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Heart murmur)
The heart sounds are the noises a physician listens to using a stethoscope over the heart. They are the sounds of the heart valves closing.
These sounds are not the same as the pulse, or the artery turbulence noises listened to when taking blood pressure.
There are normally two distinct heart sounds, often described as a lub and a dub (although the words used to describe them vary regionally).
Auscultation, the process of listening to the heart sounds, is part of the general physical exam. Auscultation is used to identify problems with the valves of the heart. Stenosis (Impaired opening of a heart valve) will cause turbulence as blood flows through the valve. The turbulance due to a stenotic valve will cause a murmur while blood flows through the valve. Insufficiency or regurgitation is the leaking of blood through the valve when the valve is supposed to be closed. Regurgitant murmurs will be heard when the valve is supposed to be closed.
The normal heart sounds
The first heart sound, known as S1, is caused by the closure of the mitral and tricuspid (the atrioventricular) valves at the beginning of ventricular systole. At the beginning of ventricular systole, the pressure in the left and right ventricles rise above the pressure in the left and right atrium, respectively, closing the mitral and tricuspid valves. It is the closure of these valves that prevents regurgitation of blood from the ventricles to the atria.
The second heart sound, known as S2, is cause by the closure of the aortic and pulmonic valves at the end of ventricular systole. As the pressure in the left ventricle falls, it will drop below the pressure in the aorta, and the aortic valve will close. Similarly, as the pressure in the right ventricle falls below the pressure in the pulmonary artery, the pulmonic valve will close.
Due to the higher pressure in the aorta compared to the pulmonary artery, the aortic valve tends to close before the pulmonic valve, so the second heart sound may have an audible split. A split S2 is made up of an A2 and a P2 components, signifying the closure of the aortic and pulmonic valves, respectively. Under normal conditions, A2 always occurs before P2.
In normal individuals, there is respiratory variations in the splitting of the second heart sound (S2). During inspiration, the 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 a normal 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.
Abnormal heart sounds
Most sounds of the heart other than S1 and S2 are abnormal heart sounds. Sometimes it is possible to hear flow through the 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 sound, known as an S3 or an S3 gallop, is due to 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. The sound is believed to be due to 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's considered an abnormal finding, suggesting volume overload of the left ventricle. In the elderly, an S3 (when present) is considered diagnostic of congestive heart failure.
S4 gallop
An S4 gallop is a fourth heart sound 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 grade 1 S4 gallop can be considered a normal finding in trained athletes and after 40 years of age. Otherwise, it occurs in a hypertrophied ventricle, when atrial kick causes a diastolic vibration. Since S4 is due to atrial kick, it cannot be heard during atrial fibrillation. Causes of a 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. This delay separates the normally faint atrial sound from the louder S1 and makes it audible.
Fixed splitting of S2
In individuals with an atrial septal defect (ASD), there is a fixed splitting of S2. This is pathognemonic of ASD, as no other cardiac defect causes a fixed splitting of S2. The reason why there is a fixed splitting of the second heart sound is that the extra blood return during inspiration gets equalized between the left and right atrium due to the communication that exists between the atria in individuals with ASD.
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.
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.
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