Comparison of Outcomes Between the Use of Silverlon® Dressing and AQUACEL® AG Dressing Post Cardiac Device Implant: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison of Outcomes Between the Use of Silverlon® Dressing and AQUACEL® AG Dressing Post Cardiac Device Implant (NCT02781779), a randomized na study. The primary outcome is Pocket Hematoma, Moderate-Severe.

2. Clinical Question

The trial was intended to examine how effective the two dressings are in preventing post-procedure wound infections, according to its brief summary. The registered primary endpoint, however, is moderate-to-severe pocket hematoma, not infection. These outcomes should not be treated as interchangeable: a hematoma is an accumulation of blood in or near the surgical incision, while infection is a separate clinical outcome. The registry describes several additional wound and skin outcomes, but those results are not all posted in the record.

The primary comparison is based on the number of participants recorded with the endpoint in each randomized arm. It does not, by itself, answer every question about wound infection, the other secondary outcomes, or outcomes beyond the stated follow-up timeframe. The record does not provide further details about participant eligibility, baseline characteristics, or how endpoint assessments were conducted.

3. Trial Design

The registry describes a randomized, parallel-group study with no masking. Participants were assigned to postoperative Silverlon® or AQUACEL® AG dressing. The trial is listed as completed, with a recorded enrollment of 147. Its phase is listed as NA. The sponsor is Kansas City Heart Rhythm Institute.

The registry records a start date of 2016-06 and a primary completion date of 2017-12. These are registry dates and do not establish the precise dates on which every participant was enrolled, treated, or followed. The record does not describe the randomization sequence, allocation concealment, or procedures for implementing the assignment. It also does not report whether participants, clinicians, or endpoint assessors were otherwise aware of treatment assignment; the masking entry is NONE.

The two groups are compared on a binary primary outcome: whether a participant had a moderate-to-severe pocket hematoma within the stated timeframe. The posted arm data list 2 participants with the outcome among 78.0 in the Silverlon® group and 2 among 69.0 in the AQUACEL® AG group. The primary assessment timeframe is 7-10 days post implant.

The registry lists Wound Drainage, Pocket Dehiscence, Rash After Removal, Site Itching/Burning, and Skin Erythema as secondary outcomes. It posts result entries for the first three; results for Site Itching/Burning and Skin Erythema are not reported in the registry record. There are no reported analyses listed for the secondary outcomes. The record does not describe an analysis population, missing-data handling, or a prespecified statistical analysis plan.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: Immunocompromised patients and those on non-standard antibiotic regimens were excluded.

Overall Study

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 Pocket Hematoma, Moderate-Severe, measured over 7-10 days post implant.

The primary endpoint is the number of participants with a moderate-to-severe pocket hematoma, assessed at 7-10 days post implant. The registry defines a pocket hematoma as an accumulation of blood in or near the surgical incision arising from a defect in hemostasis, such as blood-vessel injury. It distinguishes mild findings from the moderate-to-severe endpoint: moderate hematoma involves a large pocket effusion with swelling that causes functional impairment or pain, while severe hematoma involves specified consequences such as reoperation, prolonged hospitalization, or interruption of oral anticoagulation under the conditions described in the registry.

This outcome is relevant to the trial's postoperative wound focus because the registry notes that pocket hematoma can be associated with local discomfort, increased infection risk, surgical intervention, or longer hospital stays. Those contextual statements explain why the outcome may matter; they are not findings that this trial itself established.

The endpoint is recorded as a participant count, rather than as a continuous measurement. The primary result therefore describes how many participants in each arm were classified as having a moderate-to-severe hematoma during the specified assessment period. It does not describe mild hematomas as part of the primary outcome, nor does it measure infection directly. The registry does not report further details about endpoint adjudication, assessor training, or how uncertain classifications were resolved.

7. Results Posted in the Registry

• AQUACEL® AG: 2.9% (2/69) versus 2.6% (2/78) on control; risk difference 0.3 percentage points (95% CI -5.0 to 5.6), risk ratio 1.13 (0.16–7.81); unadjusted two-proportion z-test p = 0.901.

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.

Wound Drainage

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • AQUACEL® AG: 1.4% (1/69) versus 1.3% (1/78) on control; risk difference 0.2 percentage points (95% CI -3.6 to 3.9), risk ratio 1.13 (0.07–17.73); unadjusted two-proportion z-test p = 0.930.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between AQUACEL® AG and the control. The interval gives the range of effects that remain compatible with the data.

Pocket Dehiscence

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • AQUACEL® AG: 0.0% (0/69) versus 1.3% (1/78) on control; risk difference -1.3 percentage points (95% CI -3.8 to 1.2); unadjusted two-proportion z-test p = 0.345.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between AQUACEL® AG and the control. The interval gives the range of effects that remain compatible with the data.

