From the Guidelines
Physiological splitting of the second heart sound (S2) is a normal finding where the split between the aortic valve closure (A2) and the pulmonic valve closure (P2) widens during inspiration and narrows during expiration. This phenomenon occurs due to the changes in venous return and ventricular filling during the respiratory cycle, affecting the timing of valve closures [ 1 ].
Key Characteristics of Physiological Splitting:
- The split between A2 and P2 widens during inspiration
- The split narrows or disappears during expiration
- This pattern is a normal finding in healthy individuals and helps differentiate physiological splitting from pathological conditions
Assessment of Physiological Splitting:
- Auscultate at the pulmonic area (left upper sternal border)
- Have the patient breathe normally to observe the widening and narrowing of the split during inspiration and expiration
- A normally split second heart sound can be a reliable finding in excluding the possibility of severe aortic stenosis [ 1 ] In clinical practice, recognizing physiological splitting of S2 is crucial for distinguishing it from abnormal splitting patterns that may indicate underlying cardiac pathology, such as fixed splitting in atrial septal defects or paradoxical splitting in left bundle branch block or severe aortic stenosis [ 1 ].
From the Research
Physiological Splitting of the Second Heart Sound (S2)
- The second heart sound, S2, consists of two acoustic components, A2 and P2, due to the closure of the aortic and pulmonary valves, respectively 2.
- The aortic valve usually closes before the pulmonary valve, introducing a time delay known as the 'split' 2.
- The split normally varies in duration over the cardiac cycle, but in certain pathologies, such as atrial septal defect (ASD) or pulmonary stenosis (PS), the split becomes fixed over the cardiac cycle 2.
- The mechanism of S2 production is not directly related to the closure of the semilunar valves, but rather to the deceleration of columns of blood resulting from valve closure, which throws the cardiohemic system into vibration 3.
- The splitting of S2 can be affected by various factors, including respiration, with inspiratory augmentation of the A2-P2 interval occurring in normal subjects and patients with certain pathologies, such as aortic regurgitation 4.
- Abnormal splitting patterns, such as reversed splitting, can occur in patients with left bundle branch block, and may be related to bilateral block or interventricular mechanical dyssynchrony 5, 6.
- A novel algorithm, S-transform amplitude ridge tracking (START), has been developed to estimate the S2 splitting interval and investigate its relationship with interventricular relaxation dyssynchrony (IRD) 6.
- The START algorithm has been validated in simulated and porcine models, and has shown significant correlation between S2 splitting interval and IRD, suggesting its potential as a useful tool for assessing interventricular dyssynchrony 6.