Heart Sounds Physiology Notes

Heart Sounds Introduction

Heart sounds are the sounds produced by the mechanical activities of the heart during each cardiac cycle.

Generally, heart sounds are produced by movements of:

1. Blood through the chambers of the heart
2. Cardiac muscle
3. Valves of the heart.

The heart sounds are heard by placing the ear over the chest or by using a stethoscope or microphone. These sounds are also recorded graphically.

Read And Learn More: Medical Physiology Notes

Different Heart Sounds

• Four heart sounds are produced during each cardiac cycle. The first and second heart sounds are more prominent and resemble the spoken words ‘LUB (or LUBB) and ‘DUB’ (or DUP) respectively.
• These two heart sounds are heard by using the stethoscope.
• The third heart sound is a mild sound and it cannot be heard by using a stethoscope in normal conditions.
• But it can be heard by using a microphone. The 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.

BDS Notes	Dental Materials	Medicinal Chemistry
Clinical Medicine And Surgery	Pathology	General Medicine
Face Anatomy	Anatomy	Public Health Dentistry
Abdomen And Pelvis	Microbiology	Basic Dental Materials

Importance Of Heart Sounds

The study of heart sounds has important diagnostic value in clinical practice because the alteration in the heart sounds indicates cardiac diseases involving the valves of the heart.

Description Of Heart Sounds

First Heart Sound

First heart sound is produced during the isometric contraction period and the earlier part of the ejection period.

First Heart Sound Characteristics

• The first heart sound is a long, soft, and low-pitched sound. It resembles the spoken word ‘LUBB’.
• The duration of this sound is 0.10-0.17 seconds. Its frequency is 25-45 cycles/second.

Heart Sounds Causes

• The first heart sound is produced mainly by 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 tendinae.
• These vibrations are mainly responsible for the production of the first heart sound.

2. Vascular factor: The rush of blood from the ventricles into the aorta and pulmonary artery during the ejection period is also responsible for the production of the first heart sound.

3. Muscular factor: The 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: The vibrations produced by the atrial systole also play a role in the production of the first heart sound.

Applied Physiology

1. Reduplication of first heart sound

• Reduplication means splitting the heart sound. The First heart sound is split when the atrioventricular vaiv&s do not close simultaneously (asynchronous closure).
• Splitting of the first heart sound in normal conditions (physiological splitting) is rare.
• The pathological splitting of the first heart sound occurs in stenosis of AV valves and atrial septal defect.

2. Soft first heart sound: The heart sound becomes soft when the intensity of the 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

• The 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 walls 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: The first heart sound coincides with the peak of the ‘R’ wave in ECG.

Second Heart Sound

The second heart sound is produced at the end of the proto-diastolic period.

Second Heart Sound Characteristics: The second heart sound is a short, sharp, and high-pitched sound. It resembles the spoken word ‘DUBB’ (or DUP). The duration of the second heart sound is 0.10 and 0.14 seconds. Its frequency is 50 cycles/second.

Second Heart Sound Cause

The second heart sound is produced due to the sudden and synchronous closure of the semilunar valves.

Applied Physiology

1. Reduplication of second heart sound: The splitting of the second heart sound occurs due to ih# asynchronous closure of semilunar valves. It may occur both in physiological and pathological conditions.

Physiological splitting: Physiological splitting occurs during deep inspiration.

• Normally aortic valve closes prior to the closure of the pulmonary valve. The interval between the two widens during inspiration and narrows during expiration.
• The increased negative intrathoracic pressure during deep inspiration increases lung expansion and venous return into the right atrium.
• However, the venous return from the lungs to the left atrium is reduced during this condition.
• Because of increased venous return in the right atrium and subsequent increase in blood volume in the right ventricle, the pulmonary valve is kept open for a slightly longer time than the aortic valve.
• So the pulmonary valve closes a little later than the aortic valve causing the splitting of the second heart sound.

Pathological splitting: Pathological splitting of the second heart sound occurs during pulmonary stenosis, right bundle branch block, and right ventricular hypertrophy.

Reverse splitting: It is the splitting of the second heart sound in which the aortic valve closes after the closure of the pulmonary valve.

• It is due to the delay in emptying the 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 the aortic valve or the pulmonary valve. The aortic valve produces loud sound during systemic hypertension and coarctation (narrowing) of the aorta.
• The pulmonary valve produces a loud sound during pulmonary hypertension.

3. Soft second heart sound: The second heart sound becomes soft in heart failure.

Second Heart Sound and ECG: The 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 the T wave.

Third Heart Sound

• The third heart sound is a low-pitched sound that is produced during a rapid filling period of the cardiac cycle.
• I: is also called ventricular gallop or proto-diastolic gallop as ll is produced during the earlier part of diastole.
• Usually, the third heart sound is inaudible by •stethoscope and it can be heard only by using a microphone.

