What is the significance of the syntax score in determining the treatment approach for coronary artery disease, specifically between percutaneous coronary intervention (PCI) and coronary artery bypass grafting (CABG)?

SYNTAX Score in Coronary Artery Disease Revascularization

The SYNTAX score should be used as one component of decision-making between PCI and CABG, but its utility is limited by significant inter-observer variability and absence of clinical variables—it must be integrated with Heart Team evaluation, surgical risk scores, and patient-specific factors rather than used as a standalone decision tool. 1

Role and Limitations of the SYNTAX Score

Primary Function

• The SYNTAX score grades anatomical complexity of coronary artery disease and was validated in the SYNTAX trial to predict adverse events in PCI patients 1
• Critical limitation: The score predicts outcomes well for PCI patients but NOT for CABG patients 1
• Current guidelines give it only a Class IIb recommendation (may be useful) for guiding revascularization in multivessel CAD 1

Significant Reproducibility Problems

• Inter-observer variability shows only moderate agreement (kappa 0.45-0.58) for raw scores and score tertiles 1
• Intra-observer variability is similarly moderate (kappa 0.54-0.69) 1
• Training improves reproducibility substantially (kappa increases from 0.33 to 0.76 after training) 1
• Investigators consistently underscore compared to core lab by 3.4 points on average 2

Established Threshold Values

Score Interpretation for Treatment Selection

• Low complexity (SYNTAX ≤22): PCI is equivalent to CABG for left main disease with similar completeness of revascularization 1
• Intermediate complexity (SYNTAX 23-32): PCI should be considered as alternative to CABG for left main disease 1
• High complexity (SYNTAX ≥33): CABG generally preferred, though Heart Team may overrule 1

Prognostic Value

• In PCI patients with three-vessel disease, SYNTAX score ≥33 predicts significantly higher MACCE rates (17.9%) compared to scores ≤22 (1.4%) at one year 3
• A cutoff of 29.5 provides optimal sensitivity (82.4%) and specificity (65.6%) for predicting MACCE after PCI 3
• In STEMI patients undergoing primary PCI, high SYNTAX scores (≥23) predict 30-day mortality (18.5% vs 3.3%) and MACE (48.1% vs 9.1%) 4

Integration with Clinical Decision-Making

Mandatory Complementary Assessment

• Calculate STS risk score (Class I recommendation) to stratify surgical risk—this is more important than SYNTAX score for CABG candidates 1
• The SYNTAX score lacks clinical variables (age, diabetes, renal function, frailty) that significantly impact outcomes 1
• Heart Team evaluation should weight angiographic complexity alongside comorbidities, operator expertise, and patient preference 1

SYNTAX Score II Enhancement

• The SYNTAX II score combines anatomical SYNTAX score with clinical variables to improve decision-making 1
• Shows modest discrimination for 5-year MACE (c-index 0.62 for PCI, 0.67 for CABG) 1
• Requires further prospective validation before widespread adoption 1

Specific Clinical Scenarios

Left Main Disease

• Low SYNTAX (≤22): PCI recommended as equivalent alternative to CABG (Class I) 1
• Intermediate SYNTAX (23-32): PCI should be considered (Class IIa) 1
• High SYNTAX (≥33): CABG strongly preferred 1

Multivessel Disease with Diabetes

• CABG recommended over PCI regardless of SYNTAX score when LAD involvement present and patient is appropriate surgical candidate (Class I) 1
• This reflects superior long-term outcomes with CABG in diabetic patients that override anatomical complexity considerations 1

Three-Vessel Disease Without Diabetes

• Low-to-intermediate SYNTAX scores: PCI acceptable if similar completeness of revascularization achievable 1
• High SYNTAX scores: CABG preferred for improved survival and reduced repeat revascularization 1

Critical Pitfalls to Avoid

Common Errors

• Do not use SYNTAX score alone to make revascularization decisions—panel readings by Heart Team reduce inappropriate revascularization from 33% to 10% for CABG and improve PCI appropriateness 1
• Avoid calculating score without proper training—untrained operators show poor agreement (kappa 0.33) 1
• Do not apply SYNTAX score to predict CABG outcomes—it was not validated for this purpose 1

Addressing Variability

• Heart Team should interpret angiograms together to ensure accurate lesion representation 1
• Consider using mean of multiple physician assessments rather than single operator calculation 1
• Recognize that angiographic interpretation itself has high variability independent of SYNTAX scoring 1

Practical Algorithm

For patients with complex CAD requiring revascularization:

1. Calculate STS score for surgical risk stratification (mandatory) 1

2. Calculate SYNTAX score to assess anatomical complexity 1

3. Convene Heart Team to integrate:

   • Anatomical complexity (SYNTAX score)
   • Surgical risk (STS score)
   • Clinical comorbidities (diabetes, renal disease, frailty)
   • Completeness of revascularization achievable by each method
   • Local operator expertise and outcomes
   • Patient preference 1

4. Apply specific thresholds:

   • Diabetes + multivessel disease with LAD involvement → CABG 1
   • Left main with low SYNTAX (≤22) → PCI or CABG equivalent 1
   • Left main with intermediate SYNTAX (23-32) → Consider PCI 1
   • High SYNTAX (≥33) → Favor CABG unless prohibitive surgical risk 1