PORTuguese Research on Telemonitoring With CareLink® (PORTLink): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for PORTuguese Research on Telemonitoring With CareLink® (PORTLink) (NCT03125382), a randomized na study. The primary outcome is Number of Patient Satisfied or Very Satisfied With Carelink.

2. Clinical Question

The primary endpoint is not a direct comparison of satisfaction between CareLink and in-clinic follow-up. Its stated population is limited to the CareLink arms, and the reported comparison contrasts new implants with previous implants within those arms. That distinction matters: the primary result addresses satisfaction among CareLink users and the difference between implant-history groups, rather than whether CareLink produces greater satisfaction than in-clinic care.

The registry describes satisfaction as a semi-quantitative evaluation of CareLink and patient preference compared with traditional follow-up. Response options range from very satisfied to very unsatisfied, with a neutral category. The posted primary measure counts participants who were satisfied or very satisfied. It therefore represents a selected grouping of the response scale, rather than a complete analysis of every satisfaction category or a direct measure of clinical outcomes.

3. Trial Design

PORTLink is recorded as a randomized, parallel-group trial with no masking. The registry lists the study as completed and records enrollment of 141. The listed study period runs from 2012-04 to primary completion in 2016-10. The sponsor is Medtronic Cardiac Rhythm and Heart Failure.

The study compares CareLink telemonitoring with in-office standard visits for people with implantable cardiac defibrillators. The arm descriptions distinguish participants with new implants from participants with previous implants in both follow-up approaches. For the primary endpoint, however, only the CareLink arms apply. The displayed primary comparison is between the CareLink participants with new implants and those with previous implants; it does not use the in-office groups as the primary comparator.

Randomization and a parallel design describe how treatment groups were organized, but the registry record does not report enough detail to reconstruct the randomization procedure, allocation concealment, or whether the analysis followed the assigned groups regardless of actual follow-up. Those details are not reported in the registry record. Masking is listed as none, so the study is recorded as unmasked.

The record lists the primary outcome as the number of participants satisfied or very satisfied with CareLink at the 12 months visit. It also lists secondary outcomes covering device-related adverse events, satisfaction ratings associated with transmissions, resource use, quality of life, and unanticipated serious adverse device effects. The registry record does not provide a complete statistical analysis plan or a justification for the enrollment target. Those details 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: There were 7 screening failures;

Randomization

Reasons for not completing this period:

Follow-up

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Only applicable for Carelink arms

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 Number of Patient Satisfied or Very Satisfied With Carelink, measured over 12 months visit.

The primary endpoint counts participants who selected either “Satisfied” or “Very Satisfied” in the evaluation of the CareLink System at the 12 months visit. The registry describes a response scale that also includes neutral and dissatisfied categories, and says the evaluation concerned satisfaction and preference compared with traditional in-clinic follow-up. The posted endpoint reduces that ordered set of responses to a count of participants in the two favorable categories.

A participant count is readily interpretable as the number meeting the endpoint definition. It does not retain the distinctions between “Satisfied” and “Very Satisfied,” nor does it describe the full distribution across all response options. The result should therefore be read as the count meeting the registry’s specified threshold, not as a summary of every aspect of participants’ views.

This endpoint is useful for describing reported experience with the monitoring system. It is not a measure of arrhythmia control, device performance, or clinical benefit. The registry specifies that the primary outcome applies only to CareLink arms, so the endpoint does not directly quantify satisfaction in the in-office standard-visit arms. Its stated comparison instead concerns CareLink participants with new implants versus CareLink participants with previous implants.

7. Results Posted in the Registry

• Carelink - Previous Implants: 100.0% (34/34) versus 97.1% (34/35) on control; risk difference 2.9 percentage points (95% CI -2.7 to 8.4), risk ratio 1.03 (0.97–1.09); unadjusted two-proportion z-test p = 0.321.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Health Care Consumed Resources Between Groups Relative to Unscheduled Visits

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Carelink: mean 0.40 versus 1.10 on control; difference -0.70 (95% CI -0.96 to -0.44), standardized effect d = -0.92; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Carelink than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The registry lists secondary outcomes spanning safety, satisfaction associated with device transmissions, health-care and patient resource use, quality of life, and serious adverse device effects. The quantitative secondary result detailed in the record concerns unscheduled health-care visits between the in-office standard-visit and CareLink groups. These outcomes address different domains from the primary endpoint, which concerns satisfaction within CareLink implant-history groups.

