1. P wave: This is the first positive or negative deflection seen on an ECG. It represents the electrical impulse generated in the sinoatrial node (SA node) and travels through the atria, causing their contraction. The P wave is characterized by a smooth and rounded shape.
2. QRS complex: The QRS complex follows the P wave and is the most prominent deflection in the ECG. It represents the electrical impulse spreading through the ventricles, leading to their contraction. The QRS complex consists of three waves:
- Q wave: This is the initial negative deflection of the QRS complex. It is not always present and may be small or absent.
- R wave: This is the main positive deflection of the QRS complex. It represents the depolarization wavefront moving across the ventricular septum and the ventricular wall.
- S wave: This is the final negative deflection of the QRS complex. It occurs as the depolarization wavefront moves away from the electrodes, completing the activation of the ventricles.
3. T wave: The T wave follows the QRS complex and represents the repolarization wavefront spreading through the ventricles. It is usually positive in most leads, but it may be negative in certain leads, such as leads aVR and V1. The T wave is typically broader and less prominent compared to the QRS complex.
