Tyler Wynn
The human heart produces a variety of sounds, including heartbeats, murmurs, adventitious sounds, and gallop rhythms. Heart sounds are created by the flow of blood through the heart chambers as the cardiac valves open and close during the cardiac cycle. Vibrations from the blood flow create audible sounds, with the turbulence of blood flow being a key factor in the number of vibrations produced. The main normal heart sounds are the first and second heart sounds, often described as lub and dub, and abbreviated as S1 and S2. These sounds are produced by the closing of the atrioventricular valves and semilunar valves, respectively. In addition, there are other heart sounds, such as S3 and S4, that can be present in certain situations and hold no pathologic consequence.
| Characteristics | Values |
|---|---|
| Number of normal heart sounds | 2 |
| First heart sound | S1 |
| Second heart sound | S2 |
| Third heart sound | S3 |
| Fourth heart sound | S4 |
| Cause of heart sounds | Closure of cardiac valves, blood flow through the heart chambers, and tensing of the chordae tendineae |
| Audible sounds | Lub and dub |
| Audible in | Systole, diastole, or continuously through the cardiac cycle |
| Evaluation tool | Stethoscope |
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What You'll Learn
The first heart sound (S1)
Heart sounds are created by blood flowing through the chambers of the heart as the cardiac valves open and close during the cardiac cycle. Vibrations from the blood flow create audible sounds, and the more turbulent the blood flow, the more vibrations are created. The first heart sound (S1) is one of the two common heart sounds, the other being the second heart sound (S2). S1 is often described as "lub" in the "lub-dub" sequence of heart sounds.
The S1 sound is produced by vibrations generated by the closure of the mitral (M1) and tricuspid (T1) valves. It corresponds to the end of diastole and the beginning of ventricular systole, preceding the upstroke of carotid pulsation. Normally, M1 precedes T1 slightly. The sound is caused by the closure of the atrioventricular valves at the beginning of ventricular contraction or systole.
The S1 heart sound is composed of several high-frequency components, with only the first two being normally audible. The intensity of the sound depends on various factors, including the integrity and pliability of valvular cusps, the length of the PR interval, the strength of ventricular contraction, and the presence or absence of valvular stenosis or regurgitation. The position of the valve leaflets at end-diastole and the amount of tissue between the heart and the stethoscope can also affect the intensity of S1.
The S1 sound is typically a high-pitched sound that is best heard with the diaphragm of a stethoscope. It is audible in each of the four classic listening areas, and its intensity and quality may differ in each of these auscultatory areas. S1 is usually louder at the apex than the second sound, but at the base, both components of the second sound are normally louder than the first.
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The second heart sound (S2)
The interval between A2 and P2 normally increases during inhalation and almost disappears during exhalation. This is known as the splitting of S2 or physiological split, which is influenced by changes in intrathoracic pressure. During inhalation, the decrease in intrathoracic pressure prolongs the time required for pulmonary pressure to exceed right ventricular pressure, resulting in a wider split. In contrast, during exhalation, the intrathoracic pressure increases, causing the split to become narrower or almost disappear.
The clinical assessment of S2 is typically performed with the patient lying comfortably in the supine position and breathing normally. The examiner notes respiratory variations during quiet breathing and exaggerated breathing, with slow, regular respirations being ideal for auscultation. The patient's age is also a factor, as the likelihood of hearing a single S2 during both respiratory phases increases with age.
The subtle changes in the second heart sound can provide valuable clues about the heart's function and potential abnormalities. For example, pulmonary hypertension, severe aortic stenosis, atrial septal defect, and delays in electrical conduction can be suspected or diagnosed by paying close attention to S2.
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Heart murmurs
Murmurs can be categorised as innocent or physiological, which are benign and harmless, or pathological, which are abnormal and may indicate an underlying heart condition. Innocent murmurs are common in newborns and children and are often a normal part of development. They do not cause any symptoms or problems and usually disappear without treatment as the child grows older. However, in some cases, they may persist into adulthood without causing any health issues. Factors that can influence innocent murmurs include changes in blood flow, such as an increased heart rate during excitement or fear.
Abnormal murmurs, on the other hand, may indicate an abnormality in the heart. They are often caused by problems with the heart valves, such as aortic or mitral valve regurgitation, aortic stenosis, or mitral stenosis. Abnormal murmurs can also be caused by valvular insufficiency, which allows backflow of blood when the valve does not close completely. Additionally, certain congenital defects, such as holes in the heart or cardiac shunts, can lead to irregular blood flow and abnormal murmurs. Other conditions associated with abnormal murmurs include rheumatic heart disease, pregnancy, fever, anemia, and thyrotoxicosis.