Because these measures concern different questions and use different scales, they cannot be combined into a single overall conclusion about the monitoring approaches. A resource-use contrast does not directly validate a satisfaction result, and satisfaction does not determine the pattern of safety outcomes. The registry record does not report a comprehensive analysis linking these outcomes or testing whether one explains another.

The listed secondary outcomes include multiple endpoints, but the record gives no multiplicity strategy. When many outcomes are examined, unadjusted p-values can produce apparently notable findings by chance even if no true effect exists. This is a general statistical concern, not a claim that any particular secondary result is false. Without a prespecified hierarchy or adjustment approach reported in the registry record, secondary findings should be treated as exploratory and interpreted alongside their estimates, intervals, definitions, and completeness of reporting.

The secondary information therefore provides context rather than a unified confirmation of the primary result. The record does not report all listed outcomes with comparable numerical detail, and it does not give a complete account of the analyses behind them. That limits the strength of any broad pattern claim across secondary outcomes.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Number of Device Related Adverse Events
• Physician Satisfaction With Carelink: Total Number of Transmissions With Satisfaction Ratings
• Health Care Consumed Resources Between Groups Relative to Unscheduled Visits
• Compare Patient Consumed Resources Between Groups
• Compare Patient Consumed Resources Between Groups
• Improvement in Quality of Life
• Number of Unanticipated Serious Adverse Device Effects (USADE) Rate

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is binary for the posted comparison: a participant either falls within the combined satisfied or very satisfied categories or does not. The registry reports counts and denominators for the two CareLink groups and a risk-difference estimate with a confidence interval. A risk difference expresses the contrast between the groups’ proportions meeting the endpoint definition. Values near zero indicate little estimated separation on that scale; the interval communicates how uncertain the estimate is.

What does the confidence interval describe?

In general, a confidence interval is a range of values compatible with the observed data under the method used to calculate it. It is not a range containing a known fixed percentage of individual participant outcomes, and it does not mean that each value in the interval is equally plausible. For the primary comparison, the interval crosses zero. On the risk-difference scale, zero represents no difference between the groups. The interval therefore does not identify a clear direction for the contrast.

How should the p-value be read?

The unadjusted p-value is reported as 0.321. In general, a p-value measures how incompatible the observed data are with a specified null model, assuming the model and its assumptions apply. It is not a measure of the probability that the groups are truly the same, nor does it demonstrate equivalence. The registry record does not report a prespecified equivalence or non-inferiority margin. A non-significant result cannot substitute for such a design and analysis.

The posted comparison also gives a ratio estimate of 1.029, with interval limits of 0.973 and 1.09. Ratios express a contrast on a relative scale rather than as an absolute difference. Reading the ratio alongside the risk difference can help describe the same comparison in different terms, but neither scale changes the central limitation: this is a contrast between the CareLink new-implant and previous-implant groups, not between monitoring approaches.

What do the secondary estimates represent?

The resource-use outcome is reported as a mean number of unscheduled visits, with a standard deviation for each follow-up group. Its comparison is expressed as a mean difference with a confidence interval and an unadjusted p-value. In general, a mean summarizes the average observed value, while the standard deviation describes variability among observations. The standard error, when reported, describes the estimated uncertainty of a sample mean. These quantities answer different questions and should not be treated as interchangeable.

The registry also includes a planning illustration for this continuous outcome. It uses the observed effect as a basis for hypothetical future sample-size planning, with the stated two-sided significance level of 0.05, equal allocation, and a normal approximation. It considers planning for 100%, 75%, and 50% of the observed effect, and gives participants per arm for 80% power and 90% power. These are planning illustrations, not observed power and not evidence that the original trial was designed using those assumptions. The trial’s own sample-size justification is not reported in the registry record.

Why can variability affect a mean comparison?

In general, mean-based methods rely on assumptions about the distribution and variability of observations. Resource-use counts can be unevenly distributed, and their variability may not match the assumptions of a simple normal approximation. Over-dispersion occurs when variability is greater than expected under a chosen count model; it can make standard errors too small if the model does not account for it. The registry record does not report a model addressing over-dispersion or other distributional features for the resource-use outcome. The normal approximation stated for the planning illustration is not evidence that this was the analysis model used for the observed outcome.

