First Heart Sound

Abstract

The heart sounds (S1, S2, S3, and S4) are discrete short auditory events caused due to vibrations that are generated during the closure of the valve leaflets or tensing of the chorda tendineae.[1] They are distinct from murmurs that are longer and are caused by turbulent blood flow. They are identified by the timing in the cardiac cycle, location, intensity, pitch, and quality. The first heart sound is conventionally referred to as S1 and has multiple high-frequency components. But only the first two sets (temporally related to the closure of mitral and tricuspid valves) are identified as two components—the mitral (M1) and tricuspid (T2); M1 always precedes T1. These two components are not easily appreciated separately in health as the separation interval is < 30 ms. Being a high-pitched sound, it is best heard with the diaphragm, which may have to be applied with sufficient pressure to listen to the S1. The quality is described as booming, duller, and longer than S2. The variations in the first sound such as split, intensity, and quality can suggest the underlying pathology to some extent. Mitral component is best heard at the apex and is louder than the tricuspid component due to the higher pressures in the left side of the heart; it can be widely heard in other areas of auscultation as well.[2] [3]