What is the P-Q segment in an ECG?

What is the P-Q segment in an ECG?

• A. It depicts the right and left atrial plateau during full contraction.
• B. It depicts ventricular contraction
• C. It depicts atrial contraction only
• D. It depicts the resting membrane potential

Answer: (A)

The P-Q (PR) segment reflects AV nodal conduction time. After the atria depolarize (the P wave) and atrial contraction begins, there is a brief flat interval as the electrical impulse travels through the AV node and into the His-Purkinje system before the ventricles depolarize. This is why there is no new depolarization shown on the ECG during this segment—the ventricles are not yet activated, and the impulse is simply being slowed to allow the ventricles to fill. So, this segment does not depict atrial plateau or contraction, nor ventricular contraction, nor resting membrane potential. The atrial depolarization (and atrial contraction) is represented by the P wave, while ventricular contraction is represented by the QRS complex, and resting membrane potential is not shown as a separate segment on the ECG.

The P-Q (PR) segment reflects AV nodal conduction time. After the atria depolarize (the P wave) and atrial contraction begins, there is a brief flat interval as the electrical impulse travels through the AV node and into the His-Purkinje system before the ventricles depolarize. This is why there is no new depolarization shown on the ECG during this segment—the ventricles are not yet activated, and the impulse is simply being slowed to allow the ventricles to fill.

So, this segment does not depict atrial plateau or contraction, nor ventricular contraction, nor resting membrane potential. The atrial depolarization (and atrial contraction) is represented by the P wave, while ventricular contraction is represented by the QRS complex, and resting membrane potential is not shown as a separate segment on the ECG.