IMPULSE: A Safety and Feasibility Study of the IOWA Approach Endocardial Ablation System to Treat Atrial Fibrillation: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for IMPULSE: A Safety and Feasibility Study of the IOWA Approach Endocardial Ablation System to Treat Atrial Fibrillation (NCT03700385), a na na study. The primary outcome is The Primary Safety Endpoint for This Study is the Incidence of Early-onset (Within 7 Days of the PEF Ablation Procedure) Primary Adverse Events (AEs)..

2. Clinical Question

In practical statistical terms, the study asks whether a safety and feasibility profile can be described for participants receiving this device in the study setting. Because there is no control group, its design does not directly estimate how outcomes would compare with another procedure or with no device treatment. The registry describes the population as having paroxysmal atrial fibrillation; results should not be generalized to other groups on the basis of this record alone.

3. Trial Design

IMPULSE is registered as a prospective, single-arm, multi-center safety and feasibility study. It is marked completed, with enrollment of 40. The registry lists the intervention as the IOWA Approach Endocardial Ablation System and describes the enrolled participants as receiving that system for paroxysmal atrial fibrillation. The listed phase is not applicable.

A single-group design follows participants receiving the intervention without a concurrent randomized control arm. Allocation is listed as not applicable, and masking is listed as none. This design can describe outcomes observed among treated participants, but it does not make a like-for-like comparison with an alternative treatment. Differences between these participants and people treated elsewhere cannot be separated from treatment effects using a randomized contrast within this study.

The registry record lists a primary safety endpoint and two outcome measures, but it contains no analysis entries. The primary endpoint is the incidence of specified early-onset primary adverse events, with a stated timeframe of 7 days. The adverse-event summary separately reports serious and other adverse-event categories. Those summaries are not, by themselves, a reported result for the defined primary endpoint.

The record gives a start date of 2018-01-19 and a primary completion date of 2018-12-21. It does not describe the statistical analysis plan, the rationale for the enrollment target, interim analyses, or analysis populations. A separate planning illustration uses assumptions of a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. Those assumptions describe hypothetical planning calculations; they do not turn this single-arm study into a two-arm trial or constitute the study's reported analysis plan.

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.

Before assignment: A total of 40 patients were enrolled (signed informed consent) and 40 subjects were treated at two (2) sites in Europe.

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.

6. Primary Endpoint

The registry lists the primary outcome as The Primary Safety Endpoint for This Study is the Incidence of Early-onset (Within 7 Days of the PEF Ablation Procedure) Primary Adverse Events (AEs)., measured over 7 days.

The primary safety endpoint is the incidence of specified primary adverse events occurring within 7 days of the PEF ablation procedure. It is expressed as a percentage of participants. The event list includes death, myocardial infarction, pulmonary vein stenosis, diaphragmatic paralysis, atrio-esophageal fistula, transient ischemic attack, stroke or cerebrovascular accident thromboembolism, major pericarditis requiring intervention, cardiac tamponade or perforation, pneumothorax, vascular access complications, pulmonary edema, hospitalization, and heart block. The description excludes hospitalization solely for arrhythmia recurrence or non-urgent cardioversion. It also states that pulmonary vein stenosis or atrio-esophageal fistula occurring greater than one week after the procedure is deemed a primary adverse event.

Safety endpoints of this kind are used to describe the occurrence of clinically important complications after a procedure. A participant-level percentage can communicate how often the defined endpoint was observed in the study group, provided that the numerator, denominator, and endpoint rules are clear. It does not on its own establish that an event was caused by the device, nor does it compare risk with another treatment.

The record gives the endpoint definition and timeframe, but does not report the number or percentage of participants meeting this specific primary endpoint. The separate adverse-event summary should not be substituted for that missing endpoint result: its categories and listed terms do not identify which events fulfilled the primary endpoint definition and timing rules.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The main endpoint is binary at the participant level: each participant either meets the defined primary adverse-event endpoint or does not, according to the endpoint rules. The registry expresses it as a percentage of participants. General statistical explanation: a proportion is a descriptive estimate of how frequently an event occurs in a specified group. Its interpretation depends on a clearly defined event, a defined observation window, and a denominator that represents the participants assessed for that outcome.

