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 Management

Direct Answer

The SYNTAX score is a useful but limited anatomical tool that should guide—not dictate—the choice between PCI and CABG, with specific thresholds established for left main disease (≤22 favors equivalence, 23-32 suggests PCI as alternative, ≥33 favors CABG) but must be integrated with surgical risk assessment, Heart Team evaluation, and patient-specific clinical factors rather than used as a standalone decision tool. 1

Understanding the SYNTAX Score

The SYNTAX score quantifies the anatomical complexity of coronary artery disease based on lesion location, severity, and characteristics. 2 However, it carries significant limitations:

• Inter-observer variability is substantial, reducing its reliability as a precise measurement tool 1
• It predicts outcomes well for PCI patients but poorly for CABG patients, making it asymmetrically useful 1
• Clinical variables are completely absent from the calculation—age, diabetes, renal function, and frailty are not incorporated despite their major impact on outcomes 1
• Current guidelines assign only Class IIb recommendation for using SYNTAX score in multivessel CAD decision-making, indicating weak evidence support 1

Established Decision Thresholds

For Left Main Disease

• SYNTAX score ≤22 (Low): PCI is equivalent to CABG and recommended as an alternative 1
• SYNTAX score 23-32 (Intermediate): PCI should be considered as an alternative to CABG 1
• SYNTAX score ≥33 (High): CABG is strongly preferred over PCI 1

Prognostic Value

Higher SYNTAX scores consistently predict worse outcomes after PCI across multiple studies:

• Mortality increases significantly with higher scores (RR 2.09,95% CI 1.78-2.46) 3
• Major adverse cardiac events double in high versus low SYNTAX score groups (RR 2.03,95% CI 1.81-2.26) 3
• Repeat revascularization nearly doubles (RR 1.96,95% CI 1.69-2.28) 3
• Stent thrombosis triples in high SYNTAX score patients (RR 3.16,95% CI 2.17-4.59) 3

In three-vessel disease specifically, a SYNTAX score ≥29.5 predicts major adverse events with 82.4% sensitivity and 65.6% specificity at one year. 4

Algorithmic Approach to Decision-Making

Step 1: Calculate Surgical Risk First

The STS risk score takes priority over SYNTAX score because surgical risk stratification is more critical for CABG candidates than anatomical complexity scoring. 1 The STS score incorporates clinical variables that SYNTAX omits entirely. 1

Step 2: Calculate SYNTAX Score

Determine anatomical complexity using the online calculator (syntaxscore.com) to objectively grade disease burden. 2 This provides the anatomical framework but not the final answer. 1

Step 3: Apply Disease-Specific Overrides

For diabetic patients with multivessel disease and LAD involvement: CABG is recommended over PCI regardless of SYNTAX score when the patient is an appropriate surgical candidate, reflecting superior long-term outcomes in this population. 1 This represents a critical override where clinical factors trump anatomical scoring.

Step 4: Convene Heart Team

The Heart Team must integrate:

• Anatomical complexity (SYNTAX score) 1
• Surgical risk (STS score) 1
• Clinical comorbidities not captured by either score 1
• Completeness of revascularization achievable by each method 1
• Local operator expertise and outcomes at your specific institution 1
• Patient preference after informed discussion 1

Common Pitfalls to Avoid

Never use SYNTAX score as a standalone decision tool. The Class IIb recommendation reflects its limited utility when isolated from clinical context. 1

Do not assume SYNTAX score predicts CABG outcomes. The score was validated to predict PCI complications, not surgical results, creating an asymmetric predictive tool. 1

Do not ignore diabetes status. Diabetic patients with LAD disease benefit from CABG regardless of anatomical complexity scores. 1

Do not skip Heart Team evaluation. The multidisciplinary approach pioneered by the SYNTAX trial is now standard of care in both European and US guidelines. 2

Emerging Applications

The SYNTAX score has evolved beyond simple PCI versus CABG decisions:

• Residual SYNTAX score assesses completeness of revascularization after PCI 2
• Post-CABG SYNTAX score evaluates disease burden in patients with prior bypass surgery 5
• SYNTAX Score II incorporates clinical variables to enhance individualized decision-making 2
• Functional SYNTAX score combining anatomical scoring with physiologic assessment is under development 2

Short-Term Risk Prediction

In acute STEMI patients undergoing primary PCI, SYNTAX score predicts 30-day outcomes:

• High SYNTAX score (≥23) associates with 18.5% mortality versus 3.3% in lower scores 6
• MACE at 30 days occurs in 48.1% of high SYNTAX score patients versus 9.1% in low score patients 6

This demonstrates utility beyond elective revascularization decisions, extending to acute coronary syndrome risk stratification. 6