How is a high Society of Thoracic Surgeons (STS) risk score, indicating greater than 5% risk of mortality, interpreted and managed in a patient undergoing cardiac surgery with comorbid conditions?

STS Risk Score Interpretation and Management

The STS risk score is a validated tool that estimates operative mortality and morbidity for cardiac surgery, with scores >5% indicating high risk that should trigger Heart Team evaluation and consideration of alternative approaches, though the score must never be used in isolation as it fails to capture critical factors like frailty, cirrhosis, and malnutrition. 1

Risk Stratification Categories

The STS score stratifies patients into distinct risk categories that guide clinical decision-making:

• Low risk: <3% predicted mortality 2, 3
• Intermediate risk: 3-8% predicted mortality 3
• High risk: ≥8% predicted mortality, warranting consideration of transcatheter approaches 2, 3
• Extreme risk: ≥15% predicted mortality, suggesting potential futility 3

Clinical Application for High-Risk Patients (>5% Mortality)

When a patient has an STS score >5%, immediately convene a multidisciplinary Heart Team including the primary cardiologist, interventional cardiologist, cardiac surgeon, and the patient to determine the optimal revascularization or valve replacement strategy. 1

Decision Algorithm for High-Risk Patients:

For CABG candidates with STS >5%:

• Calculate the precise STS score using the online calculator before any treatment decision 1, 3
• Present the score to the patient as part of informed consent regarding risks, benefits, and alternatives 1
• Consider percutaneous coronary intervention (PCI) as an alternative if anatomy is suitable 3

For aortic valve replacement candidates with STS >8%:

• Strongly consider transcatheter aortic valve replacement (TAVR) over surgical AVR 1, 2
• The STS score performs particularly well at predicting outcomes when >5%, outperforming EuroSCORE II in this range 1, 4

Critical Limitations That Must Be Assessed Separately

The STS score has major blind spots that can lead to catastrophic outcomes if ignored. You must independently evaluate these factors that are NOT adequately captured by the score:

• Frailty (slow ambulation, inability to perform activities of daily living) 1, 3, 5
• Liver cirrhosis 1, 3
• Severe malnutrition or cachexia 1, 3, 5
• Advanced dementia 3
• Severe pulmonary hypertension 3
• End-stage renal, liver, or lung disease 3
• Expected survival <1 year from non-cardiac causes 1, 3

Never exclude a patient from surgery based solely on a high STS score from a single characteristic—this is explicitly inappropriate. 1, 3

Practical Management Based on Score

For STS 5-8% (intermediate-high risk):

• Proceed with detailed Heart Team discussion 1, 3
• Early surgery may provide marked survival benefit, particularly in asymptomatic severe aortic stenosis 6
• Surgical AVR remains reasonable if no contraindications to surgery exist 1

For STS 8-15% (high risk):

• TAVR should be strongly considered for aortic stenosis over surgical AVR 1, 2
• For CABG, carefully weigh against PCI with Heart Team input 3
• Expected in-hospital mortality approaches 16% with surgical AVR in this range 1

For STS >15% (extreme risk):

• This threshold suggests potential futility if life expectancy <1 year or severe functional limitations exist 1, 3
• TAVR may still be considered if quality of life improvement is realistic 3
• Surgical AVR carries prohibitive risk (>50% mortality or irreversible morbidity) 1

Predictive Performance

The STS score demonstrates excellent discrimination for adverse outcomes:

• Superior to EuroSCORE II for CABG patients, especially at mortality rates >5% 1, 4
• Strong long-term prognostic value: STS ≥8% independently predicts increased long-term mortality after TAVR 7
• High sensitivity (90.4%) for stroke prediction but moderate specificity (64.3%) 8
• Powerful tool for long-term outcome prediction in asymptomatic severe aortic stenosis 6

Common Pitfalls to Avoid

Do not use the STS score as the sole determinant of operability—it must be integrated with clinical judgment and assessment of factors the score doesn't capture. 1, 3

Do not assume the score predicts quality of life improvement or return to independent living—it only estimates short-term operative risks. 1

Do not apply the score without considering local surgical expertise and outcomes—institutional experience significantly impacts actual mortality. 1