Rules + Equations

Smith-Modified Sgarbossa Rule for Diagnosis of STEMI in the Presence of Left Bundle Branch Block

New 4-variable Formula to Differentiate Normal Variant ST Segment Elevation in V2-V4 (Early Repolarization) from Subtle Left Anterior Descending Coronary Occlusion

This is the original paper on the 3-variable formula: 

Smith SW et al. Electrocardiographic Differentiation of Early Repolarization From Subtle Anterior ST-Segment Elevation Myocardial Infarction. Annals of Emergency Medicine June 2012.

We subsequently published the 4-variable formula:

Driver and Smith. A new 4-variable formula to differentiate normal variant ST segment elevation in V2-V4 (early repolarization) from subtle left anterior descending coronary occlusion - Adding QRS amplitude of V2 improves the model.  Journal of Electrocardiology.

This formula is more sensitive and specific than the old 3-variable formula, which I have deleted.

Both were externally validated here:

I recommend this primarily as a means of recognizing otherwise unrecognized LAD occlusion.

Do not let a value below the cutoff dissuade you if you think the diagnosis is LAD occlusion.

In other words, sensitivity is much more important than specificity

It is critical to use it only when the differential is subtle LAD occlusion vs. early repol. Thus, there must be ST Elevation of at least 1 mm. If there is LVH, it may not apply. If there are features that make LAD occlusion obvious (inferior or anterior ST depression, convexity, terminal QRS distortion, Q-waves), then the equation MAY NOT apply. These kinds of cases were excluded from the study as obvious anterior STEMI.

--QTc is the computer measurement.
--RAV4 = R-wave amplitude, in mm, in lead V4.
--ST elevation (STE) is measured at 60 milliseconds after the J-point, relative to the PR segment, in millimeters.

--QRSV2 is the entire QRS amplitude in lead V2 (both R- and S-waves).

(1.062 x STE at 60 ms after the J-point in V3 in mm) + (0.052 x computerized QTc) - (0.151 x QRSV2) - (0.268 x R-wave Amplitude in V4 in mm).

A value greater than 18.2 is quite sensitive and specific for LAD occlusion.

There is a free iPhone app: "SubtleSTEMI"
There is a free Android app: "ECG SMITH"
Or go to

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