Monday, August 26, 2013

Instructions for using subtleSTEMI iPhone app



Some have asked for instructions in using the app:

1.      The warning states that it should only be used when the differential  diagnosis is normal variant anterior ST elevation (early repolarization) vs. subtle anterior STEMI

2.      Questions (these were exclusions from the study):
a.      Is there bundle branch block (if so, then the formula does not apply, answer must be “no”
b.      Is the T-wave inverted in any of V2-V6, but not due to “benign T-wave inversion”.  (If yes, then think STEMI and do not use formula)
                                                    i.     In general, if there is any T-wave inversion, the formula does not apply
                                                   ii.     If you are expert, then you can differentiate benign T-wave inversion from ischemic, and you shouldn’t need the formula anyway
c.      Is the ST segment elevated > 5 mm in any lead? 
                                                    i.     Then it should be considered to be STEMI  (If yes, then think STEMI and do not use formula)
d.      The question: "is terminal QRS distortion present (absence of both S-wave and J-wave in V2 or V3)" should read V2 and V3
                                                    i.     Early repol does not have such terminal QRS distortion.  Anterior STEMI commonly does.  (If yes, then think STEMI and do not use formula)
e.      Do any of leads V2-V6 have a convex ST segment ?  This means upward convexity. 
                                                    i.     Early repol should almost always have upward concavity in these 5 leads.  (If yes, then think STEMI and do not use formula)
f.       Significant ST depression in leads II, III, aVF?  Early repol never has reciprocal ST depression
                                                    i.     (If yes, then think STEMI and do not use formula)
g.      Is there ST depression in V2-V6?  Early repol never has precordial ST depression
                                                    i.     (If yes, then think STEMI and do not use formula)
h.      Is there Q-waves in V2-V4?  (this should say “significant, pathologic Q-waves”.  Early repol never has pathologic Q-waves
                                                    i.     (If yes, then think STEMI and do not use formula)

If the answer to all these is no, the app takes you to the formula, where you enter:

1) ST elevation in millimeters, measured at 60 milliseconds after the J-point in lead V3
2) the computerized QTc measurement
3) the R-wave amplitude as measured in lead V4.

If the internal (black box) formula returns a value > 23.4, the app will say that it is STEMI.  If it returns a value < 23.4, it will say "Early repolarization".

This is the formula:  ([1.196 x ST segment elevation 60 ms after the J point in lead V3 in mm] + 
[0.059 x QTc in ms] minus [0.326 x R-wave amplitude in lead V4 in mm])

This is the study from which it comes:

The accuracy, sensitivity for STEMI and specificity for STEMI are about 90%

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