From the Guidelines
The S2 heart sound is a crucial diagnostic tool in cardiac auscultation, representing the closure of the semilunar valves and providing valuable information about cardiac function and potential pathology, particularly in the context of aortic stenosis, where a single or paradoxically split S2 may indicate severe disease 1. The significance of the S2 heart sound lies in its ability to provide insight into the functioning of the heart valves, specifically the aortic and pulmonic valves.
- A normally split S2 is typically heard during inspiration, due to increased venous return to the right heart, which delays pulmonic valve closure.
- Abnormal splitting patterns, such as fixed splitting, paradoxical splitting, or a widely split S2, can indicate various cardiac conditions, including atrial septal defect, left bundle branch block, aortic stenosis, or right bundle branch block 1.
- An accentuated S2 may suggest pulmonary hypertension, while a diminished S2 can occur in cases of aortic stenosis, highlighting the importance of careful auscultation in diagnosing and managing cardiac disease 1. In the context of aortic stenosis, the S2 heart sound plays a critical role in diagnosis, as a single or paradoxically split S2 can confirm the presence of severe disease, making it an essential component of cardiac assessment in clinical practice 1.
From the Research
Significance of the S2 Heart Sound
The second heart sound (S2) is a crucial component of the cardiac cycle, consisting of two acoustic components: A2 and P2.
- A2 is due to the closure of the aortic valve
- P2 is due to the closure of the pulmonary valve 2, 3, 4, 5. The time delay between A2 and P2 is known as the "split" and is an important aspect of cardiac diagnosis.
Components of S2
The aortic valve usually closes before the pulmonary valve, introducing a time delay between the two components.
- The mean interval between aortic valve closure and the onset of A2 was found to be 12 msec, with a range of 5 to 25 msec 3.
- The mean interval between pulmonary valve closure and the onset of P2 was found to be 60 msec, with a range of 30 to 75 msec 3.
Clinical Significance
The split in S2 can be used to diagnose various cardiac conditions.
- In normal cases, the split varies in duration over the cardiac cycle 4.
- In certain pathologies, such as atrial septal defect (ASD) or pulmonary stenosis (PS), the split becomes fixed over the cardiac cycle 4.
- Automatic techniques, such as wavelet transform and hidden Markov models, can be used to segment S2 and estimate the delay between A2 and P2 2, 4, 5.
Phono-Echocardiographic Correlation
Studies have shown that the first component of S2 coincides with the closure of the aortic valve, suggesting that the origin of A2 may be related to aortic valve closure 6.