What does the endpoint definition determine?

The event list and timing rules determine which observations count. The primary endpoint is described as early-onset, within 7 days of the procedure, while the description separately says pulmonary vein stenosis or atrio-esophageal fistula occurring greater than one week after the procedure shall be deemed a primary adverse event. These statements create an endpoint rule that includes a specific exception to the general early-onset description. Analyses of this endpoint would need to apply the registry's stated definitions consistently. The registry record does not report how each possible event was adjudicated or how the timing exception was applied in practice.

Some hospitalization is excluded: the description says hospitalization solely because of arrhythmia recurrence or non-urgent cardioversion does not count. That distinction matters because a broad event category may contain episodes that do and do not satisfy the primary endpoint definition. The adverse-event summary reports categories and terms, but it does not show which entries fulfilled every endpoint criterion. For that reason, category-level adverse-event counts should not be treated as a direct calculation of the primary endpoint.

What can a single-group estimate tell the reader?

General statistical explanation: an estimate from one group describes outcomes in that group under the conditions in which it was observed. A concurrent control group can support a comparison by accounting for some background differences through the study design, especially when treatment assignment is randomized. A single-arm study has no such within-trial contrast. Its event summaries can be informative descriptions, but cannot by themselves establish how outcomes would have differed under another intervention.

The registry lists 40 enrolled participants and reports adverse-event category figures. It does not report the number of participants assessed for the primary endpoint or the endpoint result. A complete participant-level percentage requires both a count meeting the endpoint and the relevant denominator. The enrollment total should not automatically be assumed to be the denominator for every outcome, because outcome-specific analysis populations and missing observations are not described in the registry record.

How should uncertainty be understood?

General statistical explanation: estimates based on a finite group are uncertain. A confidence interval is a statistical range that conveys uncertainty around an estimate under a specified method and assumptions. A narrower interval generally indicates greater precision, while a wider interval indicates less precision. Intervals do not eliminate design limitations, measurement issues, or bias. The registry record does not report a confidence interval for the primary safety endpoint, and no interval should be inferred from the adverse-event counts without conducting a new calculation.

When event counts are small, the estimate may be sensitive to the occurrence or absence of only a few events. General explanation: exact or appropriately chosen interval methods can be useful for binary outcomes when ordinary large-sample approximations may be unreliable. The registry record does not state which method, if any, was planned or used for interval estimation. It also does not report an inferential analysis entry.

What do the planning assumptions mean?

The planning illustrations are described as calculations based on a fraction of an observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. These are assumptions for hypothetical planning, rather than findings from the trial. The illustrations do not report observed power, and they should not be interpreted as evidence of a randomized comparison. IMPULSE is registered as a single-group study, so the two-arm structure belongs only to the planning scenario.

General statistical explanation: a sample-size calculation depends on assumptions about the effect to detect, variability or event frequency, significance level, power target, and design. Changing the assumed effect changes the amount of information required. A planning calculation is not a retrospective measure of whether a completed study had adequate power, and it does not replace an analysis of observed outcomes. The registry record does not report the original sample-size justification or the rationale for enrolling 40 participants.

Over-dispersion is a general concern when count data vary more than an assumed model allows; it can make standard errors too small and confidence intervals too narrow if ignored. That concept is not directly a reported method for this binary participant-level endpoint, and the registry record does not report an over-dispersion assessment. More broadly, no detailed statistical model or analysis procedure is reported, so methodological choices beyond the listed planning assumptions remain unknown.

