In a normal ECG, what does the P wave indicate?

• A. Ventricular repolarization
• B. Atrial depolarization
• C. Atrial repolarization
• D. Ventricular depolarization

Answer: (B)

The P wave on a normal ECG is indicative of atrial depolarization. This electrical activity occurs when the sinoatrial (SA) node, which is the heart’s natural pacemaker, sends an electrical impulse that spreads through the atria, causing the atrial muscle cells to contract and pump blood into the ventricles.

This contraction follows the depolarization of the atrial cells, leading to the characteristic upward deflection seen in the P wave on the ECG. A key aspect of understanding the P wave within the context of the entire cardiac cycle is recognizing its role in initiating the heartbeat by allowing for coordinated and efficient blood flow from the atria to the ventricles.

The other options refer to different aspects of the cardiac electrical cycle. For instance, ventricular repolarization is represented by the T wave, while atrial repolarization occurs during the QRS complex but is typically obscured by the larger QRS deflection. Ventricular depolarization, represented by the QRS complex, refers to the electrical activity that triggers the ventricles to contract. Understanding the specific electrical events represented by different waves on the ECG is crucial for interpreting cardiac function effectively.