STS Score in Thoracic Surgery
The Society of Thoracic Surgeons (STS) score is a validated risk prediction tool that calculates the predicted risk of mortality and major morbidities for patients undergoing cardiac surgical procedures, serving as the primary benchmark for preoperative risk assessment, patient selection, and shared decision-making in cardiac surgery. 1, 2
Primary Purpose and Validation
The STS Risk Calculator provides objective, validated estimates of operative risk for individual patients undergoing coronary artery bypass grafting (CABG) and valve procedures based on clinical factors, with annual calibration to ensure predicted rates equal observed rates. 1, 2
The American College of Cardiology and American Heart Association recommend calculating the STS score for all patients being considered for CABG to facilitate informed consent regarding risks, benefits, and alternatives. 1
The STS score demonstrates excellent predictive value for estimating risk of adverse events and performs better than EuroSCORE II for CABG patients, particularly at higher (>5%) predicted mortality rates. 1, 3
Risk Stratification Categories
Low risk is defined as STS-PROM <3%, intermediate risk as 3-8%, high risk as ≥8%, and extreme risk as ≥15%. 2
An STS-PROM score >15% may indicate futility of transcatheter aortic valve replacement (TAVR), as these patients showed no appreciable benefit in all-cause mortality compared to medical therapy in clinical trials. 2
For mitral valve repair in primary mitral regurgitation, an STS score <1% indicates low surgical risk. 4
Clinical Applications in Decision-Making
The STS score is essential for Heart Team discussions to determine optimal treatment strategy between surgical and transcatheter approaches for aortic valve replacement. 2, 4
The score guides selection between percutaneous coronary intervention (PCI) versus CABG, allowing clinicians, patients, and families to have reasonable estimates of operative risk. 1
Risk assessment using the STS score should be performed before all cardiac surgical procedures as part of the shared decision-making process. 4
Calculation and Data Requirements
Access the official STS calculator at the STS website and enter comprehensive patient-specific variables including demographic factors (age, gender), cardiac factors (left ventricular ejection fraction, presence of heart failure), comorbidities (renal function, pulmonary disease), and procedure-specific factors. 2, 4
The STS score for valve surgery incorporates 24 covariates, making it highly specific to valve heart disease. 5
Key variables include age, gender, functional status, previous cardiac surgery, left ventricular ejection fraction, pulmonary hypertension, renal function, emergency status, and type of valve procedure (repair versus replacement). 4
Important Limitations and Caveats
The STS score has significant limitations and does not adequately account for frailty, liver cirrhosis, malnutrition, end-stage renal disease, advanced oxygen-dependent lung disease, slow ambulation, severe pulmonary hypertension, advanced dementia, or severe cachexia. 1, 2, 4
Excluding patients from surgery based solely on higher risk derived from a single characteristic or the STS score alone is inappropriate. 1
The score should not be used in isolation but must be integrated with clinical judgment and reviewed by a multidisciplinary Heart Valve Team comprising cardiac surgeons, interventional cardiologists, imaging specialists, anesthesiologists, and geriatric specialists. 2, 4
No risk score can accurately predict events in an individual patient, and the STS score should be used as a guide while clinical judgment and multidisciplinary dialogue remain essential. 1
Performance Characteristics
The STS score shows poor discrimination for predicting 30-day and 1-year mortality in patients undergoing TAVR across all surgical risk categories, with area under the curve values of approximately 0.64-0.68. 6, 7
The STS score overestimates 30-day mortality in TAVR patients but has better calibration than EuroSCORE II in high-risk surgical patients. 3, 7
In asymptomatic severe aortic stenosis, the STS score is a powerful tool for predicting long-term outcome and selecting patients (particularly those at intermediate risk) who benefit markedly from early surgery. 8
The current online STS calculator produces significantly lower predicted risk of mortality than the 2008 model, resulting in reclassification of approximately 19% of patients into lower risk categories. 9