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In an ECG, what does the P Wave signify?

  1. Ventricular contraction

  2. Atrial depolarization

  3. Heart rate variations

  4. Ventricular repolarization

The correct answer is: Atrial depolarization

The P wave in an ECG represents atrial depolarization, which is the electrical activity that triggers the contraction of the atria. During this phase, the sinoatrial (SA) node, the heart's natural pacemaker, generates an electrical signal that spreads through the atria, causing them to contract and push blood into the ventricles. Understanding the role of the P wave is crucial in interpreting an ECG, as it indicates the normal functioning of the atria and the initiation of the heart's electrical cycle. This event is the first part of the cardiac cycle, leading to the subsequent depolarization and contraction of the ventricles, which is represented by other waveforms on the ECG.