What causes S3 and S4?

  1. I realize I'm getting a little trigger happy with my questions, but my very first test in nursing school is going to be on Tuesday. So I guess I'm getting a little jittery at this point...

    Far as heart sounds go - what exactly causes S3 and S4? Most of the sources that I have read at this point all seem to agree that S3 is due to ventricular "resistance" of blood flow and S4 is due to ventricular hypertrophy or stiffness. Based on those explanations: With S3, I guess I'm a little confused over what would even make the ventricles "resist" blood flow in the first place - and how or why such an event would create an audible sound. With S4 - ventricular stiffness - again, why would that create an actual sound? (ie, Is that from blood flow somehow bouncing off the ventricular walls?)

    Also, is S4 in any way an aggravation of an S3-based condition? Is it possible to hear an S4 without necessarily hearing an S3 (and if so, how would you know the difference)?

    Again, I apologize if these are dumb questions. I promise, I really did make A's in my A&P classes...
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  3. by   adria37
    Try here :-) for a simplified explaination


    The first heart sound - S1 - is in time with the pulse in your carotid artery in your neck. The sound of the tricuspid valve closing may be louder in patients with pulmonary hypertension due to increased pressure beyond the valve. Non-heart-related factors such as obesity, muscularity, emphysema, and fluid around the heart can reduce both S1 and S2.
    The position of the valves when the ventricles contract can have a big effect on the first heart sound. If the valves are wide open when the ventricule contracts, a loud S1 is heard. This can occur with anemia, fever or hyperthyroid.
    When the valves are partly closed when the ventricule contracts, S1 is faint. Beta-blockers produce a fainter S1. Structural changes in the heart valves can also affect S1. Fibrosis and calcification of the mitral valve may reduce S1, while stenosis of the mitral valve may cause a louder S1.

    The second heart sound marks the beginning of diastole - the heart's relaxation phase - when the ventricles fill with blood. In children and teenagers, S2 may be more pronounced. Right ventricular ejection time is slightly longer than left ventricular ejection time. As a result, the pulmonic valve closes a little later than the aortic valve.
    Higher closing pressures occur in patients with chronic high blood pressure, pulmonary hypertension, or during exercise or excitement. This results in a louder A2 (the closing sound of the aortic valve).
    On the other hand, low blood pressure reduces the sound. The second heart sound may be "split" in patients with right bundle branch block, which results in delayed pulmonic valve closing. Left bundle branch block may cause aortic valve closing (A2) to be slower than pulmonic valve closing (P2).

    During diastole there are 2 sounds of ventricular filling: The first is from the atrial walls and the second is from the contraction of the atriums. The third heart sound is caused by vibration of the ventricular walls, resulting from the first rapid filling so it is heard just after S2. The third heart sound is low in frequency and intensity. An S3 is commonly heard in children and young adults. In older adults and the elderly with heart disease, an S3 often means heart failure.

    The fourth heart sound occurs during the second phase of ventricular filling: when the atriums contract just before S1. As with S3, the fourth heart sound is thought to be caused by the vibration of valves, supporting structures, and the ventricular walls. An abnormal S4 is heard in people with conditions that increase resistance to ventricular filling, such as a weak left ventricle.
  4. by   Daytonite
    don't try to make this more complicated than it is. your question is "why would that create an actual sound". the actual heart sounds are created by the physical events the occur inside the patient's chest. more specifically, the motions of the valves of the heart or the blood. normally, the s1 and s2 are the only sounds that are present. s3 and s4 are abnormal and represent pathophysiology.
    s1 - closure of the mitral valve and tricuspid valves (the atrioventricular valves)
    s2 - closure of the aortic and pulmonic valves (the semilumar valves)
    hearing the opening of the valves is considered an abnormal finding and these are denoted as opening snaps (atrioventricular valve) or ejection clicks (semilunar valves) and are due to stenosis of some kind.
    s3 (ventricular gallop) - caused by blood from the left atrium slamming into an already overfilled ventricle during early diastolic filling
    s4 (atrial gallop) - created by blood trying to enter a stiff, non-compliant left ventricle and slamming against it during atrial contraction late in diastole
    (from http://medicine.ucsd.edu/clinicalmed/heart.htm)
    please use the links in the "health assessment resources, techniques, and forms" thread in nursing student assistance forum (https://allnurses.com/forums/f205/he...ms-145091.html) to help you find the answers to these questions you have. a good anatomy and physiology book by your side will also serve you well. wasn't a&p a pre-requisite to taking this class?
  5. by   Jedi of Zen
    Quote from daytonite
    s3[/size][/b] (ventricular gallop) - caused by blood from the left atrium slamming into an already overfilled ventricle during early diastolic filling
    s4 (atrial gallop) - created by blood trying to enter a stiff, non-compliant left ventricle and slamming against it during atrial contraction late in diastole

    according to my textbook, s3 is a normal sound heard in those under 30 (esp children); s4 is also normal & heard in healthy older adults, children, and athletes. otherwise, s3 and s4 are abnormal sounds. (fundamentals of nursing, 6th ed. potter & perry, p. 724).

    so, going on that, does that mean that the description that you posted above holds true regardless of whether s3 or s4 is occuring as a normal sound (ie in kids and certain adults) or as an abnormal sound (ie, adults with unhealthy hearts)?

    (oh, and to answer your question - at my school, a&p i & ii can be done either as co-reqs or pre-reqs. i did them both as pre-reqs, and still use my book frequently.)
    Last edit by Jedi of Zen on Sep 17, '07