Heart sounds

The heart sounds are the noises (sound) generated by the beating heart and the resultant flow of blood through it. This is also called a heartbeat. In cardiac auscultation, an examiner uses a stethoscope to listen for these sounds, which provide important information about the condition of the heart.

In healthy adults, there are two normal heart sounds often described as a lub and a dub (or dup), that occur in sequence with each heart beat. These are the first heart sound (S₁) and second heart sound (S₂), produced by the closure of the AV valves and semilunar valves respectively. In addition to these normal sounds, a variety of other sounds may be present including heart murmurs and adventitious sounds, or clicks.

Heart murmurs are generated by turbulent flow of blood, which may occur inside or outside the heart. Murmurs may be physiological (benign) or pathological (abnormal). Abnormal murmurs can be caused by stenosis restricting the opening of a heart valve, causing turbulence as blood flows through it. Valve insufficiency (or regurgitation) allows backflow of blood when the incompetent valve is supposed to be closed. Different murmurs are audible in different parts of the cardiac cycle, depending on the cause of the murmur.

Normal heart sounds

First heart tone S₁, the "lubb"

The first heart tone, or S₁, is caused by the sudden block of reverse blood flow due to closure of the atrioventricular valves, mitral and tricuspid, at the beginning of ventricular contraction, or systole. When the pressure in the ventricles rises above the pressure in the atria, venous blood flow entering the ventricles is pushed back toward the atria, catching the valve leaflets, closing the inlet valves and preventing regurgitation of blood from the ventricles back into the atria. The S₁ sound results from reverberation within the blood associated with the sudden block of flow reversal by the valves.

Second heart tone S₂ (components A₂ and P₂), the "dub"

The second heart tone, or S₂, is caused by the sudden block of reversing blood flow due to closure of the aortic valve and pulmonic valve at the end of ventricular systole, i.e 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 aortic valve leaflets and is stopped by aortic (outlet) valve closure. Similarly, as the pressure in the right ventricle falls below the pressure in the pulmonary artery, the pulmonic (outlet) valve closes. The S₂ sound results from reverberation within the blood associated with the sudden block of flow reversal.

Splitting of the second heart sound

During inspiration, negative intrathoracic pressure causes increased blood return into the right side of the heart, yet some slowing of emptying from the left side. The increased blood volume in the right ventricle causes the pulmonic valve to stay open longer during ventricular systole. This causes an increased delay in the P₂ component of S₂ relative to the A₂ component. During expiration, the positive intrathoracic pressure causes decreased blood return to the right side of the heart. The reduced volume in the right ventricle allows the pulmonic valve to close earlier at the end of ventricular systole, causing P₂ to occur earlier, and "closer" to A₂. It is physiological to hear a "splitting" of the second heart tone in younger people, during inspiration and in the "pulmonic area", i.e. the 2nd ICS (intercostal space) at the left edge of the sternum. During expiration, the interval between the two components normally shortens and the S2 sounds becomes merged.

Extra heart sounds

The rarer extra heart sounds are heard in both normal and abnormal situations.

Third heart sound S₃

Rarely, there may be a third heart sound S3. The third heart sound or protodiastolic sound is not of valvular origin, as it occurs at the beginning of diastole just after S2. This sound occurs when the left ventricle is not very compliant, and at the beginning of diastole the rush of blood into the left ventricle causes vibration of the valve leaflets and the chordae tendinae.

The third heart sound is normal in children and young adults, but disappears before middle age. Abnormal reemergence of this sound late in life indicates a pathological state, often a sign of a failing left ventricle as in congestive heart failure. This sound is called a protodiastolic gallop, a type of gallop rhythm.

Fourth heart sound S₄

The rare fourth heart sound S4 is sometimes audible in healthy children, but when audible in an adult is called a presystolic gallop. This gallop is a sign of a pathologic state, usually a failing left ventricle. This sound occurs just after atrial contraction. The combined presence of S3 and S4 is a quadruple gallop. At rapid heart rates, S3 and S4 may merge to produce a summation gallop.

