Which ECG pattern shows atrial contraction originating at the SA node?

Which ECG pattern shows atrial contraction originating at the SA node?

• A. QRS Complex
• B. P Wave
• C. T Wave
• D. PR Segment

Answer: (B)

Atrial contraction starts when the atrial muscle depolarizes, initiated by the sinoatrial (SA) node in the right atrium. As the impulse spreads through the atria, this depolarization is recorded on the ECG as the P wave. The P wave appears before the QRS complex, which is the ventricular depolarization, and before the T wave, which is ventricular repolarization. The PR segment reflects the time it takes for the impulse to travel from the atria through the AV node to the ventricles. So the pattern that shows atrial contraction originating at the SA node is the P wave.

Atrial contraction starts when the atrial muscle depolarizes, initiated by the sinoatrial (SA) node in the right atrium. As the impulse spreads through the atria, this depolarization is recorded on the ECG as the P wave. The P wave appears before the QRS complex, which is the ventricular depolarization, and before the T wave, which is ventricular repolarization. The PR segment reflects the time it takes for the impulse to travel from the atria through the AV node to the ventricles. So the pattern that shows atrial contraction originating at the SA node is the P wave.