Relationship Between LINQ™ Subcutaneous Impedance and Right-sided Hemodynamic Measurements: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Relationship Between LINQ™ Subcutaneous Impedance and Right-sided Hemodynamic Measurements (NCT03608826), a na na study. The primary outcome is Comparison of Reveal LINQ™ Subcutaneous Impedance (Units of Ohms) With Pulmonary Artery Pressure (Units of mmHg) From a Swan-Ganz Catheter During Right Heart Catheterization Procedures in Patients With Heart Failure..

2. Clinical Question

The study asks whether changes in Reveal LINQ™ subcutaneous impedance correspond to right-sided hemodynamic measurements in patients with heart failure. Its primary objective describes two settings: short-term drug and/or exercise challenges during right heart catheterization, and long-term daily trends in physiologic data. The registry record identifies pulmonary artery pressure measured with a Swan-Ganz catheter during right heart catheterization as the pressure measure to be compared with subcutaneous impedance.

This is a question about measurement relationships. It is not, by itself, a test of whether a treatment improves heart failure outcomes or whether impedance can replace catheter-based assessment. The registry record does not report an estimated relationship, the precision of that estimate, or a conclusion from the primary analysis. It therefore describes what the investigators intended to examine, rather than establishing whether the measurements tracked together.

3. Trial Design

The registry classifies the study as completed and single-group, with enrollment of 12. It lists Heart Failure as the condition and Medtronic Cardiac Rhythm and Heart Failure as the sponsor. The recorded start date is 2018-07-13, and the primary completion date is 2021-05-07. Phase is recorded as NA. Allocation is also recorded as NA, and masking is NONE.

The single arm is described as receiving investigational RAMware downloaded onto the LINQ device. Because there is no separate control arm in the record, differences between treatment groups cannot be estimated. The study instead focuses on whether impedance measurements relate to hemodynamic measurements and other physiologic data. The registry description includes short-term drug and/or exercise challenges during right heart catheterization and long-term daily trends. It does not give further details about the timing or conduct of those challenges.

The primary outcome is framed as a comparison of Reveal LINQ™ subcutaneous impedance, in ohms, with pulmonary artery pressure, in mmHg, measured using a Swan-Ganz catheter during right heart catheterization procedures. Its listed timeframe is 18 months. The record also lists secondary outcomes concerning changes in impedance and LINQ™ activity before acute decompensated heart failure events. The record lists 4 outcome measures, but does not report analyses for them.

This design is appropriate to describe as an observational measurement relationship within a single study group, not as a randomized comparison. The record does not report a control group, random assignment, or masking. It also does not report enough procedural detail to determine how many measurements each participant contributed, how measurements were paired, or how participants were selected for catheterization or follow-up.

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.

6. Primary Endpoint

The registry lists the primary outcome as Comparison of Reveal LINQ™ Subcutaneous Impedance (Units of Ohms) With Pulmonary Artery Pressure (Units of mmHg) From a Swan-Ganz Catheter During Right Heart Catheterization Procedures in Patients With Heart Failure., measured over 18 months.

The primary endpoint concerns the comparison of Reveal LINQ™ subcutaneous impedance with pulmonary artery pressure measured during right heart catheterization using a Swan-Ganz catheter. Impedance is recorded in ohms and pressure in mmHg. The primary objective describes examining changes in these measurements during short-term drug and/or exercise challenges, as well as relating long-term daily physiologic trends to hemodynamic measurements. The listed timeframe is 18 months.

The reason for examining the relationship is to characterize whether a device-derived subcutaneous measurement varies in relation to a right-sided hemodynamic measure. This is a measurement question: it concerns how two physiologic signals correspond, not whether an intervention changes clinical outcomes. A strong or weak relationship, if estimated, would need to be interpreted with its uncertainty and with attention to how and when the measurements were collected.

The registry lists the endpoint unit as participants and the measure as a count of participants. It does not report the operational definition of a successful comparison, an association estimate, a threshold, or participant-level endpoint results. No primary analysis result is reported in the registry record. Consequently, the endpoint’s intended measurement comparison is identifiable, but the posted record does not establish the direction or strength of the relationship.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record gives the study structure and outcome description, but does not report the statistical analysis plan or primary analysis results. The concepts below are general statistical explanations; they should not be read as a description of analyses performed in this study.

What does a relationship between measurements mean?

In general, an association analysis asks whether values of one measurement tend to vary with values of another. For this study, the stated measurements are subcutaneous impedance and pulmonary artery pressure. An analysis might describe the direction and strength of their co-variation, but the record does not say which statistical measure was used. It reports no association estimate, confidence interval, or p-value. The objective alone does not establish that the association was positive, negative, or present.

