Heart sounds are the sounds produced by mechanical activities of heart during each cardiac cycle. Heart sounds are produced by:
- Flow of blood through cardiac chambers.
- Contraction of cardiac muscle.
- 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 Heart Sounds
Four heart sounds are produced during each cardiac cycle:
- First Heart Sound
- Second Heart Sound
- Third Heart Sound
- 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’ (Of 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.
Description Of Heart Sounds
1- First Heart Sound
First heart sound is produced during isometric contraction period and earlier part of ejection period.
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 head sound.
i- 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.
ii- 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.
iii- 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.
iv- Atrial Factor
Vibrations produced DY the atrial systole also play a role in the production of the 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.
1- Reduplication Of First Heart Sound
Reduplication means splitting of the heart sound. First heart sound is split when the atrioventricular valves do not close simultaneously (asynchronous closure). Splitting of first heart sound in normal conditions (physiological splitting) is rare. Pathological splitting of first heart sound occurs in stenosis of atrioventricular valves and atrial septal defect.
2- Soft First Head Sound
Head sound becomes soft when the intensity of sound decreases. A soft first heart sound is heard in low blood pressure, severe heart failure, myocardial infarction and myxedema.
3- Loud Or Accentuated First Heart Sound
First heart sound becomes louder or accentuated (becoming prominent) in conditions like mitral stenosis, Wolff-Parkinson-White syndrome and acute rheumatic fever. It is loud in patients with thin chest wall also.
4- Cannon Sound
Cannon sound refers to the loud first heart sound that is heard intermittently: It is heard in ventricular tachycardia and complete atrioventricular block.
First Heart Sound And ECG
First heart sound coincides with peak of ‘R’ wave in ECG.
2- Second Heart Sound
Second heart sound is produced at the end of protodiastolic period.
Second heart sound is produced due to the sudden and synchronous closure of the semilunar valves.
Second heart short 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.
1- Reduplication Of Second Heart Sound
Splitting of second heart sound occurs due to asynchronous closure of semilunar valves. It may occur both in physiological and pathological conditions.
- Physiological Splitting: It occurs during deep inspiration. Normally aortic valve closes prior the closure of pulmonary valve. Interval between the two valves widens during inspiration and narrows during expiration. Increased negative intrathoracic pressure during deep inspiration increases lung expansion and venous return into right atrium. However, the venous return from lungs to left atrium is reduced during this condition. Because of increased venous return in right atrium and subsequent increase in blood volume in right ventricle, pulmonary valve is kept open for slightly longer time than the aortic valve. So, the pulmonary valve closes little later than the aortic valve causing splitting of second heart sound.
- Pathological Splitting: The splitting of second heart sound occurs during pulmonary stenosis, right bundle branch block and right ventricular hypertrophy.
- Reverse Splitting: It is the splitting of second heart sound, in which aortic valve closes after the closure of pulmonary valve. It is due to the delay in emptying of left ventricle. It is also called paradoxical splitting (paradoxical = contradictory or opposite). Reverse splitting is common in left bundle-branch block, aortic stenosis and left ventricular hypertrophy.
2- Loud Or Accentuated Second Heart Sound
Loud or accentuated second heart sound is produced by the closure of either aortic valve or pulmonary valve. Aortic valve produces loud sound during systemic hypertension and contraction (narrowing) of aorta. Pulmonary valve produces loud sound during pulmonary hypertension.
3- Soft Second Heart Sound
Second heart sound becomes soft in heart failure.
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.
3- 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.
Third heart sound is produced by the rushing into ventricles and vibrations set up in the wall during rapid filling phase. It may also vibrations set up in chordae tendineae.
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 stethosc0pe, the condition is called triple heart sound. Third heart sound is usually heard best with the bell stethoscope placed at the apex beat area, patient is in left lateral decubitus (lying on left side) position.
Third Heart Sound And ECG
Third heart sound appears between ‘T’ and ‘P’ of ECG.
4- 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.
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.
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 per 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 semilateral 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.