Diagnostic ST elevation for the Universal Definition of Myocardial Infarction is defined by the ESC/ACCF/AHA;

As new ST elevation at the J point in at least 2 contiguous leads of ≥2 mm (0.2 mV) in men or ≥1.5 mm (0.15 mV) in women in leads V2–V3 and/or of ≥1 mm (0.1 mV) in other contiguous chest leads or the limb leads (In the absence of LVH or LBBB). (Thygesen  K., Alpert  J.S., Jaffe  A.S., et al; Third universal definition of myocardial infarction. Circulation. 2012;126:2020-2035.)

• Other conditions which are treated as a STEMI; New LBBB, Isolated posterior MI (reciprocal changes in chest leads).

• Multilead ST depression with coexistent ST elevation in lead aVR has been described in patients with left main or proximal left anterior descending artery occlusion. (Go  A.S., Barron  H.V., Rundle  A.C., et al;National Registry of Myocardial Infarction 2 Investigators Bundle-branch block and in-hospital mortality in acute myocardial infarction. Ann Intern Med. 1998;129:690-697.)

Analysis of the ST-segment morphology

Because STEMI is not the most common cause of ST-segment elevation amongst chest pain patients, we need to consider other factors like reciprocal changes to shore up the diagnosis. Another factor that can assist you is an analysis of the morphology of the ST-segment. When determining AMI versus non-AMI with the ECG, these various findings should be used in the consideration of the overall clinical picture.

Morphology of the ST segment in STEMI

Acute STEMI may produce ST elevation with either convex, obliquely straight morphology or concave.

The normal ST segment should have an upward concavity sometimes referred to as a “take-off”. When an ST segment loses its upward concavity and becomes straight or upwardly convex, it’s suggestive of acute myocardial infarction.

Draw an imaginary line between the J point and the apex of the T wave. If the ST-segment is even with or above that line, then it’s “non-concave” which is suspicious for acute myocardial infarction.

This finding is not particularly sensitive, but it is fairly specific.

Image from Brady W, Syverud S, Beagle C et al. Electrocardiographic ST-segment Elevation The Diagnosis of Acute Myocardial Infarction by Morphologic Analysis of the ST Segment. Acad Emergency Med. 2001;8(10):961-967. (I have added the faces to it.)

ST elevation in Other Conditions

It’s also a good idea to be well versed in the typical appearance of the STEMI mimics; LVH, early repolarization, LBBB, pericarditis, ventricular aneurysm, hyperkalemia, Takotsubo cardiomyopathy & Brugada syndrome.

Analysis of some researches about the ST segment morphology

1- A comparison of AMI and non-AMI ECG syndromes; (Am J Emerg Med. 2002 Nov;20(7):609-12. Brady WJ1, Perron AD, Ullman EA, Syverud SA, Holstege C, Riviello R, Ghammaghami C.)

• Performed a retrospective comparative review of the electrocardiographic features of various STE syndromes, focusing on differences between AMI and non-AMI syndromes.

• 599 chest pain patients were entered in the study with 212 (35%) individuals showing STE, 55 (26%) with electrocardiographic AMI and 157 (74%) with non-AMI electrocardiographic syndromes.

• Anatomic location within the AMI group included 32 inferior and inferior variants, 18 anterior and anterior variants, and 5 lateral; non-AMI anatomic locations included 56 inferior and inferior variants, 98 anterior and anterior variants, and 3 lateral; anterior STE occurred significantly more often in non-AMI syndromes.

• The morphology of the STE occurred in significantly different rates between AMI and non-AMI patterns, concave more often in non-AMI patterns (P <.00001) and nonconcave more often in AMI (P <.00001).

2- Upwardly concave ST segment morphology is common in acute left anterior descending coronary occlusion; (Stephen W. Smith MD, J Emerg Med. 2006 Jul;31(1):69-77.)

• ST elevation in anterior precordial leads, in association with upwardly concave morphology is characteristic of pseudoinfarction patterns such as early repolarization. A retrospective review was done of EKG of 37 patients with LAD occlusion.

