Many pathologic cardiac conditions can be diagnosed by auscultation of the heart sounds. Note that heart sounds are discrete, short audible events from a specific cause — different from a heart murmur. A murmur is due to turbulence of blood flow and can, at times, encompass all of systole or diastole. The main normal heart sounds are the S1 and the S2 heart sound. The S3 can be normal, at times, but may be pathologic. A S4 heart sound is almost always pathologic. Heart sounds can be described by their intensity, pitch, location, quality and timing in the cardiac cycle.
FIRST HEART SOUND(S1)- The first heart sound results from the closing of the mitral and tricuspid valves. The sound produced by the closure of the mitral valve is termed M1, and the sound produced by closure of the tricuspid valve is termed T1. Four factors affect the intensity of the first heart sound:
- Chest wall thickness: The first factor is the thickness of the chest wall. Individuals with obesity will have a soft S1, whereas thinner people will have a more intense S1.
- Length of PR interval: A short PR interval results in an accentuated S1, whereas a long PR interval results in a soft S1.
- Valve leaflet mobility: Mild to moderate mitral stenosis results in a loud S1, whereas severe to critical mitral stenosis results in a soft S1.
- Ventricular contraction rate: The faster the heart rate and the faster the rise in ventricular pressure, the louder the S1.
SECOND HEART SOUND(S2)- The second heart sound is produced by the closure of the aortic and pulmonic valves. The sound produced by the closure of the aortic valve is termed A2, and the sound produced by the closure of the pulmonic valve is termed P2.
THIRD HEART SOUND(S3)- The third heart sound, also known as the “ventricular gallop,” occurs just after S2 when the mitral valve opens, allowing passive filling of the left ventricle. The S3 sound is actually produced by the large amount of blood striking a very compliant LV. A S3 heart sound is often a sign of systolic heart failure, however it may sometimes be a normal finding.
FOURTH HEART SOUND(S4)- The fourth heart sound, also known as the “atrial gallop,” occurs just before S1 when the atria contract to force blood into the LV. If the LV is noncompliant, and atrial contraction forces blood through the atrioventricular valves, a S4 is produced by the blood striking the LV. A S4 heart sound is often a sign of diastolic HF, and it is rarely a normal finding (unlike a S3).