Safety and Efficacy of the Accent Magnetic Resonance Imaging™ (MRI) Pacemaker and Tendril MRI™ Lead: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Safety and Efficacy of the Accent Magnetic Resonance Imaging™ (MRI) Pacemaker and Tendril MRI™ Lead (NCT01576016), a non-randomized na study. The primary outcome is Freedom From Right Atrial (RA) Lead-related Complications in the Acute Period.

2. Clinical Question

3. Trial Design

This was a prospective, multi-center clinical study of the Accent MRI system, including the Tendril MRI lead. The registry describes its purpose as evaluating safety and efficacy in a patient population indicated for pacemaker implantation within and outside the MRI environment. The study is classified as non-randomized, parallel, and unmasked. Enrollment was 950, and the registry status is completed. The listed start date is 2012-03-30 and the primary completion date is 2018-02-02.

The registry distinguishes a Lead Safety phase from an MRI phase. In the Lead Safety group, patients implanted with an Accent MRI system were followed to evaluate Tendril MRI lead safety. In the MRI-scan group, implanted patients received an MRI scan to evaluate system safety and efficacy in the MRI environment. These are different study experiences, not randomized treatment assignments. Any difference in their observed figures could reflect differences in the groups, the phases, follow-up, or other factors; the record does not establish that a between-group difference would be caused by MRI exposure.

The primary endpoint concerns freedom from right atrial lead-related complications during the acute period, defined as implant through 2 months. Other listed outcomes include freedom from system-related complications and atrial and ventricular capture thresholds at the MRI visit. The registry lists 12 outcome measures but no analyses. Detailed recruitment procedures, site count, follow-up beyond the listed endpoint timeframes, and the statistical analysis plan are not reported in the registry record.

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: The MRI phase was originally designed as a randomized study, with MRI and control groups, but due to challenges encountered with patient recruitment, it was later changed to a non-randomized study.

Lead Safety

Reasons for not completing this period:

MRI Safety

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: 99 of the 920 enrolled subjects had no RA lead and hence did not contribute any data towards this endpoint.

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: A subset of participants from the lead safety phase (225) were included in the "MRI Phase." 30 supplemental scans were performed in Australia for a total of 255 participants in the MRI Phase. Each Phase was analyzed separately.

6. Primary Endpoint

The registry lists the primary outcome as Freedom From Right Atrial (RA) Lead-related Complications in the Acute Period, measured over Implant through 2 months.

The primary endpoint is the percentage of patients who did not have a right atrial lead-related complication between implantation and the 2 month study visit. The registry labels the measure as freedom from right atrial lead-related complications in the acute period and gives its unit as percentage of subjects. A confidence interval is identified as the measure of dispersion, but neither the percentage nor its interval is reported in the registry record.

This type of endpoint is used to describe the proportion of a defined group without a specified complication over a stated follow-up period. It focuses on short-term lead safety rather than on a comparison with an untreated or randomized control group. The registry states that 99 of the 920 enrolled subjects had no right atrial lead and therefore did not contribute data to this endpoint. It does not provide a further account of the endpoint denominator, missing observations, or the handling of participants who did not complete the study visit.

In general, an endpoint is most interpretable when its event definition, observation window, analysis population, and denominator are clear. The registry identifies the event category and time window, but the absent result and limited population detail prevent assessment of the observed level of freedom from complications or its precision.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a binary percentage endpoint: whether a participant did or did not have a right atrial lead-related complication during the specified acute period. The endpoint is expressed as the percentage of subjects without such a complication. The registry identifies a 95% confidence interval as the dispersion measure, but does not report the primary percentage or interval. The analysis method used to calculate an interval is not reported in the registry record.

What does a confidence interval communicate?

In general, a confidence interval describes statistical uncertainty around an estimate, under the assumptions of the method used to construct it. For a percentage, it conveys how precisely the observed proportion is estimated from the analyzed participants. It does not correct for bias in who entered the study, missing observations, unclear event definitions, or differences between groups. A confidence interval also does not establish that an endpoint is clinically important. Since the primary estimate and interval are not reported in the registry record, the precision of this trial's primary result cannot be assessed.

How should the design shape interpretation?

In general, random allocation can help make comparison groups similar with respect to measured and unmeasured characteristics, on average. This study is recorded as non-randomized and unmasked, and its two phases represent distinct experiences: a lead-safety evaluation and an MRI-scan group. The registry does not describe these phases as a randomized comparison. Consequently, a numerical difference between their observations would not, on its own, identify an effect caused by scanning or by a device component. No adjusted comparative analysis is reported in the registry record.

Masking can reduce the influence of knowledge of group assignment on some assessments and decisions. The registry lists no masking. Whether lack of masking could influence event recognition or reporting depends on the endpoint and study procedures, which are not described in enough detail to determine. This is a design consideration, not evidence that any reported event count is biased.