Rash After Removal

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • AQUACEL® AG: 2.9% (2/69) versus 0.0% (0/78) on control; risk difference 2.9 percentage points (95% CI -1.1 to 6.9); unadjusted two-proportion z-test p = 0.130.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between AQUACEL® AG and the control. The interval gives the range of effects that remain compatible with the data.

The secondary results with posted data show a mixed pattern rather than a consistent direction across all outcomes. Some comparisons have estimated differences close to zero, while others point in different directions. Their confidence intervals span zero, and the registry does not report analyses for every listed secondary outcome. The overall pattern therefore does not provide a clear, uniform secondary-outcome signal that would resolve the uncertainty in the primary comparison.

These endpoints complement the primary result by describing other aspects of wound condition and skin response around dressing removal. They do not replace the primary assessment of moderate-to-severe pocket hematoma, and they do not directly settle the study's stated interest in wound infection. The outcomes have different definitions and assessment contexts, so they should be interpreted separately rather than combined into a single claim about dressing performance.

Results for Site Itching/Burning and Skin Erythema are not reported in the registry record. The posted results also do not include reported analyses for the secondary outcomes. Consequently, the available secondary information is incomplete, and the record does not establish how these outcomes were prioritized or analyzed relative to one another.

The reported secondary p values are unadjusted. General explanation: When several outcomes are examined, the chance of finding at least one apparently unusual result by chance can increase. Adjusting for multiple comparisons is one way researchers may address this issue, but the registry does not report a multiplicity adjustment. Unadjusted secondary findings therefore carry less weight as confirmatory evidence, particularly when the results are incomplete and the analysis plan is not reported.

The most cautious reading is that the secondary outcomes add descriptive context but do not establish a coherent pattern or strengthen a definitive conclusion about the primary endpoint.

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

• Wound Drainage
• Pocket Dehiscence
• Rash After Removal
• Site Itching/Burning
• Skin Erythema

9. Statistical Interpretation

10. Statistical Methods Explained

The primary comparison is a binary-outcome comparison: each participant is classified as having or not having a moderate-to-severe pocket hematoma during the stated timeframe. The registry reports counts by randomized arm and a risk difference comparing AQUACEL® AG with Silverlon®. The concepts below explain how such summaries are generally read; the registry record does not report every method detail used for this trial.

What does a risk difference represent?

General explanation: A risk difference subtracts the event risk in one group from the event risk in another. In this comparison, the order is AQUACEL® AG minus Silverlon®. A value of zero represents equal estimated risks; a positive value indicates a higher estimated risk in the first-named group, and a negative value indicates a lower estimated risk in that group. The posted estimate is 0.003. The registry also reports the two arm-level event risks as 0.026 and 0.029, respectively. These are the values used in the registry comparison; they should not be confused with the participant counts.

What does the p value say?

General explanation: A p value evaluates how compatible the observed data are with a statistical model that assumes no group difference. It is not the probability that the no-difference assumption is true, and it does not measure the clinical importance of an effect. The reported primary p value is unadjusted and equals 0.901. The registry record does not specify the exact test or model used to calculate it, so a more detailed account of that calculation is not reported in the registry record.

How should the confidence interval be read?

General explanation: A confidence interval represents uncertainty around an estimated effect under the assumptions of the method used to calculate it. A narrow interval indicates greater precision than a wide interval. When an interval for a risk difference includes zero, the data do not isolate a difference in one direction. The primary interval runs from -0.050 to 0.056, covering both negative and positive differences. The registry record does not report the confidence level or the method used to construct this interval.

What do the event counts contribute?

The primary arm entries give the number of participants with the endpoint and the number of participants in each arm. Those counts are the basis for the displayed event risks and comparison. General explanation: When event counts are low, a small change in the number of events can materially affect a group estimate. Estimates can consequently be uncertain, even when the observed counts look similar. That is relevant to interpreting these results, but it does not identify the exact statistical method or explain why the estimate has its particular interval.

What is and is not specified about the analysis?

The registry identifies the study as randomized, parallel, and unmasked, and it posts an unadjusted comparison. It does not report a detailed statistical analysis plan, the comparison test, the confidence-interval procedure, covariate adjustment, or the handling of missing outcome data. It also does not report analysis populations such as intention-to-treat or per-protocol. These details should not be inferred from the posted estimates.

The registry's comparison is therefore best interpreted at the level it actually reports: a difference in recorded event risks, with an interval and an unadjusted p value. General explanation: Random assignment can support a fair comparison when it is implemented and analyzed appropriately, but it does not remove uncertainty from a study with few observed events, nor does the registry's randomization label alone establish how missing data or protocol deviations were handled.

