SOLITAIRE™ FR With the Intention For Thrombectomy (SWIFT) Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for SOLITAIRE™ FR With the Intention For Thrombectomy (SWIFT) Study (NCT01054560), a randomized na study. The primary outcome is Recanalization [Thrombolysis in Myocardial Infarction (TIMI) 2 or 3] Without Symptomatic Intracranial Hemorrhage.

2. Clinical Question

The registry record describes a randomized comparison of two devices used for mechanical thrombectomy in subjects diagnosed with acute ischemic stroke. Its stated purpose was to assess substantial equivalence of the SOLITAIRE™ FR Revascularization Device against the legally marketed MERCI Retrieval System®, while evaluating safety and efficacy in subjects requiring mechanical thrombectomy.

The endpoint combines a measure of vessel blood flow with specified safety and treatment conditions. It therefore asks about a particular immediate procedural outcome, rather than neurological status over longer follow-up. Secondary outcomes listed in the registry include time to initial recanalization, neurological outcome at 30 and 90 days, mortality, symptomatic intracranial hemorrhage, and non-fatal stroke-related morbidity. The posted results include some, but not all, of those secondary outcomes.

3. Trial Design

The SWIFT Study is listed as a completed, randomized, parallel-group trial with no masking. The registry lists enrollment of 144 and identifies Medtronic Neurovascular Clinical Affairs as the sponsor. The recorded start was 2010-01, and primary completion was 2011-07. The phase is recorded as NA. The record names the SOLITAIRE™ Device as the experimental device and the MERCI® Device as the control.

Random allocation means that assignment to the two treatment groups was determined through a random process, as described by the registry’s design classification. The parallel-group label indicates that participants were assigned to one device group rather than being described as crossing between the devices. The record says masking was none; it does not report additional details about who knew each assignment or whether any outcome assessment procedures were masked.

The registry’s primary endpoint concerns immediate post-treatment recanalization. For that endpoint, the Core Lab evaluated 56 participants in the SOLITAIRE FR group and 54 in the MERCI group. The record states that data were unavailable for two participants from the randomized SOLITAIRE cohort and one from the randomized MERCI cohort. These endpoint-specific numbers differ from the overall enrollment and should not be treated as the number analyzed for every outcome. The secondary endpoint denominators also vary: the registry reports different participant counts for time to initial recanalization and for neurological outcomes at 30 and 90 days.

The registry record does not report the original sample-size justification, the planned allocation ratio, detailed eligibility criteria, the randomization method, the treatment protocol, or a prespecified statistical analysis plan. It also does not report any formal interim analyses. Those omissions limit what can be said about the trial’s intended analysis beyond the design labels and endpoint descriptions recorded in the registry.

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: Study had Roll-in period. Participating centers in the United States were required to enroll two (2) roll-in subjects prior to the subject randomization. There were a total of 31 roll-in subjects. Only data from the randomized cohort was used for both primary efficacy analysis and the safety endpoint analysis.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Data was unavailable for two subjects from the randomized Solitaire and one from the randomized Merci cohort. Thus, the Core Lab evaluated data from 56 in the Solitaire FR group and 54 in the Merci group.

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 Recanalization [Thrombolysis in Myocardial Infarction (TIMI) 2 or 3] Without Symptomatic Intracranial Hemorrhage, measured over Immediately post treatment.

The primary endpoint is the percentage of subjects with successful arterial recanalization of the occluded target vessel, defined as a Thrombolysis in Myocardial Infarction (TIMI) score of 2 or 3 following use of either device. The assessment is specified for immediately after treatment. The endpoint also requires that the successful recanalization occur without symptomatic intracranial hemorrhage and without rescue therapy within 3 passes.

The registry describes TIMI as a measure of distal flow perfusion and revascularization before and following therapy. A score of 0 indicates no perfusion; a score of 1 indicates perfusion past the initial occlusion without distal branch filling; a score of 2 indicates perfusion with incomplete or slow distal branch filling; and a score of 3 indicates full perfusion with filling of all distal branches. The endpoint counts scores 2 and 3 as successful recanalization.

