This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Safety and Efficacy Study of Tendril MRI™ Leads in Standard Bradycardia Pacing Indication (NCT01528150), a registered phase not stated study. The primary outcome is Freedom From RA and RV Lead-related Complications.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01528150 |
| Phase | Phase not stated |
| Condition | Bradycardia |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 466 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Abbott Medical Devices |
| Results posted | Yes |
2. Clinical Question
Population
Patients with a standard bradycardia pacing indication were included. The registry record reports 466 enrolled participants and states that 464 patients were implanted. Among those implanted, 463 received Accent MRI systems with Tendril MRI leads; one received a device that was not an Accent MRI system and was excluded from primary endpoint analyses.
Intervention
The study evaluated the Accent MRI system, consisting of an Accent MRI pacemaker and Tendril MRI leads. The registry describes the study as observational and focuses on safety and efficacy in the stated pacing population.
Comparator
A like-for-like control group is not described. The registry record does not state an allocation method, and the listed arms are not a randomized comparison.
Primary question
The primary endpoint was freedom from right atrial and right ventricular lead-related complications, assessed during acute and chronic periods up to 12 months after implantation. The numerical endpoint result is not reported in the registry record.
The central statistical question is therefore whether the registry reports the proportion of the primary endpoint population without the specified lead-related complications, and how precisely that proportion was estimated. The endpoint description defines the complication types and follow-up periods, but the posted record does not provide the number of participants meeting the endpoint, the estimated percentage, or its confidence interval. Without those results, the endpoint cannot be quantified from the registry record.
The record also lists adverse-event counts and serious adverse-event terms. Those figures provide a separate description of reported events; they do not substitute for the primary endpoint result. The study has no stated randomized comparator, so its observations do not by themselves estimate a comparative treatment effect.
3. Trial Design
This was an observational study of the Accent MRI system with Tendril MRI leads in patients with a standard bradycardia pacing indication. The stated purpose was to assess the safety and efficacy of the leads as part of the Accent MRI system. The record identifies Abbott Medical Devices as the sponsor and lists the study status as completed.
The registry record lists enrollment as 466. It states that 464 patients were implanted. Of those implanted, 463 received the Accent MRI system with Tendril MRI leads, while one received a device that was not an Accent MRI system; that patient was excluded from primary endpoint analyses. The record does not explain the difference between enrollment and the number implanted, so no reason for that difference can be inferred.
The study began in 2012-02, and primary completion was recorded in 2014-06. The primary endpoint followed participants up to 12 months after implantation. Its description separates an acute period, from implantation to the 2 month visit, and a chronic period, from the 2 month visit through the 12 month visit.
The record does not state an allocation method or describe a randomized control group. It lists an Accent MRI System arm, but the record cautions that the arms are not a like-for-like control comparison. Accordingly, the design information does not support interpreting the listed groups as randomized treatment groups or as a controlled comparison. The protocol, recruitment procedures, and details of any additional follow-up are not reported in the registry record.
The registry lists one outcome measure and no analyses. The primary endpoint is named, but its observed result and statistical analysis are not reported in the registry record. The sample-size rationale and a prespecified statistical analysis plan are also 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.
Overall Study
| Stage | Accent MRI System |
|---|---|
| STARTED | 466 |
| COMPLETED | 422 |
| NOT COMPLETED | 44 |
Analysis population for the primary outcome, as defined in the registry: A total of 464 patients were implanted. 463 patients (99.78%) were implanted with Accent MRI™ systems with the Tendril MRI™ leads while the remaining 1 patient (0.22%) was implanted with a device that was not an Accent MRI™ system. This patient was excluded from all primary endpoint analyses.
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.
| Characteristic | Unit | Accent MRI System |
|---|---|---|
| Participants analysed | 466 | |
| Age, Continuous | years | 71.74 (SD 11.71) |
| Sex: Female, Male: Female | Participants | 194 |
| Sex: Female, Male: Male | Participants | 272 |
| AtrioVentricular-Block (AV-Block): No AV Block | participants | 179 |
| AtrioVentricular-Block (AV-Block): 1st Degree AV Block | participants | 41 |
| AtrioVentricular-Block (AV-Block): 2nd Degree AV Block | participants | 99 |
| AtrioVentricular-Block (AV-Block): 3rd Degree AV block | participants | 147 |
| Sick Node Dysfunction: Sick Node Dysfunction | participants | 205 |
| Sick Node Dysfunction: No Sick Node Dysfunction | participants | 261 |
| Neurocardiogenic Syncope: Previous Neurocardiogenic Syncope | participants | 75 |
| Neurocardiogenic Syncope: No Previous Neurocardiogenic Syncope | participants | 391 |
6. Primary Endpoint
The registry lists the primary outcome as Freedom From RA and RV Lead-related Complications, measured over up to 12 months post-implant.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | 97.5% Confidence Interval |
| Unit | percentage of participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is freedom from right atrial and right ventricular lead-related complications. It is expressed as a percentage of participants, with the registry specifying a 97.5% confidence interval. The endpoint description says that safety is evaluated separately for an acute period, from implantation to the 2 month visit, and a chronic period, from the 2 month visit through the 12 month visit. Follow-up extends up to 12 months post-implant.