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("IOWA Approach Endocardial Ablation")
n      <- c(40)
events <- c(1)
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  IOWA Approach Endocardial Ablation  40  1  2.5  0.1  13.2  0.4  12.9  0.6  12.9

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists two outcome measures and no analysis entries. It does not report a multiplicity strategy, such as whether analyses were prioritized or whether adjustments were planned when several outcomes or comparisons were examined. Without that information, it is not possible to assess how the risk of chance findings across multiple analyses was handled. The absence of analysis entries should not be taken to mean that no analyses were performed outside the registry; it means the registry record does not document them.

The record does not describe missing-data handling, participant flow by outcome, or the analysis populations used. In general, missing outcome information can affect a percentage if the people with observed outcomes differ from those without observed outcomes. A clear analysis would identify the number eligible, the number assessed, and the treatment of unavailable or indeterminate outcomes. Those details are not reported in the registry record for the primary endpoint.

The enrollment figure is 40, but it is not enough on its own to establish the denominator used for every result. The record also does not state whether an intention-to-treat, per-protocol, or other analysis population was used. These terms describe different rules for deciding which participants contribute to an analysis; the choice can matter when participants do not complete follow-up or have incomplete outcome data.

General statistical explanation: multiplicity and missingness are separate issues. Multiplicity concerns interpretation across several statistical tests or outcomes; missingness concerns unavailable data and the assumptions used to address it. The registry record does not provide enough detail to judge either issue for the primary endpoint.

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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: atrial fibrillation (5.0%), atrial tachycardia (5.0%), cardiac tamponade (2.5%), calculus urinary (2.5%), arteriovenous fistula (2.5%).

The registry's adverse-event summary reports 7 of 40 participants in the serious category, 7 of 40 in the other category, and 0 deaths. These are descriptive figures from the posted adverse-event information. They should not be read as the result for the defined primary safety endpoint, because the record does not report how many participants met that endpoint's full event and timing criteria.

The listed serious-event terms and their stated percentages are atrial fibrillation at 5.0%, atrial tachycardia at 5.0%, cardiac tamponade at 2.5%, calculus urinary at 2.5%, and arteriovenous fistula at 2.5%. The registry record does not explain whether these terms represent distinct participants, recurrent events, or overlapping categories. They therefore should not be added together or interpreted as a total participant percentage.

General statistical explanation: adverse-event summaries describe events recorded during a study; they do not establish causation. In a single-arm study, there is no concurrent control group to estimate how frequently the same events would have occurred without the intervention or with another treatment. The summaries also do not establish the severity, duration, or clinical course of each event unless those details are explicitly reported. The registry record does not provide those additional details for the listed terms.

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

The registry record establishes that IMPULSE was a completed, prospective, multi-center, single-arm study of the IOWA Approach Endocardial Ablation System in participants with paroxysmal atrial fibrillation, with enrollment of 40. It defines a primary safety endpoint based on specified adverse events and a stated timeframe. It also posts summary adverse-event figures, including 7 of 40 participants affected in each of the serious and other categories and 0 deaths.

Those observations are descriptive. The primary endpoint's participant count and percentage are not reported in the registry record, and the adverse-event categories do not show which events met the primary endpoint definition. The posted information therefore does not quantify the specific primary safety endpoint. It also does not report uncertainty intervals or an inferential analysis for that endpoint.

The record does not establish whether the device caused any listed event. Adverse events can occur in the setting of a procedure for reasons that cannot be separated using this single-arm design. Without a concurrent comparator, the study does not estimate a relative treatment effect or show how safety outcomes would differ under an alternative. A zero death count in the posted summary is a descriptive observation in this study group, not proof that a risk is absent.

Nor does the registry information establish effectiveness. The study is described as a safety and feasibility evaluation, and the available record does not present a comparative efficacy result. Completion status indicates that the study is marked completed; it does not mean that every result, analysis detail, or follow-up outcome is reported in the registry.

General statistical explanation: statistical precision and causal interpretation are different. A result may be estimated precisely but still lack a suitable comparison for causal conclusions; conversely, a comparative design can still yield uncertain estimates. In this record, both the missing primary endpoint result and the absence of a control group constrain what can be concluded. The findings should be interpreted as registry-described observations from this particular study, not as a general estimate for all people with atrial fibrillation or all settings.

