Here are some steps you can follow to interpret an ECG:

  1. Familiarize yourself with the ECG paper: The ECG paper has horizontal lines called “small squares” and vertical lines called “large squares.” These lines are used to measure the duration and voltage of the electrical activity of the heart, respectively.
  2. Identify the various waves and intervals on the ECG: The ECG trace represents the electrical activity of the heart as it passes through different parts of the heart. The various waves and intervals you will see on the ECG include:
  • P wave: Represents atrial depolarization
  • PR interval: Measures the time it takes for the electrical impulse to travel from the atria to the ventricles
  • QRS complex: Represents ventricular depolarization
  • ST segment: Represents the plateau phase of ventricular depolarization
  • T wave: Represents ventricular repolarization
  1. Determine the heart rate: To determine the heart rate, count the number of large squares between two R waves (the peak of the QRS complex) and divide this number by the number of seconds represented by those large squares. For example, if 5 large squares are between two R waves, and each large square represents 0.2 seconds, the heart rate is 5 large squares / 0.2 seconds = 25 beats per second, or 150 beats per minute.
  2. Assess the rhythm: Look for a regular pattern of P waves and QRS complexes. If the pattern is regular, the rhythm is normal. If the pattern is irregular, the rhythm is abnormal.
  3. Look for abnormalities: Abnormalities on an ECG can include abnormal waves or intervals, arrhythmias (abnormal heart rhythms), and conduction abnormalities.

There are many possible abnormalities that can appear on an electrocardiogram (ECG or EKG), and the specific diagnosis will depend on the specific pattern of waves and intervals seen on the ECG trace. Some common abnormalities include:

  • Arrhythmias: An arrhythmia is an abnormal heart rhythm, and there are many different types of arrhythmias that can be diagnosed based on the ECG. Examples include atrial fibrillation, atrial flutter, supraventricular tachycardia, ventricular tachycardia, and ventricular fibrillation.
  • ST segment abnormalities: The ST segment represents the plateau phase of ventricular depolarization. ST segment abnormalities can be caused by ischemia (a lack of blood flow to the heart muscle), infarction (a heart attack), or other conditions.
  • T wave abnormalities: T wave abnormalities can be caused by ischemia, infarction, or other conditions.
  • QT interval prolongation: The QT interval represents the total duration of ventricular depolarization and repolarization. Prolongation of the QT interval can be a sign of a potentially life-threatening arrhythmia called torsades de pointes.

To diagnose these and other abnormalities, a healthcare provider will interpret the ECG in the context of the patient’s clinical presentation and any other relevant test results. In some cases, additional testing such as an echocardiogram (ultrasound of the heart) or cardiac catheterization may be needed to confirm the diagnosis.