Third Heart Sound Characteristics: The third heart sound is a short and low-pitched sound. The duration of this sound is 0.07-0.10 seconds. Its frequency is 1-6 cycles/second.

Third Heart Sound Cause

• Third heart sound is produced by the rushing of blood into ventricles during the rapid filling phase.
• When blood flows rapidly, vibrations are set up in the ventricular wall resulting in the production of sound.
• It may also be due to vibrations set up in cardae tendinae.
• Conditions, when Third Heart Sound Becomes Audible by Stethoscope The third heart sound, can be heard by stethoscope in children and athletes.
• Pathological conditions when the third heart sound becomes loud and audible by stethoscope are aortic regurgitation, cardiac failure, and cardiomyopathy with dilated ventricles.
• When a third heart sound is heard by a stethoscope the condition is called triple heart sound (see below).
• The third heart sound is usually heard best with the bell of the stethoscope placed at the apex beat area when the patient is in the left lateral decubitus position.

Third Heart Sound and ECG; It appears between the 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 that is 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 Characteristics: The fourth heart sound is a short and low-pitched sound. The duration of this sound is 0.02-0.04 seconds. And its frequency is 1-4 cycles/second.

Fourth Heart Sound Cause

• Fourth heart sound is produced by contraction of atrial musculature during atrial systole.
• During atrial systole, vibrations are set up in the atrial musculature and in the flaps of the atrioventricular valves.
• Some vibrations are also set up in the ventricular myocardium due to ventricular distention during atrial systole.
• The vibrations set up in these structures are responsible production of the fourth heart sound.

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 an audible fourth heart sound.
• When the fourth heart sound is heard by a stethoscope the condition is called triple heart sound.
• It is usually heard best with the bell of the stethoscope placed at the apex beat area when the patient is in a supine or left semi-lateral position.

Fourth Heart Sound and ECG: The fourth heart sound coincides with the interval between the end of the ‘P’ wave and the onset of the ‘Q’ wave.

Triple And Quadruple Heart Sounds

Triple Heart Sound Or Gallop Rhythm

• Triple heart sound or triple rhythm is an abnormal rhythm of the 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 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: It is produced in some conditions like myocardial infarction and severe hypertension.

Quadruple Heart Sound

• Quadruple heart sound is an abnormal rhythm of the heart characterized by four clear heart sounds during each heartbeat. It is also called rhythm.
• It is due to third and fourth heart sounds that are heard besides first and second heart sounds. It is also called a quadruple gallop.
• Quadruple heart sound is also indicative of serious cardiovascular disease.

Conditions when Quadruple Heart Sound is Produced: It 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 phonocardiogram.

By Using Stethoscope

• The first and second heart sounds are heard in the auscultation areas by using the stethoscope.
• The chest piece of the stethoscope is placed over 4 areas on the chest, which are called auscultation areas, The four auscultation areas are:

Mitral Area (Bicuspid Area)

• It is in the left 5th intercostal space about 10 cm away from the midline (midclavicular line). This is the area of the apex beat.
• The sound produced by the closure of the mitral valve (first heart sound) is transmitted well into this area.

Apex beat area

• The mitral area is also called the apex beat area since the apex beat is felt in this area.
• Apex beat is the thrust of the apex of the ventricles against the chest wall during systole.

Tricuspid Area: This area is on the xiphoid process. The sound produced by the closure of the tricuspid valve (first heart sound) is transmitted well into this area.

Pulmonary Area

• The pulmonary area is on the left 2nd intercostal space close to the sternum.
• The sound produced by the closure of the pulmonary valve (second heart sound) is heard well in this area.

Aortic Area

• This area is over the right 2nd intercostal space close to the sternum.
• In this area, the sound produced by the closure of the aortic valve (second heart sound) is heard well The 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 the pulmonary and aortic areas.
• It is also heard in other areas with less intensity.

By 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.

By 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 a polygraph. All four heart sounds can be recorded in a phonocardiogram.
• It helps to analyze the frequency of the sound waves.
• Appearance of Heart Sounds in Phonocardiogram
• In a phonocardiogram, the heart sounds are recorded in the following manner.

First Heart Sound

• The first heart sound is recorded as a single group of waves. The waves are of small amplitude to start with.
• Later the amplitude rapidly rises and falls to form a crescendo and diminuendo series of waves. About 9-13 waves appear.

Second Heart Sound: The second heart sound appears as a single group of waves, which have the same amplitude. About 4-6 waves are recorded.

Third Heart Sound: The third heart sound is found in a phonocardiogram with only 1-4 waves grouped together.

Fourth Heart Sound: Mostly, the fourth heart sound merges with the first heart sound. If it appears in a separate form, it has 1-2 waves with very low amplitude.