Combining vessel flow with the specified safety and rescue-therapy conditions makes the endpoint more restrictive than a measure of recanalization alone. It captures an immediate technical outcome and incorporates whether symptomatic intracranial hemorrhage or rescue therapy occurred within the stated procedural conditions. It does not, by itself, describe later neurological function, survival, or longer-term disability. Those topics appear among the listed secondary outcomes, but they are distinct questions and have different follow-up periods.

In general, a clearly defined endpoint helps make the treatment comparison interpretable by specifying the event counted, the assessment time, and the relevant population. The registry’s description supplies those elements for this primary outcome, although it does not report a fuller analysis plan or further detail about endpoint adjudication.

7. Results Posted in the Registry

• MERCI® Device: 24.1% (13/54) versus 60.7% (34/56) on control; risk difference -36.6 percentage points (95% CI -53.8 to -19.5), risk ratio 0.40 (0.24–0.67); unadjusted two-proportion z-test p = <0.001.

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.

Time to Initial Recanalization

• 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:
  • MERCI® Device: mean 58.70 versus 47.00 on control; difference 11.70 (95% CI -2.76 to 26.16), standardized effect d = 0.33; z-test p = 0.113.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between MERCI® Device and the control. The interval gives the range of effects that remain compatible with the data.

Good Neurological Outcome at 30 Days

• Endpoint type: Binary: the percentage of participants with the event (counts rebuilt from the posted percentages and group sizes).
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • MERCI® Device: 33.3% (17/51) versus 50.9% (28/55) on control; risk difference -17.6 percentage points (95% CI -36.1 to 0.9), risk ratio 0.65 (0.41–1.04); unadjusted two-proportion z-test p = 0.067.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between MERCI® Device and the control. The interval gives the range of effects that remain compatible with the data.

Good Neurological Outcome 90 Days

• Endpoint type: Binary: the percentage of participants with the event (counts rebuilt from the posted percentages and group sizes).
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • MERCI® Device: 33.3% (16/48) versus 58.2% (32/55) on control; risk difference -24.8 percentage points (95% CI -43.5 to -6.2), risk ratio 0.57 (0.36–0.91); unadjusted two-proportion z-test p = 0.012.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the proportion with the event is statistically lower for MERCI® Device than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The secondary results add information about procedural timing and neurological outcomes at follow-up, but they do not all point to the same level of statistical certainty. The time-to-initial-recanalization comparison and the 30-day neurological outcome comparison have unadjusted confidence intervals that include the no-difference value. The 90-day neurological outcome comparison has an unadjusted interval that does not include that value. These patterns are compatible with the primary result being more clearly separated from the null than some secondary estimates, while also emphasizing that the endpoints assess different outcomes at different times.

The secondary findings should be read alongside, rather than substituted for, the primary endpoint. Immediate recanalization is a procedural outcome; later neurological status is a distinct clinical measure. A higher proportion meeting the primary definition does not establish that every later outcome will show a corresponding difference. Nor can the secondary outcomes be combined into one overall result without a stated method for doing so.

Each secondary comparison is unadjusted. In general, when many outcomes are examined, the chance of obtaining at least one apparently notable result by chance can increase. Statistical adjustment or a prespecified hierarchy can address aspects of this multiplicity, but the registry record does not report whether either approach was used for the posted secondary outcomes. The unadjusted p-values and intervals therefore carry less confirmatory weight than a single prespecified primary comparison, particularly when the statistical plan is not available.

The registry lists mortality, symptomatic intracranial hemorrhage, and non-fatal stroke-related morbidity among its secondary outcomes, but results for all listed secondary outcomes are not posted in the record summarized by these results. Their absence from the posted outcome estimates means that their comparative results cannot be assessed from the registry record. It does not imply that no events occurred or that the groups were the same on those outcomes.

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

• Time to Initial Recanalization
• Good Neurological Outcome at 30 Days
• Good Neurological Outcome 90 Days
• Mortality
• Symptomatic Intracranial Hemorrhage
• Non-fatal Stroke-related Morbidity

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is a binary endpoint: each evaluated participant either met the registry’s definition of successful recanalization without symptomatic intracranial hemorrhage or rescue therapy within 3 passes, or did not. The reported percentages describe the proportion meeting that definition in each group. The registry lists 56 evaluated participants for SOLITAIRE and 54 for MERCI for this endpoint. Data were unavailable for two randomized SOLITAIRE participants and one randomized MERCI participant, as stated in the endpoint population description.

