What happens to atrial pressure, heart sounds, and ECG during the ventricular ejection phase of the cardiac cycle?

Let's explain these points about the cardiac cycle, جدة. This phase describes ventricular ejection.

• (4) Atrial pressure:

  • Initially, atrial pressure decreases. This happens because the ventricles are contracting and shortening, which pulls the A-V fibrous ring (the structure holding the A-V valves) downwards. This downward movement widens the atrial cavities, temporarily increasing their volume and thus decreasing the pressure within them.
  • Therefore, the correct option is (b) Pulling of the A-V fibrous ring downwards during ventricular contraction.
  • After this initial drop, atrial pressure then gradually increases again due to the continuous flow of blood returning to the atria from the veins (venous return).

• (5) Sounds:

  • The first heart sound (S1), which is caused by the closure of the A-V valves (mitral and tricuspid) at the very beginning of ventricular contraction, can still be heard for a brief period as this phase (ventricular ejection) begins.

• (6) ECG (Electrocardiogram):

  • During ventricular ejection, the S-T segment is recorded on the ECG. This segment represents the period when the entire ventricular muscle is depolarized and contracting.
  • The T wave, which signifies the beginning of ventricular repolarization (the electrical recovery of the ventricles), starts to be recorded towards the end of this phase.