Assessing the Hemodynamic Benefits of Cardiac Resynchronization Therapy in Children Following Open-Heart Surgery: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Assessing the Hemodynamic Benefits of Cardiac Resynchronization Therapy in Children Following Open-Heart Surgery (NCT00397514), a registered phase not stated study. The primary outcome is Cardiac Index.

2. Clinical Question

The clinical rationale recorded for the study is that the heart’s electrical activation can vary with the pacing site, and that different activation patterns may affect pumping. The trial therefore focuses on an immediate hemodynamic measure during postoperative pacing, rather than reporting a long-term clinical outcome as its primary endpoint. The registry also lists outcomes related to blood pressure, low output syndrome, cardiac tissue motion, support requirements, electrical conduction, and bypass time.

The question should be read narrowly. The listed endpoint and pacing period concern measurements around a brief postoperative pacing protocol. The record does not establish how the findings relate to longer-term recovery, nor does it provide outcome values with which to assess the direction or size of any change.

3. Trial Design

The registry identifies NCT00397514 as a completed study sponsored by the University of British Columbia. Its recorded start is 2006-10, and its primary completion is 2009-11. Enrollment is recorded as 34. The condition is congenital heart defects, and the intervention entry is labeled “Congenital Heart Surgery Patients.” These registry descriptors do not, by themselves, specify how many participants contributed data to each endpoint or analysis.

The intervention description concerns pacing before extubation after congenital heart surgery. It describes 20 min. of either conventional RV or BiV pacing, preceded and followed by 10 min. of recovery time. The primary endpoint is cardiac index, with measurements specified at baseline and after 20 minutes of pacing. Although the description mentions both pacing approaches, the record does not give a randomized allocation, an allocation method, or a clear arm-by-arm account that would support interpreting the approaches as a balanced parallel-group comparison. The registry explicitly notes that this is not a randomized comparison and that the arms are not a like-for-like control comparison.

The record lists secondary outcomes of systolic blood pressure, incidence of low output syndrome, tissue Doppler imaging indices, inotropic support, ventilatory support, QRS duration, and cardio-pulmonary bypass time. The tissue Doppler category includes tissue velocities, tissue tracking, regional strain, and regional strain rates. The registry states that there are 8 outcome measures. It does not provide an analysis entry for those measures.

Important design details are not reported in the registry record, including the full eligibility criteria, the allocation process, the planned sample-size justification, the intended statistical model, and the analysis populations. Completion status indicates that the study is listed as completed; it does not substitute for a report of the methods or numerical findings.

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: One patient was excluded due to pacing wire malfunction. Four consented but we were not able to adequately capture and pace their left ventricle intraoperatively. Two consented, but underwent early extubation, and we were not able to perform the study in time. One family withdrew from the study. One patient had poor echocardiographic windows.

Overall Study

Reasons for not completing this period:

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: The number of participants analyzed was 25 due to the withdrawal of 9 participants after enrolment as specified.

6. Primary Endpoint

The registry lists the primary outcome as Cardiac Index, measured over Baseline and after 20 minutes of pacing.

Cardiac index is the primary endpoint. It expresses cardiac output relative to body surface area, with the registry recording the unit as L/min/m2. In general, indexing cardiac output to body surface area helps describe circulatory performance in a way that accounts for differences in body size. This is relevant in a pediatric surgical population, where body size can vary.

The registry specifies a median with full range as the summary format and identifies baseline and after 20 minutes of pacing as the measurement times. A median describes the middle observation when values are ordered. The full range gives the lowest and highest observed values, so it conveys the spread at the extremes but does not show the distribution of values between them. Neither summary alone indicates the precision of an estimated treatment contrast.