The primary comparison is expressed as a risk difference. In general, a risk difference subtracts the proportion with the event in one group from the proportion in the other, using a stated direction. Here the registry comparison is oriented as MERCI relative to SOLITAIRE, so its negative estimate corresponds to a lower observed event proportion in the MERCI group. The estimate is -0.366, with a confidence interval from -0.538 to -0.195. These values are reported as posted; no further conversion or re-expression is needed to understand the stated direction.

The primary p-value is unadjusted and reported as p < 0.001. In general, a p-value describes how incompatible the observed data are with a specified null model, assuming that model and the analysis assumptions hold. It is not the probability that the null hypothesis is true, nor does it measure the size or clinical importance of a difference. The registry record does not report the full statistical analysis plan, including the exact test used for the posted primary comparison, so the p-value should be read as the registry’s posted unadjusted result rather than as evidence of a particular unreported testing procedure.

The secondary continuous outcome, time to initial recanalization, is reported as a mean with a standard deviation in each group. The posted mean is 47.0 minutes in the SOLITAIRE group, with a standard deviation of 37.3, among 47 participants. In the MERCI group, the mean is 58.7 minutes, with a standard deviation of 33.8, among 46 participants. The comparison is a mean difference of 11.7 minutes for MERCI relative to SOLITAIRE, with a confidence interval from -2.761 to 26.16 and an unadjusted p-value of 0.113. In general, a mean difference compares group averages, while standard deviations describe variation among participant measurements within each group. A confidence interval for the mean difference reflects uncertainty in the estimated contrast, not the spread of individual participant times.

The registry also posts binary percentages for neurological outcomes at follow-up. For good neurological outcome at 30 days, the denominators are 55 and 51; for good neurological outcome at 90 days, they are 55 and 48. Their posted comparisons are risk differences with confidence intervals and unadjusted p-values. Each outcome has its own denominator and follow-up time, so these results should not be combined into a single endpoint or assumed to represent the same participants.

In general, confidence intervals give a range of values compatible with the data under the statistical method and assumptions used. Their width conveys precision: a narrower interval indicates greater precision than a wider one on the same scale. Whether an interval includes the null value depends on the comparison scale. For a difference, the null is no difference; for a ratio, it is no relative difference. The registry posts risk ratios and odds ratios for the binary outcomes as well as risk differences, but the main interpretation can remain with the risk-difference scale, whose direction is clear from the group ordering.

In general, binary outcomes can be analyzed using methods that model event probabilities or compare observed proportions. The registry record does not state which specific method produced each posted estimate and interval. The descriptive percentages and posted comparison statistics can still be reported without attributing them to an unreported method. Likewise, the record does not describe adjusted analyses, covariate handling, or a strategy for missing endpoint data. The differing denominators are visible in the outcome summaries, but the reason for missingness beyond the primary endpoint’s stated unavailable data is not reported in the registry record.

In general, randomization is intended to support a fair comparison by making assignment independent of participant characteristics in expectation. It does not guarantee that the observed groups are identical in a particular trial, and it does not remove the importance of complete outcome follow-up, prespecified analysis, or appropriate handling of missing data. No masking was recorded for this trial. That feature is relevant when interpreting outcomes that may involve judgment or procedures, although the registry does not report additional details about outcome-assessment safeguards.

Several planning illustrations accompany the outcome comparisons. In general, such calculations use an assumed effect size and statistical model to estimate how many participants may be needed for a desired power under those assumptions. They are not evidence about the trial’s actual power after results are known. The assumptions stated for these illustrations are discussed in the sample-size reading. The trial’s original design assumptions and sample-size justification are not reported in the registry record.

The registry identifies the trial’s aim as demonstrating substantial equivalence. In general, an equivalence analysis is designed to assess whether a treatment difference lies within a prespecified acceptable range in either direction. The registry record does not report the equivalence margin, the formal test, or the analysis population specified for that purpose. Consequently, the posted comparative estimates do not, on their own, supply all the information needed to interpret a formal equivalence claim.