14. Why This Trial Matters Statistically

IMPULSE illustrates an important distinction in clinical-trial reporting: defining a safety endpoint is not the same as reporting its result. The registry gives a detailed list of events and a timeframe for the primary endpoint, but does not state how many participants met that definition or the resulting percentage. Readers therefore cannot directly evaluate the stated primary safety outcome from the record, even though adverse-event category summaries are present.

The study also shows why design matters to interpretation. A prospective, multi-center study can collect observations across participating centers, but a single-arm design remains descriptive rather than comparative. The number of participants and adverse-event counts do not create a randomized control comparison. Any planning illustration that assumes two arms is distinct from the actual trial design.

General statistical explanation: safety reporting benefits from clear definitions, denominators, observation windows, and transparent handling of participants with incomplete information. Event terms can overlap, and broad categories may not map one-to-one to a composite primary endpoint. Reporting the endpoint numerator and denominator alongside uncertainty estimates would make the precision of a participant-level proportion easier to assess. The registry record does not report these primary-endpoint details.

The record also makes visible the limits of registry-based interpretation. Completion status and enrollment are useful design descriptors, while analysis populations, missing-data methods, multiplicity handling, and the statistical analysis plan are not reported. This distinction helps readers avoid treating absent methodological detail as if it were evidence that a particular method was or was not used. A careful statistical reading separates what the registry documents from what remains unknown.

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 most direct limitation for interpreting safety is that the registry record defines the primary endpoint but does not report its observed participant count or percentage. The posted adverse-event categories cannot fill that gap because the record does not map the listed categories and terms to the endpoint's event definitions and timing rules.

The single-arm design has no concurrent control group. As a result, the posted outcomes cannot support a randomized comparison or distinguish treatment-associated events from events that might arise in the same population without the device. The study is described as multi-center, but the record does not provide center-specific results or explain whether outcomes varied across centers.

The record does not report detailed participant characteristics, eligibility criteria, outcome-specific denominators, follow-up completeness, missing-data procedures, event adjudication procedures, or analysis populations. It also does not describe the statistical analysis plan, multiplicity handling, interim analyses, or the sample-size justification. These omissions limit assessment of the precision, completeness, and analysis choices behind the posted results.

The endpoint description combines a general 7-day timeframe with a stated rule that pulmonary vein stenosis or atrio-esophageal fistula occurring greater than one week after the procedure is deemed a primary adverse event. The record does not report how this rule affected the endpoint count. The serious and other adverse-event categories also lack an explanation of overlap, so the category totals should not be combined or assumed to represent mutually exclusive participants.

Finally, the record describes a safety and feasibility study in participants with paroxysmal atrial fibrillation. It does not provide evidence in the record for broader populations or comparative effectiveness. These are limits of the available registry information and design, not findings that any outcome did or did not occur beyond the figures explicitly posted.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: IMPULSE: A Safety and Feasibility Study of the IOWA Approach Endocardial Ablation System to Treat Atrial Fibrillation — NCT03700385.
• Registry record last updated 2020-09-23; status last verified 2020-09.
• Results first posted 2020-09-23.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

IMPULSE is a completed, prospective, single-arm, multi-center safety and feasibility study of the IOWA Approach Endocardial Ablation System for paroxysmal atrial fibrillation. The registry lists enrollment of 40, a start date of 2018-01-19, and a primary completion date of 2018-12-21. Allocation is not applicable and masking is listed as none.

The primary safety endpoint concerns specified adverse events within 7 days of the PEF ablation procedure, with additional timing language for pulmonary vein stenosis and atrio-esophageal fistula. The primary endpoint result is not reported in the registry record. The posted adverse-event summary reports 7 of 40 participants in the serious category, 7 of 40 in the other category, and 0 deaths. The registry lists two outcome measures and no analysis entries. It does not report the statistical analysis plan, missing-data handling, analysis populations, multiplicity procedures, or sample-size justification.