Murmurs of the heart

Health News,  April, 1991  

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Heart or cardiac murmurs are prolonged vibrations between the normal heart sounds, heard when listening to the heart through a stethoscope, audible as a "whoosh" or burning different from the normal "lub-dub" of the heart beat. Heart murmurs are often harmless or innocent due to slight irregularities in the normal flow of blood through the cardiac valves. They may be detected in as many as half the children seen in a busy family physician's or pediatrician's office. Heart murmurs are also increasingly diagnosed in otherwise healthy young adults, especially women. An estimated one in 20 people has some kind of heart murmur, frequently of no consequence.

Distinguishing normal from abnormal heart sounds

The heart beat is divided into two main parts - diastole (the relaxation phase of the heart beat) and systole (the contraction or pumping phase). Normal heart sounds arise from the opening and closing of the heart's four cardiac valves. (SEE DIAGRAM.)

What does a heart murmur signify?

The physician's task is to tell the difference between harmless or innocent murmurs that can be more or less ignored and those that signal some cardiac abnormality such as a hole in the partition between the heart's two sides or a leaky, narrowed or otherwise malfunctioning heart valve. A careful check-up, taking age into account, can separate heart murmurs that need further medical investigation from those that can be left alone and/or ignored. The timing, character and intensity of a heart murmur help to classify and identify its source and whether or not it needs to be checked out by a cardiologist.

Heart murmurs present since childhood are often harmless or innocent, while those that arise later on in life may be serious. Many childhood murmurs fade with time, vanishing before the age of 30. Those that persist longer may warrant further investigation, such as an echocardiogram (ultrasound examination). Some murmurs should be followed and checked every few years. For example, a murmur resulting from a congenitally defective heart valve might be faint in childhood but later become loud due to narrowing or calcification (hardening) of the valve. Heart murmurs in children, young adults, athletes and pregnant women are often innocent. Many murmurs in the elderly, due to sclerosis (thickening) of a heart valve, are also considered innocent. Athletes often have innocent heart murmurs because their rigorous training increases the heart's size and ability to pump blood with each heart beat. The extra blood pumped by the heart may produce a harmless "flow" murmur that's heard when the athlete is lying down but tends to disappear when he or she is upright.

Many physicians argue that when an unusual heart sound is innocent and means nothing, the person shouldn't be told since the knowledge of a murmur may evoke needless anxiety. But other physicians think it better to tell the patient and/or family about an innocent heart murmur, in case - at some future medical examination - a different physician thinks it's new and possibly serious.

Classifying heart murmurs

Murmurs are classified according to their causes - an unusually narrow or stenosed valve; an incompetent, regurgitant or leaky valve and an innocent murmur. They are also categorized according to whether they occur in the systolic (pumping) or diastolic (relaxation) phase of the heart beat. Heart murmurs audible throughout the systolic and diastolic phases of the heartbeat are termed "continuous" murmurs.

Heart murmurs can be caused by:

* minor structural irregularities in the heart valves that cause innocent "flow" murmurs due to eddies or turbulence in the flow of blood through the heart - like those seen in a river flowing around rocks, bridge supports and other obstructions that alter the flow.

* a larger than usual amount of blood flowing through the heart - innocent flow murmurs (as in pregnant women and athletes).

* a narrowed or stenosed valve that obstructs the normal amount of blood flowing through it. There is more turbulence than usual when blood flows through a narrowed valve. Murmurs due to valvular stenosis can be serious

* a regurgitant or leaky ("incompetent") valve that causes a murmur as blood backs up through it.

* a fistula, hole or small opening in the partition between the heart's right and left sides (which separates the arterial and venous circulation inside the heart).

* a floppy or prolapsed mitral valve - known as mitral valve prolapse - where valve closure is imperfect and blood slips backward,. giving a slight click, murmur or both.

How are heart murmurs detected?

There are several tests for verifying the presence of a heart murmur and its type. Initial testing is with the stethoscope to monitor heart sounds. Echocardiograms may be ordered following a physician's initial diagnosis. An echocardiogram, which takes about half an hour, is a completely painless, safe and non-invasive test. Using ultrasound and sometimes special Doppler microphones, it provides a detailed visual, two dimensional image of the heart in action, giving an accurate picture of the four cardiac valves as they open and close. Generally, people whose echocardiograms reveal heart valve malfunction go on for further investigation.