11. Confidence Intervals and Precision

The primary risk-difference estimate is -0.366, with a confidence interval from -0.538 to -0.195. The interval is entirely on the negative side of the no-difference value for the stated MERCI-minus-SOLITAIRE comparison. This indicates that the posted primary estimate is not especially close to the null under the interval method used. Its width still matters: the data are compatible with a range of possible differences, not only the point estimate. The confidence interval communicates uncertainty around the group contrast rather than a range containing a specified proportion of individual outcomes.

In general, a confidence interval is calculated by a statistical procedure that reflects sampling variability under its assumptions. It does not account automatically for every possible source of uncertainty, such as missing outcome data, deviations from a planned analysis, or unmeasured bias. The registry record does not provide enough detail to assess all such sources or identify the precise interval procedure used. The primary endpoint denominators are 56 and 54, and the record notes unavailable data for three randomized participants across the two cohorts.

The secondary intervals are less uniform in their relation to the null. For time to initial recanalization, the mean-difference interval runs from -2.761 to 26.16. For good neurological outcome at 30 days, the risk-difference interval runs from -0.361 to 0.009. Both intervals include the no-difference value on their respective scales. The 90-day risk-difference interval runs from -0.435 to -0.062 and does not include that value. These are unadjusted secondary comparisons, and the intervals do not account for the fact that multiple outcomes were examined unless an adjustment was made; such an adjustment is not reported in the registry record.

Precision depends in part on the amount of information available for an outcome. The evaluated participant counts vary across endpoints, and the reported intervals differ in width and scale. In general, a larger sample can improve precision when other conditions are comparable, but observed precision also depends on outcome frequency and variability. These results should be interpreted using each endpoint’s own confidence interval and denominator rather than assuming that the primary endpoint’s precision applies to every secondary outcome.

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 sample-size illustrations are based on planning assumptions, not on the trial’s original documented design. For the binary outcomes, the displayed figures mean participants per arm. For time to initial recanalization, they also mean participants per arm, because that outcome is not a time-to-event planning calculation; the registry’s stated convention is that time-to-event tables give total events, while all other calculations give participants per arm. The posted outcome is a mean in minutes, and its planning illustration follows the participants-per-arm convention.

The calculations use a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is a stated fraction of the observed effect: the observed effect itself, 75% of the observed effect, or 50% of the observed effect. The registry record does not report the trial’s own original sample-size assumptions or justification, so these figures should not be read as the planned enrollment target for SWIFT.

The 80% power column represents the estimated participants per arm under which the planning method would have an 80% chance of detecting the assumed effect, if the assumptions hold. The 90% power column gives the corresponding estimate for a 90% chance. Power is a property of a planned design under specified assumptions; it does not describe the probability that a result already observed is correct. These figures are planning illustrations, not observed power.

Rows describing a smaller fraction of the observed effect call for more participants per arm. That pattern is expected in general: smaller differences are harder to distinguish from random variation, so a larger sample is typically needed for the same target power. The resulting estimates depend on the observed effect used as the starting point and should not be treated as a guarantee that a future study will achieve a particular result.

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 = 0.607; treatment proportion p₁ = 0.241; average p̄ = 0.424.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6989 = 1.3698.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6491 = 0.5463.
4. n = (1.3698 + 0.5463)² / (-0.3664)² = 27.3, rounded up to 28 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 <- 0.607142857142857                          # control proportion
p1 <- 0.240740740740741                          # 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(1054560)
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 = 28 (80% power), 37 (90% power)
 75% of observed effect: n per arm = 51 (80% power), 68 (90% power)
 50% of observed effect: n per arm = 116 (80% power), 155 (90% power)
power.prop.test: 27.3 
Simulated power at n = 28 per arm: 0.805 (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 identifies one primary endpoint and lists multiple secondary outcomes, with some secondary results posted. The primary comparison is reported with an unadjusted p-value. The secondary comparisons are also unadjusted. The registry record does not report a multiplicity strategy, such as a correction for multiple comparisons, an ordered testing procedure, or a hierarchy governing interpretation of the secondary outcomes. This matters because repeated testing across several outcomes can increase the chance of at least one result appearing statistically notable even when there is no underlying difference for those outcomes. Without a reported plan, the secondary p-values are best treated as exploratory or supportive rather than as a set of independent confirmatory claims.