The posted estimates are unadjusted. An unadjusted comparison does not account for other participant characteristics or possible differences in follow-up unless those are built into the method. The registry record does not report adjusted analyses for the primary endpoint. The listed analysis count is 0, and the reported analyses field is empty. These omissions mean that the record does not establish which models, covariates, or analysis populations were planned or used beyond the posted summaries.

11. Confidence Intervals and Precision

The primary risk-difference estimate is 0.029, with a confidence interval from -0.027 to 0.084. The interval spans zero and includes both negative and positive values. This indicates that the direction of the difference is not precisely determined by the posted data. The interval also conveys that the estimate is uncertain enough to be compatible with a range of group contrasts, rather than pinning down a single value.

The confidence interval should be interpreted on the risk-difference scale, where zero means no difference. Its limits are not predictions for individual participants and do not describe the range of satisfaction responses. They quantify uncertainty in the estimated group contrast under the calculation method. The registry record does not report the method used to construct the interval, so its assumptions cannot be independently assessed from the record alone.

The reported ratio estimate and interval offer a relative-scale description of the same comparison. As with the risk difference, the interval includes the null value for a ratio, which is 1. The point estimate alone should not be used to imply a definite group advantage when the interval is broad enough to include values on both sides of the null.

Precision depends on the amount of information in the data, the event pattern, and the analysis method. The displayed denominators for the primary endpoint are 35 and 34. Those group sizes and the close counts are relevant to interpreting the uncertainty, but they do not justify a claim of equivalence. The registry record does not report a target precision or a margin defining a difference small enough to be considered unimportant.

12. Multiplicity, Missing Data and Analysis Populations

The registry record lists multiple secondary outcomes, but it does not report a multiplicity procedure or an outcome hierarchy for interpreting multiple statistical tests. When several hypotheses are tested, the chance of at least one apparently unusual result can increase. General approaches include adjusting for multiple testing or defining a prioritized testing sequence in advance. The registry record does not say whether either approach was planned or used, so unadjusted secondary results should be treated cautiously.

The record lists 0 analyses and has no reported analyses entry, despite containing posted outcome summaries and comparisons. It does not describe a complete statistical analysis plan, including the intended handling of covariates, missing observations, or deviations from assigned follow-up. Those details are not reported in the registry record.

Missing-data handling is especially relevant for a participant-reported satisfaction endpoint. The record gives counts and denominators for the CareLink groups but does not explain how missing satisfaction responses were treated, whether all eligible participants completed the assessment, or how the denominators were determined. It also does not report sensitivity analyses for missing outcomes. No assumption about missingness, such as whether it was random, can be made from the posted information.

The analysis population is also not specified beyond the primary endpoint’s statement that it applies only to CareLink arms. The registry record does not state whether the analysis was intention-to-treat, per-protocol, or based on participants with available outcome data. Nor does it report how participants were classified if their received follow-up differed from their assigned group. These omissions limit assessment of possible bias and make it difficult to reproduce the analysis from the registry record.

13. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: exarcebation chronic kidney disease (3.6%), pulmonary embolism (3.6%), death (2.9%), pulmonary edema (2.9%).

The registry reports serious-event figures separately for the in-office standard-visit and CareLink groups, distinguishing new implants from previous implants. It records serious events affecting 1 participant in the In Office Standard Visit-New group, 2 in the In Office Standard Visit-Previous group, 1 in the Carelink - New Implants group, and 2 in the Carelink - Previous Implants group. The record also reports death counts of 1, 2, 1, and 2, respectively, for those same groups.

These are descriptive registry counts, not estimates of comparative safety. The record does not provide a statistical comparison, event timing, person-time, or details sufficient to determine whether events were related to the device, monitoring approach, or other causes. Serious adverse events should not be treated as identical to serious adverse device effects; the registry lists unanticipated serious adverse device effects as a separate outcome.

The listed serious-event terms and percentages describe reported events but do not establish causation or a rate difference between approaches. Without fuller definitions and follow-up details, the figures should be read as a safety snapshot rather than as proof for or against a safety difference.

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

The primary result describes satisfaction or very high satisfaction among participants assigned to the two CareLink implant-history groups. It shows that the posted counts were 34 of 35 for CareLink - New Implants and 34 of 34 for CareLink - Previous Implants. The reported risk difference and interval do not establish a clear difference between those groups. They also do not establish equivalence, because the registry record does not report an equivalence margin or an analysis designed to demonstrate equivalence.

