Substrate Targeted Ablation Using the FlexAbility™ Ablation Catheter System for the Reduction of Ventricular Tachycardia: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Substrate Targeted Ablation Using the FlexAbility™ Ablation Catheter System for the Reduction of Ventricular Tachycardia (NCT02130765), a randomized na study. The primary outcome is Number of Subjects Who Experienced an ICD Shock Event..

2. Clinical Question

3. Trial Design

STAR-VT (NCT02130765) is recorded as a randomized, parallel-group study with no masking. The registry lists an enrollment of 64 and a status of terminated. The recorded start is 2014-11, and the primary completion date is 2016-07-25. The reason for termination is not reported in the registry record.

The planned comparison was catheter ablation with ICD/CRT-D and routine drug therapy against ICD/CRT-D with routine drug therapy. Although the stated objective refers to scar-based ablation using the FlexAbility™ system, the record does not provide further procedural details, device programming specifications, or drug regimens. The phase is listed as NA.

The primary outcome lists one event among 7 randomized ablation participants and one among 8 randomized control participants. Separate registry-subject and early-withdrawal groups are also listed for this outcome: the registry group has 26 participants and no events, while the early-withdrawal group has 19 participants and no posted value. These groups should not be treated as additional randomized comparison arms. Safety reporting uses different group counts for randomized ablation participants, so the outcome and safety denominators should be read separately.

The record does not report the randomization procedure, allocation concealment, recruitment details, or a reason for the difference between the enrollment count and the posted primary-outcome groups. It also does not report the protocol’s planned sample-size justification or a statistical analysis plan. The recorded design permits a description of the intended comparison, but not a full reconstruction of how participants were allocated, followed, or included in analyses.

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

Reasons for not completing this period:

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

6. Primary Endpoint

The registry lists the primary outcome as Number of Subjects Who Experienced an ICD Shock Event., measured over 12 months.

The primary endpoint counts participants who experienced an ICD shock event through 12 months of follow-up. The registry description includes both appropriate and inappropriate shocks. It is therefore a participant-level binary outcome: each participant is counted according to whether an event occurred, rather than the endpoint being a total count of all shocks. A participant with more than one shock would still be represented as a participant who experienced an event in this measure.

Shock events are used as a clinical outcome because they record an event experienced by participants with an ICD or CRT-D. Including both appropriate and inappropriate shocks follows the endpoint definition in the registry; the record does not provide separate primary-outcome counts for those categories. Nor does it report how shocks were adjudicated, how follow-up was collected, or how events after withdrawal were handled.

The posted randomized-group counts are one participant with an event among 7 in the ablation group and one among 8 in the control group. These raw counts are descriptive. Because the groups have different posted denominators, the counts alone do not convey a standardized comparison. No comparative effect estimate, confidence interval, or hypothesis-test result is reported in the registry record. The endpoint description also does not establish that every participant completed the stated follow-up period.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is binary at the participant level: a participant either experienced an ICD shock event during the specified follow-up timeframe or did not. For a binary endpoint, a basic descriptive summary gives the number of participants with an event and the number assessed in each group. The registry reports those counts for the randomized ablation and control groups, but does not report a modeled comparison or an uncertainty interval.

What a comparative estimate would describe

In general, a treatment comparison for a binary outcome can be expressed using measures such as a difference in event proportions or a relative measure. Each summarizes the contrast between groups in a different way. Such measures are most informative when accompanied by a confidence interval, which describes the range of values compatible with the data under the method’s assumptions. A confidence interval is not a guarantee that the true effect lies within its limits, and its width reflects both the data and the method used. No comparative estimate or confidence interval is reported for this primary outcome, so these quantities cannot be interpreted for STAR-VT from the registry record.

Small group counts make uncertainty especially relevant: a single participant’s outcome can have a substantial influence on a group summary when few participants contribute. The posted counts should therefore not be treated as precise estimates of what would occur in a larger population. This is a general statistical consideration, not a claim about an unreported analysis. The registry does not identify an inferential method or provide a result that quantifies uncertainty.

Randomization and masking

The design is recorded as randomized and parallel, with no masking. Randomization is generally intended to support a fair comparison by assigning participants to groups through a chance process; it does not ensure that small groups will have matching characteristics. The registry does not report the randomization method, sequence generation, or concealment procedure. With no masking recorded, participants and study personnel were not described as masked, but the record does not specify whether outcome assessors or adjudicators were masked. No further details should be inferred.

A parallel-group design compares groups assigned to different strategies over the study period. The registry describes ablation with ICD/CRT-D and routine drug therapy versus ICD/CRT-D and routine drug therapy. It does not report crossover, adherence, procedural completion, or the extent to which participants followed their assigned strategy. The reported group counts alone do not reveal how those issues were addressed.

