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The population undergoing mitral valve surgery has changed significantly, without a reduction in case volumes, since the arrival of transcatheter edge-to-edge repair (TEER) as a minimally invasive alternative.

Nationwide, there was a downtrend in both intermediate-risk and high-risk surgical mitral valve repair (MVr) volumes at centers that adopted TEER for degenerative mitral regurgitation (MR). The median annualized institutional MVr volume nevertheless stayed around 30 per center (32 before adoption vs 29 after first TEER, P=0.06), reported Andrew Vekstein, MD, a cardiothoracic surgeon at Duke Clinical Research Institute in Durham, North Carolina, and colleagues.

Notably, passing the hurdle of the first institutional TEER was associated with reduced odds of mortality after MVr at 30 days (adjusted OR 0.73, 95% CI 0.54-0.99) and over 5 years (adjusted HR 0.75, 95% CI 0.66-0.86) among participating hospitals, they noted in the .

These improvements in mortality were significantly greater than equivalent trends in coronary artery bypass grafting, "suggesting that the introduction of TEER rather than other perioperative/operative care factors alone may have influenced surgical MVr outcomes," Vekstein and team suggested.

In 2013, the FDA first approved the MitraClip for the treatment of severe degenerative MR in people at prohibitive surgical risk. The indication was expanded to functional MR in 2019.

MitraClip was recently folded into the category of TEER technology for reimbursement purposes, and to make room for competitors such as the , which was approved for degenerative MR by the FDA last September.

"The slight downtrend in intermediate-risk patients (by PROM [predicted risk of mortality] and age) may suggest that "indication creep" has occurred with lower-risk patients already being referred to TEER," Vekstein's group noted.

This theory is supported by the 2020 Society of Thoracic Surgeons (STS)/American College of Cardiology (ACC) transcatheter valve therapy report, which showed a significant decrease in the median calculated surgical predicted risk of mortality for patients undergoing TEER, said interventional cardiologists Matthew Sherwood, MD, MHS, of Inova Heart and Vascular Institute in Falls Church, Virginia, and Wayne Batchelor, MD, MHS, also of Duke Clinical Research Institute, in an .

"Low-risk patients are less likely to have surgical complications while in hospital, recover more quickly, and are more likely to survive to the 5-year timepoint compared with their higher-risk counterparts. This shift in case mix would seem to be a more likely explanation for the modest improvement in outcomes for surgical MVr," Sherwood and Batchelor wrote.

Important questions remain regarding the relative net clinical benefit, or detriment, of shifting large volumes of surgical MVr to TEER. Researchers are currently studying the comparative efficacy and safety of TEER in patients at low or moderate surgical risk in several randomized trials, namely and .

The present study relied on linked records from a prospective STS database and Medicare administrative claims. Vekstein and colleagues identified 13,959 patients who underwent MVr at 278 institutions that became TEER-capable from July 2011 through December 2018.

Each center had a median annualized TEER volume of 17 procedures during the study period. Sites with an annualized TEER volume below the fifth percentile (six cases per year) over the study period were excluded.

Patients undergoing MVr after the introduction of TEER tended to be slightly younger (median 72 vs 73 years, P<0.001) and less commonly presented with comorbidities such as chronic lung disease (4.7% vs 7.6%, P<0.001) and New York Heart Association functional class III or IV heart failure (18.5% vs 27.8%, P<0.001).

Vekstein and colleagues reported improved trends in in-hospital mortality, major morbidity, heart failure hospitalization, and mitral valve reintervention that did not appear to be unique to MVr and may be due to temporal improvements in general perioperative care.

Such a difference-in-difference analysis is a "useful and previously validated statistical technique, but the challenge of separating the effects of time, improvement in experience, and surgical techniques from other factors remains difficult," Sherwood and Batchelor cautioned.

"Short-term data were derived from the STS registry which, although representative of MVr across the United States, relies on self-reported outcomes. Also, only approximately two-thirds of the MVr population could be linked to the Centers for Medicare & Medicaid Services database for evaluation of long-term outcomes," they added.

Vekstein's group also acknowledged the usual limitations of a retrospective large registry study, including selection bias and unmeasured confounding.

For now, "the results would seem to be good news for surgeons, interventionalists, and patients alike. The study suggests that initiation of TEER procedures does not adversely impact a center's surgical MVr volume and may have a positive effect on short-term and long-term outcomes," the editorialists wrote.

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