Patients who received a mechanical prosthesis for surgical replacement of aortic or mitral valves derived a significant long-term survival benefit versus those who received a biologic prosthesis, according to a study in the New England Journal of Medicine.

The long-term mortality benefit was present in individuals up to 70 years old for mitral valves and patients up to 55 years old for aortic valves. The findings challenge the current trend of more biologic valves being implanted, particularly in younger patients, wrote lead researcher Andrew B. Goldstone, MD, PhD, and colleagues.

“Previous studies of mitral valve replacement (MVR) have suggested that biologic prostheses may be safe in younger patients,” the authors wrote. “Our findings challenge this assertion and suggest that the current trend toward abandoning mechanical mitral valves in younger patients should be tempered. The large sample size that is required in order to detect a mortality difference in this population suggests that smaller studies were underpowered, and some studies lack generalizability because of strict exclusion criteria or restriction to a single center.”

Goldstone et al. studied data from 9,942 patients who underwent aortic valve replacement (AVR) and 15,503 who underwent MVR in California from 1996 through 2013. Those who had previous cardiac surgery, multiple valve replacements, aortic valve repair or mitral valve repair were excluded.

Patients were stratified by age group: 45 to 54 and 55 to 64 years for AVR; and for MVR, 40 to 49, 50 to 69 and 70 to 79 years. The following results were reported:

• For AVR, biologic valves were used 11.5 percent of the time in 1996 and 51.6 percent of the time in 2013. For MVR, the usage rate of biologic valves jumped from 16.8 percent to 53.7 percent. This trend was evident across all age groups for both procedures.
• 15-year mortality in AVR patients aged 45 to 54 was predicted at 30.6 percent or patients receiving biological valves and 26.4 percent for those receiving mechanical valves. There were no significant differences for 30-day mortality in either age group, or for long-term mortality in patients aged 55 to 64.
• Likewise, for MVR patients, 15-year mortality was higher for recipients of a biologic prosthesis in patients aged 40 to 49 (44.1 percent vs. 27.1 percent) and 50 to 69 (50 percent vs. 45.3 percent). There was no significant difference in long-term mortality among patients in their 70s at the time of surgery. Thirty-day mortality only differed in the 40-49 age group—5.6 percent for biologic valves and 2.2 percent for mechanical valves.

For both MVR and AVR, the authors noted, mechanical prostheses were associated with a significantly lower risk of reoperation but higher risks of other complications. Younger patients generally had reoperations sooner than older patients did.

“The mortality benefit that is afforded by mechanical prostheses comes at the cost of higher risks of bleeding and, in some age groups, stroke,” Goldstone and colleagues wrote. “Both events appeared to be associated with higher long-term mortality in our study and may be factors in the mortality advantage that was seen with biologic prostheses in older patients. However, for younger patients, these risks are clearly outweighed by the advantages of mechanical valves.”

The authors acknowledged the 18-year length of the study raises concerns over whether changes in practice over time influenced results. In addition, the growth of alternative treatments such as mitral valve repair and transcatheter aortic valve replacement may have biased the results.

“As transcatheter technologies develop, the risk associated with reoperative surgery will change,” they wrote.