Heart sound Definition.
Heart sounds are the sounds produced by mechanical activities of heart during each cardiac cycle. Heart sounds are produced by:
1. Flow of blood through cardiac chambers.
2. Contraction of cardiac muscle.
3. Closure of valves of the heart.
Heart sounds are heard by placing the ear over the chest or by using a stethoscope or microphone. These sounds are also recorded graphically.
Different Form of Heart Sounds.
Four heart sounds are produced during each cardiac cycle:
1. First heart sound.
2. Second heart sound.
3. Third heart sound.
4. Fourth heart sound.
First and second heart sounds are called classical heart sounds and are heard by using the stethoscope. These two sounds are more prominent and resemble the spoken words ‘LUB, (or LUBB) and ‘DUBB’ (or DUP), respectively. Third heart sound is a mild sound and it is not heard by using stethoscope in normal conditions.
But it can be heard by using a microphone. Fourth heart sound is an inaudible sound. It becomes audible in pathological conditions only. This sound is studied only by graphic registration, i.e. the phonocardiogram.
Importance of Heart Sounds.
Study of heart sounds has important diagnostic value in clinical practice because alteration in the heart sounds indicates cardiac diseases involving valves of the heart.
Classification of different form of heart sounds
| Features | First heart sound | Second heart sound | Third heart sound | Fourth heart sound |
| Occurs during | Isometric contraction period and part of ejection period . | Protodiastole and part of isometric relaxation. | Rapid filling phase. | Atrial systole. |
| Characteristics. | Long, soft and low pitched Resembles the word ‘LUBB’. | Short, sharp and high pitched Resembles the word ‘DUP’. | Low pitched. | Inaudible sound. |
| Cause . | Closure of atrioventricular valves. | Closure of semilunar valves. | Rushing of blood into ventricle. | Contraction of atrial musculature. |
| Duration (sec) . | 0.10 to 0.17 . | 0.10 to 0.14. | 0.07 to 0.10 . | 0.02 to 0.04. |
| Frequency (cycles per sec) | 25 to 45. | 50. | 1 to 6. | 1 to 4. |
| Relation with ECG | Coincides with peak of ‘R’ wave. | Precedes or appears 0.09 second after peak of ‘T’ wave. | Between ‘T’ wave and ‘P’ wave. | Between ‘P’ wave and ‘Q’ wave. |
| Number of vibrations in phonocardiogram. | 9 to 13. | 4 to 6. | 1 to 4. | 1 to 2 |
Elaboration of heart Sounds.
First heart Sound.
First heart sound is produced during isometric contraction period and earlier part of ejection period .
Causes of First heart sound.
Major cause for first heart sound is the sudden and synchronous (simultaneous) closure of atrioventricular valves. However, some other factors are also involved. Four types of factors are responsible for the production of the first heart sound.
1. Valvular factor.
Synchronous closure of atrioventricular valves set up the vibrations in the valvular leaflets and chordae tendineae. These vibrations are mainly responsible for the production of the first heart sound.
2. Vascular factor.
Rush of blood from the ventricles into aorta and pulmonary artery during ejection period is also responsible for the production of the first heart sound.
3. Muscular factor.
Myocardial tension and the contraction of ventricular muscle during isometric contraction and the ejection periods also add to the production of the first heart sound.
4. Atrial factor.
Vibrations produced by the atrial systole also play a role in the production of the first heart sound.
Characteristics of first heart Sound.
First heart sound is a long, soft and low-pitched sound. It resembles the spoken word ‘LUBB’. The duration of this sound is 0.10 to 0.17 second. Its frequency is 25 to 45 cycles/second.
First Heart Sound and ECG .
First heart sound coincides with peak of ‘R’ wave in ECG.
Second Heart Sound.
Second heart sound is produced at the end of protodiastolic period.
Cause of second heart Sound.
Second heart sound is produced due to the sudden and synchronous closure of the semilunar valves.
Characteristics of second heart sound.
Second heart sound is a short, sharp and high-pitched sound. It resembles the spoken word ‘DUBB’ (or DUP). Duration of second heart sound is 0.10 to 0.14 second. Its frequency is 50 cycles/second.
Second Heart Sound and ECG .
Second heart sound coincides with the ‘T’ wave in ECG. Sometimes, it may precede the ‘T’ wave or it may commence after the peak of ‘T’ wave.
Third heart Sound .
Third heart sound is a low-pitched sound that is produced during rapid filling period of the cardiac cycle. It is also called ventricular gallop or protodiastolic gallop, as it is produced during earlier part of diastole. Usually, the third heart sound is inaudible by stethoscope and it can be heard only by using microphone.
Causes of Third heart sound.
Third heart sound is produced by the rushing of blood into ventricles and vibrations set up in the ventricular wall during rapid filling phase. It may also be due to vibrations set up in chordae tendineae.
Characteristics of Third Heart Sound .
Third heart sound is a short and low-pitched sound. Duration of this sound is 0.07 to 0.10 second. Its frequency is 1 to 6 cycles/second.
Conditions when Third Heart Sound becomes Audible by Stethoscope.
Third heart sound can be heard by stethoscope in children and athletes. Pathological conditions when third heart sound becomes loud and audible by stethoscope are aortic regurgitation, cardiac failure and cardiomyopathy with dilated ventricles.
When third heart sound is heard by stethoscope, the condition is called triple heart sound . Third heart sound is usually heard best with the bell of stethoscope placed at the apex beat area, when the patient is in left lateral decubitus (lying on left side) position.
