By Jeffrey Zimmet, MD, PhD

Associate Professor of Medicine, University of California, San Francisco; Director, Cardiac Catheterization Laboratory, San Francisco VA Medical Center

Dr. Zimmet reports no financial relationships relevant to this field of study.

SYNOPSIS: In this analysis of MitraClip procedures from the Transcatheter Valve Therapy registry, the authors demonstrated improvements in procedure success and safety with increasing institutional experience with the device.

SOURCES: Chhatriwalla AK, Vemulapalli S, Holmes DR Jr, et al. Institutional experience with transcatheter mitral valve repair and clinical outcomes: Insights from the TVT registry. JACC Cardiovasc Interv 2019;12:1342-1352.

Stone GW. Volume-outcome relationships for transcatheter mitral valve repair: More is better. JACC Cardiovasc Interv 2019;12:1353-1355.

MitraClip is the only commercially available device for transcatheter mitral valve repair (TMVR) in the United States. The FDA approved it in 2013 for the treatment of degenerative mitral regurgitation (MR). Notably, the device has been available in Europe since 2007 for an expanded indication that includes both degenerative and functional MR. Most TMVR procedures in the United States are tracked through the Society of Thoracic Surgeons (STS)/American College of Cardiology Transcatheter Valve Therapy (TVT) registry. Although overall device safety and procedural success have been reported to be high, there is wide variability among operators and institutions in procedure volume for this relatively complex procedure. Chhatriwalla et al sought to investigate the relationship between hospital experience and clinical outcomes.

To do this, the authors examined TVT registry data from commercial MitraClip cases performed in the United States between November 2013 and September 2017. During this period, the authors analyzed 12,334 procedures performed at 275 centers. As expected for this population, patients were elderly (mean age, 81 years) with multiple comorbidities, including coronary disease and prior cardiac surgery, that placed them in the category of high or prohibitive risk for mitral valve surgery. Median STS mortality scores were 5.9% for mitral valve repair and 8.3% for mitral valve replacement. Ninety-three percent had 3+ or 4+ MR, and 84.8% were classified as New York Heart Association class III or IV by symptoms. In keeping with the original U.S. approval of the device, 86.5% had degenerative mitral valve disease.

Institutions were divided into tertiles by cumulative case experience. Tertile 1 included sites with between one and 18 cases of experience. Tertile 2 included 174 sites with between 19 and 52 cases of experience. Tertile 3 included 83 sites with between 53 and 482 cases of experience. Although baseline characteristics were similar among the groups, the highest tertile had higher rates of functional MR, hypertension, dialysis dependence, and leaflet calcification (but lower STS risk scores and rates of mitral stenosis).

Predictably, with increasing case experience, procedure duration decreased (139 minutes, 116 minutes, and 94 minutes, respectively among the three tertiles; P < 0.001), as did radiation exposure as measured by cumulative air kerma. This was seen despite the more common use of multiple clips as opposed to a single clip in the highest-tertile patients. Procedural success, defined as resulting MR grade ≤ 2+ without mortality or need for cardiac surgery, was similar among the groups, with a small but statistically significant improvement with higher experience (91.2%, 91.2%, and 92.9%, respectively; P = 0.006). Optimal procedural success, defined as achieving MR grade of ≤ 1+ without major complications, had a more noticeable improvement among sites in tertile 3 compared with the others (62.0%, 65.5%, and 72.5%, respectively; P < 0.001), while overall procedural complications were significantly less frequent among the more experienced sites (13.6%, 12.0%, and 11.5%, respectively; P = 0.013). However, there was no significant difference seen with major complications, including death (around 2% in each group), stroke, and cardiac perforation. A learning curve analysis showed that procedural success improved significantly after the first 50 cases and continued to improve up to 200 cases. The authors concluded that increased cumulative center case volume correlates with improved clinical outcomes with MitraClip, including successful reduction in MR, fewer complications, and shorter procedure times.


Measurement of volume-outcome relationships in interventional procedures always is a difficult topic, not only because of the complexities of obtaining accurate results, but also because of the politics of the inevitable discussion around the often-competing goals of maintaining quality while preserving access. In this study, clear improvements in outcome were seen after an institution’s first 50 cases or so, with continued improvement up to the first 200 cases. It is notable that, in contrast to other interventional procedures such as percutaneous coronary intervention and transcatheter aortic valve replacement, MitraClip has been a relatively lower-volume procedure in general. The median number of cases performed per site over the entire study period was only 30, while 101 of the 275 reporting sites performed 18 or fewer procedures. A relatively small number of sites achieved what the authors termed a “very high” case experience (more than 150 procedures).

On the topic of proctoring new centers and operators, one interesting aspect of this study was the observation that in adjusted (rather than the unadjusted data summarized above) models, only the association of procedure time with institution experience remained statistically significant. This suggests that case selection, rather than straightforward procedural skill (which explains faster completion of procedures), may play an outsized role in overall outcomes. Centers with more experience are likely to use that knowledge to choose patients who are most likely to benefit, while higher continuing volumes allow operators the confidence to turn down patients who will not. Whether remote assistance with case selection, rather than onsite proctoring of procedures, is a viable option for improving outcomes is an open question.

Data from this study are certain to fuel arguments on both sides of the quality vs. outcomes debate. In a related editorial, Stone noted that of course outcomes improve with experience in this complex procedure involving multiple team members and skill sets. Despite posing a large set of questions about learning curves, quality metrics, and patient selection, Stone avoided offering concrete recommendations. For now, referring physicians should make themselves aware of the case experience of their TMVR centers and consider sending more complex patients to larger referral institutions.