STEMI Criteria
Clinical symptoms consistent with ACS (generally of ≥ 20 minutes duration) with persistent (> 20 minutes) ECG features in ≥ 2 contiguous leads of:
- 2.5 mm (i.e ≥ 2.5 small squares) ST elevation in leads V2-3 in men under 40 years, or ≥ 2.0 mm (i.e ≥ 2 small squares) ST elevation in leads V2-3 in men over 40 years
- 1.5 mm ST elevation in V2-3 in women
- 1 mm ST elevation in other leads
- new LBBB (LBBB should be considered new unless there is evidence otherwise)
It is also important to note that the STEMI criteria above cannot be used with a Left Bundle Branch Block or a ventricular paced rhythm, where the Sgarbossa criteria can be applied instead
How fast should an ECG be done if a patient is presenting with chest pain to ED?
Should have an electrocardiogram done within 10 minutes of presentation to the Emergency Department
Draw and ECG line and label it
What is the isolectric line in ECG?
- TP interval/TP segment
- The line where there is no underlying cardiac electrical activity, and this is the baseline from which you measure all ST segment elevations or depressions in relation to the J point.
- The TP segment is defined as the segment that starts at the end of the T wave and ends at the beginning of the P wave.
What is the ST segment and what does it represent?
- The portion of the ECG that starts at the end of the S wave and ends at the beginning of the T wave.
- represents the interval between ventricular depolarization and repolarization
How is the ST segment normally seen compared to TP segment?
Normally, it is isoelectric with the TP segment
What is the J point?
The J point marks the change of inflection from the end of the S wave to the being of the ST segment
How is ST elevation measured?
the the degree of ST segment elevation is measured from the isoelectric line (the TP segment) to the J point, and is commonly measured in millimeters
ST segment morphology
- The shape of the ST segment can be helpful in assessing whether an ECG demonstrates a STEMI.
- Classically the ST elevations are described as “tombstone” and convex in appearance.
- However, other morphologies such as concave or straight elevations might be seen in STEMI as well.
- Concave ST segment was historically thought to be benign, but STEMIs can present with this morphology. Please review the whole ECG for signs of a STEMI, and do not only look at the morphology
What are contiguous leads>
Contiguous leads are leads that represent arterial territories that are next to each other. In general, contiguous leads are:
- For the precordial leads, they are the neighboring leads (V3 and V4, for example)
- II, III and AVF are contiguous leads for the inferior portion of the myocardium
- I and AVL are contiguous leads for the high lateral portion of the heart (this one is often forgotten)
- For the posterior leads, V7, V8 and V9 are contiguous leads
Evolution of ECG changes in STEMI
The general progression of the ECG changes in a STEMI follows:
Acute, hyperacute T waves form. These form in the first minutes to hours of a STEMI. A hyperacute T wave is characterized by an increase in the amplitude and the width of the T wave.
Next, ST elevations will develop.
Followed by the development of Q waves.
Later, the T wave will invert.
Reciprocal ECG changes in STEMI
Reciprocal changes in STEMIs are the ST depressions found on the ECG that are on the opposite side of the heart of the myocardial infarction. It is important to note that the absence of reciprocal changes does not preclude the presence of a STEMI, but the presence of reciprocal changes makes it more likely.
STEMI territories, draw them
- STEMIs are classically categorized by the portion of the heart that is affected by the myocardial infarction: anterior, posterior, lateral and inferior.
- By understanding which portion of the heart is affected, you also begin to determine which coronary artery is occluded.
STEMI territory and corresponding coronary artery
Which coronary artery occlusion carries the worst prognosis?
Anterior STEMIs generally result from the occlusion of the left anterior descending coronary artery, and carries the worst prognosis of all STEMIs given the larger infarct size
ECG changes in posterior STEMI
When thinking of posterior STEMIs, it is important to remember the quote above, as these acute coronary artery occlusions can present without ST elevations on the 12 lead ECG. This occurs because the normal 12 lead ECG looks at the anterior part of the heart, and only the reciprocal changes of a posterior can be seen on the 12 lead ECG.
Posterior STEMIs are caused by an occlusion of posterior descending coronary artery. On a normal 12 lead ECG, it can be recognized by:
ST depression in the anterior leads
Prominent R waves in leads V2-3
Upright anterior T waves
To help confirm your diagnosis, you can also perform a posterior ECG. This can be performed by placing the leads on the patient’s back. The leads should be placed:
V7- At the level of V6, place at the posterior axillary line
V8- At the tip of the scapula at the level of V6
V9- Left paraspinous region at the level of V6
To call a posterior STEMI, it is important to note that you only need 0.5mm of ST elevation in the posterior leads. An important thing to note is that the posterior ECG is not sensitive enough to rule out a posterior STEMI, so providers should act on the initial 12-lead ECG.
STEMI equivalents on ECG
De Winter’s Sign
What is De winter’s sign?
The De Winter’s sign is a sign of an occlusion of the left anterior descending artery, and should be viewed as an equivalent to an anterior STEMI. The ECG findings of De Winter’s sign are:
Upsloping ST depression greater than 1mm in the precordial leads
Prominent, tall, and symmetrical T waves in the precoridal leads
Absence of ST elevation in the precordial leads
Reciprocal ST elevation of 0.5mm-1mm in AVR
Left bundle branch block in ECG significance
- Historically, a new left bundle branch block (LBBB) was considered a STEMI equivalent.
- However, studies suggested that the true incidence of an acute coronary occlusion in a presumed new LBBB was low, and the American Heart Association dropped a new LBBB as a STEMI equivalent.
- It is important to note that some of these patients with a new LBBB will have an acute coronary occlusion.
-To make the patient with chest pain who has a LBBB even more challenging, the traditional STEMI criteria cannot be applied to an ECG with LBBB. - To overcome these hurdles, some providers will use a bedside echocardiogram to check for wall-motion abnormalities to try to identify patients with LBBB on ECG who have acute coronary artery occlusion.
- The Sgarbossa criteria was developed to identify patients with LBBB or have a ventricular-paced rhythm who have a STEMI based on ECG findings
What is concordant ECG changes
concordant ST segment changes mean that the QRS segment amplitude and the ST segment deviation both point in the same direction. For example, concordant ST segment changes include:
ST segment elevation with a positive QRS amplitude
ST segment depression with a negative QRS amplitude
What is discordant ECG changes
discordant ST changes are changes when the amplitude of the QRS segment is opposite to the deviation of the ST segment. For example, discordant ST segment changes include:
ST segment elevation with a negative QRS amplitude
ST segment depression with a positive QRS amplitude.
Sgarbossa Criteria for STEMI
Concordant ST elevation > 1mm in leads with a positive QRS (score 5)
Discordant ST elevation > 1mm in leads V1-V3 (score 3)
Excessively discordant ST elevations > 5mm (score 2)
An ECG with a score greater than or equal to 3 is suggestive of a STEMI.
What does left bundle branch block and happens in the heart to cause it?
= LBBB does signify underlying heart disease but may be new or a chronic change.
- LBBB is caused by blockage of the left segment of the Bundle of His and causes ventricular depolarization to occur in a right to left direction (as opposed to the normal left to right).
Common benign causes of ST elevation
- Ventricular Paced Rhythm
- Benign Early Repolarization (BER)
- Left Ventricular Hypertrophy (LVH)
