Why third heart sound is absent in mitral stenosis?

NEET PG
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Why third heart sound is absent in mitral stenosis?

The third heart sound (S3) is an audible sound associated with the early phase of diastole, occurring after the second heart sound (S2). In the case of mitral stenosis, the S3 heart sound is often diminished or absent. This is due to specific cardiac dynamics and altered hemodynamics associated with mitral stenosis.

Here’s why the third heart sound (S3) may be absent or reduced in mitral stenosis:

  1. Reduced Ventricular Compliance:
  • Mitral stenosis leads to decreased compliance or flexibility of the left ventricle. The narrowed mitral valve restricts the normal flow of blood from the left atrium to the left ventricle during diastole. This reduced compliance limits the ability of the ventricle to rapidly fill with blood, diminishing the production of the S3 heart sound associated with rapid ventricular filling.
  1. Impaired Ventricular Filling:
  • The impaired ventricular filling in mitral stenosis limits the volume and velocity of blood entering the left ventricle during early diastole. The S3 heart sound is typically generated by the vibrations of the ventricular walls when blood rapidly fills the ventricle. In mitral stenosis, this rapid filling is compromised due to the narrowed valve, resulting in a reduced intensity or absence of the S3 sound.
  1. Delayed Ventricular Filling:
  • Due to the obstruction at the mitral valve, blood takes longer to pass from the left atrium to the left ventricle. The delayed filling time further diminishes the intensity of the S3 heart sound or may cause it to be inaudible during auscultation.

In contrast, conditions that lead to increased ventricular filling, such as congestive heart failure (CHF), can enhance the production and audibility of the S3 heart sound.

It’s important to note that the absence or reduction of the S3 heart sound in mitral stenosis is a characteristic clinical finding. The presence or absence of S3, along with other auscultatory findings, helps healthcare professionals diagnose and assess the severity of heart conditions, including mitral stenosis. Always consult a healthcare provider for a comprehensive evaluation and accurate diagnosis.