What can be inferred from the adverse-event figures?

The registry lists counts at risk, serious adverse-event figures, other adverse-event figures, and deaths separately for the Lead Safety and MRI phases. In general, counts are easiest to compare when the groups have comparable follow-up, event definitions, and ascertainment, and when denominators refer to clearly defined analysis populations. The record does not report the follow-up duration for the adverse-event summaries, person-time, or whether the figures count distinct participants or event occurrences. The values should therefore be read as descriptive entries rather than as directly comparable measures of risk.

For rare outcomes, a percentage alone may be imprecise, especially when the number of events is small. In general, a confidence interval can help show that uncertainty, while transparent denominators and consistent follow-up help interpret it. The registry's listed serious-event terms are accompanied by percentages, but the available details do not provide uncertainty intervals or denominator definitions for each term. No further precision can be inferred from those percentages.

What do the planning assumptions mean?

The registry describes a sample-size planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. Such calculations are planning illustrations, not evidence of the trial's original design or of the precision achieved in the completed study. They are not observed power. The registry record does not report the numerical planning outputs or the trial's own sample-size justification. It also does not identify a randomized two-arm comparison; the stated assumptions should not be mistaken for the study's actual allocation.

In general, a sample-size calculation depends on the target effect, outcome variability or event probability, significance level, desired power, allocation, and analysis method. Changing the target effect changes the required sample size. A calculation based on an observed effect can be especially uncertain because the observed estimate itself may be imprecise. The available record does not provide enough numerical inputs or output values to evaluate the planning illustration further.

What is unknown about the analysis?

The registry lists 12 outcome measures and 0 analyses. It does not report the statistical model for the primary endpoint, a prespecified testing hierarchy, adjustment for multiple outcomes, interim analyses, or sensitivity analyses. In general, methods should be matched to the outcome and design, and uncertainty should be interpreted in light of the planned analysis. No method can be attributed to this study beyond the endpoint's stated percentage and confidence-interval format. The analysis population and handling of incomplete follow-up are also not reported in the registry record.

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("Lead Safety Phase")
n      <- c(821)
events <- c(798)
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  Lead Safety Phase  821  798  97.2  95.8  98.2  95.8  98.1  95.8  98.1

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 12 outcome measures, including the primary freedom-from-complications endpoint and secondary outcomes for system-related complications and capture thresholds at the MRI visit. It lists 0 analyses. The registry record does not describe a multiplicity strategy, such as a prespecified order for testing outcomes or an adjustment to account for multiple statistical tests. It is therefore not possible to determine whether any reported inferential results would have controlled the overall chance of false-positive findings across outcomes.

Missing-data handling is not reported in the registry record. The record notes that 99 of the 920 enrolled subjects had no right atrial lead and did not contribute data to the primary endpoint. It does not describe other exclusions, incomplete visits, withdrawal, censoring, imputation, or sensitivity analyses. The total enrollment is listed as 950, while the endpoint note refers to 920 enrolled subjects; the record does not reconcile those figures. No endpoint denominator or accounting of missing observations is reported.

The analysis populations are not otherwise specified. The record does not state whether participants were analyzed according to implantation, MRI receipt, follow-up completion, or another rule. In general, transparent accounting of eligibility, endpoint contribution, and missing observations is needed to judge how representative an estimate may be of the enrolled group. Without those details and the endpoint result, the impact of missingness or outcome multiplicity cannot be assessed.

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 0.5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: ra lead related: lead dislodgement or migration (2.6%), rv lead related: lead dislodgement or migration (0.8%), procedure related: pneumothorax (0.4%), system related: cardiac tamponade (0.3%), procedure related: infection (0.3%).

The registry lists adverse-event figures separately for the Lead Safety and MRI phases. For the Lead Safety phase, the record gives 920 at risk, 70 serious adverse events, 60 other adverse events, and 132 deaths. For the MRI phase, it gives 255 at risk, 0 serious adverse events, 1 other adverse event, and 0 deaths. These are phase-specific entries and should not be read as a randomized comparison.

The serious-event terms listed include right atrial lead-related dislodgement or migration at 2.6%, right ventricular lead-related dislodgement or migration at 0.8%, and procedure-related pneumothorax at 0.4%. System-related cardiac tamponade and procedure-related infection are each listed at 0.3%, while right atrial lead-related elevated pacing thresholds are listed at 0.2%.

The registry entries do not explain whether event counts refer to unique participants or occurrences, how long participants were observed for these summaries, or how the listed percentages were calculated. The 132 deaths are listed for the Lead Safety phase, but cause and attribution are not reported in these details. The counts and percentages are descriptive entries; they do not alone establish comparative risk or causation.

