This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for QUARTO-II Study to Evaluate the Management of Patients Resynchronized With the QuartetTM LV Quadripolar Lead (NCT01733368), a registered phase not stated study. The primary outcome is Safety Outcomes in CRT Responders and Non-Responders.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01733368 |
| Phase | Phase not stated |
| Condition | Heart Failure |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 198 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Abbott Medical Devices |
| Results posted | Yes |
2. Clinical Question
Population
Patients with heart failure who were resynchronized with the Quartet left ventricular quadripolar lead. The registry record reports enrollment of 198 participants. It also describes the primary safety-outcome population as patients experiencing a clinical safety event before the 6-month follow-up visit; how this wording was applied is not reported in the registry record.
Intervention
Management after implant of the Quartet left ventricular quadripolar lead. The brief summary says that patient optimization and evolution would be evaluated over 6 months after implant. Specific management strategies or rules for selecting a pacing vector are not reported in the registry record.
Comparator
No randomized or like-for-like control comparison is established by the record. It lists responder patients with non-conventional and conventional left ventricular pacing vectors as secondary outcome groups, but assignment to those groups and their use as a comparative design are not reported in the registry record.
Primary question
What safety outcomes—mortality, cardiovascular or all-cause hospitalization, or a combined endpoint of death and all-cause hospitalization—were recorded by 6 months after implant among the stated CRT responder and non-responder population? The registry record names these outcomes but reports no analyses of them, so it does not provide an estimated comparison or a quantified answer to that question.
The study title and summary focus on management and patient evolution following resynchronization with a Quartet lead. The primary outcome title refers to safety outcomes in CRT responders and non-responders, while the description lists mortality and hospitalization outcomes. These elements indicate the subject of the research, but they do not establish a causal question about the lead relative to another device or treatment. The record does not state how CRT response was defined, how patients came to use a particular pacing vector, or whether responders and non-responders were intended as formal comparison groups.
The listed secondary outcomes count responder patients with non-conventional and conventional left ventricular pacing vectors. Those labels describe groups of responders by vector type, but the registry record does not give the criteria for a conventional or non-conventional vector or a statistical comparison between the groups. As a result, the clinical question that can be stated from the record is descriptive: which safety events and responder categories were to be assessed during follow-up. The registry record does not report numerical results for the primary safety outcome or the secondary outcomes.
3. Trial Design
QUARTO-II is listed as an observational study in patients resynchronized with the Quartet left ventricular quadripolar lead. Heart failure is the listed condition, and the registry record names Abbott Medical Devices as the sponsor. The study is marked completed, with a start date of 2012-11 and a primary completion date of 2015-08. Enrollment is listed as 198.
The brief summary describes evaluation of optimization and patient evolution over 6 months after implant. The primary outcome timeframe is also 6 months after implant. This indicates a post-implant follow-up focus, but the registry record does not describe the visit schedule, the duration of follow-up for each participant, or what counted as completion of follow-up. It also does not report whether all enrolled participants contributed data through the stated timeframe.
The listed primary outcome is titled “Safety Outcomes in CRT Responders and Non-Responders.” Its description names mortality, cardiovascular and all-cause hospitalizations, and a combined endpoint of death and all-cause hospitalization. The listed secondary outcomes concern responder patients with conventional and non-conventional left ventricular pacing vectors. The record does not define response or describe how pacing-vector categories were assigned.
The registry record does not state an allocation method or identify a randomized comparison. It therefore does not establish treatment arms that can be interpreted as like-for-like control groups. The observational designation is important: group differences, if reported, could reflect how patients were selected, treated, or classified, as well as the outcomes being studied. No adjustment strategy for such differences is reported. The record lists four outcome measures, but it does not contain analysis results for them. Its status as completed describes the study record status, not the availability of a reported estimate for every planned outcome.
4. Participant Flow and Accounting
The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.
Overall Study
| Stage | Quadripolar Left Ventricular Lead (Quartet Lead) |
|---|---|
| STARTED | 198 |
| COMPLETED | 167 |
| NOT COMPLETED | 31 |
Analysis population for the primary outcome, as defined in the registry: Patients with the 6-month follow-up completed and echocardiographic measurements available
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.
