Chronic ischemic mitral regurgitation and LV remodeling: new insights from a combined magnetic resonance and speckle tracking analysis

Background: Few studied compared transthoracic echocardiography (TTE) with cardiac magnetic resonance imaging (c-MRI) for evaluating the alterations of LV mechanics occurring in chronic ischemic mitral regurgitation (CIMR).Purpose: We assess if there were a relationship between the size and the location of the post-MI fibrosis, investigated with MRI and the alterations of the LV mechanics, examined with speckle-tracking echocardiography (STE), and if this link may affect the severity of CIMR. Methods: 27 pts (mean age 61.4±14) with CIMR underwent TTE and c-MRI with delayed enhancement (DE) analysis in the same day between the 6th and the 7th week after the acute event. Results: We found a significant correlation between TTE and c-MRI regarding LV end-diastolic (R=0.75, p<0.001), end-systolic volumes (R=0.90, P<0.001) and ejection fraction (EF) (R=0.87, p<0.001). Pts with anterior MI displayed a nonsevere CIMR (EROA=0.18±0.01cm2), but a greater LV remodeling (p=0.006), lower EF (p=0.003) and lower global longitudinal strain (GLS) (p<0.001) compared to pts with inferior and/or lateral MI. On the other hand, these latter pts had a severe CIMR (EROA=0.28±0.07 cm2, p=0.002) and a greater tenting area (p=0.003). EROA was related to volumes and GLS in pts with anterior MI, while to the base rotation and mitral annulus contractility in those with inferior and/or lateral MI. Moreover, there was a significant GLS reduction in the segments with DE at c-MRI, with a decreasing deformation gradient from the peri-infarct area (-12.8±4%), to the area with subendocardial DE (-8.7±4%) and with transmural DE (-7.2±0.9%). In pts without transmural DE at inferior segments there was a mild CIMR, whilst the pts with DE at least in one of the inferior segment showed mild CIMR in 50% of the cases, moderate in 25% and severe in the other 25% (p=0.04). Furthermore, pts with a DE in the inferior segments have a higher prevalence of asymmetric tethering (p=0.004), a greater EROA (p=0.03) and impaired basal rotation (p=0.02) compared to those without inferior DE. Finally, the longitudinal strain of the inferior segments with transmural DE was linked to the dimension of vena contracta (r=0.73, p=0.007). The semi-quantitative estimation of the myocardial fibrosis was given as percentage of the segments with transmural fibrosis over the total number of segments, whilst the implication of the inferior segments was evaluated with the index TS/INF (percentage of the segments with transmural scar normalized for the eight inferior segments). The TS/INF was linked with the tenting area (r=0.69, p=0.005) and with the coaptation depth (r=0.84, p<0.001). Conclusions: The inferior location of the transmural fibrosis after MI is related with a major severity of CIMR, a higher prevalence of asymmetric tethering, a lower mitral annulus contractility and a greater impairment of the basal rotation. The combined use of STE and c-MRI could be interesting for the clinical evaluation of these pts