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|Wed, 02-08-2006 - 6:47pm|
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.
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.
The additional tests may include chest X-rays and detailed electrocardiograms - heart wave patterns obtained by placing electrodes on the chest (a painless test). If there is any evidence of a significant murmur the person will be referred to a cardiologist for further assessment. The cardiologist may use a variety of clinical tests to examine heart function such as having the person breathe in and out while checking the heart, also testing its action during positional changes, after sit-ups, when going from squatting to standing, during leg lifts and handgrip exercises to determine whether and how a heart murmur should be treated.
Mitral valve prolapse - one of the commonest heart murmurs
Mitral valve prolapse (MVP) also known as the "click-murmnur syndrome" (after the sounds heard through the stethoscope), or a "floppy valve," is one of the commonest causes of a heart murmur in young adults, especially women. No one knows why, but about four per cent of adults have a click, often accompanied by a late systolic murmur where there's some looseness in the leaflets of the mitral valve and its supports The mitral valve separates the heart's left atrium and left ventricle - preventing blood from flowing backwards as the left ventricle contracts and pumps blood to the rest of the body. First recognized in the 1960s, MVP was originally thought to be a harmless and very common condition but has since been more accurately defined. At almost any workplace or social gathering someone now seems to have a heart murmur due to MVP. This sudden flurry of heart murmurs isn't an epidemic but simply means that a probably ancient quirk of nature is more often recognized. In the past, MVP was attributed mainly to some illness, particularly rheumatic fever. But this theory is now discounted since many people who've never had rheumatic fever have a mitral valve murmur that's not due to a diseased valve but simply one that billows as the heart contracts. Ideally its flaps shut tightly to form a taut seal. But if the mitral valve is slightly floppy and doesn't shut completely its flaps or leaflets may billow (prolapse) as it closes, causing a click. If the valve billows enough to prevent proper closure, there will be an accompanying murmur (hiss or vibration).
MVP murmurs tend to run in families and may be an inherited trait. Studies suggest that they are most common in slim, tall women with "model-type" figures, long arms and a flattish ribcage. Mild mitral valve prolapse isn't usually serious but a loud murmur may be accompanied by significant symptoms and, in serious cases, there may be degeneration or loss of elasticity (myxomatosis) of the mitral valve leaflets. However, a prolapsed mitral valve does not generally worsen, usually posing no medical problem other than a possibly increased vulnerability to heart infections. MVP is sometimes linked to connective tissue disorders and can occur in the severely malnourished or women with anorexia nervosa (eating disorders).
In 90 per cent of cases, MVP is no cause for worry. Most people with MVP do not suffer symptoms such as lightheadedness, chest pain, palpitations and shortness of breath any more frequently than the general population. However, these symptoms should always be assessed. (They often surface only during times of stress or fatigue.) In those with a prolapsed mitral valve who have only a click and no audible murmur, clinical diagnosis and a five year follow-up are all that's needed. People with MVP who also have a faint systolic murmur should have an echocardiogram and, in the absence of leaflet thickening or significant valve insufficiency (leaking), should be checked every two years to see if the murmur gets louder or changes. Rarely, a prolapsed mitral valve degenerates, causing irregular heart beats and, in extreme cases, heart failure, necessitating use of medication and perhaps surgery. Beta blockers may be prescribed for those who have persistent symptoms or discomfort. If MVP is accompanied by arrhythmias (heart rhythm disturbances), a cardiologist should be consulted and other tests may be advised.
Among those with MVP who have both a click and a murmur, approximately 10 per cent have significant mitral valve regurgitation and thickened valve leaflets putting them at increased risk of bacterial endocarditis (heart infection). These people need to take preventive (prophylactic) antibiotics when they visit the dentist or have surgery. Preventive antibiotics before dental procedures and surgery are usually recommended for anyone who has a significant MVP murmur - to forestall a possible heart valve infection, although many now question its necessity or effectiveness. Since heart valves have little or no blood supply themselves, a bacterial infection can quickly take hold and damage an abnormal valve, possibly leading to a life-threatening cardiac infection. Those with MVP who have a loud murmur and regurgitation or valve thickening sufficient to put them at higher than average risk of bacterial endocarditis, should be informed about the safest antibiotic to use before going to the dentist or having surgery. They must be told which antibiotic to take and how much. Penicillin is the usual choice, but people allergic to it may use erythromycin before dental work or some forms of surgery.
In conclusion: heart murmurs are very common, most often due to a slight turbulence in the normal flow of blood through the cardiac valves. Innocent murmurs need no treatment or expensive testing procedures. More serious or pathological heart murmurs from defective heart valves need to be closely followed. Modem techniques, such as echocardiography, allow any significant heart murmurs to be watched so that medications and/or necessary corrective surgery can be accurately timed for the murmuring heart before it undergoes any irreversible damage.
The sounds of the heart's valves are:
* First heart sound - due to closing of the mitral and tricuspid valves, within the heart.
* Second heart sound - due to closure of the pulmonary and aortic valves.
* Third heart sound - due to the early filling of blood (into the right and left ventricles), which may be a normal sound in young people, but later in life may signify heart failure.
* Fourth heart sound - late ventricular filling sound, which may denote a non-compliant or "stiff" ventricle.
* Ejection click - opening of the aortic and pulmonary valves, a normal sound, often heard after the first heart sound.
Other heart sounds - not directly linked to any particular valve - may also be heard. These include the summation gallop (heard in heart failure) and the mid-systolic click (heard in those with a prolapsed or floppy mitral valve).
When is a heart murmur serious?
A heart murmur may indicate nothing more than some insignificant turbulence in cardiac blood flow, or it may signal a serious heart problem. For example, one heart valve may not open or shut properly or there could be some structural defect in the heart that's causing the murmur - perhaps a congenital defect present since birth.
Innocent heart murmurs usually stem from the systolic (pumping) phase of die heart beat, due to a slight turbulence in the ejection of blood through the aortic and pulmonary valves. They are often not associated with any disability or medical cause and show no clinical, radiographic or electrocardiographic evidence of anything other than normal blood flow through the heart. However, some systolic murmurs, due to a narrowed valve, are more serious.
By contrast, diastolic and continuous murmurs are always due to some disease and/or faulty cardiac flow. Serious, non-congenital heart murmurs are usually caused by some degenerative disease or infection, such as rheumatic fever (formerly very common, now less so) - following a streptococcal throat infection that damages the valve(s). The long-term consequences of an abnormal cardiac valve can be heart enlargement and eventual heart failure. Some damaged heart valves need to be surgically repaired or re laced.
Treatment of heart murmurs
Innocent murmurs by definition require no treatment. Most organic or pathological murmurs need preventive antibiotics before dental work or surgery. A medically threatening heart murmur may call for medications and/or heart surgery, the urgency depending upon the severity of valve or heart damage. Current medical opinion tends to favour valve repair where possible rather than replacement to spare the patient some of the problems associated with mechanical valves. But artificial valves are often needed because surgical valve repair may not be feasible. Close monitoring for life is necessary for those with valve replacement as there's still no perfect substitute for the human heart valve. Blood-thinners may have to be taken and artificial valves often develop structural flaws which necessitate repeat surgery.