11. Confidence Intervals and Precision

The primary risk difference estimate is 0.003. Its reported confidence interval extends from -0.050 to 0.056. The interval includes zero and extends in both directions, so the data do not precisely determine whether the underlying event risk was higher in the AQUACEL® AG group or in the Silverlon® group. The estimate itself is close to zero, but the interval allows for differences on either side of that estimate.

Precision concerns the range of effects reasonably compatible with the estimate and its statistical method. It is distinct from whether a result crosses a significance threshold. In this trial, the posted interval indicates substantial uncertainty about the size and direction of the primary comparison. The equal event counts do not narrow that uncertainty enough to support a conclusion that the groups have identical risks.

The registry record does not report the confidence level or the method used to calculate the interval. That missing information limits how specifically the interval can be interpreted. The record also does not report a prespecified threshold for a clinically important difference, so the interval cannot be assessed against such a threshold from the registry information alone.

The primary endpoint is assessed at 7-10 days post implant. The interval pertains to that endpoint and timeframe; it does not quantify uncertainty for wound infection, longer-term outcomes, or secondary endpoints. The posted estimate should therefore be understood as an imprecise comparison of moderate-to-severe pocket hematoma during the stated period, not as a precise estimate of every possible outcome associated with either dressing.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm because the endpoint is a binary participant outcome, not a time-to-event outcome. The registry's planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is defined as the stated fraction of the observed effect. The trial's own original design assumptions are not reported in the registry record.

The 80% power column describes the planned number of participants per arm under the stated assumptions for a design intended to have an 80% chance of detecting the specified effect if that effect is the true one. The 90% power column describes the corresponding planning target for a 90% chance. These are design illustrations, not guarantees that a future study will detect an effect.

For planning at 100% of the observed effect, the figures are 37,284 participants per arm for 80% power and 49,912 participants per arm for 90% power. At 75% of the observed effect, they are 65,296 and 87,412 participants per arm, respectively. At 50% of the observed effect, they are 144,696 and 193,706 participants per arm, respectively. The pattern reflects a general statistical principle: smaller effects are harder to distinguish from random variation and require more participants under otherwise unchanged assumptions.

These values are not observed power. They are planning illustrations based on the observed effect and the assumptions stated in the registry; the observed trial results are the event counts and comparison estimates, not a retrospective power calculation.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.026; treatment proportion p₁ = 0.029; average p̄ = 0.027.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.2305 = 0.4518.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.2305 = 0.1940.
4. n = (0.4518 + 0.1940)² / (0.0033)² = 37,283.2, rounded up to 37,284 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.0256410256410256                          # control proportion
p1 <- 0.0289855072463768                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(2781779)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 37,284 (80% power), 49,912 (90% power)
 75% of observed effect: n per arm = 65,296 (80% power), 87,412 (90% power)
 50% of observed effect: n per arm = 144,696 (80% power), 193,706 (90% power)
power.prop.test: 37283.2 
Simulated power at n = 37,284 per arm: 0.801 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary outcome and five secondary outcomes. It posts result entries for Wound Drainage, Pocket Dehiscence, and Rash After Removal, but results for Site Itching/Burning and Skin Erythema are not reported in the registry record. The record does not explain why results for those listed outcomes are absent or whether they were collected.

No multiplicity strategy is reported. The posted secondary comparison p values are unadjusted. General explanation: If researchers test several outcomes, interpreting each result as though it were the only test can make chance findings appear more persuasive than they are. A prespecified hierarchy, adjustment procedure, or distinction between confirmatory and exploratory analyses can help readers understand the intended interpretation. Such details are not reported in the registry record, so the secondary p values should not be treated as multiplicity-controlled evidence.

The registry does not report missing-data rates, reasons for missingness, imputation procedures, or sensitivity analyses. It is therefore not possible to determine from the record whether all randomized participants contributed outcome data, how any unavailable assessments were handled, or whether missingness could have affected the comparisons.

The analysis populations are also not reported. The record does not identify whether results were analyzed according to randomized assignment, treatment received, or another population definition. It does not report protocol deviations or exclusions from analysis. These omissions limit assessment of how the randomized design was carried through into the reported comparisons.

In addition, the registry does not provide a detailed statistical analysis plan, a description of the tests used, or a confidence-interval method. These omissions do not invalidate the posted numbers, but they limit independent evaluation of how the results were generated and how endpoint multiplicity and missing information were handled.

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

The registry records the same number of participants with moderate-to-severe pocket hematoma in each arm: 2 in the Silverlon® group and 2 in the AQUACEL® AG group. The estimated risk difference is 0.003 for AQUACEL® AG compared with Silverlon®, and the confidence interval ranges from -0.050 to 0.056. The interval spans both directions and is consistent with substantial uncertainty about the underlying difference.

