What are the Sgarbossa criteria for diagnosing acute myocardial infarction in patients with left bundle‑branch block or ventricular paced rhythm?

Sgarbossa Criteria for Diagnosing Acute Myocardial Infarction in LBBB and Ventricular Paced Rhythm

The Sgarbossa criteria consist of three specific ECG findings that identify acute myocardial infarction in patients with left bundle branch block or ventricular paced rhythm, with high specificity (>90%) but variable sensitivity, and any patient meeting these criteria requires immediate reperfusion therapy. 1, 2

The Three Sgarbossa Criteria

Criterion 1: Concordant ST-Elevation

• ST-segment elevation ≥1 mm in leads with a positive (upward) QRS complex 1, 2
• This is the most useful criterion with sensitivity 73% and specificity 92% in LBBB 1, 2
• In ventricular paced rhythm: sensitivity 18%, specificity 94% 1, 2
• Positive likelihood ratio of 16 makes this highly predictive of acute coronary occlusion 3

Criterion 2: Concordant ST-Depression in V1-V3

• ST-segment depression ≥1 mm in precordial leads V1, V2, or V3 (leads with dominant S waves) 1, 2
• Sensitivity 25%, specificity 96% in LBBB 1, 2
• In ventricular paced rhythm: sensitivity 29%, specificity 82% 1, 2

Criterion 3: Excessive Discordant ST-Elevation

• ST-segment elevation ≥5 mm in leads with a negative (downward) QRS complex 1, 2
• Sensitivity 19%, specificity 82% in LBBB 1, 2
• In ventricular paced rhythm: sensitivity 53%, specificity 88% 1, 2
• This criterion has the lowest specificity and has been refined in newer research (Smith-modified criteria use proportional ST/S ratio ≤-0.25 instead, improving sensitivity to 91%) 4

Physiologic Basis

Normal LBBB creates secondary ST-T wave changes that are discordant (opposite direction) to the QRS complex, making standard STEMI criteria unreliable 1:

• Leads with predominantly negative QRS complexes normally show ST elevation and positive T waves 1
• Leads with large monophasic R waves normally show ST depression and inverted T waves 1
• Loss of this normal discordance (becoming concordant) indicates myocardial injury 1, 2

Clinical Application Algorithm

Step 1: Identify the Population

Apply Sgarbossa criteria to patients with: 1

• Left bundle branch block (new or old) AND suspected acute coronary syndrome
• Ventricular paced rhythm AND ischemic symptoms
• Do NOT assume new LBBB alone equals STEMI - most patients with new LBBB do not have acute coronary occlusion 1, 5

Step 2: Measure ST Segments

• Measure ST deviation at the J-point relative to the PR segment 1
• Check for concordance: ST deviation in the same direction as the main QRS deflection 1, 2
• Measure absolute ST elevation in discordant leads 1

Step 3: Apply Criteria and Act

If ANY ONE criterion is present: 1, 2, 6

• Immediate reperfusion therapy is indicated 2, 6
• Primary PCI is preferred - door-to-balloon time ≤90 minutes 2, 6
• If PCI unavailable within 90 minutes AND symptom onset <3 hours: administer fibrinolytic therapy (Level B recommendation) 1, 6
• For high-risk patients with symptom onset 3-6 hours: consider fibrinolytic therapy if PCI delayed >90 minutes (Level C recommendation) 6

If NO criteria are met: 1, 6

• Obtain serial ECGs to detect evolving changes 1
• Measure troponin at 1-2 hours after symptom onset 1
• Consider emergency angiography if ongoing ischemic symptoms persist despite medical therapy 1

Critical Pitfalls and Caveats

Low Sensitivity Warning

The major limitation is low individual sensitivity (19-73%), meaning many patients with acute MI will NOT meet Sgarbossa criteria 1, 2, 7, 3:

• Cannot use these criteria to exclude MI 3
• A negative Sgarbossa score does not rule out acute coronary occlusion 5, 3
• Serial ECGs and troponins are essential when criteria are absent 1, 7

High Specificity Advantage

When present, Sgarbossa criteria have excellent specificity (>90%) and positive predictive value (>90%) 1, 2, 5:

• A Sgarbossa score ≥3 (weighted scoring system) has 98% specificity for acute coronary occlusion 5
• Patients meeting criteria should receive immediate reperfusion without delay 2, 6, 5

Common Errors to Avoid

• Do NOT treat all new LBBB as STEMI equivalent - this leads to excessive false catheterization lab activations 5
• Do NOT rely on LBBB being "new or presumably new" alone - use Sgarbossa criteria or angiography 1, 5
• Do NOT dismiss ongoing ischemic symptoms when Sgarbossa criteria are absent - proceed to emergency angiography 1
• Compare to prior ECG when available to determine if LBBB is truly new 1

Special Considerations for Ventricular Pacing

• Sgarbossa criteria apply to ventricular paced rhythm with similar diagnostic utility 1, 2, 8
• Consider reprogramming the pacemaker temporarily to assess intrinsic rhythm if patient is not pacemaker-dependent 1
• Do not delay invasive investigation while attempting pacemaker reprogramming 1

Enhanced Modified Criteria

Recent research suggests replacing the 5 mm discordant ST-elevation criterion with an ST/S ratio ≤-0.25 (Smith-modified Sgarbossa criteria) improves sensitivity from 52% to 91% while maintaining 90% specificity 4:

• Measure ST elevation and divide by depth of S wave in discordant leads 4
• If ratio ≤-0.25, consider this equivalent to meeting Sgarbossa criteria 4
• This modification has been validated for acute coronary occlusion 4