| Characteristic | Unit | Quadripolar Left Ventricular Lead (Quartet Lead) |
|---|---|---|
| Participants analysed | 198 | |
| Age, Continuous | years | 66.01 (SD 10.22) |
| Sex: Female, Male: Female | Participants | 52 |
| Sex: Female, Male: Male | Participants | 146 |
| New York Heart Association (NYHA) Classification: NYHA I | Participants | 5 |
| New York Heart Association (NYHA) Classification: NYHA II | Participants | 77 |
| New York Heart Association (NYHA) Classification: NYHA III | Participants | 111 |
| New York Heart Association (NYHA) Classification: NYHA IV | Participants | 5 |
| Cardiovascular Etiology: Ischemic, Non-ischemic: Ischemic | Participants | 80 |
| Cardiovascular Etiology: Ischemic, Non-ischemic: Non-ischemic | Participants | 118 |
| QRS Duration | miliseconds (ms) | 168 (SD 22.22) |
| QRS Morphology: Left Bundle Branch Block (LBBB) | Participants | 168 |
| QRS Morphology: Right Bundle Branch Block (RBBB) | Participants | 20 |
| QRS Morphology: Interventricular Conduction Delay (IVCD) | Participants | 8 |
| QRS Morphology: Unknown | Participants | 2 |
| Ejection Fraction (EF) | percentage (%) | 26.87 (SD 7.38) |
| Left Ventricular End Systolic Volume (LVESV) | milliliters (ml) | 155.17 (SD 75.10) |
6. Primary Endpoint
The registry lists the primary outcome as Safety Outcomes in CRT Responders and Non-Responders, measured over 6 months after implant.
| Element | Registry entry |
|---|---|
| Result type | Count Of Participants |
| Measure of spread | not applicable |
| Unit | Participants |
| Endpoint classification | Binary Endpoint |
The primary outcome is titled “Safety Outcomes in CRT Responders and Non-Responders.” The listed measures are mortality, cardiovascular hospitalization, hospitalization for any cause, or a combined endpoint of death and all-cause hospitalization. The timeframe is 6 months after implant, and the unit is participants. The outcome is characterized as a count of participants, so its intended form is a count of people meeting an event definition rather than a continuous measurement.
Safety outcomes are used to describe clinically important events observed during follow-up. A combined endpoint can bring more than one event type into a single outcome definition, but its interpretation depends on which events qualify and how the combination is constructed. In this record, the description identifies possible components, but it does not clarify whether the listed measures are separate endpoints, alternatives, or components analyzed together. The registry record also does not specify how recurrent hospitalizations, timing, or multiple events in one participant were handled.
The stated population wording refers to patients experiencing a clinical safety event before the 6-month follow-up visit. That wording does not clarify how participants without an event were represented in the count or whether the population definition was intended to include all enrolled participants. The registry record does not provide a numerical primary-outcome result, an analysis denominator, or an estimate of uncertainty. Consequently, the endpoint description identifies what was to be assessed, but it does not establish the observed frequency or precision of the primary outcome.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record gives important context for interpreting the study: it is observational, concerns patients resynchronized with a Quartet lead, and describes follow-up over 6 months after implant. It does not report analyses for the listed outcomes. Thus, the primary safety-outcome description should be read as an outcome plan or definition in the record, not as a numerical finding about mortality, hospitalization, or their combination.
The safety listing reports 50 participants affected by serious adverse events among 198 at risk, and 15 affected by other adverse events among 198 at risk. It also reports 6 deaths. These are descriptive registry figures. The record does not provide an analysis comparing these figures with a control group, nor does it establish that the adverse-event categories are mutually exclusive. They should not be added together or treated as independent groups. The listed serious-event terms include atrial or ventricular arrhythmia at 5.6%, lead dislodgement at 5.1%, exacerbation of heart failure at 4.0%, bleeding/hematoma at 1.5%, death at 1.0%, and pneumonia at 1.0%. The record does not describe the denominator or method used for these term percentages.
Counts and percentages describe the events recorded under the registry’s definitions; they do not by themselves show whether an event was caused by the lead or by its management. An observational study without a stated randomized comparison cannot separate an exposure effect from differences among patients or other factors that may influence both treatment and outcomes. The registry record does not report an adjusted analysis that could address such differences.
Precision also cannot be judged for the primary endpoint from the record because it contains no primary-outcome estimate, confidence interval, or analysis denominator. A confidence interval, as a general statistical concept, expresses uncertainty around an estimated quantity; its width depends in part on the information available and the variability of the data. Without a reported estimate and interval, the precision of the primary outcome cannot be assessed. The listed adverse-event counts are also not accompanied by confidence intervals or other uncertainty measures.
The secondary outcomes name responder groups by pacing-vector type, but no results or comparative analyses are reported for them. The registry record does not define response or explain how vector selection occurred. Consequently, it cannot support a claim that one vector category had better outcomes or that the lead changed patient outcomes. The appropriate reading is limited to the study’s observational scope, its stated follow-up and endpoints, and the descriptive safety counts recorded.