This result does not demonstrate that the dressings are equivalent. Establishing equivalence would require an appropriate design and a prespecified margin for what would count as an acceptably small difference; such a margin and an equivalence analysis are not reported in the registry record. Nor does the result establish that one dressing is superior. The unadjusted p value of 0.901 does not prove that there is no effect.

The primary endpoint is hematoma, not infection. Although the brief summary describes wound infection prevention as the study's purpose, the posted primary comparison cannot be read as a direct comparison of infection outcomes. The registry lists other wound and skin outcomes, but not all of their results are reported. Thus the primary finding does not settle those separate questions either.

The timeframe also matters: the primary outcome is recorded at 7-10 days post implant. The posted result does not establish what may occur outside that assessment period. The registry record does not provide longer-term follow-up results, detailed participant characteristics, or information sufficient to assess how broadly the findings apply to other settings.

In statistical terms, the observed comparison is inconclusive and imprecise. It describes the outcomes recorded in this randomized trial, but it does not support a definitive claim of benefit, harm, or equivalence. No medical recommendation follows from the posted result alone.

16. Why This Trial Matters Statistically

This trial illustrates why the event counts, effect estimate, and confidence interval should be read together. The arm counts are equal, but the risk-difference interval extends in both directions. Looking only at the equal counts could encourage an overly definite conclusion, while the interval makes clear that the comparison remains uncertain.

It also illustrates the importance of aligning the study purpose with the endpoint used for interpretation. The brief summary refers to prevention of post-procedure wound infections, whereas the registered primary endpoint is moderate-to-severe pocket hematoma. Hematoma may be relevant to wound care, but it is not the same outcome as infection. Statistical conclusions should remain tied to the outcome actually measured and posted.

The randomized design is relevant to comparing the two assigned dressings, but the registry's lack of detail about the analysis population, missing data, endpoint procedures, and multiplicity limits how fully the analysis can be evaluated. This is a useful reminder that a numerical result is only one part of statistical interpretation; endpoint definitions, follow-up, analysis methods, and reporting completeness also matter.

Finally, the planning illustrations show how strongly sample-size requirements depend on the effect targeted. Under the registry's stated assumptions, smaller fractions of the observed effect correspond to larger planning figures. These estimates describe hypothetical future designs, not the power or certainty of the completed trial. Keeping that distinction clear helps prevent planning calculations from being mistaken for evidence about the observed comparison.

17. 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 comparison is based on few recorded events: each arm has 2 participants with moderate-to-severe pocket hematoma. The confidence interval is broad and includes differences in both directions, limiting precision. The registry does not report a clinically important difference threshold against which the estimate could be judged.

The study is listed as unmasked. The record does not report whether endpoint assessors were blinded, how hematomas were adjudicated, or what steps were taken to reduce bias in classifying the outcome. It also does not report participant characteristics or eligibility details sufficient to assess how closely the enrolled group reflects other CIED populations.

The primary assessment timeframe is 7-10 days post implant. The registry does not report longer-term primary outcome results. Although infection prevention is mentioned in the brief summary, infection is not the posted primary endpoint, and the registry record does not provide a primary infection comparison.

Reporting is incomplete for the listed secondary outcomes: results for Site Itching/Burning and Skin Erythema are not reported in the registry record. The record also does not report an analysis plan, multiplicity handling, missing-data procedures, analysis populations, or details of the statistical tests and interval methods. These omissions restrict evaluation of the secondary findings and the robustness of the primary comparison.

The registry lists no reported analyses for the secondary outcomes. This does not establish that no analyses were conducted; it means they are not reported in the registry record. The findings should be interpreted within these limits.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Comparison of Outcomes Between the Use of Silverlon® Dressing and AQUACEL® AG Dressing Post Cardiac Device Implant — NCT02781779.
• Registry record last updated 2023-03-10; status last verified 2020-04.
• Results first posted 2023-03-10.
• 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.

21. Record Summary

This completed, randomized, parallel-group, unmasked trial compared postoperative Silverlon® dressing with AQUACEL® AG dressing after cardiac device implantation. The registry lists enrollment of 147, a start date of 2016-06, and a primary completion date of 2017-12. The primary endpoint was moderate-to-severe pocket hematoma at 7-10 days post implant.

The primary event count was 2 among 78.0 in the Silverlon® arm and 2 among 69.0 in the AQUACEL® AG arm. The posted risk difference for AQUACEL® AG compared with Silverlon® was 0.003, with a confidence interval from -0.050 to 0.056 and an unadjusted p value of 0.901. This is an imprecise comparison that does not establish the direction or size of an underlying difference.

The registry lists five secondary outcomes but posts results for three. Details about missing data, analysis populations, multiplicity handling, and the statistical analysis plan are not reported in the registry record.