Heart sounds

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The heart sounds are the noises (sound) generated by the beating heart and the resultant flow of blood through it. In cardiac auscultation, an examiner uses a stethoscope to listen for these sounds, which include heart tones, or sounds, produced by heart valves closing, heart murmurs, and adventititious sounds, or clicks.

Heart sounds are usually divided into the normal heart sounds and the pathological sounds which indicate disease. The two distinct normal heart tones are often described as a lub and a dub (or dup), and occur in sequence with each heart beat. Murmurs are generated by turbulent flow of blood within the heart. Stenosis, or impaired opening of a heart valve, causes turbulence as blood flows through it. Valve insufficiency, or regurgitation, allows backflow of blood when the valve is supposed to be closed. In these situations, murmurs will be heard in the corresponding part of each cardiac cycle.


The normal heart sounds

The first heart tone, or S1, is caused by the 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, these valves close to prevent regurgitation of blood from the ventricles into the atria.

The second heart tone, or S2, is caused by the closure of the aortic and pulmonic valves at the end of ventricular systole. As the left ventricle empties, its pressure falls below the pressure in the aorta, and the aortic valve closes. Similarly, as the pressure in the right ventricle falls below the pressure in the pulmonary artery, the pulmonic valve closes.

Due to the higher pressure in the aorta compared to the pulmonary artery, the aortic valve normally closes before the pulmonic valve, so the second heart tone may have an audible split. A split S2 is made up of an A2 and a P2 components, caused by the closure of the aortic and pulmonic valves, respectively.

The splitting of the second heart tone varies with the phases of respiration. During inspiration, negative intrathoracic pressure causes increased blood return into the right side of the heart. 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. 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 the splitting of the second heart tone by younger people and during inspiration. During expiration normally the interval between the two components shortens and the tone becomes merged.

Abnormal heart sounds

Sounds other than S1 and S2 are usually abnormal, although sometimes flow may be heard through the a normal aortic valve, due to increased cardiac output. This flow murmur is a normal variant, commonly heard in children and pregnant females.

S3 gallop

A third heart tone, known as an S3 or an S3 gallop, or ventricular gallop, occurs during ventricular filling. It is commonly heard at the apex of the heart in athletes and young individuals, and may be heard in the third trimester of pregnancy. S3 is believed to be produced by rapid vibration of the left ventricle due to brisk filling with blood from the left atrium. If an S3 is heard in the elderly, it is considered an abnormal, and suggests volume overload, congestive heart failure, or loss of the normal ventricular flexibility.

S4 gallop

A fourth heart tone, known as an S4 gallop, or atrial gallop, is due to resistance to atrial filling following atrial contraction, and is heard just before S1. An S4 is usually considered an abnormal heart sound. However, a low-volume, or grade 1, S4 gallop can be considered a normal finding in trained athletes and patients younger than 40 years of age. In disease, it occurs in the enlarged heart of hypertrophied ventricle, when atrial kick causes a diastolic vibration. Since S4 is due to atrial activity, it cannot be heard during atrial fibrillation. Other causes of this left-sided S4 include hypertensive heart disease, coronary artery disease, aortic stenosis, and cardiomyopathy. The less common right-sided S4 often gets louder with inspiration. Causes of right-sided S4 include pulmonary hypertension and pulmonic disease. An S4 may also be associated with delayed conduction between atria and ventricles separating the normally faint atrial tone from the louder S1 and making it audible.

Abnormalies of S2

In individuals with an atrial septal defect (ASD), the extra blood return during inspiration gets equalized between the left and right atrium due to the communication that exists between them. This eliminates the respiratory changes in S2, producing the fixed splitting of S2 which is pathognemonic of ASD. A wide, fixed, split of S2 may be caused also by an acute pulmonary hypertension, or pulmonic stenosis.

When P2 component occurs before A2 component, this may be caused by right ventricular pacemaker or ectopic beats, severe aortic valve disease, or patent ductus arteriosus may abnormally delay A2, causing it to precede P2. In these cases, the inspiratory delay of P2 will cause it then to strengthen during or after A2. This reversal of the normal phasic splitting is called paradoxical splitting of S2.

S2 may be normally timed but of abnormal volume. In hypertension, the aortic valve closes more loudly resulting in a loud A2, while in a less common condition, pulmonary hypertension, the intensity of P2 is increased.

Heart murmurs

Murmurs are produced by any condition which produces noisy, or turbulent, flow of blood. This most commonly results from narrowing or leaking of valves or the presence of abnormal passages through which blood flows in or near the heart. Without their cause being known, murmurs can still be designated according to the part of the cardiac cycle in which they are heard, as systolic or diastolic. More accurately we can divide phases of the cardiac cycle into three parts: proto-, meso- and tele- systole or diastole. For telediastole we usually use the term presystole. Murmurs are also classified by their shape (crescendo, decrescendo, crescendo-decrescendo), loudness and frequency range (high-pitched, low-pitched), point of maximum volume on the chest wall and spreading in different directions (how does the murmur loudness change in different directions).

So-called accidental or innocent murmurs are commonly heard in children as their hearts gradually attain adult form, or in athletes or pregnant women due to increased cardiac output passing through normal-sized valves. These murmurs are never diastolic. Their loudness depends on the body position and breathing.

At other times flow murmurs occur when cardiac output increases, as in febrile illnesses or hyperthyroidism, without cardiac disease.

Other abnormal sounds

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, while 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. Patients with pericarditis, an inflammation of the sac surrounding the heart (pericardium), may have an audible pericardial friction rub. This is a characteristic stracthing, 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.

Cardiac conditions and related heart sounds

Many cardiac conditions can cause heart murmurs. However, the murmurs produced often change with the severity of the cardiac disease. Often, the astute physician can diagnose a cardiac condition solely on the murmur and related physical examination. Clinically more important and also more frequent are heart sounds

Aortic insufficiency

Aortic insufficiency is the abnormal leaking of blood from the aorta to the left ventricle. The murmur of acute aortic insufficiency (often due to aortic dissection or endocarditis) may be very soft or even absent. The murmur of chronic aortic insufficiency has the following characteristics:

  • Systolic ejection click
  • Ejection murmur
  • S3 present
  • Holodiastolic decrescendo murmur (If radiation to the right parasternal region, consider ascending aortic aneurysm)
  • Austin flint murmur (an apical diastolic rumble due to mitral regurgitation)

Interventions that alter heart sounds

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.

Respiratory changes

Inspiration causes a decrease in intrathoracic pressure, allowing air to enter the lungs. This decrease in intrathoracic 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 during expiration and right sided murmurs generally decrease in intensity during expiration.

Recording Heart Sounds

With the advent of electronic stethoscopes, it is now possible to conveniently record heart sounds. Thinklabs electronic stethoscope provides a port to output stethoscope sounds to an external recording device, such as a notebook computer 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.

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