What does a fixed split S2 (second heart sound) mean?

From the Guidelines

A fixed split S2 (second heart sound) is a strong indicator of an atrial septal defect (ASD), as it suggests an abnormal communication between the left and right atria, leading to increased flow through the pulmonary valve and a subsequent delay in the closure of the pulmonary valve [ 1 ].

Key Points

• A fixed split S2 is characterized by a consistent interval between the aortic and pulmonary components of the second heart sound during both inspiration and expiration [ 1 ].
• This finding is often associated with a grade 2/6 midsystolic murmur in the pulmonic area and left sternal border, which further supports the diagnosis of an ASD [ 1 ].
• The presence of a fixed split S2 in a patient with a cardiac murmur should prompt further evaluation for an ASD, including echocardiography and other diagnostic tests [ 1 ].
• It is essential to consider other potential causes of a fixed split S2, such as pulmonary disease or other cardiac conditions, and to evaluate the patient's overall clinical presentation and medical history [ 1 ].

Clinical Implications

• The diagnosis of an ASD is crucial, as it can lead to pulmonary overcirculation, right ventricular failure, and other complications if left untreated [ 1 ].
• A fixed split S2 is a significant finding that should prompt further evaluation and potential referral to a cardiologist for definitive diagnosis and treatment [ 1 ].

From the Research

Definition of Fixed Split S2

A fixed split S2 refers to a condition where the time delay between the closure of the aortic valve (A2) and the pulmonary valve (P2) remains constant over the cardiac cycle, unlike the normal variation in splitting duration observed in healthy individuals 2.

Causes of Fixed Split S2

Fixed splitting of the second heart sound can be associated with certain pathological conditions, such as:

• Atrial septal defect (ASD) 2
• Pulmonary stenosis (PS) 2 Other conditions, such as right bundle-branch block (RBBB), may not necessarily result in a wide split S2, and the presence of a normal or wide split S2 in these cases may not be directly correlated with the underlying condition 3.

Measurement and Detection of Fixed Split S2

Various techniques have been developed to measure and detect the split in the second heart sound, including:

• Discrete wavelet transform (DWT) and continuous wavelet transform (CWT) 2, 4
• Support vector machine (SVM) combined with time-frequency maps obtained with CWT 5
• Novel methodologies using estimated parameters, such as the split coefficient of S2 and adaptive number of S2 6