9. Statistical Methods Explained
The record describes a binary outcome type and characterizes the primary measure as a count of participants. In general, binary outcomes classify an observation into event or no-event status for a defined outcome and timeframe. A count of participants with an event is interpretable only alongside a clearly specified population and denominator. Here, the record gives a timeframe of 6 months after implant and a unit of participants, but the primary outcome population wording is not fully clear. The registry record does not report a primary analysis denominator or a numerical primary result.
What does an event count tell the reader?
In general, an event count says how many participants met a stated event definition in the population being analyzed. It does not, by itself, describe the chance of an event unless the relevant denominator and observation period are clear. The safety listing includes counts of participants affected and counts of deaths, but it does not provide the primary outcome analysis or explain how those safety listings map to each component of the primary endpoint. These figures should therefore be read as descriptive information, not as a complete analysis of the primary endpoint.
Why does the observational design matter?
In general, randomized allocation can help balance measured and unmeasured characteristics across comparison groups. An observational study does not obtain that protection through random assignment. Differences between groups can reflect factors associated with who received a particular treatment or how a group was defined, as well as any treatment-related effect. The registry record does not state an allocation method and explicitly does not establish a randomized, like-for-like control comparison. It also does not report an adjustment model, covariates, or a prespecified approach to confounding. No causal interpretation should be inferred from the outcome descriptions or safety counts alone.
What would uncertainty measures add?
As a general statistical explanation, a confidence interval gives a range of values compatible with the observed data under the assumptions of the analysis. A point estimate without an interval can conceal substantial uncertainty, particularly when events are uncommon or data are incomplete. The record does not report confidence intervals or other uncertainty measures for the primary outcome or the safety counts. Therefore, the precision of any underlying population estimate cannot be evaluated from the registry record.
How should the event categories be understood?
The primary outcome description names mortality, cardiovascular hospitalization, hospitalization for any cause, and a combined death and all-cause hospitalization endpoint. In general, a composite endpoint is interpreted through both its overall result and the contribution of each component; components may differ in frequency and clinical importance. The registry record does not clarify whether each item is a separate analysis, whether the combined outcome is the primary definition, or how events occurring in the same participant were counted. It also does not specify how repeated hospitalizations were handled. Those details matter because different counting rules can lead to different interpretations.
For adverse-event summaries, serious and other events are separate labels in the record, with affected-participant counts listed for each. The record does not define these classifications or report whether the same participant could appear in both. The serious-event terms are presented with percentages, but their denominator and coding rules are not stated. General statistical interpretation therefore requires caution: a percentage is meaningful only when its base population and event-counting method are understood.
What can a planning illustration show?
In general, sample-size planning uses assumptions about the expected effect, variability, significance level, allocation, and desired power to illustrate the information a future study might need. The registry record states that its planning illustration is based on an observed effect and assumes a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It also says that the effect to detect is a stated fraction of the observed effect. For time-to-event tables, the stated quantity is a total number of events; for other tables, it is participants per arm.
These are planning assumptions, not evidence that the study was designed or analyzed that way. The record does not report the trial’s own sample-size justification, and no randomized two-arm comparison is established. Any sample-size illustration based on an observed effect is conditional on that effect and the stated assumptions; it is not observed power and does not show that the study had a particular probability of detecting a true effect. The registry record contains no analysis results for the primary or secondary outcomes, so a planning illustration cannot substitute for an outcome estimate.
What analysis details are absent?
The registry record reports no analyses for the outcomes. It does not describe an analysis model, adjustment for baseline differences, handling of missing observations, analysis populations, censoring rules, or checks of model assumptions. These are not minor reporting details: they determine which participants and events contribute to an estimate and how uncertainty is quantified. In their absence, the descriptive registry figures should not be read as adjusted comparisons or as complete follow-up analyses.
10. Multiplicity, Missing Data and Analysis Populations
The registry record lists four outcome measures, names a primary safety outcome, and identifies secondary outcomes concerning responder patients with conventional and non-conventional pacing vectors. When a study evaluates multiple endpoints or groups, the chance of at least one apparently notable result can increase if each is tested separately. As a general statistical practice, investigators may specify a hierarchy, adjust for multiple comparisons, or treat analyses as exploratory. The registry record does not report a multiplicity strategy, a testing hierarchy, or adjusted analyses. It also reports no outcome analyses, so there are no reported inferential results to interpret in light of multiplicity.
