- February is American Heart Month, the perfect time to brush up on your knowledge of heart sounds.
- Auscultation of the heart involves listening carefully for the different heart sounds and for the presence of murmurs or rubs.
- Systolic heart sounds include the 1st heart sound (S1) and clicks.
- Diastolic heart sounds include the 2nd, 3rd, and 4th heart sounds (S2, S3, and S4), as well as knocks and snaps.
Happy American Heart Month! To show our appreciation for this wonderful organ, and of course, raise awareness for heart health, we're sharing an excerpt from our Medical Student Core to review the most important things you need to do when listening to heart sounds during a cardiovascular exam.
No matter where you're at in your medical career, cardiac auscultation is an essential skill! Did you know that a doctor’s cardiac exam skills don't improve, on average, after your third year of med school? Avoid being part of this unfortunate statistic and start brushing up on your knowledge of heart sounds with the Medical Student Core excerpt on cardiovascular examinations below.
What is heart auscultation?
Auscultation of the heart involves listening carefully for the different heart sounds and for the presence of murmurs or rubs. Certain sounds are heard best at different locations over the chest, axilla, or back or with the patient in different positions. We'll review the basics.
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Heart sounds are brief sounds produced by the opening and closing of valves. Systolic heart sounds include the 1st heart sound (S1) and clicks. Diastolic heart sounds include the 2nd, 3rd, and 4th heart sounds (S2, S3, and S4), as well as knocks and snaps.
Heart sounds — S1
S1 is a high-pitched sound caused by the closing of the mitral and tricuspid valves just after the beginning of systole. Mitral valve closure occurs first and is the louder component of S1. Several conditions affect the intensity, or loudness, of S1:
- S1 is soft or absent in conditions that cause the mitral valve to begin closing earlier than normal, prior to the onset of systole. Examples of this situation include MR, acute aortic regurgitation (AR; increased LV pressure causes early mitral valve closure), or a severely calcified mitral valve.
- S1 is loud (i.e., the mitral valve slams shut) when there is a short PR interval, MS, or hyperdynamic ventricular function.
Heart sounds — S2
S2 is a low-pitched sound caused by the closing of the aortic (A2) and pulmonic (P2) valves at the beginning of diastole. A2 usually occurs just before P2. This physiologic split is larger during inspiration because the increased volume of blood in the RV prolongs RV systole and delays closure of the pulmonic valve. There are several abnormal forms of S2 splitting:
- A widely split S2 varies with respiration, but the splitting does not disappear on expiration. This often is due to a delay in closure of the P2, as in severe pulmonic stenosis (PS), acute pulmonary embolism (PE), or complete right bundle-branch block (RBBB). These conditions cause delayed or prolonged contraction of the RV. Early closure of the aortic valve (A2) also causes widely split S2, as in MR.
- A fixed split S2 does not vary with respiration. This finding occurs with an atrial septal defect (ASD), due to the increased RV flow. There is no variation in aortic and pulmonary valve closure that normally occurs with respiration. RV failure is another cause of a fixed split S2.
- A paradoxically split S2 is due to delay of aortic valve closure (A2), with P2 occurring before A2. In this case, the split is larger during expiration instead of during inspiration. This is commonly caused by left bundle-brand block (LBBB), or with severe LV outflow tract obstruction such as in AS or severe HCM.
Heart sounds — S3
S3 is an abnormal heart sound in adults. When present, it occurs in early diastole, immediately after S2. It indicates the end of rapid ventricular filling.
On auscultation, it creates a pattern that sounds like "Ken-tuck-y," corresponding to S1, S2, then S3. This often is referred to as a "gallop," a term coined in 1847 to describe the cadence of 3 heart sounds occurring in rapid succession.
The sound is thought to be due to the tensing of the chordae tendinae. S3 often is a normal finding in pregnant women and young children. However, in adults, it usually indicated severe LV systolic dysfunction, especially conditions that increase early LV filling, such as acute ventricular failure or severe aortic or mitral regurgitation. An S3 in a patient with LV dysfunction is a poor prognostic indicator.
Note that S3 is best heard during expiration (so that the heart will be closer to the chest wall), using the bell of the stethoscope with the patient in the left lateral decubitus position (i.e., the patient is lying on his left side).
Heart sounds — s4
S4 is an abnormal heart sound. When present, it occurs just before S1 at the end of diastole. On auscultation, it sounds like "Tenn-e-ssee," corresponding to S4, S1, and S2, also referred to as a "gallop." S4 is caused by increased ventricular filling during atrial contraction, occurring in patients with decreased ventricular compliance.
You may hear an S4 in ischemic heart disease, AS, HCM, diabetic cardiomyopathy, and hypertensive heart disease with concentric hypertrophy. Note that S4 sometimes occurs with S3 in patients with LV systolic dysfunction but that S4 alone indicates LV diastolic dysfunction.
Note that like S3, S4 is best heard using the bell of the stethoscope with the patient in the left lateral decubitus position.
Heart sounds — other
Clicks occur only during systole and are single or multiple. They are briefer and have a higher pitch than S1 or S2. In MVP, a click occurs in mid to late systole and is thought to be due to abnormal tension on the valve leaflets or chordae tendinae.
A diastolic knock is a loud, high-pitched, thudding sound that occurs at the same time as S3. It indicates the sudden cessation of rapid ventricular filling due to the presence of a noncompliant pericardium, as in constrictive pericarditis.
An opening snap is a brief, high-pitched sound heard best with the diaphragm of the stethoscope at the left lower sternal border (LLSB).
Start refining your auscultation skills for American Heart Month! Check out MedStudy Heart Sounds to practice recognizing the most important (and the rarest) heart sounds.
Get the Medical Student Core to read the full cardiology section plus 19 more topics to review for step exams, classes, and beyond!