Subtle Anterior STEMI Calculator (4-Variable)

Subtle STEMI 4-Variable Calculator

QTc Interval

QRS Amplitude in V2

R-wave Amplitude in V4

ST Elevation 60ms After J-point in V3

4-Variable Score: –

–

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

Why Use

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.

When to Use

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

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)

Pearls / Pitfalls

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 ).

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.

More Information

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.