Abnormal sounds

Aortic area, pulmonic area, tricuspid area and mitral area are the area where we auscultate the heart. Heart murmurs are produced as a result of turbulent flow of blood, turbulence sufficient to produce audible noise. They usually are heard as a whooshing sound. The term murmur only refers to a sound believed to originating within blood flow though or near the heart; rapid blood velocity is necessary to produce a murmur. Though unreliable, soft murmurs are less likely to reflect a serious, if any, health problem; loud murmurs essentially always reflect a problem. Yet most heart problems do not produce any murmur.

• Regurgitation through the mitral valve is by far the most commonly heard murmur, sometimes fairly loud to a practiced ear, even though the volume of blood flow may be quite small. Yet, though often obvious, probably about 20% of cases of mitral regurgitation, though obvious using echocardiography, do not produce an audible murmur.

• Stenosis of the aortic valve typically produces a systolic ejection murmur. This is more common in older adults or in those individuals having a two, not a three leaflet aortic valve.

• Regurgitation through the aortic valve, if marked, is sometimes audible to a practiced ear with a high quality, especially amplified stethoscope.

• Regurgitation through the tricuspid or pulmonic valves essentially never produces audible murmurs.

• Other audible murmurs are associated with abnormal openings between the left ventricle and right heart or from the aortic or pulmonary arteries back into a lower pressure heart chamber.

As noted, several different cardiac conditions can cause heart murmurs. However, the murmurs produced often change in complex ways 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.

Clicks: With the advent of newer, non-invasive imaging techniques, the origin of other, so-called adventitial sounds or "clicks" has been appreciated. These are short, high-pitched sounds.

• The atrioventricular valves of patients with mitral stenosis may open with an opening snap on the beginning of diastole.

• Patients with mitral valve prolapse may have a mid-systolic click along with a murmur.

• Aortic and pulmonary stenosis may cause an ejection click immediately after S₁.

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

There are a number of interventions that can be performed that alter the intensity and characteristics of abnormal heart sounds. These interventions can be performed to differentiate the different heart sounds and obtain a diagnosis of the cardiac anomaly that causes the heart sound. (See Heart murmur#Interventions that change murmur sounds.)

Inhalation pressure also causes an increase in the venous blood return to the right side of the heart. Therefore, right-sided murmurs generally increase in intensity with inspiration. The increased volume of blood entering the right sided chambers of the heart restricts the amount of blood entering the left sided chambers of the heart. This causes left-sided murmurs to generally decrease in intensity during inspiration.

With expiration, the opposite hemodynamic changes occur. This means that left-sided murmurs generally increase in intensity with expiration. Having the patient lie supine and raising their legs up to a 45 degree angle facilitates an increase in venous return to the right side of the heart producing effects similar to inhalation-increased blood flow.

Surface anatomy

The opening and closing of the valves is usually much less loud than the sound of the blood rushing through the valve and "colliding" with the subsequent barrier. Because of this, auscultation to determine function of a valve is usually not performed at the position of the valve, but at a downstream position where the listener can best hear the blood colliding after the valve is closed.

• Pulmonic valve (to pulmonary trunk): second intercostal space (left)
• Aortic valve (to aorta): First intercostal space (right)
• Mitral valve (to left ventricle): fifth intercostal space (left)
• Tricuspid valve (to right ventricle): fourth intercostal space (left)

Recording heart sounds

With the advent of electronic stethoscopes, it is now possible to conveniently record heart sounds. One electronic stethoscope manufactured by Thinklabs provides a port to output stethoscope sounds to an external recording device, such as a laptop or MP3 recorder. The same connection can then be used to listen to the recordings through the stethoscope headphones, allowing for faithful reproduction of low-frequency murmurs and other heart sounds.

See also

• Physical examination
• Precordial examination
• Anatomy
  • Heart
  • Heart valve
    • Aortic valve
    • Pulmonic valve
    • Mitral valve
    • Tricuspid valve
• Pathophysiology
  • Mitral stenosis
  • Mitral regurgitation
  • Aortic stenosis
  • Aortic insufficiency
  • Pulmonic stenosis
  • Pulmonic insufficiency
  • Tricuspid stenosis
  • Tricuspid insufficiency
• Heart murmur
• Benign paediatric heart murmur

End Notes

1. ^  "The Cardiovascular System." Bates, B. A Guide to Physical Examination and History Taking. 9h Ed. 2005.

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