Defining the clinical need and indications: who are the right patients for transcatheter mitral valve replacement.

Mitral regurgitation (MR) can be divided into two major etiologies, primary and secondary MR. Primary MR, also termed degenerative or organic MR, is a disease of the valve itself and is treated routinely by surgical repair in all but prohibitive risk patients. In these patients, transcatheter repair techniques, including edge to edge repair with the MitraClip device have been largely successful and widely adopted. Transcatheter placement of artificial chords has also been performed. The potential role for transcatheter mitral valve replacement (TMVR) in primary MR will likely be quite limited. Secondary or functional MR is due to a disease of the left ventricle and not the valve itself. The MR is a result of dilation of the left ventricle causing distraction of the papillary muscles with tethering of the mitral leaflets and lack of leaflet coaptation. Medical therapy is the mainstay treatment, with resynchronization used in appropriate patients. Surgical repair, usually with an undersized annuloplasty, is used in a limited number of patients. Transcatheter edge to edge repair is used extensively outside the US in secondary MR and is the subject of a pivotal trial in the US. However, it is in this group of patients with secondary MR that there is the largest clinical unmet need and, hence, the greatest potential opportunity for TMVR. At least ten TMVR platforms are in early feasibility, first in human, or preclinical trial stages. Four devices have cumulative early human experience in <100 patients. In this article, we discuss those patients most likely to benefit from TMVR and detail lessons learned from the first human studies regarding patient selection.