ECG : P waves

The P wave is a crucial component of the electrocardiogram (ECG), representing the electrical activity associated with atrial depolarization. This phase precedes the contraction of the atria, marking the initiation of the cardiac cycle. Understanding the characteristics of P waves, including their morphology, duration, amplitude, and axis, is essential for clinicians to assess normal atrial function and identify various cardiac pathologies.

Physiologically, the P wave originates from the sinoatrial (SA) node, which is located in the right atrium near the superior vena cava. As the primary pacemaker of the heart, the SA node generates electrical impulses that propagate through the atria, resulting in atrial contraction. The P wave's appearance on the ECG reflects this electrical activity and provides insights into atrial health and function.

When analyzing the sinus complex, the first wave, known as the P wave, represents atrial depolarization. During the cardiac cycle, when the valves between the atria and ventricles open, approximately 70% of the blood in the atria flows passively into the ventricles due to gravity and the suction effect caused by the expanding ventricles. Atrial contraction is required for the remaining 30% of the blood to be pushed into the ventricles. Consequently, only a relatively small...