Association is not the same as agreement. Two measures may vary together while having different scales or while differing systematically in level. Conversely, a study of agreement asks how closely measurements correspond in a way relevant to interchangeability. The registry record describes a relationship comparison and does not report an agreement criterion or validation threshold. It therefore does not establish that impedance can substitute for catheter-based pressure measurement.

Why does measurement timing matter?

Repeated measurements from the same participant are generally correlated: observations from one person may be more alike than observations from different people. General statistical methods account for this dependence when estimating uncertainty. Treating every observation as independent when it is not can make uncertainty appear smaller than it is. The registry record does not report how many readings were collected per participant, how readings were paired, or what method was used to account for repeated measurements.

Timing also defines the question being estimated. Short-term measurements during drug and/or exercise challenges concern change in a procedural setting. Daily trends concern patterns over time. A single summary could conceal differences between those contexts, while separate analyses would answer distinct questions. The record does not report whether the investigators analyzed these settings separately, combined them, or specified another approach.

What would an uncertainty interval tell a reader?

In general, a confidence interval gives a range of values compatible with an estimate under the assumptions of the statistical method. A narrow interval indicates greater precision than a wide interval, although precision does not establish clinical importance or remove bias. Because the registry record does not report an estimate or confidence interval for the primary relationship, its precision cannot be assessed. A p-value, if reported, would address compatibility with a specified null model; it would not measure the size or practical importance of a relationship. No primary p-value is reported.

What is the relevance of the single-group design?

A single-group measurement study can describe within-group patterns and associations. It does not provide a randomized control group against which to estimate a comparative treatment effect. A relationship between impedance and pressure could also be influenced by context, participant characteristics, timing, or other physiologic changes. Statistical adjustment can address measured covariates under suitable assumptions, but the record does not report whether adjustment was planned or performed. No causal interpretation follows from the design description alone.

How should planning illustrations be understood?

In general, a sample-size calculation is a planning exercise based on assumptions about the effect to detect, variability, significance level, allocation, and statistical method. It is not an observed result and should not be described as observed power. The registry’s planning assumptions describe an illustration based on a fraction of an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The record also notes that time-to-event illustrations use total events, while other illustrations use participants per arm. These are not descriptions of this single-group study’s actual design. The registry record does not report a trial-specific sample-size justification or enough result information to interpret a planning illustration as a basis for this study’s primary analysis.

General interpretation of a measurement study also depends on the data structure and missingness. If some participants or measurements are unavailable, the analyzed observations may not represent all enrolled participants. The record does not describe missing-data handling, an analysis population, or sensitivity analyses. These details are necessary to understand how an estimate was formed and whether its uncertainty reflects incomplete observations.

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("Observation")
n      <- c(11)
events <- c(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  Observation  11  0  0.0  0.0  28.5  -0.0  25.9  0.2  26.5

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists 4 outcome measures, including the primary impedance-pressure comparison and secondary outcomes concerning changes in impedance and activity before acute decompensated heart failure events. It lists 0 analyses. No multiplicity strategy is reported in the registry record. That means the record does not explain whether a primary outcome was given priority in formal testing, whether secondary outcomes were treated as exploratory, or whether any adjustment was planned for examining multiple outcomes. Without such information, a reader cannot assess how a collection of statistical tests would affect interpretation of any reported p-values. No outcome-specific p-values are reported.

Missing-data methods are also not reported in the registry record. It does not state whether missing measurements were expected, how missing impedance or pressure readings were handled, or whether participants with incomplete data were included in particular analyses. The effects of missingness depend on why observations are absent; no assumption about that reason can be made from the record.

The record does not define an intention-to-treat, per-protocol, or other analysis population. It therefore does not specify which enrolled participants or measurements would contribute to a primary estimate. Enrollment is listed as 12, but enrollment alone does not identify the number included in any analysis. The record does not report interim analyses, a prespecified statistical analysis plan, or sensitivity analyses. These details are not reported in the registry record; their absence there does not establish whether such procedures were conducted outside the record.

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

Serious events with the highest arm-level rate: death (25.0%), hospitalization (8.3%).

The safety record describes a single arm with 12 participants at risk for serious adverse events. It records 4 participants with serious adverse events and 3 deaths. It records 0 other adverse events among 12 participants at risk. The listed serious adverse-event terms include Death at 25.0% and Hospitalization at 8.3%.

These figures describe events recorded in the study group. They do not establish that the device, RAMware, catheterization, or another study procedure caused an event. The registry record does not provide an attribution assessment, event timing, severity details beyond the serious-event classification, or a control group for comparison. It also does not explain whether the listed terms can overlap within participants. Therefore, the percentages for terms should not be interpreted as mutually exclusive categories or as a treatment-attributable risk.