Planning assumptions and observed data

The registry describes planning illustrations based on a fraction of the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. Those are planning assumptions, not the trial’s reported sample-size justification. The justification for the trial’s sample size is not reported in the registry record. A planning illustration asks what sample size might be needed under specified assumptions; it does not show that the trial had that sample size or that the assumed effect is reliable.

Such planning quantities are not observed power. Observed power is not a substitute for an effect estimate and its uncertainty after a study has been conducted. Here, no numerical comparative estimate or analysis result is reported for the primary endpoint, so the planning framework cannot supply evidence about the observed treatment contrast. The numeric planning results are not reported in the registry record.

What is absent from the analysis record

The registry lists zero analyses and does not report a statistical analysis plan, model, adjustment strategy, or hypothesis test for the primary endpoint. It does not state whether the primary analysis was intended to follow an intention-to-treat, per-protocol, or other population definition. It also does not report how missing outcome data were to be handled. These omissions matter because the choice of population and missing-data method can affect the interpretation of a treatment comparison.

The posted binary counts do not support a recalculated two-arm comparison in this record. No recalculated estimate should be substituted for a sponsor analysis; the registry does not post one. In general, recalculation from summary counts can only reflect the information represented by those counts and cannot recover adjustment, adjudication, or analysis details that are not reported. For STAR-VT, interpretation should remain with the raw posted counts and the stated limitations, rather than implying a statistical method that the record does not describe.

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("Randomized Subjects-Ablation", "Randomized Subjects- Control", "Registry Subjects")
n      <- c(7, 8, 26)
events <- c(1, 1, 0)
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  Randomized Subjects-Ablation  7  1  14.3  0.4  57.9  2.6  51.3  3.2  52.7
ARM  Randomized Subjects- Control  8  1  12.5  0.3  52.7  2.2  47.1  2.8  48.2
ARM  Registry Subjects  26  0  0.0  0.0  13.2  0.0  12.9  0.1  12.8

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 3 outcome measures and identifies one secondary outcome: the number of subjects with cardiovascular hospitalizations or a cardiovascular-related emergency-room visit. It does not provide a multiplicity plan, explain whether additional outcomes were prespecified, or report analyses for the listed secondary outcome. The primary endpoint has no posted comparative analysis. Without a stated plan, it is not possible to assess how the study handled the chance of false-positive findings across multiple outcomes or analyses.

The primary outcome lists 19 early-withdrawal participants without a posted value. The record does not report why these participants withdrew, when withdrawal occurred, whether outcome follow-up continued, or how missing endpoint data were handled. It also does not report an imputation method or sensitivity analysis. No missing-data assumption should be inferred from the absence of a value.

Several populations appear in the registry outcome and safety listings: randomized participants, registry participants, and early-withdrawal participants. The record does not report formal analysis-population definitions or state that an intention-to-treat or per-protocol analysis was conducted. The primary endpoint and safety listings also use different counts for randomized ablation participants. The reason is not reported in the registry record. These population and denominator differences limit direct comparison across outcome listings and make it important to keep each result tied to its stated group.

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 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: elevated thresholds (18.2%), atrial fibrillation (12.5%), pneumonia (12.5%), acute bacterial endocarditis (9.1%), dyspnea (9.1%).

For all enrolled subjects, the registry lists 64 at risk, 9 affected by serious adverse events, 4 affected by other adverse events, and 1 death. These are separate reported counts; the record does not explain whether participants could appear in more than one adverse-event category or provide event-level details for every group. They should not be added together to create a total number of affected participants.

In the safety listing, randomized ablation participants have 11 at risk, with 5 affected by serious adverse events, 1 by other adverse events, and no deaths. The randomized control group has 8 at risk, with 2 affected by serious adverse events, 2 by other adverse events, and no deaths. The registry-subject group has 26 at risk, with 2 affected by serious adverse events, 1 by other adverse events, and 1 death. The early-withdrawal group has 19 at risk, with no reported serious adverse events, other adverse events, or deaths. These safety groups are not necessarily identical to the primary-outcome populations.

The listed serious-event terms include Elevated Thresholds at 18.2%, Atrial Fibrillation and Pneumonia at 12.5% each, and Acute Bacterial Endocarditis, Dyspnea, and Peripheral Arterial Occlusion at 9.1% each. The registry excerpt does not provide enough context to establish the denominator or detailed coding basis for these term percentages. The counts describe what was recorded; they do not establish that an event was caused by a particular treatment or permit a definitive comparison of safety between groups.

