Question

select the correct answer.
an individual’s ekg shows changes in atrial contraction. which image shows contraction of the atria?

Explanation:

Step1: Recall Atrial Contraction Mechanics

Atrial contraction (atrial systole) occurs when the atria contract to push blood into the ventricles. The electrical signal (from the SA node) spreads through the atria first, causing them to contract. In heart diagrams, atrial contraction is associated with the atria actively pumping (shown by arrows or color changes indicating contraction, often with the AV valves open to allow blood flow to ventricles).

Step2: Analyze Each Image

• Left Image: Shows electrical signals spreading through the atria (arrows in atria) and blood moving from atria to ventricles (open AV valves, blood flow direction). This matches atrial contraction (atria contracting to push blood into ventricles).
• Middle Image: Likely shows ventricular contraction (ventricles contracting, AV valves closed, blood moving out to arteries), not atrial.
• Right Image: May show later stages of ventricular contraction or relaxation, not atrial contraction.

Answer:

The Left Image