Missing-data methods are not reported in the registry record. It does not state how participants without a recorded 6-month assessment were handled, whether follow-up was complete, or how missing event information was distinguished from absence of an event. It also does not report the number of participants contributing to the primary endpoint analysis. Those omissions prevent assessment of whether the analyzed population differed from the enrolled population or whether missing follow-up could affect interpretation.
Analysis populations are not described. The registry record does not say whether analyses were intended to include all enrolled participants, only participants with a particular follow-up status, or groups defined by responder status or pacing vector. It also does not report a prespecified adjustment strategy for this observational study. Consequently, the listed endpoint names and descriptive safety figures do not establish which population was used for a formal comparison or how potential differences among patients were addressed.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Quadripolar Left Ventricular Lead (Quartet Lead) | 50 | 198 | 25.3% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Quadripolar Left Ventricular Lead (Quartet Lead) | 6 of 198 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 1% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Quadripolar Left Ventricular Lead (Quartet Lead) | 15 of 198 |
Most frequent serious adverse event terms
| Event term | Organ system | Quadripolar Left Ventricular Lead (Quartet Lead) |
|---|---|---|
| Atrial or Ventricular arrhythmia | Cardiac disorders | 11 of 198 |
| Lead Dislodgement | Product Issues | 10 of 198 |
| Exacerbacion of Heart Failulre | Cardiac disorders | 8 of 198 |
| Bleeding/Hematoma | Surgical and medical procedures | 3 of 198 |
| Death | Cardiac disorders | 2 of 198 |
| Pneumonia | Respiratory, thoracic and mediastinal disorders | 2 of 198 |
| Infection | Surgical and medical procedures | 2 of 198 |
| Acute Calculous Cholecystitis | Hepatobiliary disorders | 1 of 198 |
| Cardiac arrest and death | Cardiac disorders | 1 of 198 |
| Cardiac Tamponade | Cardiac disorders | 1 of 198 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Quadripolar Left Ventricular Lead (Quartet Lead) |
|---|---|---|
| Bleeding/Hematoma | Surgical and medical procedures | 7 of 198 |
| phrenic nerve/diaphragmatic/extracardiac stimulation | Product Issues | 3 of 198 |
| Upgrade of the device to DDD by adding atrial lead | Surgical and medical procedures | 1 of 198 |
| Shiver and physical discomfort during implant | Surgical and medical procedures | 1 of 198 |
| carbon dioxide narcosis | Surgical and medical procedures | 1 of 198 |
| Coronary sinus dissection | Surgical and medical procedures | 1 of 198 |
| Inappropriate ATP | Product Issues | 1 of 198 |
| Nause and vomiting | Surgical and medical procedures | 1 of 198 |
| Pain in the implant site | Surgical and medical procedures | 1 of 198 |
Serious events with the highest arm-level rate: atrial or ventricular arrhythmia (5.6%), lead dislodgement (5.1%), exacerbacion of heart failulre (4.0%), bleeding/hematoma (1.5%), death (1.0%).
The registry safety listing reports 50 participants affected by serious adverse events among 198 at risk and 15 participants affected by other adverse events among 198 at risk. It also lists 6 deaths. These are separate registry entries and should not be added together: the record does not say whether categories overlap or whether every death is included in another listed category.
The serious-event terms are reported as atrial or ventricular arrhythmia, 5.6%; lead dislodgement, 5.1%; exacerbation of heart failure, 4.0%; bleeding/hematoma, 1.5%; death, 1.0%; and pneumonia, 1.0%. The registry record does not report the denominator or coding rules for these term percentages, nor whether a participant could contribute to more than one term. The percentages therefore describe the registry’s listed terms, but do not establish mutually exclusive groups or a comparison with another treatment.
Serious adverse-event counts are descriptive safety information. They do not, by themselves, establish that an event was caused by the lead, and the record does not provide an adjusted or randomized comparison that would support attribution. These figures also do not replace the missing analysis of the stated primary safety endpoint.
12. What the Result Does, and Does Not, Mean
The registry record establishes that QUARTO-II was an observational study of patients resynchronized with the Quartet left ventricular quadripolar lead, with evaluation described over 6 months after implant. It names mortality and hospitalization outcomes and includes descriptive adverse-event counts. Those details show the safety topics recorded and the study’s follow-up focus.
The record does not report analyses for the primary or secondary outcomes. It therefore does not give a numerical estimate for the primary endpoint, an uncertainty interval, or a comparison of outcomes between responders and non-responders. It also does not report comparative results for conventional and non-conventional pacing vectors. The listed safety counts cannot fill that gap: they are not a reported estimate of the primary endpoint and are not presented as a like-for-like comparison.
