What Causes The Heart Sounds?
Heart sounds are acoustic events created by valve closure and blood flow dynamics in the heart during the cardiac cycle. Normal heart sounds include S1 and S2, while S3 and S4 indicate physiological or pathological states. This guide explains causes, timing, characteristics, murmurs, clinical relevance, diagrams, NEET MCQs, and FAQs.
This Story also Contains
- What Are Heart Sounds?
- Primary Heart Sounds (S1 and S2)
- Additional Heart Sounds (S3 and S4)
- Abnormal Heart Sounds – Murmurs
- Clinical Importance of Heart Sounds
- Heart Sounds NEET MCQs (With Answers & Explanations)
- Recommended video for "Heart Sounds"
What Are Heart Sounds?
Heart sounds are the sounds emitted by the closure of the heart valves and the flow of the blood in the heart chambers. First, the normal sounds S1 and S2 are the opening of the atrioventricular valves: tricuspid and mitral, and semilunar valves – pulmonary and aortic, respectively.
Why Heart Sounds Are Important in Diagnosis
They are useful for evaluating conditions concerning the performance of heart and heart beat. Extra-systolic sounds, such as S3 and S4 or murmurs, suggest disease states like congestive heart failure, valvular diseases, and/or congenital anomalies. Therefore, there is a need to distinguish and understand these sounds if any intervention or management of cardiovascular diseases is to be done.
Primary Heart Sounds (S1 and S2)
The primary heart sounds are listed below:
First Heart Sound (S1)
S1 also known as the first heart sound is the sound produced by the closure of the fourth atrioventricular valve; the mitral and tricuspid.
Timing: This is at S1 that ventricular systole initiates and it is a phase whereby the ventricles contract to eject blood.
Characteristics: This sound is well known as the ‘lub’ sound and is louder and lasts longer than the second sound.
Second Heart Sound (S2)
The second heart sound (S2) that is produced by the closure of semilunar valves includes aortic and pulmonary valves.
Timing: S2 is widely viewed as concluding ventricular systole while the process of diastole is thought of as the process through which the ventricles remain open and eject their blood.
Characteristics: This sound is known as ‘dub’; it is slightly different from S1 in the way that it is shorter than S1 and also has a sharper sound.
The table below shows the comparison between S1 and S2 heart sounds:
Feature | S1 | S2 |
Valves | AV valves closing | SL valves closing |
Timing | Marks start of systole | Marks end of systole |
Pitch | Lower and dull | Higher and sharp |
Duration | Longer | Shorter |
Additional Heart Sounds (S3 and S4)
The additional heart sounds are listed below:
S3 – Ventricular Gallop
S3 is produced by early diastolic filling of the ventricles as a result of blood being remarked into the relatively non-contracted ventricles by the atria.
Timing: S3 is conducted after S2, this is perhaps in the first phase of the diastolic phase of the cardiac cycle.
Characteristics: It is a loud, low-pitched sound sometimes referred to as a ventricular gallop and is worse with the diaphragm of the stethoscope.
Clinical significance: S3 can be physiological in young individuals and physically fit individuals because of increased cardiac output, but in the elderly, it may be a sign of heart failure/volume overload.
S4 – Atrial Gallop
S4 is produced by atrial systole against the closed and stiff or thick ventricles, resulting in increased blood turbulence.
Timing: S4 happens immediately before S1, specifically in the beginning of diastroke as the atria eject blood onto the ventricles.
Characteristics: It is a low-pitched, low-frequency murmur that is described as having an ‘atrial gallop’.
Clinical significance: S4 is normally seen in conditions that diminish the ventricles’ compliance, for example, hypertensive heart disease or left ventricular hypertrophy.
Abnormal Heart Sounds – Murmurs
The abnormal heart sounds are listed below:
Causes of Murmurs
Heart murmurs are noises associated with blood flow through and/or around the heart and its valves or from structural abnormalities in the heart, including stenosis and incompetence. These irregularities cause a turbulent circulation of blood and this as we all know is measured as a murmur.
Types of Murmurs
Systolic Murmurs: They happen between S1 and S2 when ventricles are contracting. There are usual types such as those due to aortic stenosis or mitral regurgitation.
Diastolic Murmurs: Occur during ventricular diastole between S2 and S1 extremely close to each other. Examples of benign heart sounds include those produced by aortic stenosis or murmurs from it or murmurs from mitral stenosis.
