EFFECTS OF LEFT-VENTRICULAR VOLUME OVERLOAD PRODUCED BY MITRAL REGURGITATION ON DIASTOLIC FUNCTION

We hypothesized that the left ventricle's ability to compensate for the volume overload produced by mitral regurgitation (MR) depends, at least in part, on associated changes in left ventricular (LV) diastolic function. Indexes of the rate of LV pressure decline, the rate and extent of early diastolic filling, and LV diastolic stiffness were measured with simultaneous echocardiography and catheterization in the baseline state (baseline), immediately after creation of MR (acute MR), and 3 mo after creation of MR (chronic MR). Data are means +/- SD. MR caused LV dilation, end-diastolic dimension increased from 4.3 +/- 0.4 in baseline to 4.7 +/- 0.5 in acute MR and 5.8 +/- 0.1 cm in chronic MR (P < 0.05 vs. baseline for both). Chronic MR caused eccentric LV hypertrophy; LV-to-body weight ratio increased from 3.6 +/- 0.3 in baseline to 4.5 +/- 0.2 g/kg in chronic MR (P < 0.05 vs. baseline). Acute MR increased LV end-diastolic pressure from 8 +/- 4 in baseline to 15 +/- 3 mmHg (P < 0.05 vs. baseline); chronic MR did not further increase LV end-diastolic pressure (14 +/- 4 mmHg). MR increased the transmitral pressure gradient from 5 +/- 1 in baseline to 14 +/- 3 in acute MR and 20 +/- 6 mmHg in chronic MR (P < 0.05 vs. baseline for both). MR increased LV early diastolic filling rate; peak rate of increase in minor axis dimension increased from 11 +/- 2 baseline to 18 +/- 2 in acute MR and 19 +/- 2 cm/s in chronic MR (P < 0.05 vs. baseline for both). Acute MR did not change LV stiffness constants. Chronic MR decreased LV stiffness; the modulus of chamber stiffness decreased from 7.1 +/- 2.8 in baseline to 2.9 +/- 1.6 in chronic MR (P < 0.05 vs. baseline). Thus MR caused compensatory changes in LV diastolic function. These changes resulted from an increased transmitral pressure gradient and increased LV distensibility.