thumb|300px|Front of [[thorax, showing surface relations of bones, lungs (purple), pleura (blue), and heart (red outline). The locations of best auscultation for each heart valve are labeled with "M", "T", "A", and "P".<br /><br />First heart sound: caused by atrioventricular valves – Mitral (M) and Tricuspid (T). <br /><br />Second heart sound caused by semilunar valves – Aortic (A) and Pulmonary/Pulmonic (P).]]

Heart sounds are the noises generated by the beating heart and the resultant flow of blood through it. Specifically, the sounds reflect the turbulence created when the heart valves snap shut. In cardiac auscultation, an examiner may use a stethoscope to listen for these unique and distinct sounds that provide important auditory data regarding the condition of the heart.

In healthy adults, there are two normal heart sounds, often described as a lub and a dub that occur in sequence with each heartbeat. These are the first heart sound (S<sub>1</sub>) and second heart sound (S<sub>2</sub>),

produced by the closing of the atrioventricular valves and semilunar valves, respectively. In addition to these normal sounds, a variety of other sounds may be present including heart murmurs, adventitious sounds, and gallop rhythms S<sub>3</sub> and S<sub>4</sub>.

Heart murmurs are generated by turbulent flow of blood and a murmur to be heard as turbulent flow must require pressure difference of at least 30 mm of Hg between the chambers and the pressure dominant chamber will outflow the blood to non-dominant chamber in diseased condition which leads to Left-to-right shunt or Right-to-left shunt based on the pressure dominance. Turbulence may occur inside or outside the heart; if it occurs outside the heart then the turbulence is called bruit or vascular murmur. Murmurs may be physiological (benign) or pathological (abnormal). Abnormal murmurs can be caused by stenosis restricting the opening of a heart valve, resulting in turbulence as blood flows through it. Abnormal murmurs may also occur with valvular insufficiency (regurgitation), which allows backflow of blood when the incompetent valve closes with only partial effectiveness. Different murmurs are audible in different parts of the cardiac cycle, depending on the cause of the murmur.

Primary heart sounds

thumb|250px|Diagram showing relations of opened heart to front of thoracic wall. Ant. Anterior segment of [[tricuspid valve. A O. Aorta. A.P. Anterior papillary muscle. In. Innominate artery. L.C.C. Left common carotid artery. L.S. Left subclavian artery. L.V. Left ventricle. P.A. Pulmonary artery. R.A. Right atrium. R.V. Right ventricle. V.S. Ventricular septum.]]

Normal heart sounds are associated with heart valves closing:

First heart sound

The first heart sound, or S<sub>1</sub>, forms the "lub" of "lub-dub" and is composed of components M<sub>1</sub> (mitral valve closure) and T<sub>1</sub> (tricuspid valve closure). Normally M<sub>1</sub> precedes T<sub>1</sub> slightly. It is caused by the closure of the atrioventricular valves, i.e. tricuspid and mitral (bicuspid), at the beginning of ventricular contraction, or systole. When the ventricles begin to contract, so do the papillary muscles in each ventricle. The papillary muscles are attached to the cusps or leaflets of the tricuspid and mitral valves via chordae tendineae (heart strings). When the papillary muscles contract, the chordae tendineae become tense and thereby prevent the backflow of blood into the lower pressure environment of the atria. The chordae tendineae act a bit like the strings on a parachute, and allow the leaflets of the valve to balloon up into the atria slightly, but not so much as to evert the cusp edges and allow backflow of blood. It is the pressure created from ventricular contraction that closes the valve, not the papillary muscles themselves. The contraction of the ventricle begins just prior to AV valves closing and prior to the opening of the semilunar valves. The sudden tensing of the chordae tendineae and the squeezing of the ventricles against closed semilunar valves, send blood rushing back toward the atria, and the parachute-like valves catch the rush of blood in their leaflets causing the valve to snap shut. The S1 sound results from reverberation within the blood associated with the sudden block of flow reversal by the valves. The delay of T1 even more than normally causes the split S1 which is heard in a right bundle branch block.

Second heart sound

The second heart sound, or S<sub>2</sub>, forms the "dub" of "lub-dub" and is composed of components A<sub>2</sub> (aortic valve closure) and P<sub>2</sub> (pulmonary valve closure). Normally A<sub>2</sub> precedes P<sub>2</sub> especially during inspiration where a split of S<sub>2</sub> can be heard. It is caused by the closure of the semilunar valves (the aortic valve and pulmonary valve) at the end of ventricular systole and the beginning of ventricular diastole. As the left ventricle empties, its pressure falls below the pressure in the aorta. Aortic blood flow quickly reverses back toward the left ventricle, catching the pocket-like cusps of the aortic valve, and is stopped by aortic valve closure. Similarly, as the pressure in the right ventricle falls below the pressure in the pulmonary artery, the pulmonary valve closes. The S<sub>2</sub> sound results from reverberation within the blood associated with the sudden block of flow reversal.