In general, a participant-level percentage expresses how common an endpoint status is within a defined analysis population. A confidence interval conveys uncertainty around the estimate: a narrower interval indicates greater precision, while a wider interval indicates less precision. The interval does not remove limitations in how participants were selected or how outcomes were recorded.
Freedom from complications is relevant to the stated safety question because it focuses on whether lead-related complications occurred during the specified follow-up periods. However, the registry record does not report the endpoint percentage, event count, confidence interval limits, or period-specific results. It also does not explain how participants with incomplete follow-up or missing outcome information were handled. As a result, the endpoint's magnitude and precision cannot be assessed from the record.
The registry specifies the endpoint definition and reporting unit, but does not report the operational criteria used to classify a complication or the adjudication process. Those details are not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry identifies a clinically focused primary safety outcome: freedom from right atrial and right ventricular lead-related complications during acute and chronic follow-up, extending up to 12 months after implantation. It also specifies that the outcome is a participant percentage and that uncertainty was to be expressed with a 97.5% confidence interval. These details define what the endpoint was intended to measure, but they are not an endpoint result.
No numerical primary endpoint estimate, complication count, confidence interval limits, or analysis results are reported in the registry record. Therefore, the posted information does not establish the observed frequency of freedom from complications or the precision of that estimate. The registry lists one outcome measure and no analyses; the absence of a result should not be interpreted as evidence that there were no complications or that the endpoint was met.
The safety figures are separate from the primary endpoint. The adverse-event listing reports 174 serious events among 466 at risk and 78 other events among 466 at risk. It also lists serious-event terms with percentages, including Other Cardiac/cardiovascular at 5.6%, Arrhythmia at 5.4%, and infection at 4.3%. These are descriptive entries, not a randomized comparison, and the record does not establish that the event categories are mutually exclusive. A death count is not reported in the registry record.
Because the study is observational and the record does not state an allocation method or identify a comparable control group, the adverse-event figures cannot be read as a relative effect against another treatment. They describe events in the listed study group. Differences in who was included, follow-up, outcome ascertainment, or event reporting could affect comparisons with other data sources; those details are not reported in the registry record.
General statistical interpretation: an estimate is most informative when its population, endpoint definition, follow-up, and uncertainty are clear. Here, the endpoint definition and follow-up windows are stated, but the primary estimate and its uncertainty are absent. Consequently, no conclusion about the endpoint's observed frequency or its precision can be drawn from the registry record. The findings available for interpretation are limited to the stated design and the adverse-event listings.
9. Statistical Methods Explained
The registry describes the primary outcome as a percentage of participants and specifies a 97.5% confidence interval. It does not report the method used to calculate the percentage or interval, nor does it provide an analysis result. The following is general statistical context for interpreting this kind of endpoint, not a description of an analysis confirmed in the registry record.
What does a participant percentage represent?
For a binary outcome, each participant is classified according to whether the defined outcome occurred. A percentage then describes the proportion in a specified analysis population with the outcome status of interest. Interpreting it requires knowing the denominator, the outcome definition, and how incomplete observations were handled. The registry identifies the endpoint as freedom from lead-related complications but does not report the numerator or the primary analysis denominator. Its description says that one implanted patient who did not receive an Accent MRI system was excluded from all primary endpoint analyses. Other analysis-population details are not reported in the registry record.
What does a confidence interval add?
In general, a confidence interval communicates the uncertainty associated with an estimate under the assumptions of the method used. A narrower interval conveys more precision than a wider interval. The interval is not a guarantee that the underlying value lies within its limits, and it does not address systematic problems such as incomplete follow-up or outcome misclassification. The registry specifies a 97.5% confidence interval, but does not provide its limits or state the interval calculation method. It is therefore not possible to assess the precision of the primary estimate.
What can be said about the time periods?
The endpoint description defines acute follow-up as implantation to the 2 month visit and chronic follow-up as the 2 month visit through the 12 month visit. These periods distinguish early from later lead-related complications. The registry does not report period-specific estimates, event counts, or whether a participant with an event in one period could contribute to another period's result. Those analytic details are not reported in the registry record.
How should the design affect interpretation?
In general, an observational study describes outcomes in the population studied but does not provide the same protection against confounding as a randomized comparison. The registry does not state allocation and cautions that its arms are not a like-for-like control comparison. The listed adverse-event figures should therefore be read descriptively rather than as comparative estimates of an intervention effect. The record does not report an adjusted analysis or a statistical model for the primary endpoint.
