Murmurs of Heart - The heart's distress call

Heart murmurs might seem hard, confusing, crazy or even all of them. But they are not really that bad. If you think about it, they are just sounds trying to communicate. It's the human heart sending a distress call to the outside world.  

So a normal heart doesn't send these distress signals. Right? For the most part when you put your stethoscope on a patient's chest you shouldn’t be able to hear a murmur. But when you do, don’t panic. Murmurs are just sounds, waiting to be understood. So when you hear one, take a deep breath, close your eyes and just try to paint a simpler picture - a sink filling with water.

You can even try this at home if you’d like. Find a sink, open the tap half way and pay attention to the sound of the water. Now open it all the way and listen to how the sound changes. It's louder isn’t it? Now let the sink fill up completely with water. Turn the tap off and open the drain and listen to the sound closely. Now fill the sink again. Close half the drain, close the tap and drain the water out. Listen to the change in sound as the water escapes through the half open drain. So now we understand, the sound of the water is influenced by two main factors:

• How fast the water flows through a pipe or tube
• The size of the tube through which the water escapes.

So how does this apply to murmurs of the heart?

The heart is just like a giant sink, with blood instead of water flowing through it. Normally the sound made by the blood is not audible. But increased velocity of the blood (opening of the tap fully), abnormal valves through which the blood has to flow (change in the drain size), problems with myocardial structure (shape of the sink) and septal defects all cause a change in the character of the blood flow. Essentially, turbulent or disturbed flow of blood leads to a change in the sound it makes while travelling through the heart chambers and this is Murmur.

So now let us see the definition of murmurs according the 19th edition of Harrison’s Principles of Internal Medicine:

(The 4th and 5th points might seem a bit intimidating but don't worry. They'll make more sense when you read about valve defects)

“Heart Murmurs are caused by vibrations that are due to increased turbulence from

1. accelerated blood flow through normal or abnormal orifice, 
2. flow through narrowed or irregular orifice into a
3. dilated vessel or chamber or
4. back flow through an incompetent valve or
5. ventricular septal defect or patent ductus arteriosus.”

Makes sense right? Good. Now let’s move on to the good stuff. So now that we understand what murmurs are, let us understand some of the terms used to describe these murmurs. 

So when exactly do these murmurs occur?

The first thing to understand about murmurs is their timing. Depending on when the murmur is heard in relation to the cardiac cycle, the murmurs can be called systolic, diastolic or continuous murmurs. So any murmur that is heard between S1 and S2 is called a systolic murmur. Any murmur that is heard between S2 and the next S1 is called a diastolic murmur. Some murmurs exist through out the cardiac cycle and these murmurs are called continuous murmurs.

To understand intuitively, the valves involved in systolic and diastolic murmurs think about what each valve is doing during systole and diastole. For example, during a systole, the aortic and pulmonary valves are open and the tricuspid and mitral valves are closed. So there can be two ways a functional pathology exists that results in a systolic murmur:

1. When the valves that should be open, are fully or partially closed (aortic and pulmonary stenosis)
2. When the valves that should be closed, are fully or partially open (mitral and tricuspid regurgitation)

Similarly, in case of diastolic murmurs, the same idea applies. During diastole, mitral and tricuspid valves are open and aortic and pulmonary valves are closed. So in order for there to be a diastolic murmur, there should be mitral or tricuspid stenosis; or pulmonary or aortic regurgitation. Once the timing of a murmur is clear, let's move on to the next term used to describe murmurs. 

What do these murmurs sound like?

We need to understand the character or the pitch of these murmurs. They can be high pitched or low pitched. This pitch of a murmur is determined by the pressure applied on the blood being pumped. We all know that ventricles exert higher pressures upon the blood than the atria. Higher pitched murmurs are heard when the murmurs are backed by the ventricles (aortic regurgitation and aortic stenosis) and lower pitched murmurs are due to lower pressures backed by the atria. It is tempting to think that murmurs around the aortic and pulmonary valve are high pitched and murmurs around mitral and tricuspid valves are low pitched. This is not always the case! We shall see more about them when we discuss individual valve diseases.

The last characteristic that needs to be understood is the configuration or loudness of the murmur. We are going to be dealing with the physics behind it rather than the complete medical explanation because this character makes more sense when explained with the individual valve diseases. So just try to understand the concept now so that reading those topics make more sense. 

Let's go back to the sink analogy. Remember how the sound of the water got louder when you opened the tap fully because the speed of the water increased? Well, inside the heart the speed of the blood flowing through the heart is regulated by the change in pressure gradient and this pressure difference is responsible for the loudness of the murmur. For example, how fast blood flows out of the left ventricle into the aorta is dictated by the pressure difference between the aorta and the ventricle. As we all know, the larger the pressure difference, the faster the fluid travels from an area of high pressure to an area of low pressure. The faster the blood travels, the more turbulent the blood flow gets and hence, louder is the sound. So the configuration(loudness) of the murmurs can be crescendo, decresendo, crescendo-decresendo and plateau. Each of these will make more sense when we see the conditions in which they are seen. Just remember that the loudness/configuration of the murmurs is based on the pressure gradient.  

So now you know the basics of heart murmurs, reading about them in detail will be much better. Do let us know what you think!

Author: Narendran Sairam (Facebook)

Sources and citations

Loscalzo, Joseph. "Approach to a Patient with a Heart Murmur." Harrison's Principles of Internal Medicine. By Patrick T. O' Gara. 19th ed.: McGraw-Hill, 2015. 278-86.

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