The registry describes the study’s purpose as demonstrating substantial equivalence, but it does not report an equivalence margin or the formal analysis used to assess equivalence. A conventional difference test and an equivalence test answer different questions. In general, an equivalence assessment asks whether plausible differences fall within a prespecified range considered acceptable; a non-significant difference test alone does not establish equivalence. The available registry summaries therefore do not establish the formal basis or conclusion of an equivalence analysis.

Missingness is explicitly described for the primary endpoint: data were unavailable for two randomized SOLITAIRE participants and one randomized MERCI participant, leaving Core Lab evaluations for 56 and 54 participants. The registry does not report why those data were unavailable, whether the missingness was related to outcome status, or how the missing participants were handled in any full analysis population. The denominators also vary across secondary outcomes, but reasons for those variations and a general missing-data strategy are not reported in the registry record.

The trial is described as randomized and unmasked. The record does not provide a full account of the analysis population, such as whether all randomized participants were included in a particular intention-to-treat analysis, or whether per-protocol or other populations were used. It also does not report the planned treatment of protocol deviations, missing observations, or outcome adjudication beyond the Core Lab evaluation noted for the primary endpoint. These omissions limit assessment of how closely the posted results reflect the intended analysis.

15. Safety Results

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

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: cerebrovascular accident (23.6%), atrial fibrillation (19.0%), anaemia (15.5%), cerebral haematoma (14.5%), respiratory failure (14.5%).

The registry posts serious adverse event figures for 58 participants at risk in the SOLITAIRE group, of whom 49 are recorded as affected, and 55 participants at risk in the MERCI group, of whom 44 are recorded as affected. The corresponding figures for other adverse events are 37 of 58 in the SOLITAIRE group and 30 of 55 in the MERCI group. These counts are group-level summaries; they do not identify how many participants experienced multiple events or describe event timing.

The registry lists the leading serious adverse event terms with percentages: Cerebrovascular accident, 23.6%; Atrial Fibrillation, 19.0%; Anaemia, 15.5%; Cerebral haematoma, 14.5%; Respiratory failure, 14.5%; and Ischaemic stroke, 12.7%. Those terms and percentages describe the posted serious-event listing and should not be interpreted as a direct comparison between treatment groups unless a group-specific contrast is reported.

Deaths are not reported in the adverse-event summaries. The registry also does not provide a comparative statistical analysis of these adverse-event figures in the posted results. In general, event counts and affected-participant counts are not interchangeable when people can experience more than one event. The figures provide descriptive safety information, but they do not alone establish a causal difference between devices.

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

The primary result describes a higher observed percentage meeting the registry’s defined immediate recanalization endpoint in the SOLITAIRE group than in the MERCI group. The posted risk difference and confidence interval indicate that the estimated contrast is separated from no difference on the stated scale. This is a statement about the analyzed endpoint data, not a recommendation about device choice or a judgment about an individual patient’s care.

The result does not, on its own, establish a formal equivalence conclusion. Although substantial equivalence was the stated purpose, the registry record does not report the equivalence margin or the analysis needed to determine whether the formal criterion was met. Nor does the primary endpoint establish effects on all outcomes that matter to patients. It is an immediate procedural measure with requirements concerning symptomatic intracranial hemorrhage and rescue therapy within 3 passes; later neurological outcomes and safety outcomes are separate questions.

The secondary summaries offer additional observations, but their interpretation is constrained by varying denominators, unadjusted comparisons, and the absence of a reported multiplicity plan. Some posted intervals include the no-difference value and one secondary interval does not. The registry also does not post results for every outcome it lists. These features mean that the secondary evidence should not be treated as a unified or definitive account of all clinical effects.

In general, statistical significance does not by itself indicate clinical importance, and a non-significant comparison does not prove that two treatments are identical. The size and precision of the estimate, the outcome’s meaning, the design, the completeness of data, and the analysis plan all matter. Here, the primary estimate is relatively clearly separated from the null in its posted interval, but important design and analysis details are absent from the registry record.

