ECG Criteria for Detecting Myocardial Infarction

1. What is an Electrocardiogram (ECG)?

The ECG is an important tool in diagnosing myocardial infarction. The ECG helps record the electrical activity of the heart using electrodes attached to the skin, thereby creating a graph representing the heart rate as well as other heart activities.

Changes occurring in the normal ECG pattern will indicate cardiac abnormalities such as: Myocardial infarction, cardiac arrhythmias, and electrolyte disorders.

There are 3 main components of an ECG:

• P Wave: Represents atrial depolarization (contraction of the atria). The P wave is usually a small, round wave appearing before every QRS complex in a normal heart rhythm.

• QRS Complex: Reflects ventricular depolarization (contraction of the ventricles). It consists of three parts: the Q wave (the first negative wave), the R wave (the highest positive wave), and the S wave (the negative wave following the R wave). The QRS complex varies in shape and width depending on the case.

• T Wave: Represents ventricular repolarization (the recovery process of the ventricles after contraction). It is usually a slightly positive and round wave. The T wave can be altered in pathological conditions.

The electrocardiogram (ECG) helps identify a lot of information regarding the heart's structure, the function of the heart's electrical conduction system, heart rate, etc. This helps detect issues such as myocardial infarction, cardiac arrhythmias, and other heart-related pathologies. The ECG can also be used to monitor heart health over a long period, especially for those at high risk.

2. Diagnostic Criteria for Myocardial Infarction on ECG

In myocardial infarction, the ST segment on the electrocardiogram (ECG) plays a very important role in diagnosing cardiovascular pathology. The ST segment is a straight line starting from the end of the QRS to the beginning of the T wave. The ST segment on the electrocardiogram (ECG) represents the phase between the depolarization and repolarization processes of the ventricles. Specifically, the ST segment lies between the QRS complex (when the ventricles contract) and the T wave (when the ventricles recover).

Criteria for diagnosing myocardial infarction on ECG:

• ST Elevation: One of the prominent signs on the ECG when there is a myocardial infarction is the elevation of the ST segment. This usually occurs in leads corresponding to the damaged myocardial region. ST elevation typically indicates an acute coronary occlusion.

• ST Depression: Besides ST elevation, ST depression is also a sign of myocardial infarction, especially in cases of non-ST-elevation myocardial infarction (NSTEMI). This sign can be clearly seen in neighboring leads.

• Inverted T Wave: Inverted T waves can also appear in cases of myocardial infarction. This is a sign indicating ischemia and myocardial injury.

• Changes in Q Wave Shape: The appearance of a pathological Q wave is a sign indicating myocardial tissue damage. If the Q wave exists in at least two leads, this may be a sign of an old myocardial infarction.

Diagnosing myocardial infarction on ECG requires attention and experience from the doctor. Understanding the diagnostic criteria for myocardial infarction on ECG not only helps detect myocardial infarction but also contributes to protecting cardiovascular health and reducing the risk of serious complications for patients.