HEART MURMURS AND ECHOCARDIOGRAMS

Tavishi Yesterday, I witnessed (and helped with!) my very first echocardiogram on a fluffy little dog with a heart murmur. Also, when I say I "helped", I mean I pet the dog so the cardiologists and techs could do their job. But nevertheless, it was an insane moment for me. Earlier that day, I had listened to the dog's heartbeat, having been told he had a heart murmur, and was surprised to hear a whooshy (no other word to describe it) and irregular heartbeat. A heart murmur is a condition in which a heartbeat sounds differently than it should, and much less defined than the typical "lub-dub". Instead, there is a whooshy sound mixed in somewhere with the "lub-dub". Although lub-dub is a very, very professional and scientific term, each of these sounds actually has a proper name: S1 and S2. I'm fairly certain that it's because it is the first sound and the second sound, but not entirely sure. S1 initiates systole, and S2 initiates diastole. Systole is the contraction of the heart, and is when blood is pushed into the body. Diastole is the relaxation of the heart, and when the heart fills back up with blood.

This diagram is kind of ugly, but it will do. During systole, the mitral (9) and tricuspid valves (4) between the atria and ventricles close, and blood goes into the pulmonary artery (2) and the aorta (14). The closing of the mitral and tricuspid valves creates the characteristic "lub" S1 sound. During diastole, the pulmonary (16) and aortic valve close (15), and blood goes into the right (6) and left (8) ventricles. The closing of the pulmonary and aortic valves creates the characteristic "dub" S2 sound.

There are three kinds of heart murmurs: systolic, diastolic, and continuous. If the swoosh is during the S1 sound, you have a systolic heart murmur. If the swoosh is after the S1 and S2 sounds, you likely have a diastolic heart murmur. There are so many more categories, but I'm no cardiologist. Interestingly enough, a lot of people are trained in identifying what caused the heart murmur entirely off of sound. Two of the largest causes of heart murmur are valve regurgitation and valve stenosis. A valve closes after allowing blood to flow through so that there is no backflow of blood. If a valve isn't closing properly, some blood is going to go back where it came from, rather than being forced all into the ventricle/blood vessel. This phenomenon is known as valve regurgitation. When regurgitation occurs in the mitral or tricuspid valve, you have yourself a systolic heart murmur. Mitral valve regurgitation is the most common kind of valve regurgitation. Tricuspid valve regurgitation is very similar, but one of the common causes is a congenital heart defect called Ebstein's anomaly in humans, where the right ventricle size is significantly smaller and the pulmonary artery receives much less blood. Both mitral valve regurgitation and tricuspid valve regurgitation can result in atrial fibrillation, an irregular heartbeat condition. While the S2 sound remains relatively normal, the preceding S1 sound is highly variable. Below is an EKG representation of AFIB!

The dog I met yesterday had both mitral valve regurgitation, and from what I could tell from the EKG, atrial fibrillation as well. Valve stenosis is a condition in which less blood reaches the target area, but not due to regurgitation. Instead, valves are too stiff to open properly, resulting in less blood flow to the body in any case. Tricuspid and mitral valve stenosis can also be a cause of atrial fibrillation, in addition to a variety of other outcomes. Issues like these with the heart can be identified with an echocardiogram, or a heart ultrasound. Echos are really useful tools for identifying issues with the structure of the heart itself- for example, high blood pressure can often result in left ventricular hypertrophy, or a thickening of the left ventricular heart wall as a result of having to work extra hard to pump blood to the body. Ventricular hypertrophy, when left untreated, can lead to severe issues like cardiac arrest, heart failure, and more. Echocardiograms are also extremely useful tools for identifying congenital heart disorders, like Ebstein's anomaly, septal defects (hole in heart walls), and congenital valve stenosis. When identifying a potential heart murmur, regurgitation is identified by using color flow imaging, where blood flowing into one chamber is one color, and regurgitation blood is another. In the echo I witnessed yesterday, regurgitation blood was yellow. There is so much more nuance to the specifics of color flow doppler echocardiography which I am still trying to understand and learn, but it's so fascinating!