Split S2

Detailed explanation of Split S2 in cardiology

Split S2 refers to the phenomenon where the second heart sound (S2) is audibly divided into two distinct components. This occurs due to the asynchronous closure of the aortic valve (A2) and the pulmonary valve (P2) during the cardiac cycle. The splitting of S2 is a normal physiological occurrence that can vary with respiration.

Physiology

The second heart sound, S2, is primarily produced by the closure of the semilunar valves, which include the aortic and pulmonary valves. During inspiration, the negative pressure in the thoracic cavity increases venous return to the right side of the heart, leading to a delay in the closure of the pulmonary valve. This results in the splitting of S2 into two audible components: A2 and P2.

Normal Splitting

In healthy individuals, the splitting of S2 is most pronounced during inspiration and diminishes during expiration. This is known as "physiological splitting." During inspiration, the increased venous return to the right heart delays the closure of the pulmonary valve, while the aortic valve closure remains relatively unchanged.

Wide Splitting

Wide splitting of S2 can occur in conditions that delay right ventricular emptying, such as right bundle branch block or pulmonary stenosis. In these cases, the delay in P2 is more pronounced, leading to a wider interval between A2 and P2.

Fixed Splitting

Fixed splitting of S2 is characterized by a constant interval between A2 and P2, regardless of the respiratory cycle. This is often associated with an atrial septal defect (ASD), where the left-to-right shunt maintains a constant volume load on the right ventricle, leading to a persistent delay in P2.

Paradoxical Splitting

Paradoxical splitting, or "reversed splitting," occurs when the interval between A2 and P2 is greater during expiration than inspiration. This can be seen in conditions that delay left ventricular emptying, such as left bundle branch block or aortic stenosis. In these cases, A2 is delayed, causing the split to be more pronounced during expiration.

Clinical Significance

The presence and pattern of S2 splitting can provide valuable diagnostic information about underlying cardiac conditions. Auscultation of heart sounds, including the assessment of S2 splitting, is an important component of the physical examination in cardiology.

Related Pages

• Heart sounds
• Cardiac cycle
• Aortic valve
• Pulmonary valve
• Atrial septal defect
• Right bundle branch block
• Left bundle branch block