What do the planning assumptions mean?
The planning illustration is described as using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. These are assumptions for a planning calculation, not evidence about how this observational study was designed or analyzed. The listed sample-size outputs are planning illustrations, not observed power. The registry's own sample-size justification is not reported in the registry record. The primary endpoint estimate that would anchor an observed-effect-based illustration is also not reported in the registry record.
General statistical context: over-dispersion matters when data vary more than a chosen model expects, because standard errors may then be too small and intervals too narrow. That issue is not identified as part of this endpoint analysis, and no over-dispersion model or diagnostic is reported in the registry record. No further statistical methods, including interim analyses, are reported in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists one outcome measure and identifies freedom from right atrial and right ventricular lead-related complications as the primary endpoint. The description separates acute and chronic follow-up periods, but the record does not explain whether these periods were treated as separate primary tests or as components of one endpoint. It does not report a multiplicity adjustment or a prespecified hierarchy for outcomes. The statistical plan is not reported in the registry record, so the approach to multiple testing cannot be assessed.
The record reports that one implanted patient who did not receive an Accent MRI system was excluded from all primary endpoint analyses. It does not provide the primary analysis population's endpoint denominator or explain how missing observations, withdrawal, loss to follow-up, or incomplete follow-up were handled. These procedures are not reported in the registry record. Without them, it is not possible to determine how the reported analysis population would relate to all enrolled participants, or how missing outcomes might affect the endpoint estimate.
The registry lists no analyses and does not provide a primary endpoint result. It also does not report whether analyses followed an intention-to-treat, per-protocol, or other population definition. No interim analyses are reported in the registry record. A missing analysis description should not be interpreted as proof that no analysis or interim review occurred; it means the registry record does not describe them.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Accent MRI System | 174 | 466 | 37.3% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Accent MRI System | 78 of 466 |
Most frequent serious adverse event terms
| Event term | Organ system | Accent MRI System |
|---|---|---|
| Other Cardiac/cardiovascular | Cardiac disorders | 26 of 466 |
| Arrhythmia | Cardiac disorders | 25 of 466 |
| infection | Infections and infestations | 20 of 466 |
| neurological event | Nervous system disorders | 16 of 466 |
| other various | Investigations | 16 of 466 |
| Exacerbation of heart failure | Cardiac disorders | 15 of 466 |
| lead dislodgement or migration | Surgical and medical procedures | 12 of 466 |
| Muskuloskeletal event | Musculoskeletal and connective tissue disorders | 10 of 466 |
| Pulmonary events | Respiratory, thoracic and mediastinal disorders | 9 of 466 |
| hematoma/bleeding | Injury, poisoning and procedural complications | 5 of 466 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Accent MRI System |
|---|---|---|
| arrhythmia | Cardiac disorders | 27 of 466 |
| other various | Investigations | 13 of 466 |
| other cardio/cardiovascular | Cardiac disorders | 9 of 466 |
| exacerbation of heart failure | Cardiac disorders | 4 of 466 |
| hematoma/bleeding | Injury, poisoning and procedural complications | 4 of 466 |
| lead noise | Investigations | 3 of 466 |
| musculoskeletal event | Musculoskeletal and connective tissue disorders | 3 of 466 |
| neurological event | Nervous system disorders | 3 of 466 |
| pulmonary event | Respiratory, thoracic and mediastinal disorders | 3 of 466 |
| device programming | Investigations | 2 of 466 |
Serious events with the highest arm-level rate: other cardiac/cardiovascular (5.6%), arrhythmia (5.4%), infection (4.3%), neurological event (3.4%), other various (3.4%).
The registry lists 174 serious adverse events among 466 at risk and 78 other adverse events among 466 at risk for the Accent MRI System group. It also lists serious adverse-event terms with percentages: Other Cardiac/cardiovascular, 5.6%; Arrhythmia, 5.4%; infection, 4.3%; neurological event, 3.4%; other various, 3.4%; and Exacerbation of heart failure, 3.2%.
These entries are descriptive safety information. The record does not state that event categories are mutually exclusive, so the counts or percentages should not be added together to infer a total number of affected participants. The term percentages do not establish whether each participant had only one event or whether repeated events were counted. Their precise denominator and coding details are not reported in the registry record.
The registry gives no death count; that information is not reported in the registry record. The serious-event figures are not the primary lead-complication endpoint, and they do not provide a comparison with a control group. They should be interpreted as reported adverse-event listings in the study group, with the endpoint and analysis details absent from the record.
