Mode Of Production

1. Where is the S4 best recorded by an intracardiac phonocatheter, in the atrium or in the ventricle?

ANS: In the ventricle.

2. What does the apex cardiogram (apex impulse tracing) show at the time of the S4?

ANS: It shows a hump just before the systolic outward impulse. This presys-tolic hump or A wave is often large enough to be palpable.

Note: The peak of the A wave coincides with the largest vibration of the S4.

3. What causes this A wave or end-diastolic outward movement on the apex cardiogram?

ANS: It is the effect of left atrial contraction, causing a slight increase in the volume of the left ventricle (LV) at the end of diastole. This slight increase in volume before the ventricle contracts can be seen even in normal subjects on a cineangiogram with contrast material in the LV.

Note: An apical A wave may be palpable even when the S4 may be too low in frequency to be audible. On the other hand, a pathological S4 may be heard in the absence of a palpable A wave. This is obvious when you realize that only a chest that allows an apex beat to be easily palpated will allow you to palpate the A wave, yet the S4 sound may still be heard.

4. Can an S4 be produced by an atrium that is contracting against a stenotic atrioventricular (AV) valve as in mitral stenosis (MS)?

ANS: No. The atrium must be able to transmit its pressure freely to the LV, or else only a presystolic murmur will be heard.

5. What theory could account for the production of an audible S4 if it (a) occurs at the peak of atrial contraction, (b) causes such an increase in LV end-diastolic volume that it produces a recordable and often palpable systolic outward movement, and (c) is recorded best in the ventricle?

ANS: Atrial contraction, by causing eddy currents on the undersurface of the AV valves, tends to hold them upward. However, since atrial contraction also raises the volume in the ventricle, the chordae tendineae and papillary muscles are stretched at exactly the same time as the AV valves are being pulled up or held in the opposite direction. If it has enough energy, this tug on the chordae and papillary muscles could account for the sound.

E point

Apex low freq.

E point

Apex low freq.

Apex Cardiography

Apex cardiogram and phonocar-diogram from a 50-year-old man with a previous infarction. The S4 is simultaneous with a large palpable atrial hump (A wave) on the apex cardiogram. The A wave is 15% of the total apex pulse amplitude, or vertical E to O distance. Atrial humps of 15% or more of the E-O amplitude are usually palpable.

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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...

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