Assessment of Transnational Performance of the Universal Cardiac Surgical Risk Score Across International Sites (ATLAS)

ATLAS is a prospective, observational, multicenter cohort study of how accurately the Universal Cardiac Surgical Risk Score (UCSRS) predicts 30-day outcomes after adult cardiac surgery, compared head-to-head with two established models, STS-PROM and EuroSCORE II. Consecutive adult patients undergoing cardiac surgery are enrolled at each participating center over 12 months. All three scores are recorded for each patient. No score is returned to the treating team or influences clinical care. Discrimination and calibration of each score are assessed against 30-day major adverse cardiac and cerebrovascular events (MACCE). The model under evaluation, UCSRS version 3.2, was specified and calibrated against published registry mortality using simulated patients before enrollment. No simulated patient has an outcome, so no performance claim is made before this study.

Study Overview

• Status: Not yet recruiting
• Conditions: Coronary Artery Disease; Heart Valve Diseases; Cardiac Surgical Procedures
• Intervention / Treatment: Other: Risk score calculation

Detailed Description

DATA AND ANALYSIS Each site records the clinical variables from which the scores are computed, the site's own STS-PROM and EuroSCORE II values (comparators only; they never enter the UCSRS score), the Frailty Test components, and the 30-day outcome components. Sites compute no derived quantities; every derived value is computed centrally by the same code.

Data are de-identified at the site. A site either sends a de-identified patient-level dataset to the coordinating center or runs the identical standardized analysis locally and shares only summary results (c-statistic, observed/expected ratio, calibration slope and intercept), which are combined by summary-level meta-analysis. Discrimination uses the c-statistic with the DeLong test; calibration uses calibration plots, the observed/expected ratio, and calibration slope and intercept.

MODEL UNDER EVALUATION UCSRS version 3.2 (specification 3.2.0) has a single log-odds baseline computed from the patient's own clinical variables, to which it adds a required frailty correction (Frailty Test, 0-6: chair-rise, cognition assessment, hemoglobin, albumin) and optional corrections for liver function (MELD), left ventricular geometry and coronary complexity (SYNTAX), and right-heart catheterization. STS-PROM and EuroSCORE II are calculated independently by each site on the official calculators and are used only as comparators.

VERSION HISTORY Version 1.0 was published (J Cardiothorac Surg 2026; DOI 10.1186/s13019-026-04433-x), with a baseline blending STS-PROM and EuroSCORE II. Version 2.0 (27 August 2026) removed STS-PROM from the baseline. Version 2.1 (28 August 2026) rebuilt the baseline in log-odds. Version 3.0 replaced the blend with a single logistic baseline from which EuroSCORE II was removed entirely. Version 3.1 (20 September 2026) reset the calibration constant. Version 3.2 (24 October 2026) counted aortic disease once, lowered the MELD slopes, applied the frailty ladder to the odds, added CABG + AVR + MVR as an operation, and re-solved the calibration constant. Each change is recorded in a dated specification of record. The protocol registered here is ATLAS Study Protocol version 4.3 (24 October 2026), which describes UCSRS version 3.2.

SIMULATION AND CALIBRATION The calibration constants were set before enrollment against published mortality from thirteen surgical registries. For each registry, a synthetic cohort was tuned until its mean EuroSCORE II matched that registry's published observed mortality divided by its published EuroSCORE II observed/expected ratio; this is the only point at which real-world information enters. Runs scored millions of synthetic patients: about 11 million exploratory simulations in version 2.1 (which set no constant); 30,000,000-patient runs across the 13 registry-anchored cohorts in versions 3.0 and 3.1; and, in version 3.2, a 325,000-patient solve, a 520,000-patient hold-out, a 29,999,996-patient locking run and two 2,600,000-patient hold-outs. At the version 3.2 constant the median observed/expected ratio across the 13 registries was 1.0011 in the locking run, with hold-outs of 0.9968 and 0.9936. A separate 1,000,000-patient high-risk validation lowered mean predicted risk from 52.3% (version 3.1) to 20.8% (version 3.2) and the share of patients at the 70% score cap from 40.1% to 0.003%.

STRUCTURAL ENUMERATION On 15 September 2026 a complete factorial enumeration of 318,162,816 input combinations (cells, not patients) was run on a development version of the scoring engine, with a provisional intercept and no calibration shift. It covered elective first-time and redo operations and all eleven procedure codes on a deliberately adverse grid (MELD of 10 or more, hemoglobin 13 g/dL or less, albumin 4.0 g/dL or less). It was used to examine structure only: relative behavior, ordering, dynamic range and saturation at the score cap. Its absolute values are uncalibrated and are not risk estimates. In this grid EuroSCORE II, which carries a single flag for previous cardiac surgery and a single flag for thoracic aortic disease, separated a second redo sternotomy from a first redo by 0.02 percentage points and separated aortic root and arch operations from ascending replacement by 0.18 points; the UCSRS engine distinguished these operations. The results are recorded in a dated results document.

