Why Should We Repair Ischemic Mitral Regurgitation?

On the effects of leaflet microstructure and constitutive model on the closing behavior of the mitral valve

Recent long-term studies showed an unsatisfactory recurrence rate of severe mitral regurgitation 3-5 years after surgical repair, suggesting that excessive tissue stresses and the resulting strain-induced tissue failure are potential etiological factors controlling the success of surgical repair for treating mitral valve (MV) diseases. We hypothesized that restoring normal MV tissue stresses in MV repair techniques would ultimately lead to improved repair durability through the restoration of MV normal homeostatic state. Therefore, we developed a micro- and macro- anatomically accurate MV finite element model by incorporating actual fiber microstructural architecture and a realistic structure-based constitutive model. We investigated MV closing behaviors, with extensive in vitro data used for validating the proposed model. Comparative and parametric studies were conducted to identify essential model fidelity and information for achieving desirable accuracy. More importantly, for the first time, the interrelationship between the local fiber ensemble behavior and the organ-level MV closing behavior was investigated using a computational simulation. These novel results indicated not only the appropriate parameter ranges, but also the importance of the microstructural tuning (i.e., straightening and re-orientation) of the collagen/elastin fiber networks at the macroscopic tissue level for facilitating the proper coaptation and natural functioning of the MV apparatus under physiological loading at the organ level. The proposed computational model would serve as a logical first step toward our long-term modeling goal-facilitating simulation-guided design of optimal surgical repair strategies for treating diseased MVs with significantly enhanced durability.

Low-dose dobutamine stress echocardiography cannot predict mitral regurgitation reversibility after coronary artery bypass grafting

BACKGROUND

The ideal management of ischemic mitral regurgitation (MR) remains a clinical dilemma because of the suboptimal available therapeutic options. Recently, new concepts have emerged, pointing to the benefits of a patient selection approach when debating the management of moderate ischemic MR. We investigated the predictability of low-dose dobutamine stress echocardiography (DSE) in selecting candidates for CABG with moderate MR for valve repair.

METHODS

From November 2002 to May 2010, 110 candidates for first-time CABG, who were admitted to the cardiac surgery department in Day General Hospital (Tehran, Iran), were enrolled in the present cross-sectional study. DSE was performed for each case before CABG. Those with positive findings underwent CABG alone and those with negative results underwent concomitant CABG and mitral valve repair. The patients were followed up for a minimum of 60 months.

RESULTS

Of the 110 patients, 47 (42.72%) had positive test results and underwent CABG alone and 63 (57.28%) had negative DSE results and underwent concomitant CABG and mitral valve repair. The MR degree had decreased from 2.8±0.3 preoperatively to 1.46±0.6 early during the hospital stay and 1.9±0.7 during late follow-up in the CABG group. It had decreased from 2.84±0.4 preoperatively to 0.93±0.65 postoperatively but then increased to 1.41±0.9 during late follow-up, for a significant decrease in the combined group (P<.05).

CONCLUSIONS

Despite its utility in selecting CABG patients with moderate ischemic MR for valve repair from a short-term perspective, the use of DSE cannot predict the long-term outcomes of these patients.

Moderate mitral regurgitation accelerates left ventricular remodeling after posterolateral myocardial infarction

BACKGROUND

Chronic ischemic mitral regurgitation (MR) is associated with poor outcome. However, the effect of chronic ischemic MR on left ventricular (LV) remodeling after posterolateral myocardial infarction (MI) remains controversial. We tested the hypothesis that moderate MR accelerates LV remodeling after posterolateral MI.

METHODS

Posterolateral MI was created in 10 sheep. Cardiac magnetic resonance imaging was performed 2 weeks before and 2, 8, and 16 weeks after MI. Left ventricular and right ventricular volumes were measured, and regurgitant volume was calculated as the difference between LV and right ventricle stroke volumes.

RESULTS

Multivariate mixed effects regression showed that LV volumes at end diastole and end systole and LV sphericity were strongly correlated with both regurgitant volume (p < 0.0001, p = 0.0086, and p = 0.0007, respectively) and percent infarct area (p = 0.0156, p = 0.0307, and p < 0.0001, respectively). Conversely, whereas LV hypertrophy (LV wall volume) increased from 2 weeks to 16 weeks after MI, there was no effect of either regurgitant volume or percent infarct.

CONCLUSIONS

Moderate MR accelerates LV remodeling after posterolateral MI. Further studies are needed to determine whether mitral valve repair is able to slow or reverse MI remodeling after posterolateral MI.

Intraoperative TEE Assessment During Mitral Valve Repair for Degenerative and Ischemic Mitral Valve Regurgitation

Intraoperative assessment of the mitral valve (MV) in patients undergoing repair for MV regurgitation is a valuable support for the cardiac surgical team; results can be favored by adequate assessment tailored to the main condition affecting the MV. This article will review current available data for assessment of the MV in degenerative and ischemic mitral regurgitation.