The SYNTAX Score: A Tool for Assessing Coronary Artery Disease Complexity
The SYNTAX (Synergy between Percutaneous Coronary Intervention with Taxus and Cardiac Surgery) score is an anatomical-based tool that objectively determines the complexity of coronary artery disease to guide decision-making between coronary artery bypass graft (CABG) surgery and percutaneous coronary intervention (PCI). 1
Definition and Purpose
The SYNTAX score was developed during the SYNTAX trial, which compared CABG with PCI in patients with complex coronary artery disease. It serves as:
- An objective measure to grade anatomic complexity of coronary artery disease
- A tool to predict clinical outcomes after revascularization
- A guide for selecting the optimal revascularization strategy (CABG vs. PCI)
Calculation Method
The SYNTAX score is calculated based on:
- Location of coronary lesions
- Severity of stenoses (with significant stenosis defined as ≥70% diameter narrowing for non-left main disease and ≥50% for left main disease) 2
- Extent of coronary disease
The score incorporates multiple anatomical factors that contribute to increasing complexity:
- Multivessel disease
- Left main or proximal LAD artery lesion
- Chronic total occlusion
- Trifurcation lesion
- Complex bifurcation lesion
- Heavy calcification
- Severe tortuosity
- Aorto-ostial stenosis
- Diffusely diseased and narrowed segments distal to the lesion
- Thrombotic lesion
- Lesion length >20 mm 2
Each lesion is scored individually, and the total SYNTAX score is the sum of all lesion scores.
Score Interpretation
The SYNTAX score is typically divided into three categories:
- Low: ≤22
- Intermediate: 23-32
- High: ≥33 2
Higher scores indicate more complex coronary anatomy and generally favor CABG over PCI.
Clinical Significance and Impact on Decision-Making
The SYNTAX score has significant prognostic value:
- In the SYNTAX trial, the occurrence of Major Adverse Cardiac Events (MACE) correlated with the SYNTAX score for PCI patients but not for CABG patients 2
- At 12-month follow-up, outcomes were similar for CABG and PCI in patients with low SYNTAX scores
- For intermediate or high SYNTAX scores, MACE occurred more frequently after PCI than after CABG 2
- At 3 years, mortality was higher in patients with 3-vessel disease treated with PCI compared to CABG (6.2% vs. 2.9%) 2
Limitations and Advancements
The original SYNTAX score has several limitations:
- Cumbersome scoring system requiring assessment of each lesion
- Inter-observer variability in calculation (weighted kappa value of 0.45 for inter-observer reproducibility) 3
- Absence of clinical variables limits its use in estimating risk after CABG 2
To address these limitations, newer versions have been developed:
- SYNTAX Score II: Incorporates clinical variables (age, creatinine clearance, LVEF, presence of left main disease, peripheral vascular disease, female sex, and COPD) to enhance decision-making 4
- CABG SYNTAX Score: Designed for patients who have undergone prior CABG surgery 5
Role in Guidelines
The SYNTAX score is advocated in both European and US revascularization guidelines for decision-making between CABG and PCI as part of a heart team approach 1. The 2021 ACC/AHA/SCAI guideline gives a Class 2b recommendation (Level of Evidence: B-NR) for using the SYNTAX score to guide revascularization in patients with multivessel CAD 2.
Clinical Application
When applying the SYNTAX score in practice:
- For patients with low SYNTAX scores (≤22), outcomes are generally comparable between PCI and CABG
- For patients with intermediate or high SYNTAX scores (>22), CABG typically offers better outcomes, particularly for those with 3-vessel disease 2
- The score should be calculated by experienced operators to minimize variability
- Integration with clinical factors (as in SYNTAX Score II) provides more personalized risk assessment
The SYNTAX score has become an essential tool in the management of complex coronary artery disease, helping clinicians make evidence-based decisions regarding the optimal revascularization strategy.