LIMITS OF THE SIMULATIONS No simulated patient has an outcome, and no outcome model was used at any stage. Discrimination therefore cannot be assessed in simulation, and the calibration results show internal consistency, not superiority over STS-PROM or EuroSCORE II. No performance claim accompanies the current specification. The version 3.2 constants were set by the investigator before first enrollment, as a documented exception to an earlier commitment; they are not moved again before 5,000 patients are enrolled.

The coordinating investigator developed UCSRS. This is declared in all study documents and publications, and negative results will be published.

• Study Type: Observational
• Enrollment (Estimated): 5000

Contacts and Locations

• Study Contact: Name: Atiq Rehman, MD; Phone Number: (609)304-8397; Email: atiqmd@aol.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years and older (Adult, Older Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

• Sampling Method: Non-Probability Sample

Study Population

Consecutive adult patients undergoing cardiac surgery at each participating center, enrolled over a 12-month period

Description

Inclusion Criteria:

• Age 18 years or older
• Undergoing cardiac surgery at a participating institution during its enrollment period (isolated CABG, isolated valve, combined CABG and valve, multiple valve, aortic surgery, redo sternotomy, or other adult cardiac surgical procedures, on- or off-pump)
• Enrolled consecutively, without selection

Exclusion Criteria:

• Age under 18 years
• Congenital heart surgery performed under a pediatric program
• Heart transplantation or ventricular assist device implantation as the primary procedure
• Cases in which the comparator scores cannot be computed from available pre-operative data

Study Plan

How is the study designed?

Design Details

• Observational Models: COHORT
• Time Perspectives: PROSPECTIVE

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Adult cardiac surgery patients; Consecutive patients 18 years or older undergoing cardiac surgery at a participating site. Risk scores are calculated for research only and do not change care	Other: Risk score calculation; Calculation of UCSRS, STS-PROM and EuroSCORE II risk scores from pre-operative data, for assessment of discrimination and calibration against observed 30-day outcomes. UCSRS coefficients are fixed and version-locked. No effect on clinical care

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
30 day MACCE	Occurrence within 30 days after surgery of any component of a composite of all-cause mortality, permanent stroke, renal failure (per the current STS Adult Cardiac Surgery Database definition) and prolonged ventilation (more than 24 hours). STS standard definitions are applied at all sites. Used to assess discrimination and calibration of UCSRS, STS-PROM and EuroSCORE II.	30 days after surgery
30 day all cause mortality	Death from any cause within 30 days of the index procedure, or in-hospital death after day 30 where the patient has remained continuously admitted since the index procedure. Used to assess calibration (observed/expected ratio, calibration slope and intercept) of UCSRS, STS-PROM and EuroSCORE II.	30 day after surgery

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Reoperation	Reoperation for any cause within 30 days after surgery (STS definition)	30 days after surgery
Number of Participants with Deep Sternal Wound Infection	Deep Sternal wound infection within 30 days of surgery (STS definition)	30 days after surgery
Number of Participants with Major Bleeding	Major bleeding within 30 days of surgery (STS definition)	30 days after surgery

Collaborators and Investigators

• Sponsor: Union Health System
• Investigators: Principal Investigator: Atiq Rehman, MD, Union Health System

Publications and helpful links

General Publications

• Universal cardiac surgical risk score (UCSRS v1.0) a unified physiology-informed risk architecture for operative mortality prediction across all adult cardiac surgical procedures: algorithm design and prospective validation protocol; J Cardiothoracic Surgery, Accepted in July 2026; (In-Press) DOI: 10.1186/s13019-026-04433

Study record dates

Study Major Dates

• Study Start (Estimated): January 1, 2027
• Primary Completion (Estimated): December 31, 2028
• Study Completion (Estimated): December 31, 2028

Study Registration Dates

• First Submitted: October 27, 2026
• First Submitted That Met QC Criteria: November 2, 2026
• First Posted (Actual): November 5, 2026

Study Record Updates

• Last Update Posted (Actual): November 5, 2026
• Last Update Submitted That Met QC Criteria: November 2, 2026
• Last Verified: October 1, 2026

More Information

Terms related to this study

• Keywords: cardiac surgery; Frailty; risk score; risk prediction; MACCE; Calibration; operative mortality; STS-PROM; Euro Score II
• Additional Relevant MeSH Terms: Vascular Diseases; Cardiovascular Diseases; Pathologic Processes; Heart Diseases; Arteriosclerosis; Arterial Occlusive Diseases; Coronary Disease; Myocardial Ischemia; Pathological Conditions, Signs and Symptoms; Frailty; Coronary Artery Disease; Heart Valve Diseases
• Other Study ID Numbers: UCSRS ATLAS; 20263741 (Other Identifier: WCG Clinical Services)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

IPD Plan Description

Individual participant data will not be shared. The coordinating center holds pooled data made up of de-identified patient-level data from sites that choose to share it and summary results from sites that analyze locally. These are held under site data use agreements and local ethics approvals that do not permit onward sharing. Aggregate results will be published

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No