Invited Commentary

Abstract

The inability to predict the response of the left ventricle to myocardial revascularization and mitral valve repair in ischemic mitral regurgitation (MR) patients remains problematic. Morgan and colleagues [1Morgan A.E. Zhang Y. Tartibi M. et al.Ischemic mitral regurgitation: abnormal strain overestimates nonviable myocardium.Ann Thorac Surg. 2018; 105: 1754-1762Abstract Full Text Full Text PDF Scopus (10) Google Scholar] compared the ability of tagged cardiac magnetic resonance imaging (MRI) and late gadolinium-enhanced (LGE) MRI to determine the amount of nonviable myocardium in patients with ischemic MR. Their hypothesis was that strain measurements using tagged cardiac MRI overestimate the amount of nonviable myocardium in ischemic MR when compared with LGE MRI, suggesting that much of the myocardium deemed nonviable by strain measurements is actually viable but nonfunctional (ie, stunned or hibernating). This is a critical issue because it is believed that the degree of stunned myocardium in patients with ischemic MR correlates not only with functional myocardial recovery due to revascularization but also with the degree of ventricular remodeling and, thus, the success or failure of mitral valve surgery in these patients. Although LGE MRI is helpful in identifying nonviable myocardium, it is not necessarily as helpful in determining the response of viable myocardium to surgery for ischemic MR. Gadolinium chelate distributes in the extracellular space but does not cross the intact cell membrane. Through a combination of increased extracellular volume and slower washout kinetics, there is a relative accumulation of gadolinium in areas of necrosis, fibrosis, and inflammation in the late washout phase. LGE MRI depends on this relative accumulation of gadolinium in areas of damaged myocardium, but it may miss areas of diffuse fibrosis and underestimate the true extent of nonviable muscle. Grapsa and colleagues [2Grapsa J. Zimbarra Cabrita I. Jakaj G. et al.Strain balance of papillary muscles as a prerequisite for successful mitral valve repair in patients with mitral valve prolapse due to fibroelastic deficiency.Eur Heart J Cardiovasc Imaging. 2015; 16: 53-61Crossref PubMed Scopus (3) Google Scholar], using 3-D echo speckle-tracking, showed that a disproportionate increase in the deformation of the papillary muscles is a predictor of recurrent MR following mitral valve annuloplasty and that global longitudinal deformation depends on the degree of mitral regurgitation. The amount of deformation of the mitral apparatus in patients with only minor degrees of MR was zero. It would be instructive to include tagged cardiac MRI and LGE MRI in a group of patients with ischemia and no MR to compare with patients with ischemic MR. Pasque and associates used MRI-based multiparametric strain data calculated from 15,300 grid points per patient in normal volunteers and in ischemic patients with and without MR [3Lancaster T.S. Kar J. Cupps B.P. et al.Topographic mapping of left ventricular regional contractile injury in ischemic mitral regurgitation.J Thorac Cardiovasc Surg. 2017; 154: 149-158.e1Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar]. They showed that ischemic MR is caused by dysfunction of the subpapillary ventricular wall and that the free ventricular wall segments outside the subpapillary regions showed the same strain patterns in ischemic MR patients and in ischemic patients without MR. The relationships between nonviability, functional recovery, and response to surgical intervention for ischemic MR are not yet clear. What is needed now are studies comparing these types of preoperative measurements in patients with ischemic MR with similar postoperative measurements on the same patients that might clarify the preoperative parameters that are truly capable of predicting postoperative outcomes. Perhaps we would then have a better understanding of precisely how to treat ischemic MR in individual patients. Ischemic Mitral Regurgitation: Abnormal Strain Overestimates Nonviable MyocardiumThe Annals of Thoracic SurgeryVol. 105Issue 6PreviewTherapy for moderate ischemic mitral regurgitation remains unclear. Determination of myocardial viability, a necessary prerequisite for an improvement in regional contractility, is a likely key factor in determining response to revascularization alone. Myocardial strain has been proposed as a viability measure but has not been compared with late gadolinium enhancement (LGE) cardiac magnetic resonance imaging. We hypothesized that abnormal strain overestimates nonviable left ventricular (LV) segments measured with LGE and that ischemia and mechanical tethering by adjacent transmural myocardial infarction (TMI) also decreases strain in viable segments. Full-Text PDF