The safest statistical reading is therefore narrow: the posted primary data favor a larger observed proportion meeting the specified immediate endpoint in the SOLITAIRE group, within the evaluated samples. The summaries do not fully resolve equivalence, long-term effects, all safety comparisons, or the robustness of results to missing data and alternative analyses. No medical advice follows from these registry summaries.

17. Why This Trial Matters Statistically

This trial illustrates why the endpoint definition is central to interpreting a device comparison. The primary result is not simply a measure of vessel opening: it combines TIMI 2 or 3 recanalization with no symptomatic intracranial hemorrhage and no rescue therapy within 3 passes. Readers need that definition to understand what the group percentages represent and what they leave outside the question.

It also illustrates the distinction between a stated trial purpose and the evidence needed to support that purpose. The registry says the study aimed to demonstrate substantial equivalence, but does not report an equivalence margin or formal analysis. Statistical interpretation cannot fill in those missing design details after the results are known. A difference estimate and its confidence interval are informative, but they are not a substitute for a prespecified equivalence framework.

Varying denominators provide another important lesson. Overall enrollment is 144, while the primary Core Lab evaluation includes 56 and 54 participants, and secondary outcomes use other denominators. Outcome-specific sample sizes matter because precision and potential missing-data concerns vary across analyses. Readers should not assume that every result includes the same participants.

Finally, the record combines a clear primary comparison with unadjusted secondary results and incomplete reporting of several listed outcomes. This makes it useful for distinguishing the principal posted finding from supportive or incomplete evidence. It also shows why registry summaries should be interpreted with attention to analysis plans, multiplicity, missingness, and confidence intervals, not by focusing on a p-value alone.

18. 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.
• Participant counts were reconstructed from posted percentages and arm sizes, so small rounding differences are possible.

The registry record leaves several trial-specific uncertainties. It does not report the original sample-size justification, the assumptions used to plan enrollment, or the full statistical analysis plan. The posted planning illustrations are based on observed effects and should not be mistaken for the trial’s original design rationale. The record also does not give the equivalence margin or formal equivalence procedure, despite substantial equivalence being the stated study purpose.

For the primary endpoint, data were unavailable for two randomized SOLITAIRE participants and one randomized MERCI participant. The record does not explain why these data were unavailable or describe a missing-data sensitivity analysis. The Core Lab evaluation denominators are therefore smaller than the overall enrollment. Secondary endpoint denominators vary as well, without a full explanation of missingness or the analysis population used for each outcome.

The trial was unmasked according to the registry. Additional details about masking of outcome assessors or other safeguards are not reported. This is relevant context for interpreting a procedural endpoint and outcomes that may involve assessment, although the record does not establish that any particular bias occurred.

The primary result is accompanied by a confidence interval and unadjusted p-value, but the registry does not identify the precise statistical method, adjustments, or covariates used. Secondary results are unadjusted, and no multiplicity strategy is reported. Several listed secondary outcomes do not have posted results in the available record. Death counts are not reported in the adverse-event summary. Together, these reporting gaps limit assessment of robustness, completeness, and the relationship between the posted summaries and the intended analyses.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: SOLITAIRE™ FR With the Intention For Thrombectomy (SWIFT) Study — NCT01054560.
• Registry record last updated 2016-10-26; status last verified 2016-08.
• Results first posted 2016-10-26.
• 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.

22. Record Summary

The completed SWIFT Study is listed as a randomized, unmasked, parallel-group comparison of the SOLITAIRE™ Device and the commercially available MERCI® Device in subjects with acute ischemic stroke requiring mechanical thrombectomy. The registry lists enrollment of 144 and identifies Medtronic Neurovascular Clinical Affairs as sponsor. The primary endpoint was immediate recanalization at TIMI 2 or 3 without symptomatic intracranial hemorrhage or rescue therapy within 3 passes.

For the Core Lab-evaluated primary endpoint, the posted percentage was 60.7% for SOLITAIRE and 24.1% for MERCI, with a posted unadjusted risk difference of -0.366 for MERCI relative to SOLITAIRE and p < 0.001. The record reports unavailable primary endpoint data for two randomized SOLITAIRE participants and one randomized MERCI participant. Secondary results vary by outcome, and not all listed outcomes have posted results. The original sample-size rationale, detailed analysis plan, missing-data approach, and formal equivalence criteria are not reported in the registry record.