Heart Sounds

Heart Sounds and Review of Fundamentals

* Systole: The time between S1 and S2 - the blood is flowing from the heart to the lungs and body, across the pulmonic and aortic valves. The ventricles are contracting.
* Diastole: The time between S2 and S1 - the blood is flowing from the atria to the ventricles, across the bicuspid and tricuspid valves. The atria contract at the end of this phase.
* S1: The "lub" in "lub-dub". The sound is from the closing of the bicuspid and tricuspid valves, which live between the atria and ventricles. They close because the ventricles are contracting. You also hear the pulmonic and aortic valves opening at the same time as the blood is forced from the ventricles into the arteries.
* S2: The "dub" in "lub-dub". The sound is from the closing of the pulmonic and aortic valves as the pressure from the arteries becomes greater than the pressure in the ventricles - this is the end of systole. You can also hear the bicuspid and tricuspid valves opening.

A split S2 is really always occurring to some degree, as the closing of the pulmonic and aortic valves don't both occur at the same millisecond. Both valves closing make up the S2. When you breathe in, the pressure in your thorax decreases - the diaphragm creates a little vacuum. This decreased pressure means less force is placed on the pulmonic valve to close (remember that the pulmonic valve closes when the PA pressure is greater than the RV pressure) than there is during expiration. (During expiration, the pressure in the thorax, and therefore the pulmonary artery, is greater.) With the decreased force, the pulmonic valve becomes encouraged to close slightly later than it would otherwise, so it does - it becomes the second part of S2. The pressure in the aorta isn't decreased by the inspiration, and it closes the aortic valve at its regular time - as the first half of S2. When they close far enough apart for you to hear them each distinctly, that's a split S2. The take-home message is that split S2's increase their split on inspiration, and decrease their split on expiration. They're a normal finding.

An S3 sound comes right after the S2 - it sounds like a split S2, but the size of the split never changes with breathing. It's fairly normal in children and athletes. In other people, it can indicate a non-specific impairment of ventricular function - listen with the bell to determine which ventricle is making the sound (left side at the apex, right side at the xiphoid process).

An S4 sound comes right before the S1 - sounds like a "split S1." It is the sound of the ventricle filling during diastole. It becomes more pronounced when the ventricular wall gets more rigid (as in hypertrophy) such as with ischemia, aortic or pulmonic stenosis.

Murmurs can occur anywhere in the cardiac cycle. They generally indicate turbulence, often across a valve. You need to be able to identify a few things about a murmur to help you narrow down your differential:

How loud is it? Murmurs are graded on a scale with VI being the highest - I-III have no associated thrill, IV-VI do have a thrill.
1. Barely audible
2. Faint, but easily heard
3. Moderately loud
4. IV.Loud with associated thrill
5. Very loud with thrill, can hear with stethoscope off of chest
6. Very loud with thrill, can hear without a stethoscope

*
o What does it sound like? Is it a rumble, a whine, a whoosh?
o During which part of the cardiac cycle does it occur?
o Be specific - if it's during systole, is it early systolic, late systolic, or holosystolic?
o What does it do?
o Does it crescendo (get progressively louder)? Decrescendo (get progressively quieter)? Stay constant?
o Where do you hear it best? Right Upper Sternal Border (RUSB)? LUSB? LLSB? Over the PMI?
o Does it project anywhere, such as to one or both of the carotids?
o Is there a click associated with the beginning, middle, or end of the murmur?


Gallops: These are simply the presence of either S3 or S4.

Rubs: The one you're likely to hear is a "pericardial friction rub" which indicates pericarditis. It sounds like what it is - muscle rubbing against thick membrane. Sandpapery