OMI

Analysis of the ST segment for elevation should be done at the J-point, which is the point at the junction of the QRS complex and the ST segment. This is then compared to the PQ segment for elevation or depression. ST elevation with a morphology of convex or straight natures are almost always considered to be from OMI. Concave ST elevation may be from a benign etiology, but almost 1/2 of LAD occlusions have concave ST elevations.

Demonstration of J point

A. Normal J point

B and C. J point elevation (ST elevation)

D. J point depression (ST depression)

E. J/Osborn wave (occurs before J point)

There are other pathologies that can produce ST segment elevation. The details of all of these will not be mentioned here (please see other pages).

STEMI Criteria:

new ST elevation >1mm at the J-point in 2 contiguous leads except V2-V3
In V2-V3, the following cutoffs are used for ST elevation: at least 2mm in men at least 40 years old, at least 2.5mm in men less than 40, and at least 1.5mm in women
posterior and right-sided leads: >0.5mm except men<40 years old require >1mm

STEMI criteria tend to vary in V2-V3 as patients are more likely to have 'benign' ST elevation in these leads and they are the most well-represented on the EKG. This is because they cover the surface of the heart that is closest to the leads and, therefore, have the greatest amplitude. Men tend to have more 'benign' ST elevation than women in these leads and those that are younger tend to have more. This is especially seen in young, healthy athletes.

However, STEMI criteria are known to miss a number of coronary occlusions, hence the newer terminology occlusion myocardial infarction (OMI) and non-occlusion myocardial infarction (NOMI) to replace STEMI and NSTEMI. In fact, at least 25% of NSTEMIs have been found to have coronary occlusion on angiography. A number of 'STEMI equivalents' are OMIs that do not meet STEMI criteria.

Sometimes there is terminal QRS distortion, which is defined by lack of a J wave and S wave in either V2 or V3; this has been used to help differentiate OMI from early repolarization as terminal QRS distortion is associated with OMIs.

No J or S wave (terminal QRS distortion)

There is commonly reciprocal ST depression in the opposite leads. The depression is very specific for reciprocal changes when it has a 'down-up' appearance as the depressed ST segment leads to a T wave that is upright in its terminal portion. The inferior leads are opposite the lateral and anterior leads. Not all STEMIs have reciprocal ST depression, especially those that cover multiple segments on the EKG.

OMI Progression and Reperfusion

The normal progression of EKG changes in a STEMI is as follows:

hyperacute T waves
ST elevation
Q wave formation
T wave inversion
resolution of ST elevation

It is important to distinguish this from reperfusion as it is both important to understand why a cardiologist may not take a patient to the cath lab emergently with a subacute OMI and to understand reperfusion patterns so as to not actually miss recent OMIs. The reperfusion progression on an EKG is as follows:

hyperacute T waves
ST elevation
terminal T wave inversion
symmetric T wave inversion

Note that reperfusion does not develop Q waves when the T wave becomes inverted. Also note that the T wave inversion patterns are seen in a specific syndrome of reperfusion (Wellen's syndrome...).