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An early experience with transcatheter mitral valve replacement (TMVR) was mostly successful in a challenging population with severe mitral annular calcification, a multicenter registry study suggested.

The rate of technical success was 72%, mostly due to the need for a second valve in 17.2% of patients. Another 9.3% developed left ventricular outflow tract obstruction with hemodynamic compromise, reported , of Evanston Hospital, Ill., and colleagues.

Also, immediately after TMVR, the mean mitral gradient was 4 mm Hg and paravalvular regurgitation was mild or absent, they wrote in .

Further out, 30-day all-cause mortality occurred in 29.7% of patients, with cardiovascular death in 12.5%. Among the survivors at this point, 84% were mildly symptomatic or asymptomatic at 30 days (New York Heart Association functional class I or II), they stated.

Even with the high death rate, "this strategy might be an alternative for selected high-risk patients with limited treatment options," the authors suggested. "The results we report are similar to the complications and mortality reported in the initial experience with transcatheter valves designed for the mitral valve to treat patients with mitral regurgitation."

"These results are encouraging considering this represents the first human experience with a transcatheter heart valve not designed for the mitral position and used in an extremely high-risk patient population with a mean Society of Thoracic Surgeons risk score higher than in the PARTNER I trial," they noted.

In an accompanying editorial, , and , both of Abbott Northwestern Hospital in Minneapolis, called the findings "pioneering."

"A new boundary was crossed with successful TMVR therapy for severe mitral annular calcification, which previously was considered to be hostile, through the adaptation of an off-label prosthesis for the procedure. One can therefore consider, with enthusiasm, the potential possibilities for success once dedicated prostheses become available, and how the unmet needs of many patients with mitral regurgitation will be finally addressed," they wrote.

However, many questions remain concerning technique, durability, and patient selection for TMVR. Guerrero and colleagues pointed to the ongoing for more answers in the future.

Her group's retrospective analysis included 64 patients with severe mitral annular calcification who underwent TMVR with compassionate use of balloon-expandable valves. Procedures were performed from 2012 to 2015. The mean patient age was 73 and 66% were female, with a mean Society of Thoracic Surgeons score of 14.4%.

Valves involved were the SAPIEN (7.8% of cases), SAPIEN XT (59.4%), SAPIEN 3 (28.1%), and Inovare (4.7%). Access was mostly transseptal (40.6%), followed by transapical (43.8%) and transatrial (15.6%).

Besides the inherent limitations as a registry study, the investigation was weakened by a small sample size and a large amount of missing data. Additionally, "it is possible that newer repositionable and retrievable valve designs might be more beneficial in this patient population," according to the authors.

"The use of the Lotus valve and Direct Flow has been reported with success in patients with severe mitral annular calcification. The option of repositioning or retrieving the valve in the setting of TMVR-induced left ventricular outflow tract [LVOT] obstruction is an important advantage over the balloon-expandable valve technology," they pointed out.

Yet Guerrero's group cautioned that both valves can only be delivered via the transapical route at this time.

"There were no instances of annular rupture or perforation in the entire cohort, there was no moderate or severe residual mitral regurgitation in those with follow-up echocardiography (n=22), and the procedure was performed without the coaxial support and added safety of transcatheter rails in most patients," Sorajja and Gössl emphasized.

"These results are notable, as this procedure was novel for nearly all of the operators in this registry, with experience at each participating institution being markedly limited (64 patients treated at 32 sites) and with little or no guidance on technical considerations, including patient selection, annular sizing, prosthesis positioning, and complication management."

The TMVR learning curve is steep, Guerrero and colleagues agreed, though they found cardiac CT to be the best method for annulus sizing, adding that this modality can help evaluate the amount and distribution of calcium as well as show an ideal access trajectory.

Importantly, "as the operators learned about annulus sizing, LVOT obstruction risk assessment, anchorage prediction assessment and better patient selection, there was a decreased rate of major cardiac complications and overall mortality," they noted.