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

The record establishes that a prospective, multi-center device study was completed and that it included a lead-safety phase and an MRI-scan phase. It specifies a primary endpoint of freedom from right atrial lead-related complications from implantation through the 2 month study visit. It also identifies additional outcome areas and provides phase-specific adverse-event and death figures. These registry entries describe the study's scope and the kinds of outcomes tracked.

The primary endpoint result itself is not reported in the registry record. There is no observed percentage or confidence interval from which to judge the level of freedom from complications or the uncertainty around it. The record also does not report analyses for the listed outcomes. Accordingly, the endpoint definition should not be mistaken for a favorable or unfavorable finding.

The two phases do not constitute a randomized comparison as described in the registry. Different group sizes and event counts cannot show that receiving an MRI scan caused an outcome, nor can they establish a relative safety effect between phases. In general, observational descriptions can be informative about recorded events, but causal interpretation requires a design and analysis that address relevant differences between groups. Those details are not reported in the registry record.

The adverse-event entries can be read as reported counts and listed terms, with the caveat that the available record does not clarify event counting, follow-up duration, or percentage denominators. The death count is not accompanied by cause or attribution in the details available. These limitations mean that the figures do not by themselves determine whether an event was related to the device, procedure, MRI scan, or another circumstance.

In general, statistical evidence depends not only on the direction of an estimate but also on its precision, population, endpoint definition, and analysis. Since the principal result and its uncertainty are absent, the record supports a description of the research question and design, but not a conclusion about the magnitude or certainty of the primary endpoint.

14. Why This Trial Matters Statistically

This study raises a statistical issue common to device research: safety outcomes need clear definitions, observation windows, and denominators. The primary endpoint is defined as the percentage without right atrial lead-related complications from implantation through the 2 month visit, which gives the measure a specific clinical focus and time horizon. Its interpretation still depends on the analyzed population and the actual estimate, neither of which is fully reported in the registry record.

The distinction between the Lead Safety and MRI phases is important. Because allocation is non-randomized and the phases involve different experiences, their summaries do not form a like-for-like control comparison. This illustrates why a group contrast should not automatically be interpreted as a treatment effect. Study design determines what a statistical comparison can support, independent of how clearly figures are presented.

The registry also illustrates the value of reporting uncertainty. A percentage accompanied by a confidence interval can show the precision of a safety estimate, while a count alone may not. Here, the primary percentage and interval are absent, and the adverse-event summary lacks details about follow-up and event counting. Those gaps constrain interpretation even though the registry identifies the outcomes of interest.

Finally, the record lists multiple outcome measures but no analyses. Without analysis details, readers cannot assess how outcomes were selected, whether multiple testing was considered, or how incomplete observations were handled. These are not merely technical details: they shape the strength and scope of the conclusions that a study can support. The record is therefore useful for identifying the design and questions addressed, while its statistical reporting limits evaluation of the primary result.

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 is defined, but its numerical result and confidence interval are not reported in the registry record. This prevents assessment of both the estimated percentage and its precision. The record says that 99 of the 920 enrolled subjects had no right atrial lead and did not contribute to this endpoint, but does not report the final analysis denominator or explain the relationship between that count and the overall enrollment of 950.

The study is non-randomized and unmasked. The Lead Safety and MRI phases differ in their described experiences, and the registry does not define them as a controlled comparison. Any contrast between their adverse-event figures would be vulnerable to differences in participants, observation, and other factors that the record does not address. No adjusted comparative analysis is reported.

For adverse events, the registry gives phase-specific counts but does not provide details on follow-up duration, event ascertainment, or whether counts represent distinct people or event occurrences. The listed serious-event percentages have no accompanying denominator detail or confidence intervals. The death count for the Lead Safety phase is not accompanied by a reported cause or attribution in the available record.

The registry lists 12 outcome measures and 0 analyses. Statistical methods, multiplicity handling, missing-data procedures, analysis populations, and interim analyses are not reported. The record also does not give the trial's sample-size justification. These omissions limit assessment of the reliability, precision, and scope of the reported safety information.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Safety and Efficacy of the Accent Magnetic Resonance Imaging™ (MRI) Pacemaker and Tendril MRI™ Lead — NCT01576016.
• Registry record last updated 2020-11-10; status last verified 2020-10.
• Results first posted 2020-11-10.
• 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

NCT01576016 is a completed, prospective, multi-center, non-randomized, parallel, unmasked study of the Accent MRI system and Tendril MRI lead. Enrollment was 950. The registry lists a start date of 2012-03-30 and a primary completion date of 2018-02-02.

The study included a Lead Safety phase and an MRI-scan phase. Its primary endpoint was the percentage of patients without right atrial lead-related complications from implantation through the 2 month visit. The primary result and confidence interval are not reported in the registry record. The record lists 12 outcome measures and 0 analyses. It also gives adverse-event figures by phase, but does not report enough detail to interpret those counts as a controlled comparison or to assess their precision.