Why mid diastolic murmur of mitral stenosis is crescendo decrescendo ? I mean why its intensity 1st increases then decreases ?
The crescendo-decrescendo pattern of a mid-diastolic murmur in mitral stenosis is a characteristic feature related to the flow of blood across the narrowed mitral valve. To understand this, let’s break down the cardiac cycle and the hemodynamics involved in mitral stenosis.
Mitral stenosis is a condition where the mitral valve, which separates the left atrium and the left ventricle of the heart, is narrowed or stiffened, making it difficult for blood to flow from the left atrium to the left ventricle during diastole (when the heart is filling with blood).
During diastole, blood flows from the left atrium to the left ventricle through the narrowed mitral valve. The flow of blood creates a mid-diastolic murmur, which is best heard at the apex of the heart with the patient in the left lateral decubitus position.
The crescendo-decrescendo pattern of the murmur occurs because of the following hemodynamic factors:
- Initial Increase in Intensity (Crescendo):
- At the beginning of diastole, there is a rapid initial increase in the intensity of the murmur (crescendo) as blood tries to pass through the narrowed mitral valve.
- The flow of blood encounters resistance due to the narrowed valve, causing a high-velocity jet of blood through the stenotic orifice.
- Mid-Diastolic Murmur:
- The mid-diastolic murmur is the continuous flow of blood through the partially open mitral valve during mid-diastole.
- The intensity of the murmur remains relatively constant during this phase.
- Decrease in Intensity (Decrescendo):
- As diastole progresses and blood continues to flow into the ventricle, the intensity of the murmur gradually decreases (decrescendo).
- This is because the pressure gradient between the left atrium and the left ventricle decreases as more blood fills the ventricle, reducing the velocity of blood flow through the narrowed valve.
In summary, the crescendo-decrescendo pattern of the mid-diastolic murmur in mitral stenosis is a result of the dynamic flow of blood through the narrowed mitral valve during diastole. The initial increase in intensity (crescendo) is due to the forceful jet of blood encountering resistance, and the subsequent decrease in intensity (decrescendo) occurs as the pressure gradient decreases and blood flow slows down during diastole.