Heart sounds

Heart sounds

In cardiac auscultation, an examiner uses a stethoscope to listen for these sounds, which provide important information about the condition of the heart.

In healthy adults there are two normal heart sounds often described as a lub and a dub, that occur in sequence with each heart beat. These are the first heart sound (S₁) and second heart sound (S₂), produced by the closing of the AV valves and semilunar valves respectively. In addition to these normal sounds, a variety of other sounds may be present including heart murmurs, adventitious sounds, and gallop rhythms S₃ and S_4.

S₁

Caused by closure of AV valves at the beginning of ventricular systole. The first heart tone, or S₁, forms the "lubb" of "lubb-dub" or "lubb-dup" and is composed of components M₁ and T₁. Normally M₁ precedes T₁ slightly.

S₂

The second heart tone, or S₂, forms the "dub" of "lubb-dub" and is composed of components A₂ and P₂. Normally A₂ precedes P₂ especially during inspiration when a split of S₂ can be heard. It is caused by the sudden block of reversing blood flow due to closure of the aortic valve and pulmonary valve at the end of ventricular systole, i.e beginning of ventricular diastole.

S₃

It occurs at the beginning of diastole after S2 and is lower in pitch than S1 or S2 as it is not of valvular origin. Benign in some youth and trained athletes. S3 is thought to be caused by the oscillation of blood back and forth between the walls of the ventricles initiated by inrushing blood from the atria. An S3 heart sound is best heard with the bell-side of the stethoscope (used for lower frequency sounds). A left-sided S3 is best heard in the left lateral decubitus position and at the apex of the heart, which is normally located in the 5th left intercostal space at the midclavicular line.^[2] A right-sided S3 is best heard at the lower-left sternal border.

S₄

The rare fourth heart sound is sometimes audible in healthy children and again in trained athletes, but when audible in an adult is called a presystolic gallop or atrial gallop. This gallop is produced by the sound of blood being forced into a stiff/hypertrophic ventricle. It is a sign of a pathologic state, usually a failing left ventricle, but can also be heard in other conditions such as restrictive cardiomyopathy. The sound occurs just after atrial contraction ("atrial kick") at the end of diastole and immediately before S1. It is best heard at the cardiac apex with the patient in the left lateral decubitus position and holding his breath. The combined presence of S3 and S4 is a quadruple gallop. At rapid heart rates, S3 and S4 may merge to produce a summation gallop (sometimes referred to as S7).

Murmurs are extra heart sounds that are produced as a result of turbulent blood flow which is sufficient to produce audible noise. Murmurs may be physiological (benign) or pathological (abnormal). Catergorised into 6 depending on intensity of murmur(Levine scale). Common descriptive terms include rumbling, blowing, machinery, scratchy, harsh, or musical.

§ Regurgitation through the mitral valve is by far the most commonly heard murmur, sometimes fairly loud to a practiced ear, even though the volume of regurgitant blood flow may be quite small. Yet, though obvious using echocardiography visualization, probably about 20% of cases of mitral regurgitation do not produce an audible murmur.

§ Stenosis of the aortic valve is typically the next most common heart murmur, a systolic ejection murmur. This is more common in older adults or in those individuals having a two, not a three leaflet aortic valve.

Note: We don’t hear the sounds of the valves directly over the valves because the sound waves are conducted to defferent regions