Third Heart Sound and ECG.
Third heart sound appears between ‘T’ and ‘P’ waves of ECG.
Fourth heart Sound.
Normally, the fourth heart sound is an inaudible sound. It becomes audible only in pathological conditions. It is studied only by graphical recording, i.e. by phonocardiography. This sound is produced during atrial systole (late diastole) and it is considered as the physiologic atrial sound. It is also called atrial gallop or presystolic gallop.
Causes of Fourth heart Sound.
Fourth heart sound is produced by contraction of atrial musculature and vibrations are set up in atrial musculature, flaps of the atrioventricular valves during systole. It is also due to the vibrations set up in the ventricular myocardium because of ventricular
distention during atrial systole.
Characteristics of Fourth heart Sound.
Fourth heart sound is a short and low-pitched sound. Duration of this sound is 0.02 to 0.04 second. Its frequency is 1 to 4 cycles/second.
Conditions when Fourth Heart Sound becomes Audible.
Fourth heart sound becomes audible by stethoscope when the ventricles become stiff. Ventricular stiffness occurs in conditions like ventricular hypertrophy, long standing hypertension and aortic stenosis. To overcome the ventricular stiffness, the atria contract forcefully,
producing audible fourth heart sound.
When fourth heart sound is heard by stethoscope, the condition is called triple heart sound . It is usually heard best with the bell of stethoscope placed at the apex beat area, when the patient is in supine or left semi-lateral position.
Fourth Heart Sound and ECG.
Fourth heart sound coincides with the interval between the end of ‘P’ wave and the onset of ‘Q’ wave.
Triple & Quadruple heart Sounds.
Triple heart Sound or Gallop Rhythm.
Triple heart sound or triple rhythm is an abnormal rhythm of heart, characterized by three clear heart sounds during each heart beat. It is due to an abnormal third or fourth heart sound that is heard besides first and second heart sounds. It is also called gallop rhythm, since it resembles the sound of a horse’s gallop. Usually, it is indicative of serious cardiovascular disease.
Conditions when Triple Heart Sound is Produced.
Triple heart sound is produced in conditions like myocardial infarction and severe hypertension.
Quadruple heart sound .
Quadruple heart sound is an abnormal rhythm of heart, characterized by four clear heart sounds during each heart beat. It is also called quadruple rhythm. It is due to third and fourth heart sounds that are heard besides first and second heart sounds. It is also called quadruple
gallop. Quadruple heart sound is also indicative of serious cardiovascular disease.
Conditions when Quadruple Heart Sound is Produced.
Quadruple heart sound is produced in patients with congestive heart failure.
Summation Gallop.
Whenever there is tachycardia in patients with quadruple heart sound, the third and fourth heart sounds merge together and give rise to a single sound. This sound is called summation gallop and it resembles gallop rhythm.
Methods of Study of heart sounds.
Heart sounds are studied by three methods:
1. By using stethoscope.
2. By using microphone.
3. By using phonocardiogram.
1. By using stethoscope.
First and second heart sounds are heard on the auscultation areas, by using the stethoscope. The chest piece of the stethoscope is placed over four areas on the chest, which are called auscultation areas.
Auscultation Areas .
a. Mitral area (Bicuspid area).
Mitral area is in the left 5th intercostal space, about 10cm away from the midline (midclavicular line). Sound produced by the closure of mitral valve (first heart sound) is transmitted well into this area. It is also called apex beat area because apex beat is felt in this area. Apex beat is the thrust of the apex of ventricles, against the chest wall during systole.
b. Tricuspid area.
Tricuspid area is on the xiphoid process. Sound produced by the closure of tricuspid valve (first heart sound) is transmitted well into this area.
c. Pulmonary area.
Pulmonary area is on the left 2nd intercostal space, close to sternum. Sound produced by the closure of pulmonary valve (second heart sound) is heard well on this area.
d. Aortic area.
Aortic area is over the right 2nd intercostal space, close to the sternum. On this area, the sound produced by the closure of aortic valve (second heart sound) is heard well. First heart sound is best heard in mitral and tricuspid areas.
However, it is heard in other areas also but the intensity is less. Similarly, the second heart sound is best heard in pulmonary and aortic areas. It is also heard in other areas with less intensity.
2. By using microphone.
A highly sensitive microphone is placed over the chest. The heart sounds are amplified by means of an amplifier and heard by using a loudspeaker. First, second and third heart sounds are heard by this method.
3. By using phonocardiogram.
Phonocardiography is the technique used to record the heart sounds. Phonocardiogram is the graphical record of heart sounds. It is done by placing an electronic sound transducer over the chest.
This transducer is connected to a recording device like polygraph. All the four heart sounds can be recorded in phonocardiogram. It helps to analyze the frequency of the sound waves.
Appearance of Heart Sounds in Phonocardiogram.
In phonocardiogram, the heart sounds are recorded in the following manner .
First heart sound.
First heart sound is recorded as single group of waves. The waves are of small amplitude to start with. Later, the amplitude rapidly rises and falls to form crescendo and diminuendo series of waves. About 9 to 13 waves appear.
Second heart sound.
Second heart sound appears as single group of waves, which have same amplitude. About 4 to 6 waves are recorded.
Third heart sound.
Third heart sound is found in phonocardiogram with only 1 to 4 waves grouped together.
Fourth heart sound.
Mostly, the fourth heart sound merges with first heart sound. If it appears as separate form, it has 1 to 2 waves with very low amplitude.
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