Heart Sound
Table of Contents
Definition of heart sounds
Heart sounds are the sounds produced by mechanical activities of heart during each cardiac cycle.Heart sounds are heard by placing ear over the chest or by using a stethoscope or microphone.
Heart sounds are produced by:
1. Flow of blood through cardiac chambers
2. Contraction of cardiac muscle
3. Closure of valves of the heart.
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
These two heart sounds are more prominent and resemble the spoken words ‘LUB, (or LUBB) and ‘DUBB’ (orDUP), respectively.
FIRST HEART SOUND
First heart sound is produced during isometric contraction period and earlier part of ejection period
- Occurs during: Isometric contraction period and part of ejection period.
- Characteristics: Long, soft and low pitched .Resembles the word ‘LUBB’
- Cause: Closure of atrioventricular valves
- Duration (sec):0.10 to 0.17
- Frequency (cycles per sec): 25 to 45
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 end of protodiastolic period.
- Occurs during: Protodiastole and part of isometric relaxation
- Characteristics: Short, sharp and high pitched .Resembles the word ‘DUP’
- Cause: Closure of semilunar valves
- Duration (sec): 0.10 to 0.17
- Frequency (cycles per sec): 25 to 45
Second Heart Sound and ECG
Second heart sound coincides with ‘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 low-pitched sound that is produced during rapid filling period of cardiac cycle. Usually, the third heart sound is inaudible by the stethoscope and it can be heard only by using
microphone.
- Occurs during: Rapid filling phase
- Characteristics: Low pitched
- Cause:Rushing of blood
into ventricle - Duration (sec): 0.07 to 0.10
- Frequency (cycles per sec) :1 to 6
Third Heart Sound and ECG
Third heart sound appears between ‘T’ and ‘P’ waves of ECG.
FOURTH HEART SOUND
The fourth heart sound is an inaudible sound. It becomes audible only in pathological conditions.
This sound is produced during atrial systole (late diastole) and it is considered as the physiologic atrial sound. It’s also called atrial gallop or presystolic gallop.
- Occurs during: Atrial systole
- Characteristics: Inaudible sound
- Cause :Contraction of atrial
musculature - Duration (sec): 0.02 to 0.04
- Frequency (cycles per sec):1 to 4
Fourth Heart Sound and ECG
Fourth heart sound coincides with interval between end of ‘P’ wave and the onset of ‘Q’ wave.
| Features | first heart sound | second heart sound | Third heart sound | Fourth heart sound |
| Occurs during | Isometric contraction period and part o ejection period | Protodiastole and part of isometric relaxation . | Rapid filling phase | Atrial systole |
| Long , soft and low pitched . Resembles the word “LUBB” | Short , sharp and high pitched . Resembles the world “DUP” | Low pitched | Inaudible sound | |
| causes | Closure of atrioventricular valves | Closure of semilunar valves | Rushing of blood into ventricles | Contraction of atrial musculature |
| During (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 and ‘Q’ wave | Between ‘p’ waves and ‘Q’ waves |
| Number of vibrations in phonocardiogram | 9 to 13 | 4 to 6 | 1 to 4 | 1 to 2 |
Method of study of heart sounds
- By using stethoscope
- By using microphone
- By using phonocardiogram
By stethoscope
First and second heart sounds are heard in the auscultation areas, by using te stethoscope. The chest piece of stethoscope is placed over four areas on the chest, which are called auscultation areas.
- Mitral area ( Bicuspid area ) – the 5th intercostal space area, about 10 am away from mid clavicle
- Tricuspid area – on the xiphoid process
- Pulmonary area – on the left 2nd intercostal space, close to the sternum.
- Aortic area – over the right 2nd intercostal space, close to the sternum.
By microphone
A highly sensitive microphone is placed over the chest. The heart sound is simplified by means of an amplifier and heard by using a loudspeaker. First, second, and third heart sound are heard by this method.
By Phonocardiogram
Phonocardiography is the technique used to record the heart sounds. Phonocardiogram is the graphical record of the heart sounds. It is done by placing an electronic sound transducer over chest. This transducer is connected to a recording device like polygraph. All four heart sounds can be recorded in phonocardiogram . It helps to analyze the frequency of the sound waves.
Abnormal heart sounds
Triple heart sound
Triple heart sound or triple rhythm is an abnormal rhythm of heart, characterized by three clear heart sounds during each heartbeat. 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.
Quadruple heart sounds
Quadruple heart sounds is an abnormal rhythm of heart, characterized by four clear heart sounds during each heart beat . It is also called quadruple gallop. It indicates serious cardiovascular disease.
Cardiac Murmur
A cardiac murmur is abnormal or unusual heart sound. It is also called abnormal heart sound or cardiac bruit. A cardiac murmur is heard by the stethoscope, along with normal heart sounds.
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