Residency · Residency · Cardiothoracic Surgery
Preoperative Risk Assessment in Cardiac Surgery
Introduction
Preoperative risk assessment is a cornerstone of cardiac surgical practice, informing patient counseling, operative planning, and resource allocation. Accurate risk stratification enables the Heart Team to determine whether a patient is best served by surgical intervention, percutaneous therapy, or medical management. This lecture reviews validated risk models, essential preoperative evaluations, and strategies for optimizing patients before cardiac surgery.
Risk Scoring Systems
STS Risk Score
The Society of Thoracic Surgeons (STS) Predicted Risk of Mortality (PROM) is the most widely used model in North America. It is derived from the STS National Database with over 7 million records and provides procedure-specific risk estimates for isolated CABG, isolated valve, and combined procedures. Outputs include predicted mortality, morbidity, stroke, renal failure, prolonged ventilation, deep sternal wound infection, and reoperation. The model is updated periodically to reflect contemporary outcomes and patient demographics.
EuroSCORE II
The European System for Cardiac Operative Risk Evaluation is the predominant model in Europe. It is a logistic model that replaced the additive EuroSCORE I and includes 18 variables covering patient, cardiac, and operative factors. EuroSCORE II tends to overestimate risk in low-risk cohorts and underestimate in very high-risk populations. It is useful for benchmarking across institutions and national registries.
| Feature | STS PROM | EuroSCORE II |
|---|---|---|
| Origin | North America (STS National Database) | Europe (multinational) |
| Database size | >7 million records | ~22,000 patients (development cohort) |
| Model type | Procedure-specific (CABG, valve, combined) | Single model for all procedures |
| Outputs | Mortality, morbidity, stroke, renal failure, prolonged ventilation, DSWI, reoperation | Mortality only |
| Calibration | Well-calibrated across risk spectrum | Overestimates low risk; underestimates very high risk |
| Updates | Periodic (reflects current practice) | Single version (2012) |
| Primary use | Risk-adjusted outcomes; patient counseling; TAVR candidacy | International benchmarking; institutional comparison |
Limitations of Risk Models
Risk models predict population-level outcomes, not individual patient destiny. Frailty, disability, and futility are inadequately captured by current models. They do not account for institutional volume, surgeon experience, or intraoperative variables. Risk scores should supplement, not replace, clinical judgment.
Comprehensive Preoperative Evaluation
Cardiac Assessment
Coronary angiography remains the gold standard for defining coronary anatomy before valve or combined surgery. Echocardiography (TTE and TEE) assesses valvular disease, ventricular function, and wall motion abnormalities. Right heart catheterization is performed when pulmonary hypertension is suspected or for transplant/LVAD candidacy. Assessment of aortic atherosclerosis using epiaortic ultrasound or CT guides cannulation and clamping strategy.
Pulmonary Evaluation
Pulmonary function tests (PFTs) are obtained, with an FEV1 below 60% predicted increasing the risk of prolonged ventilation. Room air arterial blood gas establishes baseline PaO2 and PaCO2. Smoking cessation for at least 4-8 weeks preoperatively reduces pulmonary complications by 25-50%. Preoperative inspiratory muscle training may reduce atelectasis and pneumonia.
Renal Assessment
Baseline creatinine and estimated GFR (eGFR) are powerful predictors of postoperative outcomes. An eGFR below 30 mL/min/1.73m2 significantly increases mortality and need for renal replacement therapy. Optimization of volume status and avoidance of nephrotoxic agents preoperatively are essential, and nephrology consultation is considered for patients on dialysis or with acute kidney injury.
Neurological Evaluation
History of prior stroke or transient ischemic attack increases perioperative stroke risk. Carotid duplex ultrasound is indicated in patients with carotid bruits, prior cerebrovascular events, or significant peripheral vascular disease. Management of significant carotid stenosis (staged vs. combined approach) requires multidisciplinary discussion.
