From the Guidelines
Mitral regurgitation (MR) increases preload.
Mechanism of Increased Preload
- The regurgitant volume in MR results in LV dilation and increases in left atrial pressure and volume, which enhances total LV stroke volume enough to accommodate the regurgitant volume and to maintain the forward stroke volume within normal limits 1.
- The low impedance presented by regurgitation into the left atrium unloads the left ventricle during ventricular systole, allowing for increased LV diastolic volume and total stroke volume 1.
- In acute severe MR, a sudden volume overload is imposed on the left atrium and left ventricle, increasing LV preload and allowing for a modest increase in total LV stroke volume 1.
Clinical Implications
- The increased preload in MR can lead to LV dilation and increased pulmonary venous pressures, resulting in signs and symptoms of heart failure 1.
- The severity of MR is often quantified by the regurgitant fraction, which is used as an index for the likelihood of progressive LV myocardial remodeling, dysfunction, and eventual heart failure 1.
- In chronic primary MR, favorable loading conditions (increased preload and usually normal afterload) increase ejection phase indexes of LV function, such as LVEF, but do not affect the extent of shortening 1.
From the Research
Mitral Regurgitation and Preload
- Mitral regurgitation (MR) leads to an increase in preload, as evidenced by the volume overload in MR, which causes eccentric hypertrophy of the left ventricle 2.
- The increased end-diastolic volume in MR results in an increased stroke volume and normal ejection fraction, indicating that the left ventricle is able to compensate for the increased preload 2.
- Preload reduction has been shown to decrease mitral regurgitant volume (MRV) and improve functional mitral regurgitation (FMR) 3, 4.
- Elevated left atrial pressure, which is a key determinant of mitral valve tenting in FMR, is also influenced by preload 4.
Mechanisms of Preload Alterations
- Changes in MRV correlate better with changes in mitral annular area (MAA) than with changes in tenting height (TH) 3.
- Multiple regression analysis revealed that changes in MAA with preload alteration are the independent determinant of the changes in MRV 3.
- Left atrial volume is a key determinant of the changes in MAA, and preload reduction may help reduce FMR by decreasing left atrial and mitral annular size 3, 4.
Clinical Implications
- Preload reduction, such as with ACE inhibitors, may be beneficial in reducing FMR and improving symptoms in patients with chronic mitral regurgitation 5, 3.
- Assessment of LV systolic function in patients undergoing mitral valve repair is challenging due to the increased preload and decreased afterload in MR, but LV global strain measured by speckle tracking analysis may be a useful tool for detecting changes in contractile function after mitral valve repair 6.