Measuring cardiac index before and after pacing is intended to capture an immediate hemodynamic response during the postoperative protocol. The endpoint is therefore distinct from clinical outcomes such as duration of recovery or later health status. The record does not report the actual median values, full ranges, a change estimate, or an inferential comparison for cardiac index. It also does not report whether measurements were analyzed as paired observations or by another method. Without those results and methods, the endpoint definition can be described, but the magnitude and precision of any observed response cannot be assessed.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry’s endpoint definition uses the median and full range for cardiac index. In general, the median is useful when a distribution may be skewed or influenced by extreme observations because it is determined by the central rank rather than by the sum of all values. The full range displays the observed extremes. It can help readers see whether values vary widely, but it is sensitive to extreme observations and does not describe the concentration of most values. A median and range are descriptive summaries; they do not, by themselves, test a hypothesis or quantify the uncertainty in a difference.

What would a comparison estimate describe?

In general, a comparison estimate would summarize how the endpoint differs between the pacing conditions, or how it changes from baseline to the post-pacing measurement, depending on the analysis specified. The registry gives the measurement times but does not report a comparison estimate or analysis method. It is therefore not possible to determine whether the intended analysis was a within-participant comparison, a between-group comparison, or another approach. The record’s note that the arms are not a like-for-like control comparison is also relevant: a difference between groups would not automatically isolate the effect of pacing site.

Where measurements are taken repeatedly from the same participant, a method that accounts for their dependence can be appropriate. In general, repeated observations from one person are not statistically independent simply because they were taken at different times. The registry does not state whether the same participants received both pacing conditions, whether each participant had both measurements, or how any within-person dependence was handled. These details should not be assumed from the phrase “baseline and after 20 minutes of pacing.”

What does uncertainty add?

In general, a confidence interval describes a range of values compatible with the observed data under a specified statistical model and procedure. It helps distinguish a precise estimate from one that remains uncertain. A p-value, when reported, addresses how incompatible the data are with a specified null model; it does not state the probability that a treatment works, nor does it convey the size or clinical importance of an effect. The registry does not report a confidence interval or p-value for cardiac index. It also does not report an inferential method or model assumptions, so no such evidence can be reconstructed from the stated median and range.

For count outcomes, such as an incidence outcome, methods need to reflect the outcome’s data structure and the amount of information available. For outcomes measured over time or across several conditions, the analysis should reflect the timing and dependence of observations. These are general principles, not descriptions of methods used in this study: the statistical methods for the listed secondary endpoints are not reported in the registry record.

Why can over-dispersion matter?

In general, over-dispersion occurs when observed variation in a count outcome exceeds what a chosen count model expects. If ignored, standard errors can be too small and confidence intervals too narrow, making results look more precise than the data justify. Model choice should reflect the observed outcome distribution and study design. The registry record does not report a count model, an over-dispersion assessment, or enough numerical outcome information to evaluate whether over-dispersion is relevant to any listed endpoint. This explanation is general and should not be interpreted as a claim that over-dispersion occurred in this study.

How should planning calculations be read?

The stated sample-size assumptions describe planning illustrations computed from an observed effect, not the study’s original design justification. They use a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation; the effect to detect is expressed as a stated fraction of the observed effect. In general, such calculations ask how much information a future design might need to detect an assumed effect under specified assumptions. They are not an estimate of the study’s observed power. The registry record does not report the original sample-size justification or the planning calculation results.

The assumptions about equal allocation are part of the illustrations only and do not establish that the study itself allocated participants equally. For time-to-event illustrations, the stated convention is a total number of events; other illustrations use participants per arm. Those conventions describe how planning outputs are expressed, not the trial’s observed enrollment or outcome counts. A planning calculation based on an observed effect can also inherit uncertainty from that effect; it should not be treated as a precise forecast of a future result.

