, or whether an adjustment for multiple testing was planned. Multiplicity matters in general when several outcomes or hypotheses are tested: interpreting each result as though it were the only test can increase the chance of at least one misleading positive finding. No multiplicity procedure is reported in the registry record, so the handling of that issue is unknown.

The registry record does not report the number of participants with missing outcome data, the amount of follow-up available for each outcome, or the methods used to handle missingness. It also does not describe whether missing values were excluded, imputed, or addressed through sensitivity analyses. These approaches can lead to different interpretations, particularly if missingness is related to participants’ outcomes. No assumption about the missing-data mechanism can be made from the record.

The primary endpoint population is specified as subjects who underwent Phased RF ablation without a non-investigational catheter placed in the left atrium. The registry record does not report how many participants met those criteria or how many were included in the analysis. It does not describe an intention-to-treat population, a per-protocol population, or another analysis-set definition. The overall enrollment of 199 cannot substitute for these details. Nor does the registry record say how participants with incomplete procedural information or outcome assessment were treated. These gaps limit assessment of the analysis population, outcome completeness, and the robustness of any result.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 3% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: atrial flutter (3.9%), vascular pseudoaneurysm (2.3%), atrial fibrillation (1.6%), non-cardiac chest pain (1.6%), haematoma (1.6%).

The adverse-event information lists one Ablation group, with 129 participants at risk. It reports 28 participants affected for serious adverse events, 38 affected for other adverse events, and 0 deaths. These are registry-record counts; the record does not provide event-level totals or further detail about the counting method. The listed serious terms and percentages are atrial flutter, 3.9%; vascular pseudoaneurysm, 2.3%; atrial fibrillation, 1.6%; non-cardiac chest pain, 1.6%; haematoma, 1.6%; and bradycardia, 0.8%.

The terms are presented as the most frequent serious adverse-event terms, not as a complete description of every event. The registry record does not report the number of occurrences for each term, whether participants could contribute more than one event, or the denominator used for the listed percentages. The percentages should therefore be read as posted rather than recalculated or assigned a denominator not stated in the record. The group’s 129 participants at risk is a reported safety denominator, but the record does not explain whether that denominator applies identically to every listed term.

Serious and other adverse-event counts should not be treated as mutually exclusive totals unless the counting rules establish that they are. The registry record does not provide that clarification. The count of 0 deaths is specific to the safety information reported; it does not resolve the primary stroke endpoint, whose result is not reported in the registry record.

13. What the Result Does, and Does Not, Mean

The registry record establishes that NCT01693120 evaluated the Medtronic Phased RF Ablation System in a prospective, global, multicenter, single-group study. It defines a primary safety outcome involving stroke considered related to the procedure and/or investigational device within 30 days. That definition includes an independent clinical events committee assessment and a specified group of eligible procedures. These design details clarify what the primary question was intended to measure.

The record does not report the primary outcome count, its denominator, or an estimate with uncertainty. It therefore does not permit a conclusion about the observed frequency of the defined event. The absence of a posted result is not evidence that no events occurred, and it is not evidence that an event did occur. The registry status of TERMINATED also does not explain why the study ended or establish whether the planned follow-up and analyses were completed.

The single-group design is important to interpretation. In general, an observed event frequency in a treated group describes what occurred among participants included in that analysis; it does not, on its own, show what would have occurred under a different procedure or device. The registry record does not identify a comparator suitable for estimating a relative effect. The brief summary’s description of the study as controlled is not accompanied by details of a control group or comparative analysis.

The posted safety information gives counts for participants affected by serious and other adverse events, a death count, and selected serious-event terms with percentages. These data offer some safety description, but the record does not clarify every counting denominator or give the complete event-level context. They should not be substituted for the missing primary endpoint result. The listed secondary outcomes likewise lack results in the registry record.

In general, statistical interpretation considers both the size of an estimate and its precision, along with design and data quality. Because the primary estimate and its uncertainty are not reported, neither the magnitude nor precision of the primary outcome can be assessed. The registry information supports a description of the study question, intervention, design, and selected safety figures, but not a comparative effectiveness conclusion or a determination about the primary outcome.

