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    Subtle Anterior STEMI Calculator (4-Variable)

    Differentiates normal variant ST elevation (benign early repolarization) from anterior STEMI, more sensitive than 3-variable version.
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    INSTRUCTIONS

    Before using this calculator, make sure the EKG shows ≥1 mm ST elevation (STE) in ≥1 of the precordial leads V2-V4. If it shows any one of the following, then it is NOT normal variant, and is very likely to be LAD occlusion; such cases were excluded from the study as "obvious" MI:

    • >5 mm STE.
    • Non-concave STE.
    • Inferior reciprocal changes.
    • Anterior ST depression.
    • Terminal QRS distortion in V2 or V3:
    • Q waves in any of V2 to V4.
    • Any T wave inversion from V2 to V6.
    When to Use
    Pearls/Pitfalls
    Why Use

    Use in chest pain patients presenting with an EKG that is non-diagnostic but suspicious for anterior MI.

    • The authors specifically excluded patients with obvious MI. Using the calculator in cases that were excluded in the study may lead to a wrong result.

    Tips for EKG interpretation:

    • Measure STE at 60 ms in lead V3:

    • ST elevation at 60 ms after the J-point in lead V3, relative to the PR segment
      • Measure STE 60 ms (1½ small box after J point).
      • The baseline is the PR segment.
      • In this example, STE 60 = 4 mm.
    • Measure amplitude of R wave in V4:

    • In this example, RV4 = 9 mm.
    • Read the QTc: QTc is simply read from the computerized interpretation (uses Bazett's formula).
    • Both benign early repolarization and STEMI cause ST elevation. The challenge is to differentiate the two entities.
    • Some patients present with subtle EKG changes nondiagnostic for STEMI but still have 100% coronary artery occlusion and benefit from acute percutaneous transluminal coronary angioplasty (PTCA).
    • Using the equation in such cases can lead to timely cath lab activation, or more intensive evaluation.
    mm
    mm
    mm

    Result:

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    Next Steps
    Evidence
    Creator Insights

    Advice

    • Cath lab activation is appropriate in Smith-positive patients, in the proper clinical context. At the very least, it should prompt very frequent serial EKGs and echocardiography.
    • The formula is best used to identify patients with LAD occlusion initially thought to have normal variant early repolarization. 
    • If results indicate negative for STEMI, proceed with caution if STEMI was otherwise suspected.

    Formula

    Subtle Anterior STEMI 4-Variable Calculation = 0.052 x (Bazett-corrected QT interval, ms) - 0.151 x (QRS amplitude in lead V2, mm) - 0.268 x (R wave amplitude in lead V4, mm) + 1.062 x (ST segment elevation 60 ms after the J point in lead V3, mm)

    Facts & Figures

    Interpretation:

    Scores ≥18.2 are likely to be anterior STEMI (83.3% sensitivity, 87.7% specificity, and 85.9% diagnostic accuracy).

    Scores <18.2 are likely to be benign early repolarization.

    Dr. Stephen W. Smith

    About the Creator

    Stephen W. Smith, MD, is an emergency physician at Hennepin County Medical Center (HCMC) in Minneapolis. He is also a professor of emergency medicine at the University of Minnesota School of Medicine and runs Dr. Smith's ECG Blog. Dr. Smith's research focuses include ECG and troponin in acute myocardial infarction and health issues related to gamma hydroxybutyrate (GHB).

    To view Dr. Stephen W. Smith's publications, visit PubMed

    Content Contributors
    • Dominic Larose, MD
    About the Creator
    Dr. Stephen W. Smith
    Content Contributors
    • Dominic Larose, MD