Complexities of transcatheter mitral valve replacement (TMVR) and why it is not transcatheter aortic valve replacement (TAVR)
Transcatheter mitral valve replacement (TMVR) is currently being investigated as a procedural alternative to surgical mitral valve repair or replacement (SMVR). Early data from first-in-man trials with current devices suggest that TMVR is technically feasible but carries a high mortality. This is substantially different from the early success transcatheter aortic valve replacement (TAVR) has seen and is related to complexities of the mitral valve anatomy, differences in pathology that require mitral valve replacement as well as the impact that mitral valve replacement has on physiology and cardiac function, irrespective of the modality by which the mitral valve is replaced. Importantly, in the case of TAVR, a less invasive method is offered to accomplish the same as the traditional surgical intervention. On the other hand, valve replacement is not the recommended treatment option for the majority of mitral valve disease, and in fact is avoided whenever possible during surgery given the shortened life expectancy and increased morbidity with mitral valve replacement. Another distinction between TAVR and TMVR is the etiology and natural progression of the underlying disease and driving factors for intervention that are vastly different between aortic and mitral valve disease. The primary aortic disease treated has been aortic stenosis, which has several etiologic factors that cause a similar physiologic dysfunction and risk. Aortic valve replacement leads to improved survival and quality of life. The primary mitral valve disease targeted is regurgitation, which occurs as a primary valve defect and as a secondary consequence of ventricular dysfunction. Primary mitral regurgitation is treated by valve repair with excellent long-term outcomes. Secondary regurgitation has poor long-term outcomes with current commonly used repair techniques and limited data exists showing that correction of the regurgitation improves survival. Adoption of TMVR will require overcoming the anatomic challenges as well as generating data that supports improved survival and/or quality of life.