"lub-dub-ta" or "slosh-ing-in" If new, indicates heart failure or volume overload.

It occurs at the beginning of diastole after S2 and is lower in pitch than S1 or S2 as it is not of valvular origin. The third heart sound is benign in youth, some trained athletes, and sometimes in pregnancy but if it re-emerges later in life it may signal cardiac problems, such as a failing left ventricle as in dilated congestive heart failure (CHF). S3 is thought to be caused by the oscillation of blood back and forth between the walls of the ventricles initiated by blood rushing in from the atria. The reason the third heart sound does not occur until the middle third of diastole is probably that during the early part of diastole, the ventricles are not filled sufficiently to create enough tension for reverberation.

Murmurs can be heard in many situations in adults without major congenital heart abnormalities:

|-

| Grade 5

| Very loud, with thrill. May be heard when stethoscope is partly off the chest.

|-

| Grade 6

| Very loud, with thrill. May be heard with stethoscope entirely off the chest.

|}

Though several different cardiac conditions can cause heart murmurs, the murmurs can change markedly with the severity of the cardiac disease. An astute physician can sometimes diagnose cardiac conditions with some accuracy based largely on the murmur, related physical examination, and experience with the relative frequency of different heart conditions. However, with the advent of better quality and wider availability of echocardiography and other techniques, heart status can be recognized and quantified much more accurately than formerly possible with only a stethoscope, examination, and experience. Another advantage to the use of the echocardiogram is that the devices can be handheld.

Effects of breathing

Inhalation decreases intrathoracic pressure which allows more venous blood to return to the right heart (pulling blood into the right side of the heart via a vacuum-like effect). Therefore, right-sided heart murmurs generally increase in intensity with inhalation. The decreased (more negative) intrathoracic pressure has an opposite effect on the left side of the heart, making it harder for the blood to exit into circulation. Therefore, left-sided murmurs generally decrease in intensity during inhalation. Increasing venous blood return to the right side of the heart by raising a patient's legs to a 45-degree while lying supine produces similar effect which occurs during inhalation. Inhalation can also produce a non-pathological split S2 which will be heard upon auscultation.

With exhalation, the opposite haemodynamic changes occur: left-sided murmurs generally increase in intensity with exhalation.

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A mnemonic to remember these are:<br />MALE - Mitral and Aortic valves are Left sided and loudest in Expiration.<br />TRIP - Triscuspid is Right sided and loudest in Inspiration, also Pulmonary.-->

Interventions that change murmurs

There are a number of interventions that can be performed that alter the intensity and characteristics of abnormal heart sounds. These interventions can differentiate the different heart sounds to more effectively obtain a diagnosis of the cardiac anomaly that causes the heart sound.

Other abnormal sounds

Clicks – Heart clicks are short, high-pitched sounds that can be appreciated with modern non-invasive imaging techniques.

Rubs – The pericardial friction rub can be heard in pericarditis, an inflammation of the pericardium, the sac surrounding the heart. This is a characteristic scratching, creaking, high-pitched sound emanating from the rubbing of both layers of inflamed pericardium. It is the loudest in systole, but can often be heard at the beginning and at the end of diastole. It is very dependent on body position and breathing, and changes from hour to hour.

Surface anatomy

The aortic area, pulmonic area, tricuspid area and mitral area are areas on the surface of the chest where the heart is auscultated.

Heart sounds result from reverberation within the blood associated with the sudden block of flow reversal by the valves closing. Because of this, auscultation to determine function of a valve is usually not performed at the position of the valve, but at the position to where the sound waves reverberate.

{| class="wikitable"

|-

| Aortic valve (to aorta) || right second intercostal space || upper right sternal border

|-

| Pulmonary valve (to pulmonary trunk) || left second intercostal space || upper left sternal border

|-

| Erb's point || Left third intercostal space || left sternal border

|-

| Tricuspid valve (to right ventricle) || left fourth, fifth intercostal spaces || lower left sternal border

|-

| Mitral valve (to left ventricle) || left fifth intercostal space || left midclavicular line

|}

Recording heart sounds

Using electronic stethoscopes, it is possible to record heart sounds via direct output to an external recording device, such as a laptop or MP3 recorder. The same connection can be used to listen to the previously recorded auscultation through the stethoscope headphones, allowing for a more detailed study of murmurs and other heart sounds, for general research as well as evaluation of a particular patient's condition.

See also

  • Pulse
  • Precordial examination
  • Benign pediatric heart murmur
  • Iambic pentameter, a metre in poetry that follows a similar rhythm to the human heartbeat
  • Pulsatile tinnitus – hearing a heartbeat sound in one or both ears
  • Souffle (heart sound)

References

  • Heart Sounds – Heart Murmurs. practicalclinicalskills.com