12. What the Result Does, and Does Not, Mean
The record establishes that an observational study evaluated the Accent MRI system with Tendril MRI leads in patients with a standard bradycardia pacing indication. It defines a primary safety endpoint based on freedom from right atrial and right ventricular lead-related complications and specifies acute and chronic follow-up periods extending up to 12 months. It also reports adverse-event counts and selected serious-event terms.
It does not report the primary endpoint percentage, the number of lead-related complications, or the 97.5% confidence interval limits. Those missing results mean the primary endpoint's observed frequency and precision cannot be determined from the registry record. The absence of a posted endpoint result does not mean that no complications occurred or that the endpoint was achieved.
The adverse-event listings do not establish a causal effect or a comparative safety advantage. The study is observational, allocation is not stated, and the record cautions that the listed arms are not a like-for-like control comparison. The reported counts therefore describe the registry's study group rather than a randomized contrast.
General statistical context: a confidence interval can show how precisely a result is estimated, but it cannot resolve design limitations or missing outcome information. Even a precise estimate would apply to the population and follow-up actually analyzed; details of missing-data handling and analysis populations are not reported in the registry record. The record also does not report the endpoint's operational classification rules or adjudication procedure.
Accordingly, the registry supports a description of the study question, design, follow-up framework, and posted adverse-event entries. It does not support a numerical conclusion about the primary endpoint or a comparative claim about outcomes. The study's completion status does not fill in results that are not reported in the registry record.
13. Why This Trial Matters Statistically
This study illustrates why an endpoint definition and an endpoint result are not the same thing. The registry specifies freedom from right atrial and right ventricular lead-related complications, identifies acute and chronic observation periods, and calls for a participant percentage with a 97.5% confidence interval. Yet the endpoint estimate and interval are not reported in the registry record. A reader can understand the intended measurement without being able to evaluate its observed magnitude or precision.
It also highlights the importance of distinguishing descriptive safety reporting from comparative evidence. The adverse-event counts and serious-event terms describe the listed study group. The record does not state allocation or establish a like-for-like control group, so these figures do not quantify a comparative effect. This distinction is important when interpreting registries that contain multiple arms or event summaries without a randomized comparison.
Finally, analysis-population and missing-data details matter for participant-level percentages. The record identifies an exclusion from primary endpoint analyses but does not report the endpoint denominator, handling of missing outcomes, or analysis method. Such information is needed to understand precisely who contributed to the endpoint estimate and how uncertainty was calculated. In this case, the primary analysis result itself is also absent.
The statistical lesson is not that the device is safe or unsafe; the posted record does not establish either conclusion. Rather, it shows how design details, outcome definitions, denominators, uncertainty intervals, and analysis transparency jointly determine what a registry result can support.
14. 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 main limitation for statistical interpretation is that the primary endpoint result is not reported in the registry record. Although the endpoint definition, reporting unit, confidence-interval level, and follow-up periods are stated, the percentage, event count, and interval limits are absent. The registry lists one outcome measure and no analyses.
The study is observational, and allocation is not stated. The record cautions that the arms are not a like-for-like control comparison. Thus, the design information does not provide a randomized basis for comparing outcomes between groups. No adjusted comparative analysis is reported in the registry record.
The primary endpoint population is incompletely described. The record states that one implanted patient who received a device that was not an Accent MRI system was excluded from all primary endpoint analyses, but does not provide the final analysis denominator or explain the difference between enrollment and implantation. Missing-data handling, follow-up completeness, endpoint adjudication, and criteria for classifying lead-related complications are not reported in the registry record.
The adverse-event entries are also limited by absent detail. The record does not specify whether event categories overlap, give coding or ascertainment procedures, or report a death count. The listed serious-event percentages do not replace the primary endpoint analysis and cannot establish a comparative effect.
The registry's sample-size justification and statistical analysis plan are not reported in the registry record. Therefore, the rationale for the planned enrollment, any analysis assumptions beyond the stated planning illustration, and any interim monitoring cannot be assessed.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Safety and Efficacy Study of Tendril MRI™ Leads in Standard Bradycardia Pacing Indication — NCT01528150.
- Registry record last updated 2019-02-04; status last verified 2019-01.
- Results first posted 2016-08-31.
- 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.
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18. Record Summary
The registry describes a completed observational study of the Accent MRI system with Tendril MRI leads in patients with a standard bradycardia pacing indication. It lists 466 enrolled participants and reports that 464 were implanted. Of those implanted, 463 received Accent MRI systems with Tendril MRI leads, while one received a different device and was excluded from primary endpoint analyses.
The primary endpoint was freedom from right atrial and right ventricular lead-related complications, assessed during acute and chronic periods up to 12 months post-implant. A participant percentage and 97.5% confidence interval were specified, but the endpoint result is not reported in the registry record. The record lists adverse-event counts and serious-event terms, but no analyses. Allocation, a like-for-like control comparison, and details of missing-data handling are not reported in the registry record.