An Analysis of Myocardial Efficiency in Patients with Severe Asymptomatic Mitral Regurgitation

Abstract

Background: It is difficult to determine left ventricular systolic performance in patients with severe mitral regurgitation (MR) since left ventricular ejection fraction (EF) could be preserved until the end stages of the disease. Myocardial efficiency (MEf) describes the amount of external work (EW) done by the left ventricle per unit of oxygen consumed (mVO₂). In the present study, we aimed to investigate MEf in patients with asymptomatic severe MR using a novel echocardiographic method.

Methods: A total of 27 patients with severe asymptomatic MR and 26 healthy volunteers were included in this cross-sectional study. EW was measured using stroke volume and blood pressure, while mVO₂ was estimated using double product and left ventricular mass.

Results: There were no differences between the groups with regards to EF (66% ± 5% vs. 69% ± 7%), while MEf was significantly reduced in patients with severe MR (25% ± 11% vs. 44% ± 12%, p < 0.001). This difference was maintained even after adjustment for age, gender and body surface area (adjusted x̅: 0.44, 95% CI: 0.39-0.49 for controls and adjusted x̅: 0.24, 95% CI: 0.19-0.29 for patients with severe MR). Further analysis showed that this reduction was due to an increase in total mVO₂ in the severe MR group. MEf of thepatients who were both on β-blockers and angiotensin converting enzyme inhibitors/angiotensin receptor blockers were higher than those who were not on any drugs, but this difference was not statistically significant (32% ± 15% vs. 23% ± 9%, p = 0.41).

Conclusions: MEf was significantly lower in patients with asymptomatic severe MR and preserved EF.

Keywords: Echocardiography; Left ventricular function; Mitral regurgitation; Myocardial efficiency.

Figure 1. Two case examples for calculation of myocardial efficiency in those with and without significant mitral regurgitation. Panels A-D show echocardiograms for an otherwise healthy 35-year-old female with a blood pressure of 100/60 mmHg. Trace mitral regurgitation can be seen in panel A. Her left ventricular external work and total myocardial oxygen consumption were calculated as 35.6 j and 63.1 j, yielding a myocardial efficiency of 56.4%. Panels E-H show a 46-year-old male patient followed up with rheumatic mitral valve disease and severe eccentric mitral regurgitation (E) with normal ejection fraction. His blood pressure was 130/60 mmHg at the time of echocardiographic examination. For the latter case, left ventricular external work and total myocardial oxygen consumption were calculated as 91.3 j and 330.4 j, resulting with a much lower myocardial efficiency (27.6%) as compared to the first case.

Figure 2. Boxplot graphics for left ventricular ejection fraction (A), systolic velocity of lateral mitral annulus (B) and myocardial efficiency (C) between study groups. The only comparison that was statistically significant between groups was myocardial efficiency. Points show outlying cases.

Figure 3. Boxplot graphics for stroke work (A), minute external work (B), mVO₂ per 100 g of myocardium (C) and total mVO₂ (D) between groups. Note that there were no significant differences between groups with regards to the work being done, while oxygen consumption to generate this work was significantly higher in patients with mitral regurgitation, thus explaining the decrease in the myocardial efficiency in the latter group. Points show outlying cases. mVO₂: myocardial oxygen consumption.