The presence of heart murmurs can be detected using a stethoscope, which is a valuable tool for evaluating heart sounds. Murmurs are graded based on their loudness, with Grade I being barely audible and Grade 4 or higher being strong enough to be felt with the palm over the heart, which is known as a "thrill". While most heart murmurs are not serious, it is important to consult a healthcare provider for an evaluation and any necessary follow-up care.
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Systolic murmurs
Heart sounds are produced by blood flowing through the chambers of the heart as the cardiac valves open and close during the cardiac cycle. Vibrations from the blood flow create audible sounds, and the more turbulent the blood flow, the more vibrations are created.
Heart murmurs are a type of heart sound that can be either physiological (benign) or pathological (abnormal). Systolic murmurs are a type of heart murmur that occurs when the heart muscle contracts at the beginning of or during a heartbeat. They are typically soft, blowing sounds that are audible at the left lower sternal border. Systolic murmurs can be further categorized into early systolic, midsystolic, late systolic, or holosystolic.
Early systolic murmurs begin with the first heart sound and extend to the middle or late systole. They are usually associated with ventricular outflow tract obstruction or an abnormal amount of blood flow across normal valves. Muscular ventricular septal defects (VSD) can cause early systolic murmurs, as the septal defect closes during systole, limiting the murmur to the early part.
Midsystolic murmurs, also known as systolic ejection murmurs, include aortic stenosis, pulmonic stenosis, hypertrophic obstructive cardiomyopathy, and atrial septal defects. They begin just after the first heart sound (S1) and terminate just before the second heart sound (S2), so both S1 and S2 remain audible. The murmur of aortic stenosis is high-pitched and crescendo-decrescendo ("diamond-shaped"), located at the aortic listening post and radiating toward the neck.
Late systolic murmurs begin during the last half of systole and may or may not extend to the second heart sound.
Holosystolic murmurs, also known as pansystolic, include mitral regurgitation, tricuspid reguration, and ventricular septal defects. These murmurs have high intensity immediately after the onset of S1 and extend to just before S2, often overwhelming the S1 and S2 sounds and making them difficult to hear. The murmur of mitral regurgitation is described as a high-pitched, "blowing" sound best heard at the apex of the heart.
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Diastolic murmurs
The four most common types of diastolic murmurs are aortic valve regurgitation, pulmonary valve regurgitation, mitral valve rumbles, and tricuspid valve rumbles. The murmur of aortic regurgitation is a soft, high-pitched, early diastolic decrescendo murmur usually heard best at the third intercostal space on the left (Erb's point) at the end of expiration while the patient is sitting up and leaning forward. The murmur of pulmonary valve regurgitation is similar to that of aortic regurgitation, and differentiation may be difficult. It is an early diastolic, decrescendo murmur beginning with the pulmonary component of the second sound, best heard along the upper left sternal border. The murmur of mitral stenosis is a uniquely shaped, low-pitched diastolic murmur best heard at the cardiac apex. It is heard as a low-pitched diastolic rumble usually preceded by an opening snap, which is an extra sound heard soon after S2. Tricuspid stenosis is the rarest cause of a diastolic murmur.
Certain auscultatory techniques are essential for detecting diastolic murmurs, as they are usually more difficult to hear compared to systolic murmurs. The patient should be instructed not to breathe at the end of expiration, or told to take a deep breath, blow it all out, and then relax without breathing. The murmur may only be heard in certain areas with the patient sitting and leaning forward in relaxed expiratory apnea. Any bedside manoeuvre that transiently increases blood pressure may intensify or bring out the murmur. Proper timing of the cardiac cycle is essential.
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Frequently asked questions
Heart sounds are the discrete, short audible events produced from blood flowing through the heart chambers as the cardiac valves open and close during the cardiac cycle.
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 (S1) and second heart sound (S2).
The S1 sound is produced by the closing of the mitral and tricuspid valves at the beginning of ventricular contraction. The sound produced by the closure of the mitral valve is termed M1, and the sound produced by the closure of the tricuspid valve is termed T1.
The S2 sound is produced by the closing of the aortic and pulmonic valves at the beginning of ventricular relaxation. The sound produced by the closure of the aortic valve is termed A2, and the sound produced by the closure of the pulmonic valve is termed P2.
Additional heart sounds include S3 and S4, which are gallop rhythms that can occur in both normal and abnormal situations. Murmurs are also common additional sounds that can be physiological (benign) or pathological (abnormal).