Because allocation is not stated and the record does not establish a randomized comparison, differences among patient groups would not necessarily reflect a treatment effect. In general, observational comparisons can be influenced by patient characteristics, clinical decisions, or other factors related to both group membership and outcomes. The record does not describe an adjustment method that would address those possibilities. The listed figures consequently should not be read as proof that the lead or a particular management approach caused, prevented, or changed any event.
The record also leaves key definitions and analysis details unclear. It does not define CRT response or pacing-vector categories, clarify the precise construction of the combined endpoint, describe missing-data handling, or specify analysis populations. Without those details and reported analyses, readers cannot determine how the planned outcome definitions were implemented or how precise an estimated effect might be.
In short, the record documents the observational study’s scope and includes safety listings, but it does not provide an analyzed answer to the primary clinical question. It neither establishes benefit nor establishes lack of benefit. A conclusion about comparative effectiveness or causation would go beyond the information reported in the registry record.
13. Why This Trial Matters Statistically
This study is statistically notable because its title and outcomes distinguish CRT responders from non-responders, while the design is identified as observational and no randomized comparison is established. That combination makes the definition of groups and the handling of differences among patients central to interpretation. The registry record does not define response, explain group assignment, or report adjustment methods, so the distinction cannot be treated as a controlled comparison.
The endpoint description also illustrates why precise outcome definitions matter. Mortality, cardiovascular hospitalization, all-cause hospitalization, and a combined death and all-cause hospitalization endpoint are not interchangeable concepts. A composite can provide a single summary, but interpretation depends on its components, event counting, and follow-up rules. Those details are not reported in the registry record. The record names the outcome but does not present a corresponding analysis.
The registry’s safety figures offer descriptive counts, but their interpretation depends on definitions, denominators, overlap, and uncertainty. The term percentages have no reported denominator or coding method, and confidence intervals are not reported. This makes them useful as a record of listed events, but insufficient for a precise comparative inference.
Finally, the absence of reported analyses demonstrates a distinction between registering an outcome and reporting a result. A completed study record may identify planned outcomes and list safety information without supplying estimates, analysis populations, or missing-data methods. For biostatisticians and clinical researchers, this underscores the need to evaluate design, definitions, denominators, and analysis reporting before drawing conclusions from endpoint labels or event summaries.
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 registry record gives limited detail about the study’s conduct and analysis. Although it identifies the study as observational and marks it completed, it does not state allocation, define a control group, or describe how participants were assigned to responder status or pacing-vector categories. The record therefore does not support a randomized or like-for-like comparison.
The primary outcome description is not fully operationalized. It names mortality, cardiovascular hospitalization, hospitalization for any cause, and a combined endpoint, but does not clarify which was the primary analyzed definition or how events were counted. The population wording refers to patients experiencing a clinical safety event before the 6-month visit, without clarifying how participants without an event were handled. Definitions of CRT response and conventional versus non-conventional vectors are also not reported in the registry record.
No primary or secondary outcome analyses are reported. The record does not provide estimates, confidence intervals, analysis denominators, adjustment methods, missing-data procedures, or analysis populations. It also does not report whether follow-up was complete or how repeated events were handled. These omissions prevent assessment of precision, robustness, and the extent to which the recorded participants represent the intended study population.
The adverse-event listing is descriptive, but the registry record does not specify the denominator or coding method behind the serious-event term percentages, whether categories overlap, or how events were attributed. The listed counts do not constitute a controlled safety comparison. The record also does not report a multiplicity strategy despite listing multiple outcome measures. These limitations mean the record supports a description of study scope and recorded safety information, not a definitive estimate of comparative effect or causation.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: QUARTO-II Study to Evaluate the Management of Patients Resynchronized With the QuartetTM LV Quadripolar Lead — NCT01733368.
- Registry record last updated 2019-02-04; status last verified 2019-01.
- Results first posted 2018-03-01.
- 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.
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18. Record Summary
QUARTO-II is registered as an observational study of patients with heart failure resynchronized with the Quartet left ventricular quadripolar lead. Abbott Medical Devices is listed as sponsor. The record lists enrollment of 198, a start date of 2012-11, a primary completion date of 2015-08, and completed status. Evaluation is described over 6 months after implant.
The primary outcome concerns safety events in CRT responders and non-responders, including mortality and hospitalization outcomes. Secondary outcomes concern responder patients with conventional and non-conventional pacing vectors. The record includes descriptive adverse-event counts and listed serious-event terms, but reports no analyses for the primary or secondary outcomes. Definitions, analysis populations, missing-data methods, and comparative adjustment methods are not reported in the registry record.