Counts and percentages answer different descriptive questions, but neither provides a causal comparison in a single-group record. The safety figures should be read as reported observations during the study, not as proof for or against a causal safety effect.

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

The record establishes that ReLINQuish was a completed, single-group study designed to characterize the relationship between LINQ™ subcutaneous impedance and right-sided hemodynamic measurements in patients with heart failure. The stated comparison involves impedance and pulmonary artery pressure measured during right heart catheterization, with the broader objective also referring to short-term challenges and long-term daily trends.

What the record does not establish is the result of that comparison. It contains no reported primary association estimate, confidence interval, p-value, or participant-level outcome result. Without those results, readers cannot determine whether impedance tracked pressure, how strong any relationship was, or how precise it may have been. The objective and endpoint description should not be presented as if they were findings.

The study design also limits what could be inferred from an association, even if one were reported. A relationship between two measurements would not by itself show that one caused the other, that the device measurement could replace catheter-based measurement, or that using the measurement improves care or outcomes. The record reports no randomized control group and no comparative treatment effect.

The safety counts are descriptive observations in the single study group. They do not establish causation and cannot be compared with an unreported control group. More detailed event attribution and timing are not reported in the registry record.

Accordingly, the posted record is informative about the intended measurement question, study structure, and recorded safety events, but it is insufficient to judge the primary relationship’s magnitude, reliability, or clinical implications. Those questions remain unresolved by the results reported in the registry record.

14. Why This Trial Matters Statistically

This study raises a useful statistical question: whether an implanted device’s subcutaneous impedance measurement varies in relation to right-sided hemodynamic measurements. Addressing that question requires more than naming two physiologic measures. It requires defining how they are paired in time, what relationship is estimated, and how repeated measurements within participants are handled. Those details affect both the estimate and its uncertainty.

The study’s design highlights the difference between measurement research and comparative treatment research. A single-group study can investigate whether measures co-vary in a particular setting, but it does not estimate a randomized difference between groups. Keeping that distinction clear prevents a measurement objective from being interpreted as evidence of treatment benefit or causal effect.

The record also illustrates why outcome definitions and analysis reporting matter. The primary endpoint description identifies the impedance and pressure measures, but does not report an operational success criterion or analysis result. Without an estimate and its precision, readers cannot judge the strength or consistency of the relationship. Without information on repeated readings, missing data, and analysis populations, they also cannot fully assess how an estimate would represent the enrolled group.

Finally, a completed status does not by itself mean that interpretable results are available in the registry record. Here, the record gives study purpose and design information, but lists 0 analyses. Clear distinction between a planned question and a reported finding is essential to responsible interpretation.

15. Limitations

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

The primary limitation for interpreting this trial is that the registry record does not report results for the primary measurement relationship. It gives no estimate of association, uncertainty interval, or formal test result. The record therefore cannot support conclusions about the direction, magnitude, or precision of the relationship between impedance and pulmonary artery pressure.

The study is single-group, with allocation recorded as NA and no control arm described. This design does not provide a randomized comparator and cannot establish a comparative treatment effect. It also makes it inappropriate to interpret recorded safety events as a causal effect of the device or study procedures.

Important details about measurement collection and analysis are not reported in the registry record. These include the number and timing of paired readings, how short-term challenge measurements relate to long-term trends, the statistical method, handling of repeated observations, missing-data procedures, analysis populations, and multiplicity strategy. The record does not state an operational criterion for a meaningful or successful measurement relationship.

The enrollment listing is 12, but the number contributing to any analysis is not reported. The adverse-event record provides counts and listed terms but does not report event timing, attribution, or whether categories overlap. These gaps limit interpretation of both efficacy-related measurements and safety observations. They should be understood as reporting limitations of the registry record, not evidence that a particular procedure was or was not conducted.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Relationship Between LINQ™ Subcutaneous Impedance and Right-sided Hemodynamic Measurements — NCT03608826.
• Registry record last updated 2022-12-23; status last verified 2022-12.
• Results first posted 2022-12-23.
• 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

ReLINQuish is recorded as a completed, single-group study sponsored by Medtronic Cardiac Rhythm and Heart Failure, with enrollment of 12. Its stated purpose was to characterize the relationship between Reveal LINQ™ subcutaneous impedance and right heart hemodynamic measurements in patients with heart failure. Investigational LINQ™ HF RAMware was downloaded onto the LINQ device. The primary comparison concerns impedance and pulmonary artery pressure measured during right heart catheterization, with a listed timeframe of 18 months.

The record also lists secondary outcomes concerning impedance and activity before acute decompensated heart failure events. It reports serious adverse events in 4 participants, 3 deaths, and 0 other adverse events; listed serious-event terms include Death and Hospitalization. No primary analysis results are reported in the registry record, so the intended measurement relationship cannot be evaluated from the posted results.