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

The registry record establishes that STAR-VT set out to compare a catheter-ablation strategy plus routine drug therapy with routine drug therapy in participants with ICD/CRT-D and documented monomorphic ventricular tachycardia. Its primary endpoint counted participants with an ICD shock event, appropriate or inappropriate, through 12 months. The posted randomized-group outcome counts are one event among 7 ablation participants and one among 8 control participants.

Those counts do not, by themselves, establish a treatment effect. The registry provides no comparative estimate, confidence interval, p-value, or other primary-endpoint analysis. It also lists separate registry and early-withdrawal groups, including a group without a posted outcome value. The outcome counts therefore cannot be extended to all enrolled participants without assumptions that the registry does not report.

The safety listings offer descriptive counts of participants affected by serious and other adverse events, along with deaths. They should be read with their stated group denominators and not treated as a causal comparison. The different ablation-group denominators in the safety and primary-outcome listings further limit attempts to align those results.

The study’s stated goal was to demonstrate a superior clinical outcome while maintaining an acceptable safety profile. That goal is not itself evidence that superiority or an acceptable safety profile was demonstrated. The record does not report the reason for termination, the analysis plan, or the handling of missing outcomes. Those absences constrain interpretation of the results, but do not reveal what the unreported analyses or underlying study documents may have contained. The appropriate statistical reading is limited: the record posts sparse outcome and safety counts, but does not provide the analysis needed to quantify or establish a comparative result.

14. Why This Trial Matters Statistically

This trial illustrates the distinction between a study objective and a reported statistical result. STAR-VT aimed to demonstrate superiority, but the registry record posts only sparse primary-outcome counts and no comparative analysis. A reader cannot use the stated objective as evidence that the proposed difference was observed or established.

It also highlights why denominators matter. The primary outcome lists randomized ablation and control groups with different participant counts, while the safety listing gives a different count for the randomized ablation group. Registry and early-withdrawal groups are listed separately. Keeping these populations distinct is essential: combining them or assuming they represent the same analysis set could change the meaning of a result.

The missing primary value for early-withdrawal participants and the absence of a reported missing-data strategy add uncertainty about how complete the outcome record is. This is a statistical limitation, not evidence about why participants withdrew. Likewise, a terminated status is relevant context, but without a reported reason it cannot explain the observed data or the absent analysis.

More broadly, the example shows why counts, precision, analysis methods, and population definitions need to be read together. Event counts can be described directly, but a comparative conclusion requires an appropriate analysis and an account of uncertainty. When those elements are not reported, the sound interpretation is restrained: state what the record counts, identify what is missing, and avoid turning the study’s aim into a conclusion.

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 endpoint has sparse posted randomized-group counts, and the registry reports no comparative estimate, confidence interval, or hypothesis-test result. The absence of these analyses prevents assessment of the magnitude and precision of any group contrast. The record also lists 19 early-withdrawal participants without a primary-outcome value and does not report their reasons for withdrawal or the handling of missing outcomes.

The safety and primary-outcome listings do not use matching denominators for randomized ablation participants: the safety group lists 11 at risk, while the primary outcome lists 7. The registry does not explain this difference. It also does not report whether all listed groups had the same follow-up or how outcome status was established. The record’s terminated status has no accompanying reason, so its relationship to recruitment, follow-up, or analysis is unknown.

Further limitations include the absence of a reported sample-size justification, statistical analysis plan, analysis-population definition, and multiplicity approach. Procedural details, drug regimens, device programming, and outcome-adjudication methods are also not reported in the registry record. The displayed serious-event term percentages lack sufficient denominator and coding context in the record excerpt for detailed interpretation. These gaps restrict conclusions about the treatment comparison and the safety profile; they should not be filled by assumptions about the protocol or conduct of the study.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Substrate Targeted Ablation Using the FlexAbility™ Ablation Catheter System for the Reduction of Ventricular Tachycardia — NCT02130765.
• Registry record last updated 2019-02-12; status last verified 2019-01.
• Results first posted 2018-10-15.
• 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

STAR-VT (NCT02130765) is recorded as a randomized, parallel, unmasked study of substrate-targeted catheter ablation with ICD/CRT-D and routine drug therapy versus ICD/CRT-D and routine drug therapy. The registry lists 64 enrolled participants, a terminated status, a start of 2014-11, and primary completion on 2016-07-25.

The primary endpoint was the number of participants with an appropriate or inappropriate ICD shock event through 12 months. The posted randomized-group counts are one event among 7 ablation participants and one among 8 control participants. The record reports no comparative analyses and lists 19 early-withdrawal participants without a primary-outcome value. Safety counts are listed separately, with a different ablation-group denominator. The reason for termination, sample-size justification, statistical analysis plan, and handling of missing outcomes are not reported in the registry record.