More generally, the protocol, analysis plan, interim-analysis procedures, and planned handling of missing data are not reported in the registry record. The registry lists 0 analyses, which means no analysis entries appear in its record; it does not establish whether analyses were conducted outside the registry. Statistical interpretation must therefore remain limited to the endpoint definitions and other explicitly recorded information.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists multiple secondary outcomes alongside cardiac index. Considering multiple outcomes raises a general multiplicity issue: when many hypotheses are tested, the chance of at least one apparently unusual result can increase if each is assessed without accounting for the number of tests. Common approaches include defining a primary hypothesis in advance, prioritizing outcomes, or using an adjustment procedure. The registry identifies cardiac index as primary, but a multiplicity strategy, outcome hierarchy beyond that designation, and adjusted analyses are not reported in the registry record.

The record states that there are 8 outcome measures and lists secondary outcome categories, including tissue Doppler indices with several components. It does not report numerical results or analysis entries for those measures. It is therefore not possible to determine which outcomes were analyzed, whether all listed outcomes were measured, or whether any multiplicity adjustment was used. The absence of analysis entries should not be interpreted as evidence that no analyses occurred.

Missing-data handling and analysis populations are also not reported in the registry record. The enrollment of 34 does not establish the number contributing data to cardiac index or to any secondary outcome. The record does not state how participants with missing measurements, protocol deviations, or incomplete follow-up were handled, nor does it define an intention-to-treat, per-protocol, or other analysis population. In general, missingness can affect both the amount of information and the interpretation of comparisons, particularly when the reasons for missing measurements differ across participants or conditions.

Without a documented analysis population, missing-data approach, and multiplicity plan, the precision and robustness of any result cannot be evaluated from this record. Those omissions are reporting gaps; they do not establish that the underlying study lacked such procedures.

11. 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 1% reporting threshold.

The registry’s adverse-event entry is labeled “Pacing Protocol and RV Pacing.” It records 11 at risk and 0 affected for serious adverse events, and 11 at risk and 0 affected for other adverse events. These are the figures for the recorded group and categories; they should not be generalized to all enrolled participants or to all possible follow-up periods because the registry entry does not explain the relationship between these denominators and the enrollment figure.

The death field is null, and no top serious adverse-event terms are listed. A null death field is not a reported zero. The registry does not provide event definitions, surveillance procedures, the observation period, or an explanation of how adverse events were collected. It also does not report adverse-event information for a clearly described comparison group.

In general, a count of zero affected in a registry category means that no events are recorded in that category for the stated denominator; it does not prove that the risk is absent. Safety comparisons require clear denominators, consistent follow-up, and sufficiently detailed event reporting. The recorded figures should therefore be read as limited registry information, not as a comprehensive assessment of safety.

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

This record documents a study asking whether the pacing site used after open-heart surgery is associated with an immediate change in cardiac index. It describes a brief pacing protocol before extubation and identifies baseline and after 20 minutes of pacing as the primary measurement times. This makes the study relevant to questions about postoperative hemodynamics and the measurement of cardiac function during temporary pacing.

The record does not report the numerical cardiac-index results, the estimated difference or change, or its uncertainty. It consequently does not show whether cardiac index differed between pacing conditions or changed from baseline. It also does not report the statistical analysis used. The absence of posted numerical findings is not evidence that there was no change; it leaves the result unknown from the registry record.

The comparison structure limits what can be inferred even beyond the missing outcome values. The registry states that the study was not a randomized comparison and that the arms were not a like-for-like control comparison, while allocation is not stated. In general, nonrandom allocation may allow differences between groups to influence an observed contrast. Because the record does not describe allocation or adjustment for participant characteristics, it cannot support a causal interpretation of a hypothetical group difference.

The listed secondary outcomes indicate that the study considered more than cardiac index, including blood pressure, low output syndrome, tissue Doppler measures, support requirements, QRS duration, and bypass time. Their inclusion does not show that any particular outcome improved or worsened. Numerical results for these measures are not reported in the registry record.

The appropriate interpretation is limited: the registry defines a clinically focused question and records that the study is completed, but does not supply the primary result or enough methodological detail to assess its precision, bias, or robustness. Any claim about benefit, lack of benefit, or safety would go beyond the posted registry data.