Frailty and Functional Assessment
Defining Frailty
Frailty is a syndrome of decreased physiologic reserve that increases vulnerability to adverse outcomes. Its prevalence in cardiac surgery patients ranges from 20-50% depending on the definition used. The Fried frailty phenotype includes unintentional weight loss, exhaustion, low physical activity, slow gait speed, and weak grip strength. The presence of 3 or more criteria defines frailty, while 1-2 defines pre-frailty.
Functional Assessment Tools
| Assessment Tool | What It Measures | Abnormal Threshold | Clinical Significance |
|---|---|---|---|
| 6-minute walk test | Functional capacity | <300 meters | Increased perioperative risk |
| 5-meter gait speed | Walking speed / frailty | <0.83 m/s | Independent predictor of mortality |
| Katz ADL | Basic self-care independence | Any dependency | Increased morbidity and mortality |
| Lawton IADL | Complex functional tasks | Any dependency | Predicts postoperative disability |
| Albumin | Nutritional status | <3.5 g/dL | Malnutrition; increased wound complications |
| Grip strength | Muscle mass / sarcopenia | <26 kg (male); <18 kg (female) | Correlates with frailty |
The 6-minute walk test identifies patients at risk when the distance falls below 300 meters. The 5-meter gait speed test independently predicts mortality after cardiac surgery when speed falls below 0.83 m/s. Katz Activities of Daily Living (ADL) and Lawton Instrumental ADL scales assess functional independence. Nutritional status is evaluated through albumin (below 3.5 g/dL) and BMI (below 20 kg/m2), which indicate malnutrition and increased risk.
Prehabilitation
Structured exercise programs for 2-4 weeks before elective surgery improve functional capacity. Nutritional optimization with protein supplementation and micronutrient correction complements physical preparation. Psychological preparation and anxiety management improve postoperative recovery. Emerging evidence supports multimodal prehabilitation in reducing length of stay and complications.
Medication Management
Aspirin is continued, while P2Y12 inhibitors are held 5-7 days (clopidogrel, ticagrelor) or 7-10 days (prasugrel) before surgery. Warfarin is held 5 days with a target INR below 1.5, and DOACs are held 48-72 hours based on renal function. Beta-blockers are continued perioperatively, as abrupt withdrawal increases atrial fibrillation and ischemia risk. Statins are continued through the perioperative period for their anti-inflammatory and AF-reducing properties. ACE inhibitors and ARBs are held on the morning of surgery to reduce vasoplegia risk on cardiopulmonary bypass. Metformin is held 24-48 hours before surgery due to lactic acidosis risk with contrast and hypoperfusion.
Key Clinical Pearls
Risk scores are decision-support tools, not decision-making tools; clinical judgment and patient preferences must always be integrated. Frailty assessment should be routine in all patients over 65 undergoing cardiac surgery, with gait speed being the simplest validated measure. Preoperative optimization including smoking cessation, prehabilitation, and nutritional support meaningfully reduces complications even when initiated 2-4 weeks before surgery. Carotid screening is not universally indicated but should target patients with clinical risk factors for cerebrovascular disease. Multidisciplinary Heart Team discussion is mandatory for high-risk patients, including consideration of less invasive alternatives.
References
- Shahian DM, Jacobs JP, Badhwar V, et al. The Society of Thoracic Surgeons 2018 Adult Cardiac Surgery Risk Models. Ann Thorac Surg. 2018;105(5):1411-1418.
- Nashef SA, Roques F, Sharples LD, et al. EuroSCORE II. Eur J Cardiothorac Surg. 2012;41(4):734-745.
- Afilalo J, Mottillo S, Eisenberg MJ, et al. Addition of Frailty and Disability to Cardiac Surgery Risk Scores. Circ Cardiovasc Qual Outcomes. 2012;5(2):222-228.
- Engelman DT, Ben Ali W, Williams JB, et al. Guidelines for Perioperative Care in Cardiac Surgery: ERAS Society Recommendations. JAMA Surg. 2019;154(8):755-766.