The result does not directly compare satisfaction between CareLink and in-office standard visits. Although the study includes both follow-up approaches, the stated primary endpoint applies only to CareLink arms. It therefore cannot be used as a direct estimate of the effect of telemonitoring versus in-clinic follow-up on satisfaction.

The endpoint also captures a specific threshold on a satisfaction scale. It does not describe the entire distribution of responses, the intensity of preference, or clinical outcomes. A high count meeting the endpoint definition should not be interpreted as evidence about arrhythmia outcomes, device performance, or overall health-care benefit. Those questions require outcomes and analyses designed to address them.

The secondary resource-use result and the listed safety information add context, but they do not change the scope of the primary comparison. The registry record does not provide a complete statistical analysis plan, missing-data methods, or a clear account of the analysis population. These gaps limit conclusions about how robust the results are to analytic choices and incomplete outcome information.

In general, clinical interpretation depends on both the estimated effect and its precision, as well as the design, outcome definition, and relevance of the comparison. Here, the posted primary result is an uncertain comparison between two CareLink groups. It should not be recast as proof that one follow-up approach is superior, inferior, or interchangeable with another.

15. Why This Trial Matters Statistically

This trial illustrates why the precise comparison behind an endpoint matters. A study may include two follow-up approaches, while its primary outcome applies only to a subset of the arms. In PORTLink, the primary satisfaction result concerns CareLink participants with new implants versus CareLink participants with previous implants. It does not answer the broader question of satisfaction under CareLink compared with in-clinic follow-up.

It also illustrates the importance of reading an estimate together with its uncertainty. The observed counts are close, and the risk-difference interval crosses zero. The point estimate alone cannot establish the size or direction of a reliable underlying difference. Conversely, an unadjusted p-value that does not meet a conventional threshold would not establish that the groups are equivalent.

The trial also demonstrates that outcome domains should remain distinct. Satisfaction, unscheduled visits, quality of life, and adverse events have different meanings and measurement properties. A result in one domain does not automatically confirm or explain a result in another. When several outcomes are listed without a reported multiplicity plan, secondary comparisons deserve particular caution.

Finally, registry records can contain useful endpoint counts and estimates while leaving important analytic details unreported. Information on missing data, analysis populations, model choices, and sample-size justification helps readers assess reproducibility and bias. Its absence does not erase the posted findings, but it limits how far they can be interpreted.

16. 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.

A key limitation specific to this record is the separation between the trial’s broad comparison and the primary endpoint’s stated population. The study includes CareLink and in-office standard-visit arms, but the primary satisfaction outcome is specified only for CareLink arms. The posted primary contrast therefore concerns new versus previous implants within CareLink, rather than telemonitoring versus in-clinic care.

The endpoint combines “Satisfied” and “Very Satisfied” into a single count. The registry record does not provide the distribution across all response categories, nor does it explain how missing satisfaction responses were handled. The extent to which the posted count represents all eligible CareLink participants is therefore not clear from the record.

The study is recorded as randomized and unmasked, but the registry does not report details of sequence generation, concealment, or the analysis population. It also does not report the primary analysis plan, a sample-size justification, or a multiplicity strategy. These omissions limit assessment of whether the reported comparisons match prespecified methods and how potential biases were addressed.

Secondary outcomes are described across several domains, but numerical detail and analysis information are not comprehensive. The serious-event figures are descriptive and lack the context needed for a comparative safety assessment. The planning illustration is based on an observed secondary effect and stated assumptions; it is not a record of the original trial’s design justification.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: PORTuguese Research on Telemonitoring With CareLink® (PORTLink) — NCT03125382.
• Registry record last updated 2025-07-02; status last verified 2023-05.
• Results first posted 2024-02-05.
• 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.

20. Record Summary

PORTLink is a completed, randomized, unmasked, parallel-group study of CareLink telemonitoring and in-office standard follow-up in people with implantable cardiac defibrillators and arrhythmia. Enrollment is listed as 141, with the study period recorded from 2012-04 to primary completion in 2016-10.

The primary endpoint counts participants satisfied or very satisfied with CareLink at the 12 months visit. Its reported comparison is between CareLink participants with new implants and those with previous implants, not between CareLink and in-office follow-up. The estimate is accompanied by a confidence interval that includes zero.

The registry also lists secondary resource-use, satisfaction, quality-of-life, and safety outcomes. Details of the statistical plan, missing-data handling, analysis populations, and sample-size justification are not reported in the registry record.