What are the ST elevation criteria for diagnosing ST elevation myocardial infarction (STEMI)?

ST Elevation Criteria for Diagnosing STEMI

ST-segment elevation in acute myocardial infarction, measured at the J point, should be found in two contiguous leads and be ≥0.25 mV in men below the age of 40 years, ≥0.2 mV in men over the age of 40 years, or ≥0.15 mV in women in leads V2–V3 and/or ≥0.1 mV in other leads (in the absence of left ventricular hypertrophy or left bundle branch block). 1

Standard ST Elevation Criteria

• ST elevation must be present in at least two contiguous leads to meet diagnostic criteria for STEMI 1
• Gender and age-specific criteria apply to precordial leads V2-V3 1:
  • Men < 40 years: ≥0.25 mV (2.5 mm)
  • Men ≥ 40 years: ≥0.2 mV (2 mm)
  • Women (all ages): ≥0.15 mV (1.5 mm)
• For all other leads (I, aVL, V4-V6, II, III, aVF): ≥0.1 mV (1 mm) elevation is required regardless of gender or age 1
• Measurements should be taken at the J point (the junction between the end of the QRS complex and beginning of the ST segment) 1

Special Considerations and Atypical Presentations

Inferior MI with Right Ventricular Involvement

• In patients with inferior MI, right precordial leads (V3R and V4R) should be recorded to identify concomitant right ventricular infarction 1
• ST elevation in these leads indicates right ventricular involvement and may affect management decisions 1

Posterior MI

• Isolated ST depression ≥0.05 mV in leads V1-V3 with positive terminal T waves may represent posterior MI (ST elevation equivalent) 1
• Should be confirmed by recording additional posterior leads (V7-V9) where ST elevation ≥0.05 mV (≥0.1 mV in men >40 years) confirms posterior MI 1
• Patients with these findings should be treated as STEMI 1

Left Bundle Branch Block (LBBB)

• LBBB makes ECG diagnosis of MI challenging but still possible 1
• Concordant ST elevation (ST elevation in leads with positive QRS deflections) is one of the best indicators of ongoing MI with occluded artery 1
• Previous ECG is valuable to determine if LBBB is new (higher suspicion of MI) 1
• In patients with clinical suspicion of ongoing ischemia with new or presumed new LBBB, reperfusion therapy should be considered promptly 1

Right Bundle Branch Block (RBBB)

• RBBB usually does not hamper interpretation of ST-segment elevation 1
• Prompt management should be considered with persistent ischemic symptoms and RBBB 1

Ventricular Paced Rhythm

• Ventricular pacing may prevent interpretation of ST-segment changes 1
• May require urgent angiography to confirm diagnosis 1
• Consider reprogramming pacemaker temporarily in non-dependent patients to evaluate intrinsic rhythm 1

Left Main Coronary Obstruction

• ST depression >0.1 mV in eight or more surface leads, coupled with ST elevation in aVR and/or V1 suggests ischemia due to multivessel or left main coronary obstruction 1
• Particularly significant if patient presents with hemodynamic compromise 1

Clinical Implications

• Timely diagnosis of STEMI is critical for successful management and improved outcomes 1
• ECG monitoring should be initiated as soon as possible in all suspected STEMI patients to detect life-threatening arrhythmias 1
• A 12-lead ECG should be obtained and interpreted as soon as possible at the point of first medical contact, with a maximum target delay of 10 minutes 1
• In patients without diagnostic ST elevation but with persistent ischemic symptoms, emergency coronary angiography should still be considered 1
• Recognition of atypical ECG presentations is essential as up to 30% of STEMI patients may present with atypical symptoms 1

Pitfalls and Caveats

• Early presentation may show hyperacute T waves before ST elevation develops 1
• ST elevation can be present in conditions other than STEMI (e.g., pericarditis, early repolarization, left ventricular aneurysm) 2
• Consideration of both ST elevation and ST depression criteria can increase sensitivity for AMI detection from 50% to 84% with only a slight decrease in specificity (97% to 93%) 3
• Some patients with genuine acute coronary occlusion may present without classic ST elevation, particularly with circumflex artery occlusion, vein graft occlusion, or left main disease 1
• Extending the standard 12-lead ECG with additional leads (V7-V9) may help identify posterior MI that would otherwise be missed 1