AssessmentsAbnormal heart sounds
Abnormal heart sounds
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Justin Ling, MD, MS, Tanner Marshall, MS, Sam Gillespie, BSc, Marisa Pedron, Antonia Syrnioti, MD
If you put a stethoscope over the chest, you’ll usually hear something that sounds like lub dub, lub dub, lub dub, which repeats over and over again, with each cardiac cycle, or heartbeat.
In total, our heart has four valves- two atrioventricular valves, between the atria and the ventricles, which are the tricuspid valve, on the Left side, and the mitral valve, on the left side, and two semilunar valves, between the ventricles and the large arteries coming off of them, which are the pulmonary valve, on the right side, and the aortic valve, on the left side. Normally, in every heartbeat, some valves open, allowing blood to pass through and others close to hold blood within a chamber. The sound of the closing of each of these valves is projected onto the chest wall. The two normal heart sounds are S1, which is basically the tricuspid and mitral valve closing, and S2 which is the aortic and pulmonic valve closing. Between S1 and S2, we have systole, which is when ventricles are contracting and pushing blood out, and between S2 and S1 of the next heart cycle, we have diastole which is when blood is filling the relaxed ventricles. Together, S1 and S2 form the “lub dub” of the heart beat.
Alright, now in addition to S1 and S2, there are two other "extra" sounds that are sometimes heard in the cardiac cycle, called S3 and S4. S3 and S4 are heard in different parts of diastole. In early diastole, which is right after S2, the atrioventricular valves are open and blood is flowing from the atria into the ventricles. If there’s a lot of blood coming in, the ventricles fill up quickly, and fluid waves bounce off of the walls of the ventricles which makes them vibrate, creating a third heart sound, or S3. S3 sounds kind of like “lub-dub-ta”. In trained athletes and also in pregnancy this is totally normal and just means that the ventricles are handling extra blood volume. But an S3 can also be a sign of volume overload, like in congestive heart failure, where there’s too much volume coming into the ventricles. Now, at the end of diastole, just before S1, the atria are contracting to get that last bit of blood into the ventricles. If the ventricles are stiff, meaning that they can’t easily relax, the atria will have to contract extra hard to push that blood in, creating the fourth heart sound, or S4. So, S4 sounds kind of like "ta-lub-dub". Oftentimes, this stiffness is because the ventricular muscles have hypertrophied, or increased in size, in order to pump against high blood pressure in the aorta or pulmonary artery. In other words, S4 is typically a sign of pressure overload, or severe hypertension.
In addition to these extra heart sounds, there are also heart murmurs, which are the result of turbulent, or rough blood flow through the heart. Depending on how loud these murmurs are, they are graded on a scale from 1 through 6, where 1 is the slightest possible murmur, 3 is moderate and 6 is heard without even putting the stethoscope on the chest. Now, some children, whose hearts are perfectly healthy, have what are called “innocent” heart murmurs which are just sounds that come from the fact that their heart walls are thin and vibrate with rushing blood, and disappear as a child gets older and the heart walls thicken. An example is the so- called Still’s murmur, which is very common among young children, and is heard best at the left lower sternal border of the heart. But other murmurs are not “innocent” and can indicate a problem with the heart.
Now, systolic murmurs are the ones that can be heard between S1 and S2, kind of like “lub-whoosh-dub”. This is when the aortic and pulmonary valves are normally open, and the mitral and tricuspid valves are closed. There are four main causes for a systolic murmur - either from an aortic or pulmonary valve that’s not able to fully open, called stenosis, or from the mitral or tricuspid valve that’s not able to fully close, called regurgitation or insufficiency. In aortic or pulmonary valve stenosis the valve resists opening up for a moment before finally snapping open, and this causes a characteristic “ejection click.” Because the blood has to flow through a narrow opening in that first moment, we get increased turbulence, which creates a murmur. The murmur initially gets louder as more blood tries to squeeze through, and then as there’s less and less blood left in the ventricle that needs to go by, the murmur becomes more quiet again. This is described as a crescendo-decrescendo murmur. Aortic valve stenosis is best heard if you place a stethoscope between the second and third rib, known as the right second intercostal space, just next to the upper border of the sternum. And you can hear the murmur of pulmonary valve stenosis if you place a stethoscope in the left second intercostal space, at the left upper sternal border.
Alright, now, in tricuspid or mitral valve regurgitation, these valves aren’t able to make a perfect seal, and that allows blood to leak back from the ventricles into the atria. This movement of blood can be heard as a holosystolic murmur, because it’s possible to hear blood flowing through the valve for the duration of systole. If that comes from tricuspid valve regurgitation, it’s best heard between the fourth and fifth rib, next to the left lower border of the sternum, whereas a mitral valve regurgitation can be heard between the fifth and sixth rib, so in the left fifth intercostal space, near the midclavicular line. Another thing that helps differentiate a tricuspid valve regurgitation from a mitral valve regurgitation murmur is the presence of the Carvallo’s sign. The Carvallo’s sign is when a tricuspid valve regurgitation murmur gets louder with inhalation, because the negative pressure in the chest brings more blood back into the right atrium, and that makes the tricuspid valve regurgitation murmur even noisier. The leading cause of mitral valve regurgitation, and the most common of all valvular conditions, is mitral valve prolapse. This is when the mitral valve actually prolapses or flails back into the atrium, because the papillary muscles and connective tissue, called chordae tendineae, are too weak to keep the valve tethered. In mitral valve prolapse, there’s a mid-systolic click, which is a result of the leaflet folding into the atrium and being suddenly stopped by the chordae tendineae. If mitral valve prolapse gets severe enough, it can often progress to mitral regurgitation, meaning that the leaflets won’t make a perfect seal, so a little bit of blood leaks backward from the left ventricle into the left atrium. This will be heard as a late- systolic murmur, after the click. The mitral valve prolapse murmur is somewhat unique in that when patients squat down, the click comes later and the murmur is shorter, but when they stand or do a valsalva maneuver, the click comes sooner and the murmur lasts longer. This is because squatting increases venous return, which fills the left ventricle with more blood; increasing left ventricle volume. A roomier left ventricle means that the mitral valve leaflets have more space to hang out, and as the ventricle contracts and gets smaller, it takes just a little longer for the leaflet to get forced into the atrium. On the other hand, standing reduces venous return, making the left ventricle a bit smaller, and that forces the leaflet out earlier in the contraction.
- "Medical Physiology" Elsevier (2016)
- "Physiology" Elsevier (2017)
- "Principles of Anatomy and Physiology" Wiley (2014)
- "Aortic origin of innocent murmurs" The American Journal of Cardiology (1977)
- "Still's-like innocent murmur can be produced by increasing aortic velocity to a threshold value" The American Journal of Cardiology (1991)
- "Human Anatomy & Physiology" Pearson (2018)