Sgarbossa Criteria for Diagnosing AMI in LBBB and Paced Rhythms
The Sgarbossa criteria consist of three specific ECG findings that identify acute myocardial infarction in patients with left bundle branch block or ventricular paced rhythms, with high specificity (>90%) justifying immediate reperfusion therapy when any criterion is present. 1, 2
The Three Sgarbossa Criteria
The original criteria developed from the GUSTO-I trial include:
ST-segment elevation ≥1 mm concordant with the QRS complex (sensitivity 73%, specificity 92%) - this is the most sensitive criterion 1, 2
ST-segment depression ≥1 mm in leads V1-V3 (sensitivity 25%, specificity 96%) - this represents concordant changes in leads with dominant S waves 1, 2
ST-segment elevation ≥5 mm discordant with the QRS complex (sensitivity 19%, specificity 82%) - this represents excessive discordance beyond the normal secondary ST-T wave changes 1, 2
Scoring System and Clinical Application
A Sgarbossa score ≥3 points indicates AMI and mandates immediate reperfusion therapy. 1, 2, 3
The point system assigns:
- 5 points for concordant ST elevation ≥1 mm 1
- 3 points for concordant ST depression ≥1 mm in V1-V3 1
- 2 points for discordant ST elevation ≥5 mm 1
Patients with scores ≥3 have significantly higher 30-day mortality (23.5% vs 7.7%, P<0.001) and 1-year mortality (33.7% vs 20.2%, P<0.001) compared to those with scores <3, validating both diagnostic and prognostic utility. 3
Physiologic Rationale
The criteria exploit the normal discordance pattern in LBBB:
- Leads with predominantly negative QRS complexes normally show ST elevation and positive T waves 1, 2
- Leads with large monophasic R waves normally show ST depression and inverted T waves 1, 2
- Loss of this normal discordance (concordance) indicates myocardial injury requiring immediate intervention 1, 2
Application to Ventricular Paced Rhythms
The Sgarbossa criteria apply to right ventricular paced rhythms with similar diagnostic performance 1, 4, 5:
- ST elevation ≥5 mm discordant with QRS (sensitivity 53%, specificity 88%) 1, 2
- ST elevation ≥1 mm concordant with QRS (sensitivity 18%, specificity 94%) 1, 2
- ST depression ≥1 mm in V1-V3 (sensitivity 29%, specificity 82%) 1, 2
Treatment Algorithm
When any Sgarbossa criterion is present: 1, 2, 6
If symptom onset <3 hours AND PCI cannot be performed within 90 minutes of first medical contact: Administer fibrinolytic therapy immediately (Level B recommendation) 1, 6
If symptom onset 3-6 hours in high-risk patients AND PCI delay >90 minutes: Administer fibrinolytic therapy (Level C recommendation) 1, 6
Preferred strategy: Emergency cardiac catheterization with primary PCI regardless of time from symptom onset 2, 6
When Sgarbossa criteria are absent: Perform serial ECGs to detect evolving ischemic changes 1, 2
Critical Clinical Pitfalls
The major limitation is low sensitivity (individual criteria range 19-73%), meaning absence of Sgarbossa criteria does not exclude AMI. 1, 2 However, the high specificity (82-96%) and positive predictive value (>90%) mean that when present, these criteria reliably identify patients requiring urgent reperfusion. 1, 2, 3
Do not wait for biomarker confirmation when Sgarbossa criteria are present - the ECG findings alone justify immediate reperfusion therapy given the high specificity and mortality benefit. 1, 6, 3
The Smith-modified Sgarbossa criteria (using proportional ST/S ratio rather than absolute 5mm discordance) may improve sensitivity, though this modification has been validated primarily in LBBB rather than paced rhythms. 7, 8