**1. Introduction**

Valvular heart disease affects >100 million patients worldwide, which is estimated to increase further with the aging population and a subsequent increase in degenerative valve disease [1]. Based on analysis of the Society of Thoracic Surgery (STS) National Database, there are >40,000 mitral valve replacements being performed annually in the United States (US), with shift from mechanical to bioprosthetic valve replacements [1]. It is known that redo mitral valve surgery is associated with higher mortality compared to first mitral surgery; with 30-day mortality ranging from 6% for elective second mitral valve surgery and 17.8% for emergency surgery [2]. The risk of a third or fourth surgery is even higher; with 30-day mortality reaching up to 44% in urgent surgery [3]. As such, Transcatheter mitral valve replacement (TMVR) using aortic balloon-expandable transcatheter heart valves (THV) has been increasingly performed for patients with severe mitral valve disease who are not candidates for surgery [4]; as it emerged as a less invasive alternative option for these patients with relatively lower mortality than the predicted STS predicted rates of mortality [4]. Moreover, dedicated devices for TMVR have been developed and some are currently being studied [5–10]. Results of the clinical outcomes of TMVR are promising, but anatomical differences between mitral bioprosthetic valves, annuloplasty rings, and severely calcified mitral annulus are associated with specific procedural challenges for TMVR procedures [1, 4].
