How is the Society of Thoracic Surgeons Predicted Risk of Mortality (STS-PROM) score assessed?

How the STS-PROM Score is Assessed

The STS-PROM (Society of Thoracic Surgeons Predicted Risk of Mortality) score is calculated using an online risk calculator that requires input of specific patient variables to generate a percentage estimate of 30-day operative mortality risk. 1

Accessing the Calculator

• The calculation is performed using the official Online STS Adult Cardiac Surgery Risk Calculator, which is publicly available on the STS website 2, 1
• A separate STS/ACC TAVR In-Hospital Mortality Risk App exists specifically for transcatheter procedures, though it uses different source data and should not be directly compared to the surgical calculator 2

Required Patient Data Input

The calculator requires comprehensive entry of patient-specific variables including: 1

• Demographic factors: Age, sex, body surface area
• Cardiac factors: Left ventricular ejection fraction, presence of heart failure, prior cardiac surgery, urgency of procedure
• Comorbidities: Chronic lung disease, diabetes, hypertension, peripheral vascular disease, cerebrovascular disease, renal function (creatinine levels)
• Functional status: New York Heart Association class, presence of cardiogenic shock
• Procedure-specific factors: Type of planned cardiac surgery (isolated AVR, combined procedures, etc.)

Interpreting the Results

The calculator generates a percentage that represents predicted 30-day mortality risk: 2, 1

• Low risk: STS-PROM <3% (some sources use <4%)
• Intermediate risk: STS-PROM 3-8% (or 4-8% in some classifications)
• High risk: STS-PROM 8-15% (or >8%)
• Extreme risk: STS-PROM >15%

Clinical Application in Decision-Making

The STS-PROM score serves as the primary surgical risk stratification tool for determining candidacy for TAVR versus SAVR in aortic stenosis patients. 2, 3

• For patients with STS-PROM >15%, the score indicates potential futility of intervention, as PARTNER 1B trial data showed no appreciable all-cause mortality benefit at 5 years with TAVR compared to medical therapy in this population 2
• The score guides Heart Team discussions about procedural approach, with higher scores favoring transcatheter over surgical approaches 3, 1
• Annual calibration ensures predicted rates equal observed rates, maintaining accuracy over time 1

Critical Limitations and Pitfalls

The STS-PROM score significantly underestimates risk in certain populations and should never be used as the sole decision-making tool. 2, 3

• The score does not account for frailty, cognitive impairment, disability status, or sarcopenia—all of which profoundly impact outcomes 2, 3
• Current calculators overpredict mortality 2-to-3-fold in patients undergoing minimally invasive AVR, as the models were derived primarily from sternotomy cases 4
• The score shows poor discrimination in contemporary TAVR populations across all risk categories (AUC 0.64-0.68 for 30-day mortality) 5
• Recent updates to the STS calculator produce significantly lower scores than the 2008 model, reclassifying 19% of patients into lower risk categories, particularly those with atrial fibrillation, chronic heart failure, or NYHA class IV symptoms 6

Additional Risk Factors Not Captured by STS-PROM

The following conditions markedly limit life expectancy and functional benefit but are inadequately reflected in the STS score: 2

• End-stage renal disease or dialysis dependency
• Advanced oxygen-dependent lung disease
• Slow ambulation (6-minute walk <150 meters)
• Poor LV systolic function (LVEF <30%, stroke volume index ≤35 mL/m²)
• Severe pulmonary hypertension
• Advanced dementia or severe cognitive impairment
• Active malignancy with limited life expectancy
• Severe cachexia, sarcopenia, or frailty (dependent in >3 activities of daily living)
• Porcelain aorta or hostile chest from prior surgery

Mandatory Multidisciplinary Integration

All STS-PROM assessments must be reviewed by a Heart Valve Team comprising cardiac surgeons, interventional cardiologists, imaging specialists, anesthesiologists, and geriatric specialists before final treatment decisions. 3, 1 The team integrates the numerical score with frailty assessment, anatomic suitability, patient preferences, and factors not captured by the calculator to determine optimal management 2, 3