Aortic Valve Prosthesis-Patient Mismatch  (Size Doesn’t Make Much Difference)

abstract & commentary

By Jonathan Abrams, MD

Synopsis: A majority of patients report improvement in functional quality of life early after AVR. Similar functional recovery was demonstrated for patients along the full spectrum of valve sizes indexed to body size, even for values considered to represent severe mismatch for patient size. Factors other than prosthesis-patient size influence functional quality of life early after AVR.

Source: Koch CG, et al. Impact of Prosthesis-Patient Size on Functional Recovery After Aortic Valve Replacement. Circulation. 2005:111:3221-3229.

Prosthesis-patient mismatch relates to a smaller prosthetic valve size than the relevant native valve, in relation to a patient’s body size. There is much literature dealing with this subject. This report from the Cleveland Clinic represents 1014 patients who underwent aortic valve replacement between 1995 and 1998. Koch and colleagues’ hypothesis was that a "smaller valve size relative to body size would be reflected by less improvement and functional qual- ity of life post-operatively." They used the Duke Activity Status Index (DASI) to objectively evaluate a patient’s physical activity level and capacity. Patient were evaluated using multiple statistical techniques. In this population, 88% of the mechanical valves implanted were St. Jude Medical, representing 16% of all prostheses. Other valves included the CarboMedics mechanical valve and the Carpentier-Edwards stented bovine pericardial valve. Patients underwent a pre-op DASI evaluation at 6 and 12 months; the early post-op follow-up DASI score was used for the major data analysis and represented an average interval from surgery to survey follow-up of 8.3 months.

Results: Most patients demonstrated an improvement in functional quality of life. Of interest, those with lower baseline DASI scores, reflecting a poor level of function, had greater improvement in DASI scores than those who began with a higher baseline function, which usually stayed the same or decreased. There was no pattern or relationship found between valve size and follow-up DASI score. Valve orifice size was an unreliable predictor. However, female sex, need for transfusion, older age, and elevated creatinine were all related to "less favorable post-operative functional
recovery."

Commentary

The rationale for aortic valve replacement (AVR) includes improvement in functional capacity and quality of life. This was the case with the majority of patients in this study, and comparable to many other reports. Koch et al point out that prosthesis-patient mismatch occurs in many individuals because of a small aortic annulus. The definition of mismatch itself is variably described in different publications. The literature is inconsistent regarding the impact of mismatch on clinical outcomes; some but not all studies report an increase in mortality and morbidity, but others do not confirm any relationship with survival and prosthesis mismatch. Prior data suggest that patients with larger valves have greater improvement in the postoperative period. Koch et al’s hypothesis was that a smaller valve size indexed to body size would be related to lower functional scores; however, "measures of indexed valve size were unrelated to postoperative functional recovery period." Other factors related to functional recovery include female sex (reported in many investigations and not well understood) and increasing age, with a lower likelihood of elderly patients achieving a high postoperative DASI score. Other reports have not shown an age relationship to post-op functional capacity. A ceiling effect clearly limited many unimpaired individuals from being able to improve their DASI score, as they were highly functional to begin with.

In conclusion, while overall quality of life is improved in most patients undergoing AVR, prosthesis-patient size does not appear to influence functional recovery after AVR. A number of pre-operative variables (transfusion, age, female sex, higher creatinine) imparted "considerable emphasis on post-operative functional recovery."

This information should be useful to the general cardiologist in helping to make decisions regarding AVR. Female gender and advanced age did adversely impact postoperative functional recovery; this is not new news, but needs to be taken into account when decisions are made in elderly women whether to proceed with aortic valve surgery. It is common in echo studies to observe a high aortic gradient raising the question of prosthetic valve mismatch. Twenty-fifth to 77 percentile data are available for all valve sizes, as well as aortic valve peak and mean gradients in this paper.