Transcatheter mitral valve therapies

Abstract

Dr.O.P. Yadava, Editor-in-Chief, IJTC and Dr. V Bapat, Assistant Professor at Columbia University, New York, discuss issues related to slow development and uptake of transcatheter mitral valve replacement. Dr. Bapat stresses on the basic difference between transcatheter aortic and mitral valve interventions. He laments that issues related to mitral valve repair versus replacement and role of percutaneous MitraClip are still being hotly debated. He, however, is hopeful that technology shall evolve to make percutaneous options for secondary mitral regurgitation a viable proposition.

Electronic supplementary material

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Dr. Bapat differentiates between “technique” and “technology.” He feels cardiac surgery is a technique, which cannot be taught if one does not have talent. However, transcatheter options are technologies which can be learned more easily. As surgeons, we are at an advantage to take to this new technology due to our better understanding of cardiac anatomy and patho-physiology.

Commenting on transcatheter mitral valve replacement (TMVR), Dr. Bapat feels that there are challenges, which are related to the complexities of anatomy and physiology of the mitral valve [1] as well as engineering issues. Anatomically, mitral valve is bigger, flexible, and is not visible under fluoroscopy. Even transesophageal echocardiography (TEE) imaging is patient-dependent. There are also basic differences from transcatheter aortic valve replacement (TAVR) in the sense that transcatheter mitral valve is fixed under systolic pressure and is not diastolic as in TAVR. Further, they have to open at a very low pressure, so that the valves have to be very sophisticated and refined. Physiologically, there are issues related to closing pressure. Anticoagulation requirement in these patients and even the potential for left ventricular outflow tract obstruction are important considerations. There are major challenges for engineering as well because these valves are four times bigger than TAVR valves and have multiple components which are prone to fracture. As currently, these valves are 40 Fr in size, they cannot be deployed through the transfemoral route and are therefore implanted trans-apically. The latter, however, has been shown to be sub-optimum in TAVR experience and that remains a major limitation. The growth of TMVR therefore is going to be slow but sure enough, technology should and would evolve to surmount these problems.

Dr. Bapat introduces the concept of the tool box for TMVR consisting of repair and replacement tools, as against TAVR which has only the replacement option. Even the varied presentation of mitral regurgitation (MR), with the spectrum of primary MR varying from a flail P2 to the most extensive valvular disease, as well as no clarity of the benefits to be derived from the interventions in secondary MR are not helping matters. One does not even know at which point in time in secondary MR is survival benefit lost. Even the role of repair versus replacement is not clear, as the latter has been shown to be better in the CTS Net Trial [2]. The current state of transcatheter mitral valve repair (MVr) is that it is safe, as has been demonstrated by the MitraClip trials, but efficacy is a matter of debate [3, 4]. As against this, in TMVR, even the safety concerns exist, as the mortality may vary from 0 to 50% in various units. The first step in TMVR is to bring the mortality to under 5% and 1 year survival to at least 75% to make this technique viable.

Crystal gazing Dr. Bapat feels that for primary MR, surgical MVr techniques are very standardized and are going to stay as gold standard for times to come, but in matters of secondary MR, transcatheter options for repair and replacement look promising. Another area where transcatheter mitral valve options may be more suited than surgery is redo situations. Dr. Bapat strongly feels that all surgical trainees must undergo a rotation of at least 6 months in cath lab for learning catheter skills.