Assessment of High Thromboembolic Risk
High thromboembolic risk assessment should follow the ACCP three-tiered risk stratification scheme, which defines high risk as >10% annual risk of arterial thromboembolism (ATE) or >10% monthly risk of venous thromboembolism (VTE), based on the patient's indication for anticoagulation. 1
Risk Stratification by Clinical Indication
Atrial Fibrillation
For atrial fibrillation patients, high thromboembolic risk is defined by:
- CHADS₂ score of 5 or 6 1
- Recent stroke or TIA within 3 months 1
- CHA₂DS₂-VASc score ≥7 (in more recent guidance, though this represents a shift from traditional CHADS₂-based definitions) 1
The CHADS₂ score remains the primary validated tool in the periprocedural setting, with data demonstrating that scores of 5-6 correlate with a 30-day postoperative stroke risk of 3.6%-7.3%, compared to 1.0%-2.0% for scores of 0-2 1. The 2024 ESC guidelines recommend using CHA₂DS₂-VA score (without sex category) for general stroke risk assessment, with scores ≥2 indicating need for anticoagulation 1.
Mechanical Heart Valves
High thromboembolic risk mechanical valve patients include: 1
- Any mechanical mitral valve (annualized thrombosis risk ~22% without anticoagulation) 1
- Caged-ball valves (Starr-Edwards) in any position 1
- Tilting disc valves (Bjork-Shiley) in any position 1
- Bileaflet aortic valves with major stroke risk factors (prior stroke/TIA, atrial fibrillation, hypertension, diabetes, heart failure, age >75 years) 1
Aortic position valves without additional risk factors carry approximately 10%-12% annualized thrombosis risk off anticoagulation, while mitral position valves carry 22% risk 1.
Venous Thromboembolism
High VTE risk is characterized by: 1
- VTE within the past 3 months (especially within 1 month) 1
- Severe thrombophilias: protein C deficiency, protein S deficiency, antithrombin deficiency 1
- Antiphospholipid antibodies 1
- Multiple thrombophilias 1
- Vena caval filter in place 1
- Active cancer (particularly pancreatic, myeloproliferative disorders, brain tumors, gastric cancer) 1
The first year after VTE carries approximately 15% recurrence risk, with risk substantially higher in the first 3 months 1.
Important Clinical Considerations
Validation and Limitations
There is no validated periprocedural thromboembolic risk scheme—the ACCP stratification is based primarily on indirect evidence from non-perioperative settings 1. The scheme uses objective criteria including projected annualized ATE risk or monthly VTE risk to distinguish patient groups who may warrant aggressive periprocedural antithrombotic approaches 1.
Context-Specific Applications
The CHA₂DS₂-VASc score demonstrates modest predictive accuracy (C-statistics 0.64-0.67) in heart failure populations regardless of AF presence 2, 3. In Asian populations, the score performs comparably to Western populations, though female sex may confer lower rather than higher risk 4. The score's role is acknowledged to be limited in periprocedural DOAC management 1.
Surgery-Related Risk Amplification
Major surgery theoretically increases postoperative VTE risk 100-fold and may increase ATE risk 10-fold compared to baseline mathematical modeling assumptions 1. This procedural risk must be factored into the overall thromboembolic risk assessment 1.
Special Populations
For cancer patients with AF, standard CHA₂DS₂-VASc and HAS-BLED scores have not been fully validated 1. The ESC proposes using the T-B-I-P algorithm (thromboembolic risk, bleeding risk, drug-drug interactions, patient preferences) for anticoagulation risk assessment in this population 1.