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SAN FRANCISCO -- Transcatheter and surgical mitral valve procedures alike demonstrated a learning curve in studies reported here that some said has implications for the organization of these services in the U.S.

There was no debate that a volume-outcome relationship exists in mitral valve repair and replacement among panelists at a press conference for the late-breaking clinical trials session at the annual (TCT) meeting.

The learning curve is important because of the expected "explosion" in mitral valve procedures now that the MitraClip has been recently approved by the FDA for secondary mitral regurgitation in heart failure, said Robert Bonow, MD, of Northwestern University in Chicago.

Geographical organization of facilities becomes increasingly important as stakeholders ponder how to maintain volumes and operator experience while preserving access to procedures in the mitral space -- a controversy that has already taken hold in transcatheter aortic valve replacement.

Starting in July 2020, "the U.S. News and World Report will be publicly reporting center volumes as well as mortality for TAVR. Then, the professional societies, in the TVT Registry in December, will be publicly reporting the same thing," said fellow panelist Michael Mack, MD, of Baylor Scott & White Health in Dallas.

"MitraClip is not that far along," he predicted. "Probably another year after that."

"It just strikes me that hospital systems are too competitive," said Adnan Chhatriwalla, MD, of Saint Luke's Mid America Heart Institute in Kansas City, Missouri. He acknowledged a current proposal for a tiered valve system in the U.S. but also suggested that some hospitals could be mitral valve centers while others focus on TAVR.

This would be one way to make things less competitive so that experienced operators can continue to provide good care, he said.

MitraClip Procedures

Operators start to get good at the MitraClip procedure only after 50 or so cases, according to an analysis of the TVT Registry from the American College of Cardiology and Society of Thoracic Surgeons.

Odds of optimal procedural success in transcatheter mitral valve repair -- survival with residual MR less than grade 1 and no conversion to cardiac surgery -- grew increasingly likely with greater operator experience: 63.9% for cases up to 25, 68.4% for cases 26-50, and 75.1% for cases thereafter (P<0.001).

A similar trend was noted for the likelihood of acceptable procedural success -- leaving patients with up to grade 2 residual MR without death or cardiac surgery -- as chances grew slightly better with growing case experience (91.4%, 92.4%, 93.8%, P<0.001), Chhatriwalla reported.

"The learning curve for MitraClip appears to flatten after approximately 50 cases. However, the overall duration of the learning curve may exceed 200 cases," he added, noting that the findings persist after adjustment and in continuous variable analyses.

"[I]t may be prudent for less experienced operators to be cognizant of where they sit on the 'learning curve' and to pay particular attention to case selection early in their experience, considering that more complex patients may be referred to more experienced centers for treatment when prudent," Chhatriwalla's team suggested in their report simultaneously published in the Journal of the American College of Cardiology.

The study was based on the nearly 15,000 MitraClip procedures performed from November 2013 to March 2018 by 562 operators at 290 sites participating in the TVT Registry.

Only 116 operators accrued more than 50 MitraClip cases during the study period. "It could take years to get there if you're a lower-volume operator," Chhatriwalla said.

With more experience, operators took less procedure time and cut back on radiation exposure. They became more likely to use more than one clip, place these in the A2-P2 (central) and A3-P3 (medial) segments, and opt for atrial septal defect closure as well.

Greater experience was associated with reductions in cardiac perforation and blood transfusion; however, there was no improvement in stroke, single-leaflet device attachment, trans-septal complications, urgent cardiac surgery, or in-hospital mortality rates.

The study was limited by its retrospective and observational nature.

"Of note, our study focused only on short-term procedural and in-hospital outcomes, and further research into long-term results is needed, particularly as these patients commonly have severe morbidities that may impact their survival despite early procedural success," Chhatriwalla and colleagues added.

Nonetheless, the MitraClip learning curve is noticeably different from that for TAVR, commented panel moderator Ajay Kirtane, MD, of Columbia University Medical Center/NewYork-Presbyterian Hospital in New York City.

Generally, the more complex the procedure, the more important the volume-outcome association, suggested Mack, and MitraClip is certainly more complex than TAVR. It's not just about the repair either -- it's also the patient selection, the etiology of the valve disease, and the intraprocedural imaging, he said.

Mitral Valve Surgery

As for surgeons, mitral valve repair and replacement require fewer cases to gain proficiency and avoid 30-day operative mortality for the patient, according to a study reported at TCT.

Individual surgeons appeared to be over the hump after achieving 35 cases per year, reported Vinay Badhwar, MD, of WVU Heart & Vascular Institute in Morgantown, West Virginia.

On the hospital level, greater annual procedural volume was associated with better outcomes with an inflection point around 75 cases per year for both patient death and successful repair rates, Badhwar's group found in the analysis based on a Society of Thoracic Surgeons database representing more than 95% of all adult mitral valve operations in the U.S.

The dataset included more than 55,000 patients with primary MR who went under the knife at 1,111 hospitals in the hands of 3,137 surgeons. Post-procedural outcomes were retrieved from the Centers for Medicare & Medicaid Services.

There were 148 hospitals (14%) that met the 75-cases-a-year threshold; 303 surgeons (13%) performed at least 35 cases annually.

"These numbers actually show not only is there a clear , but the number of surgeons and hospitals providing this degree of good outcomes is actually higher than ... currently thought," Badhwar said.

Notably, centers in the lowest volume quartile (fewer than 11 cases annually) were more likely than the highest quartile (more than 46 a year) to offer mitral surgery to patients without insurance and to treat more black and Hispanic patients and people presenting with New York Heart Association class III/IV symptoms.

"These findings may further inform guideline-directed efforts to define access to experienced hospitals and surgeons for primary MR or complex mitral valve disease," Badhwar told the audience.

Mack suggested that mitral valve surgery should be its own "super-subspecialized" field.

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