These simultaneous left atrial and left ventricular pressure curves illustrate the relationship of the hemodynamic events to the timing and contour of the systolic murmur in acute and chronic mitral regurgitation. The configuration of the murmur in mitral regurgitation is the result of the compliance characteristics of the left atrium.
In acute mitral regurgitation, the left atrium is relatively small and not very compliant. The regurgitant jet, therefore, causes left atrial pressure to rise rapidly in systole, characterized by the large v wave. As the left atrial pressure approaches left ventricular pressure in late systole, the degree of regurgitation is reduced, hence, the murmur is decrescendo.
In chronic mitral regurgitation, the large left atrium is more compliant. The regurgitation jet, therefore, causes a modest systolic increase in left atrial pressure. The murmur begins with mitral closure and continues up to and through aortic closure. The difference between the left ventricular pressure and left atrial pressure remains high throughout this period. This results in a plateau shaped murmur.
Acute MR
[Sounds]
Chronic MR
[Sounds]
MR Murmur
The murmur of acute mitral regurgitation may be confused with that of aortic stenosis or ventricular septal defect. If the regurgitant jet of acute mitral regurgitation is directed anteriorly toward the aortic root, the murmur may radiate to the base and, at times, even radiate into the carotid, thus, the murmur may simulate that of aortic stenosis. However, the difference in the carotid pulse should help discriminate between the two conditions. In differentiating acute mitral regurgitation from ventricular septal defect, the presence of a thrill suggests a ventricular septal defect, especially when the thrill is located at the left sternal border.