In ECG, the P wave represents:

Appeared in: JODHPUR AIIMS SNO-2018

Explanation

The P wave is the first positive deflection on the ECG before the QRS complex.
It represents the electrical impulse originating from the sinoatrial (SA) node and spreading across the right and left atria.
This process is known as atrial depolarization, which leads to the mechanical contraction of the atria (atrial systole).

Option B: Ventricular depolarization is represented by the QRS complex, which is the large, spiked waveform following the P wave. This reflects the electrical activation of the heart's lower chambers (ventricles).
Option C: Ventricular repolarization is represented by the T wave. This wave follows the QRS complex and signifies the electrical recovery or 'reset' of the ventricles.
Option D: Atrial repolarization is the electrical recovery of the atria. This event occurs simultaneously with ventricular depolarization. Because the QRS complex is so much larger electrically, it completely masks the atrial repolarization wave, making it invisible on a standard ECG.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Interpretation of ECG Waveforms as background academic context rather than a clinical decision trigger.
Nurses must be able to analyze the P wave's presence, shape, and relationship to the QRS complex to identify various arrhythmias. For example, absent P waves are a hallmark of atrial fibrillation.
Abnormalities in the P wave can indicate atrial enlargement. A tall, peaked P wave ('P pulmonale') can suggest right atrial enlargement, while a broad, notched P wave ('P mitrale') can suggest left atrial enlargement.
What if? If P waves are present but are not consistently followed by a QRS complex, it could indicate an atrioventricular (AV) block. This means the electrical signal is being delayed or blocked on its way from the atria to the ventricles, a condition that requires prompt medical evaluation.

How to Approach the Question

First, identify the core of the question. It asks for the physiological event corresponding to the P wave on an ECG. This is a factual recall question.
Recall or visualize the standard ECG waveform, as shown in the provided image. The P wave is the first small, upward wave.
Systematically associate each part of the ECG with its event in the cardiac cycle: P wave = Atrial Depolarization, QRS complex = Ventricular Depolarization, T wave = Ventricular Repolarization.
Evaluate each option against this knowledge.
Option A correctly matches the P wave with atrial depolarization.
Options B, C, and D describe other parts of the cardiac cycle (QRS complex, T wave, or a hidden wave), making them incorrect.

Concept Tested & Keywords

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E6 Medicine Harrison 22e Part 1 p. 1909-1911

E6 Medicine Davidson Principles Practice 24e p. 468-470

Practise the full JODHPUR AIIMS SNO-2018

Attempt every question from this paper in a timed mock, then review the full solution for each one.