• Concave morphology was found in 16 of 37 (43%), 4 with terminal QRS distortion. It is concluded that concave morphology cannot be used to exclude STEMI with LAD occlusion. Many patients with LAD occlusion have borderline ST elevation. Concave morphology is associated with a shorter duration of symptoms.

T wave changes in coronary occlusion

Hyperacute T waves

• Broad, asymmetrically peaked or ‘hyperacute’ T-waves are seen in the early stages of STEMI & often precede the appearance of ST elevation.

• Classically, coronary vessel occlusion leads to elevation of the ST-segments. However, the earliest findings on an ECG are subtle changes in the T-wave shape and size. When a coronary artery is occluded, within the first 30 minutes, the T-wave amplitude increases. (Dressler, W and Roesler, H. High T waves in the earliest stage of myocardial infarction.  Am Heart J.  1947 Nov;34(5):627-45.)

• Loss of precordial T-wave balance occurs when the upright T wave is larger than that in V6. This is a type of hyperacute T wave. The normal T wave in V1 is inverted. An upright T wave in V1 is considered abnormal — especially if it is tall, and especially if it is new. This finding indicates a high likelihood of coronary artery disease, and when new implies acute ischemia.

 

In N Engl J Med 2008, de Winter, Verouden, Wilde, and Wellens' in a letter described a new ECG pattern without ST-segment elevation that signifies occlusion of the proximal LAD.

• Instead of the signature ST-segment elevation, the ST segment showed a 1- to 3-mm upsloping ST-segment depression at the J point in leads V1 to V6 that continued into tall, positive symmetrical T waves. The QRS complexes were usually not widened or were only slightly widened, and in some there was a loss of precordial R-wave progression. In most patients there was a 1- to 2-mm ST-elevation in lead aVR. (You can see in the front ECG)

• They recognized this characteristic ECG pattern in 30 of 1532 patients with anterior myocardial infarction (2.0%). Although tall symmetrical T waves have been recognized as a transient early feature that changes into overt ST elevation in the precordial leads, in these patients this pattern was static, persisting from the time of first ECG until the preprocedural ECG was performed and angiographic evidence of an occluded LAD was obtained (i.e., 30 to 50 minutes). Despite successful procedures in all cases, there was considerable loss of myocardium, with a median creatine kinase MB peak of 342 μg per liter.

ECG 26 min from symptom onset. Underwent primary PCI because of an occlusion of the proximal LAD.

How to make right diagnosis in chest pain patients with borderline ST segment elevation?

1- ECG findings should be used in the consideration of the overall clinical picture, history & examination.

2- Compare the previous ECG and the new ECG or take after 15 and 30 min another ECGs.

3- The presence of reciprocal ST depression helps confirm the STEMI diagnosis.

4- For STEMI non-concave ST-segment is not particularly sensitive finding, but it is fairly specific.

5- Hyperacute T-waves are seen in the early stages of STEMI & often precede the appearance of ST elevation.

6- Evaluation of wall motion by echo while a patient is experiencing chest pain can be useful when the electrocardiogram is nondiagnostic. Evaluation of wall motion may also be useful if there is electrocardiographic or laboratory evidence of MI even in the absence of chest pain. (ACCF/ASE/AHA , et al. J Am Coll Cardiol 2011; 57:1126.) Severe ischemia produces regional wall motion abnormalities that can be visualized echocardiographically within seconds of coronary artery occlusion. (Hauser AM, Gangadharan V, Ramos RG, et al. Echocardiographic observations during coronary angioplasty. J Am Coll Cardiol 1985; 5:193.) These changes occur prior to the onset of electrocardiographic changes or the development of symptoms. (Beller GA. Myocardial perfusion imaging for detection of silent myocardial ischemia. Am J Cardiol 1988; 61:22F.)

 

 

Compilation by Dr. Samad Ali Moradi; according to author's work experience, heart journals and guidelines.