14. Why This Trial Matters Statistically

This study is statistically notable because its central question concerns a defined safety event in a device-based procedure, while its registered design is single-group. That combination makes clear separation between descriptive safety reporting and comparative inference essential. Counts in the treated group can describe observed events among analyzed participants, but the registry record does not describe a randomized comparator that would support attribution of differences to the Phased RF System.

The endpoint definition also illustrates why the analysis population and event definition matter. The primary outcome is restricted by a 30-day symptom-onset window, the procedure context, catheter deployment, and an independent committee’s relatedness judgment. These conditions establish what qualifies as an event for the endpoint. Yet the number of participants satisfying the stated population definition and the observed event count are not reported in the registry record. Without these pieces, a reader cannot evaluate the event frequency or its precision.

Another statistical issue is the distinction between an observed result and a planning assumption. The related sample-size illustrations are described as based on the observed effect and on assumptions involving a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. Those illustrations are not the study’s design justification, and their two-arm allocation assumption does not match the listed single-group model. They should not be interpreted as observed power or as evidence that the study was designed around those assumptions.

Finally, the record’s reporting gaps matter independently of the study’s event counts. The reason for termination, analysis populations, missing-data handling, multiplicity approach, and primary result are not reported in the registry record. Statistical conclusions depend not only on a named outcome, but also on who was analyzed, how outcomes were assessed, and how uncertainty was quantified. The record identifies several of those questions without resolving them, making careful limits on interpretation as important as the available design details.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The primary limitation for interpreting this trial is that the registry record does not report the primary outcome result. No event count, endpoint denominator, effect estimate, or confidence interval is reported. As a result, the central safety question cannot be answered from the registry information. Overall enrollment of 199 does not supply the missing endpoint denominator, because the primary population has additional procedure-related eligibility conditions.

The study is listed as single-group, allocation NA, and unblinded. The brief summary calls it controlled, but no comparator group or comparative analysis is described. This leaves no registry-reported basis for a like-for-like treatment comparison. The record also does not provide the analysis plan, sample-size justification, missing-data methods, multiplicity strategy, or definitions of analysis populations. These omissions prevent assessment of how the primary and secondary outcomes were statistically evaluated.

The study status is TERMINATED, and the reason for termination is not reported in the registry record. The record does not establish whether all planned follow-up was completed or whether termination affected enrollment or analysis. The primary completion date is recorded, but does not explain the status or the completeness of outcome ascertainment.

Safety reporting is also limited. The record lists affected-participant counts and selected serious adverse-event terms with percentages, but does not clarify the denominator for each term, the total event counts, or whether participants could contribute multiple terms. The listed terms are not a complete account of all adverse events. The record’s designation of an independent clinical events committee for the primary outcome is informative, but detailed adjudication procedures and masking of committee members are not reported.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Evaluation of the Phased Radio Frequency Ablation System — NCT01693120.
• Registry record last updated 2025-02-13; status last verified 2025-02.
• Results first posted 2018-03-22.
• 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.

19. Record Summary

NCT01693120, Evaluation of the Phased Radio Frequency Ablation System, is registered as a prospective, global, multicenter, single-group, unblinded investigational device study sponsored by Medtronic Cardiac Ablation Solutions. Enrollment is listed as 199. The intervention was the Medtronic Phased RF Ablation System, and the study status is TERMINATED. The primary outcome was the number of participants with procedure- and/or device-related stroke within 30 days, as assessed by an independent clinical events committee.

The registry record lists three secondary outcomes: 6-month post-procedure effectiveness, acute procedural success, and pulmonary vein stenosis. It reports safety figures for the Ablation group, including 129 participants at risk, 28 affected by serious adverse events, 38 affected by other adverse events, and 0 deaths, along with selected serious-event terms and percentages. The primary outcome result, the reason for termination, and key analysis details such as missing-data handling and analysis populations are not reported in the registry record. The single-group design does not provide a described like-for-like randomized comparator.