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HOUSTON -- Occurrence of patient-prosthesis mismatch in surgical aortic valve replacement (SAVR) procedures appears to impact survival and long-term complications but use of transcatheter aortic valve replacement (TAVR) in patients with smaller aortic annuli may prove better for the patient, researchers reported here.

In one study, instructor in surgery at the Geisel School of Medicine at Dartmouth University, Hanover, N.H., reported that in cases of severe mismatch in SAVR patients, the 10-year adjusted overall survival was 35% compared to a 10-year adjusted overall survival of 46% among patients where there was no patient-prosthesis mismatch (P<0.0001).

And in a second study presented at the annual meeting of the Society of Thoracic Surgeons, professor of surgery at the University of Michigan, Ann Arbor, reported that TAVR appeared superior to SAVR in 2-year measurements of effective orifice area irrespective of initial annulus size, but especially so with smaller annuli.

Deeb and colleagues also found that patient-prosthesis mismatches were more common in SAVR patients with small and medium annuli, which were not seen in TAVR patients. Deem said that patients with small and medium annular size should be strongly considered for TAVR.

Prosthesis‐patient mismatch occurs when the effective orifice area of the inserted prosthetic valve is too small in relation to body size. Such a mismatch generates higher than expected gradients through normally functioning prosthetic valves, and that can lead to symptoms, need for re-operation, and reduced life expectancy, said chief of cardiothoracic surgery at Oregon Health and Science University in Portland. Song moderated a late-breaker session at which Deeb's work was presented.

In his study, Fallon accessed data from the Society of Thoracic Surgeons Adult Cardiac Surgery Database, identifying 59,779 SAVR patients who were 65 years of age or older who had undergone isolated surgical aortic valve replacement between 2004 and 2014. These patients were linked to Medicare claims data. The extent of patient-prosthetic mismatch was calculated using literature-derived effective orifice areas for commonly used valves. The mismatch was stratified by degree of mismatch: None was a mismatch of less than or equal to 0.85 cm²/m²; moderate was 0.85-0.65 cm²/m², and severe mismatch was less than 0.65 cm²/m².

In the study, patients judged to have no mismatch accounted for 21,053 of the cohort; 32,243 patients fit the moderate criteria and 6,483 patients were judged to have had severe mismatch. The severe mismatch patients were about 75 years of age; the patients in the other groups were about 77 years of age, a significant difference (P<0.0001). About 48.5% of the patients in the study were women. The average body mass index was 28.4 kg/m², with significant differences between the groups. Those with no mismatch had a body mass index of 26.7 kg/m² compared with a body mass index of 32.7 kg/m² in those with severe mismatch.

Fallon said that there was a significant 8% increase in mortality when the moderate group was compared to the group with no mismatch (HR 1.08 [95% CI 1.05-1.12]); there was a 32% increased risk of mortality when the severe group was compared with the group with no mismatch (HR 1.32 [95% CI 1.25-1.39]), and there was a 22% increased risk of mortality when the moderate group was compared with the severe group (HR 1.22 [95% CI 1.16-1.28]).

Readmission rates followed a similar pattern, with a rate of 17% over 10 years for patients with no mismatch versus 22% of the patients with severe mismatch (P<0.0001), he said in his oral session. The rates for a re-do aortic valve replacement were low but also depended on extent of mismatch. About 3% of those with severe mismatch required a new valve compared with 1.2% of those with no mismatch (P<0.001).

Fallon noted that his research indicates that the rate of mismatch has been declining over the last decade.

In his study, Deeb drew on data from a previous trial comparing TAVR to SAVR. He and colleagues scrutinized various relationships between the size of the prosthesis, the size of the aortic annulus and whether the patients underwent surgical replacement procedures or TAVR. There were 389 patients in the TAVR group and 347 patients in the surgical group.

When comparing the two methods of implanting the devices, he observed no difference in mortality for patients with large annuli – a 26.2% mortality among the 115 patients treated with TAVR compared with a 26.6% mortality among the 96 patients who underwent surgical replacement (P=0.99). There was a numerical advantage to using TAVR in the patients with small annuli -- 22.6% mortality among the 104 patients treated with TAVR and a 25.2% mortality among the 74 patients treated with surgery (P=0.70). But in the moderate group, there was an 18.3% mortality among the 170 TAVR patients compared with a 29.9% mortality among the 177 patients undergoing surgical replacement.

In discussing the trials, moderator Song told 麻豆传媒, "For patients with a small aortic valve annulus, Dr. Deeb's study suggests that the patients have better valve function after undergoing a TAVR as opposed to a surgical aortic valve replacement. This will help to inform clinical decision making."

"It won't just put people into a bucket, but it is another factor that helps us add to the clinical scenario along with the patients' age, how active they are, what kind of surgical candidate they are."

Song said that mismatch can occur even when the devices fit perfectly – they still can act differently in the body which can impact their function. "You can't determine how the device with function in an individual until after the implant is completed," he said. "A mismatch doesn't mean you will have complications down the road, but it does increase the risk that complications will occur."