The Fixed Split of S2

1. What can cause a fixed or relatively fixed split of the S2?

b. Heart failure, because it prevents the ventricles from responding to changes in volume and pressure [4]. The heart in failure is relatively insensitive to changes in filling pressure; for example, a rise in the LV end-diastolic pressure of a few millimeters of mercury in the normal ventricle can almost double cardiac output. In the failing ventricle the output rises only slightly or not at all.

Note: A relatively fixed split in the supine position is a variation of normal in children and young men. The reason is unknown. It will not be fixed in the sitting position.

2. Why is the S2 split in ASD relatively fixed?

ANS: In ASD the LV does not become smaller on inspiration and may even become larger because on inspiration vena caval blood is drawn into the right atrium, whose pressure then rises and thereby decreases the left-to-right shunt. This nonshunted left atrial blood passes instead through the mitral valve into the LV and thus tends to keep LV volume constant during inspiration.

The increased inflow into the right atrium on inspiration (vertical solid arrows) causes a decreased flow through the ASD and thus increased flow through the mitral valve.

3. Does the P2 move normally with respiration in the presence of an ASD?

ANS: With normal respiration the P2 moves only slightly. But with deep inspiration the P2 in patients with ASD can move almost normally.

4. How does the A2 move in ASD?

ANS: Either not at all or slightly toward the P2 on inspiration. This latter movement is actually a reversal of normal movement.

On inspiration the P2 is shown to be moving to the right away from the S1 by two mechanisms, the increased volume in the RV and the decreased impedance of the pulmonary circuit. The A2 is shown moving to the left (toward the Sj) by only one mechanism, the decreased volume in the LV. In ASDs the P2 moves with inspiration due only to its increased volume, because there is no significant impedance effect when the lung vessels are overfilled because of the shunt flow. The A2 may either not move at all with inspiration or actually move in the same direction as the P2.

On inspiration the P2 is shown to be moving to the right away from the S1 by two mechanisms, the increased volume in the RV and the decreased impedance of the pulmonary circuit. The A2 is shown moving to the left (toward the Sj) by only one mechanism, the decreased volume in the LV. In ASDs the P2 moves with inspiration due only to its increased volume, because there is no significant impedance effect when the lung vessels are overfilled because of the shunt flow. The A2 may either not move at all with inspiration or actually move in the same direction as the P2.

Was this article helpful?

0 0
Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

Get My Free Ebook


Post a comment