Continuous Murmurs: Last the duration of the cardiac cycle such as those due to ductus arteriosus.
Clinical Importance of Heart Sounds
Heart murmurs are very vital in diagnosing heart diseases as well as judging the severity of the diseases. These may signify structural abnormalities of the heart and assist in the subsequent investigations and management plans.
Heart Sounds NEET MCQs (With Answers & Explanations)
Types of questions asked from this topic are:
Primary and additional heart sounds
Abnormal heart sounds
Practice Questions for NEET
Q1. Identify the subsequent stage that immediately follows the 'dup' (second heart sound):
Isovolumetric contraction
Isovolumetric relaxation
Third heart sound
Atrial systole
Correct answer: 2) Isovolumetric relaxation
Explanation:
The second heart sound, often referred to as 'dup,' occurs during the closure of the semilunar valves (pulmonary and aortic valves) at the beginning of ventricular diastole. After the 'dup' sound, the heart progresses into the phase known as isovolumetric relaxation. During isovolumetric relaxation, both the atrioventricular (AV) valves (mitral and tricuspid valves) and semilunar valves are closed. The ventricles are in a relaxed state, and no blood is being actively ejected or filled into the chambers. Instead, the ventricles are momentarily in a state of isovolumetric relaxation, where the pressure in the ventricles decreases, and the heart muscle begins to relax and prepare for the next cardiac cycle.
Hence, the correct answer is option 2) Isovolumetric relaxation.
Q2. Doctors use a stethoscope to hear the sounds produced during each cardiac cycle. The second sound is heard when:
Ventricular walls vibrate due to gushing in of blood from atria
Semilunar valves close down after the blood flows into vessels from ventricles
AV node receives signal from SA node
AV valves open up
Correct answer: 2) Semilunar valves close down after the blood flows into vessels from ventricles
Explanation:
During each cardiac cycle, two prominent sounds are produced which can be easily heard through a stethoscope. The first heart sound (lub) is associated with the closure of the tricuspid and bicuspid valves whereas the second heart sound (dub) is associated with the closure of the semilunar valves. The second heart sound (dub) is associated with the closure of the semilunar value.
Hence, the correct answer is option 2) Semilunar valves close down after the blood flows into vessels from ventricles.
Q3. Which of the following is the first heart sound (S1) and what causes it?
Lub, caused by the closure of the aortic valve.
Dub, caused by the closure of the mitral valve.
Lub, caused by the closure of the mitral valve.
Dub, caused by the closure of the tricuspid valve.
Correct answer: 3) Lub, caused by the closure of the mitral valve.
Explanation:
"Lub" is the foremost heart sound (S1), which is produced when the tricuspid and mitral valves close. These valves are situated between the heart's bottom chambers, ventricles, and upper chambers, or atria. The sound is made when the ventricles contract to force blood out during the beginning of the heart's pumping phase, known as ventricular systole. These valves stop blood from returning to the atria when they are closed. The heartbeat's typical "Lub-Dub" rhythm begins with this "Lub" sound, with the "Dub" originating from the closure of additional valves in the subsequent phase.
Hence, the correct answer is option 3) Lub, caused by the closure of the mitral valve.
Also Read:
Recommended video for "Heart Sounds"
Frequently Asked Questions (FAQs)
S1 is initiated at the onset of systole due to the closure of both the mitral and tricuspid valves whereas; S2 happens at the end of systole due to the closure of both the aortic and pulmonary valves. S1 is normally as loud format as a “lub” sound while S2 is in the format of a “dub” sound.
Heart murmurs are identified via auscultation, making use of the stethoscope; any sounds that are abnormal during the cardiac cycle. In some cases, echocardiography, Doppler studies, and phonocardiography might be carried out to establish the cause, time, and kind of the murmur.
Thus, abnormal heart sounds like the extra sounds or murmurs can be indicative of different configurations or heart diseases like valve diseases, heart failures, or congenital heart diseases. It necessarily leads to web research to find out what has caused it to occur in the first place.
Incorporating heart sounds into analysis of a patient’s condition offers useful information regarding their heart ailment. Their presence, timing and quality may be useful in diagnosing valve disorders, heart failure, and structural heart abnormalities.
S1 is due to the closure of the atrioventricular valves, that is mitral and tricuspid valves during the phase of the initial systole. This closure makes an initial sound of ‘lub’, which is the sound of the heart contracting.