What are the diagnostic and management approaches for patients with Right Bundle Branch Block (RBBB) and suspected acute coronary syndrome, including the use of Sgarbossa (ECG interpretation criteria)?

Sgarbossa Criteria for RBBB: A Critical Clarification

The Sgarbossa criteria were specifically developed and validated for diagnosing acute myocardial infarction in patients with LEFT bundle branch block (LBBB), NOT right bundle branch block (RBBB), and should not be applied to RBBB patients. 1, 2, 3

Why This Distinction Matters

RBBB Does Not Obscure ST-Segment Analysis

• RBBB does not significantly interfere with standard ST-segment interpretation for acute MI diagnosis, unlike LBBB which creates discordant ST-segment changes that obscure typical STEMI patterns 4
• In RBBB, the initial ventricular depolarization (QRS onset and mid-portion) remains relatively normal, allowing standard STEMI criteria to be applied directly 4
• The ST-segment changes in RBBB are minimal compared to LBBB, where profound secondary repolarization abnormalities make standard ST-elevation criteria unreliable 1, 2

The Sgarbossa Criteria: LBBB-Specific Tool

The three Sgarbossa criteria were designed specifically for LBBB 1, 3:

1. ST-elevation ≥1 mm concordant with QRS complex (sensitivity 73%, specificity 92%) 1
2. ST-depression ≥1 mm in leads V1-V3 (sensitivity 25%, specificity 96%) 1
3. ST-elevation ≥5 mm discordant with QRS complex (sensitivity 19%, specificity 82%) 1

• These criteria address the specific problem of discordant ST-segment changes that occur in LBBB, where ST-segments normally deviate opposite to the QRS direction 3
• The modified Sgarbossa criteria (Smith modification) further refined the third criterion using a proportional rule (ST-elevation/S-wave ratio ≤-0.25), improving sensitivity from 49% to 80% while maintaining 99% specificity—again, specifically for LBBB 5

Correct Approach for RBBB with Suspected ACS

Use Standard STEMI Criteria

• Apply conventional ST-segment elevation criteria directly to patients with RBBB: ≥1 mm ST-elevation in two contiguous leads (or ≥2 mm in precordial leads) 4
• Obtain a 12-lead ECG within 10 minutes of first medical contact 2
• RBBB itself is a marker of increased cardiovascular risk and higher short- and long-term mortality in ACS, but does not require special ECG interpretation criteria 4

Clinical Caveats for RBBB

• RBBB in the setting of acute MI indicates more extensive myocardial damage, often involving the septum, and is associated with significantly higher morbidity and mortality 4
• New RBBB with acute MI suggests proximal left anterior descending artery occlusion with septal involvement 4
• Serial ECGs should be performed when clinical suspicion remains high despite initial non-diagnostic findings 2

Reperfusion Strategy

• For RBBB patients meeting standard STEMI criteria, proceed with primary PCI (goal: first medical contact-to-device time ≤90 minutes) 2
• If PCI unavailable within 90 minutes and symptom onset <3 hours, administer fibrinolytic therapy 1, 2

Common Pitfall to Avoid

• Do not attempt to apply Sgarbossa criteria to RBBB patients—this represents a fundamental misunderstanding of both the criteria's purpose and the electrophysiologic differences between LBBB and RBBB 1, 2, 3