Heart sounds are essential diagnostic parameters to indicate the clinical state of the heart and also for prognosis of diseases.
Percussion is used mainly to determine the size of the heart by outlining its borders. Dullness is normally heard over the left area of the heart and partially over the right. Deviation from the expected finding may indicate Cardiac enlargement or displacement and warrants further study.
Auscultation involves listening for heart sounds with the stethoscope, similar to the procedure used in assessing breath sounds.
Origin of Heart sounds
The heart sounds are produced by the opening and closing of the valves and the vibration of blood against the walls of the heart and vessels. Normally two sounds- S1 and S2 are heard, which correspond respectively to the familiar “lub dub” often used to describe the sounds. S1 is caused by the closure of the tricuspid and mitrial valves (sometimes called the atrioventricular valves). Right ventricular contraction follows tricuspid valve closure, and left ventricular contraction follows mitrial valve closure. The contractions (systole) occur slightly before the tricuspid valve (right side). Normally this split of the sounds is so close that it is not audible except occasionally at the apex of the heart.
S2 is the result of the closure of the pulmonic and aortic valves (sometimes called semilunar valves). Aortic valve closing (left side) occurs slightly before pulmonic valve closing (right side). The interval between S2 and S1 is diastole, or relaxation, of the heart. Normally the split of the S2 and S1 is diastole or relaxation, of the heart. Normally the split of the two sounds in S2 is distinguishable and widens during inspiration, since inspiration prolongs right ventricular filling and delays pulmonic valve closure. “Physiologic splitting” is a significant normal finding that should be elicited. “Fixed splitting”, in which the split in S2 does not change during inspiration is an important diagnostic sign of atrial septal defect.
It is important to note that the anatomic location of valves does not correspond to the area where the sounds are heard the best. The auscultatory sites are located in the direction of the blood flow through the valves.
Two other heart sounds-S3 and S4-may be produced. S3 is the result of vibrations produced during ventricular filling. It is normally heard only in some children and young adults. But it is considered abnormal in older individuals. S4 is caused by the recoil of vibrations between the atria and ventricles following atrial contraction, at the end of diastole. It is rarely heard as a normal heart sound usually it is considered indicative of further cardiac evaluation.