Читать книгу Predicting Heart Failure - Группа авторов - Страница 70

Discrete bursts of auditory vibrations that differ in intensity (volume), frequency, quality, and duration are known as heart sounds, the sounds for a normal heartbeat being first heart sound (called lub) and second heart sound (called dub). The first heart sound consists of multiple high-frequency elements where only the first two among them can be heard normally. These two normally audible sound waves occur simultaneously when the mitral and tricuspid valves close. The first heart sound indicates the beginning of ventricular systole and the end of mechanical diastole. The second heart sound is described as a discrete burst of vibration that occurred due to the immediate closure of the aortic valve and pulmonic valve. The second heart sound consists of two components – the aortic component and the pulmonic component – with the aortic valve and pulmonic valve being the sources of the second heart sound. The second heart sound is produced at the end of ventricular contraction and it indicates the beginning of ventricular diastole and the end of mechanical systole.

Apart from the normal first and second heart sounds, unusual third and fourth heart sounds are found in healthy as well as unhealthy individuals. The third heart sound, or ventricular gallop, is an additional unusual sound produced after the first and second heart sound. It is generated when a large amount of blood strikes the left ventricle and happens when the mitral valves open after the second heart sound, allowing passive blood flow to the left ventricle. The fourth heart sound, or atrial gallop, is a low-pitched sound that occurs before the first heart sound as the ventricle fills late in its diastole due to atrial contraction. The fourth heart sound results from vibrations produced within the ventricle, and it is also known as the atrial sound because its development requires an effective atrial contraction.

Generally, the cardiologist examines the heart sound by cardiac auscultation technique using a stethoscope. The unusual pattern of heart sound can indicate a serious underlying heart condition. The first and second heart sound are common, while the third and fourth are unusual in healthy individuals. However, while the third heart sounds can be audible in healthy individuals below 40 years of age [14] and pregnant women [15], in people younger than 40 they are considered abnormal and a possible early indication of heart diseases including heart failure. The fourth heart sound is very rare in healthy individuals, but common in patients with heart diseases.

Heart murmurs are the type of abnormal sound generated in the heart as a result of the turbulent flow of blood. These murmurs are generated either by blood flow through an abnormal valve or by abnormalities in the internal chamber of the heart. In most cases, the murmurs are not serious and do not require quick medication or a hospital visit. However, in a few cases, the abnormal murmurs are due to heart valve problems present at birth, or caused by cardiac shunts or septal defects.