13. Why This Trial Matters Statistically

Statistically, this study highlights the difference between defining an endpoint and reporting evidence about it. Cardiac index is specified with a unit, summary measure, and measurement times, which makes the intended physiological quantity identifiable. Yet without its observed values and a comparison estimate, the endpoint definition cannot answer the research question. Transparent reporting of both estimates and uncertainty is necessary for readers to judge what the data support.

The design description also matters for interpretation. A pacing comparison may be clinically interesting, but the registry explicitly says the comparison is not randomized and the arms are not like-for-like controls. Statistical methods cannot automatically remove bias created by an unclear allocation process or differences between groups. A clear account of allocation and analysis is important for distinguishing an observed association from a causal effect.

The record also illustrates why outcome multiplicity and analysis populations matter. Several secondary outcomes are listed, while the analysis entries and missing-data procedures are not reported. Readers cannot tell which outcomes were analyzed, how many observations contributed, or how uncertainty was handled. These details affect how much confidence to place in any result, especially when outcomes differ in scale and structure.

Finally, planning illustrations should remain separate from study findings. Calculations based on an observed effect and specified assumptions can inform planning for a future study, but they do not show the power actually achieved or replace the observed estimate and its precision. For this record, the central statistical lesson is the need to report the outcome results, comparison method, analysis population, and uncertainty alongside a clearly framed clinical question.

14. Limitations

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

The primary limitation of the registry record is that it defines cardiac index as the primary endpoint but does not report its observed values or a statistical comparison. There is no reported confidence interval, p-value, or analysis estimate with which to assess magnitude or precision. The registry’s 0 analyses entry indicates that analysis results are not listed in the record; it does not establish whether analyses were performed elsewhere.

The comparison is not randomized, allocation is not stated, and the registry warns that the arms are not a like-for-like control comparison. The descriptions do not provide sufficient detail to establish how participants were assigned to RV or BiV pacing or whether each participant experienced each condition. This limits interpretation of any possible contrast and prevents readers from evaluating confounding or dependence between measurements.

Enrollment is recorded as 34, but outcome-specific denominators and analysis populations are not reported. The record does not explain missing measurements, exclusions, protocol deviations, or the number contributing data at each measurement time. Eligibility criteria and participant characteristics are also not reported in the registry record, limiting assessment of who the findings would describe.

The record lists secondary outcomes but does not report their numerical findings, analysis methods, or a multiplicity plan. The serious and other adverse-event entry provides counts for a named group, but does not describe event surveillance, follow-up duration, or how its denominators relate to enrollment. The null death field is not a zero count.

Finally, details of the statistical analysis plan, sample-size justification, interim analyses, and missing-data methods are not reported in the registry record. These limitations concern what can be evaluated from the registry information; they should not be taken as proof that the underlying study lacked additional methods or results.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Assessing the Hemodynamic Benefits of Cardiac Resynchronization Therapy in Children Following Open-Heart Surgery — NCT00397514.
• Registry record last updated 2017-12-18; status last verified 2017-11.
• Results first posted 2013-08-30.
• 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.

18. Record Summary

NCT00397514 is listed as a completed study sponsored by the University of British Columbia, with enrollment of 34. Its recorded start is 2006-10 and primary completion is 2009-11. The study concerns congenital heart defects and postoperative pacing after open-heart surgery.

The protocol description specifies 20 min. of either conventional RV or BiV pacing before extubation, with 10 min. of recovery time before and after pacing. Cardiac index is the primary endpoint, summarized by median and full range at baseline and after 20 minutes of pacing. Secondary outcomes include blood pressure, low output syndrome, tissue Doppler indices, inotropic and ventilatory support, QRS duration, and cardio-pulmonary bypass time.

The registry states that the comparison is not randomized and is not a like-for-like control comparison; allocation is not stated. Numerical primary and secondary outcome results, analysis methods, analysis populations, and missing-data procedures are not reported in the registry record. The adverse-event entry records 0 affected in its serious and other categories for the stated denominators, while the death field is null.