Valve treatment for patients with advanced renal disease poses a significant challenge for any cardiac surgeon. These patients are complex, fragile, and consequently high-risk, and the literature regarding the optimal type of prosthesis remains controversial. The choice of prosthesis type must consider several specific factors in this patient group, such as their limited life expectancy, hemorrhagic and thrombotic risks, accelerated valve degeneration due to electrolyte imbalance, and increased risk of endocarditis due to frequent arteriovenous fistula manipulations. Some studies show certain advantages of mechanical prostheses over biological ones in the aortic position, though this does not settle the debate (as previously discussed in a blog entry). The decision for the mitral position is even more challenging, as there are no conclusive studies favoring one type of prosthesis. This uncertainty led the American College of Cardiology (ACC) and the American Heart Association (AHA) in 2006 to retract their 1998 recommendation on mechanical mitral prostheses for these patients, as it was based on two studies from the 1970s with a total of only 4 patients.

The current study analyzes the outcomes of mitral valve replacement in dialysis-dependent patients with advanced renal disease at a high-volume tertiary center. All patients who underwent mitral valve surgery from 2002 to 2019 were retrospectively reviewed, excluding those with mitral valve repair. Only patients with advanced renal disease on dialysis were selected. The decision on prosthesis type was based on patient preferences and the discretion of the physicians. The primary goal of the study was to assess, at 5 years, mortality, the mitral prosthesis reintervention rate, and the incidence of moderate or greater prosthetic stenosis.

During this period, approximately 8,168 mitral valves were operated on, with about 480 surgeries on the mitral valve each year. Among these, 177 patients were on dialysis, representing roughly 10 cases per year. Of these, 118 (67%) were biological prostheses and 59 were mechanical. Patients who received a biological prosthesis were older and had more comorbidities such as diabetes mellitus, dyslipidemia, previous myocardial infarction, and a history of cerebrovascular accidents. In contrast, patients with mechanical prostheses, besides being younger (48 years vs. 61 years; p < .001), had a higher prevalence of previous mitral valve repair. No significant differences were found in the length of hospital stay between the two groups. With a median follow-up of 234 days, adjusted 5-year survival was similar for both groups. Both groups showed a high early mortality rate of over 20%, with actuarial survival of less than 50% at 2 years. No statistically significant differences were observed in reintervention rates or structural valve degeneration. Stroke events were more frequent in patients with mechanical prostheses (15% vs. 6%; p = .041). Endocarditis was the most common reason for reintervention, with 9 cases, 5 of which occurred in the mechanical prosthesis cohort. Four patients with bioprostheses underwent reintervention due to structural degeneration.

The authors conclude that mitral valve replacement in dialysis-dependent patients carries high midterm morbidity and mortality. When choosing a prosthesis, the decreased life expectancy of these patients should be considered.

COMMENTARY:

Having references on outcomes in high-risk procedures is essential for making informed decisions and for comparing outcomes with other centers. Nowadays, this is even more relevant due to the option of transcatheter access. In fact, this approach today would be purely compassionate, as patients with advanced renal disease on hemodialysis are currently excluded from clinical trials on transcatheter mitral prostheses. If equivalence between biological and mechanical prostheses were eventually demonstrated, the transcatheter mitral bioprosthesis would not be the option of choice for this group of patients unless they were formally rejected for surgical treatment.

Various published studies on this topic show that it is difficult to generalize for this patient group. One of the main concerns when implanting a bioprosthesis is the potential for early degeneration. Patients with advanced renal disease have tertiary hyperparathyroidism, which leads to hypercalcemia and hyperphosphatemia, both of which contribute to valve calcification and, therefore, accelerated degeneration of bioprostheses. This led to 4 reinterventions (3%) among 118 bioprosthesis patients in a cohort with a median survival of less than 2 years. However, what should catch our attention most is the high rate of endocarditis in these patients. Dialysis patients have an 18-fold increased risk of endocarditis compared to the general population. This explains why 70% of reoperations in this study were due to endocarditis. Therefore, our primary concern should be endocarditis rather than prosthetic degeneration. Although this study lacked sufficient power to determine in which type of prosthesis this was more common, a prior meta-analysis suggested higher rates of endocarditis in bioprosthesis recipients. This could be explained by the greater susceptibility of bioprostheses to transient bacteremia due to germ adhesion to tissue material, as well as the larger volume and surface area of artificial structures in bioprostheses compared to mechanical prostheses. Future studies should explore this hypothesis.

It is essential to mention the limitations of this study to interpret the results in context. The retrospective nature of the study prevents randomization of the groups, making comparisons, although adjusted, not entirely comparable. There may be confounding effects from variables such as age and the duration until cardiac surgery, with associated risk factors such as diabetes mellitus or renal disease, which add to the consideration of whether these are present or absent. Lastly, despite the availability of data from a high-volume center, the sample size of these patients was very limited, which hinders solid conclusions.

In conclusion, when determining a prosthesis type for dialysis-dependent patients with advanced renal disease, we should not only consider age, patient preference in terms of anticoagulation, and the risk of prosthetic degeneration but also the bleeding risk, thromboembolic events, increased risk of endocarditis, and life expectancy, among other aspects. The decision will never be easy, so the debate continues.

REFERENCE:

Iyengar A, Song C, Weingarten N, Rekhtman D, Herbst DA, Shin M, et al. Prosthesis Choice in Dialysis Patients Undergoing Mitral Valve Replacement. Ann Thorac Surg. 2023 Nov;116(5):963-970. doi: 10.1016/j.athoracsur.2023.05.015.