Abstract
Background:
Improved durability of modern biologic prostheses and growing experience with the transcatheter valve-in-valve technique have contributed to a substantial increase in the use of bioprostheses in younger patients. However, discussion of prosthetic valve selection in dialysis patients remains scarce as the guidelines are updated. This study aims to compare long-term outcomes between propensity score-matched cohorts of dialysis patients who underwent primary aortic valve replacement with a mechanical prosthesis or a bioprosthesis.
Materials and Methods:
Longitudinal data of dialysis patients who underwent primary aortic valve replacement between 1 January 2001 and 31 December 2018, were retrieved from the National Health Insurance Research Database.
Results:
A total of 891 eligible patients were identified, of whom 243 ideally matched pairs of patients were analyzed. There was no significant difference in all-cause mortality (hazard ratio 1.11, 95% CI: 0.88–1.40) or the incidence of major adverse prosthesis-related events between the two groups (hazard ratio 1.03, 95% CI: 0.84–1.25). In patients younger than 50 years of age, using a mechanical prosthesis was associated with a significantly longer survival time across 10 years of follow-up than using a bioprosthesis (restricted mean survival time) at 10 years: 7.24 (95% CI: 6.33–8.14) years for mechanical prosthesis versus 5.25 (95% CI: 4.25–6.25) years for bioprosthesis, restricted mean survival time difference 1.99 years, 95% CI: −3.34 to −0.64).
Conclusion:
A 2-year survival gain in favor of mechanical prostheses was identified in dialysis patients younger than 50 years. The authors suggest mechanical prostheses for aortic valve replacement in these younger patients.
Keywords: aortic valve replacement, bioprosthesis, dialysis, mechanical prosthesis
Introduction
Highlights
Our study had investigated the late outcomes after surgical aortic valve replacement from one of the largest published cohorts of dialysis patients.
In this population-based cohort study of dialysis patients, a 2-year survival gain in favor of mechanical prostheses in the aortic valve position was identified in patients younger than 50 years.
The population of patients receiving dialysis continues to grow rapidly as a result of increases in the availability of dialysis and in the prevalence of risk factors for chronic kidney disease, including population aging, hypertension, diabetes mellitus, and toxic environmental exposures1,2. By 2030, the estimated worldwide use of renal replacement therapy will be more than double the number in 2010 at an all-time high of 5.439 million (3.899–7.640 million) people, with the most growth in Asia3. Cardiovascular disease is the leading cause of morbidity and mortality in patients on dialysis and is manifested as heart failure in 30–40%, coronary artery disease in 35–45%, and valvular heart disease in 15–20% of the dialysis population2. In patients requiring dialysis, valvular heart disease is diagnosed at a rate 4–5 times higher and is estimated to progress two times faster than the general population, which could be partially attributed to the higher incidence of aortic and mitral valve calcification in cases with abnormal metabolism of calcium and phosphate4,5.
In heart valve replacement surgery, prosthetic valve selection should be a shared decision-making process, considering patients’ values and preferences, comorbidities and life expectancy, medical compliance, expected bioprosthetic valve durability, and the avoidance of patient–prosthesis mismatch. The trade-off between the risk of reintervention for bioprosthetic valve deterioration and the risk of long-term anticoagulation needed for mechanical valves should be discussed on an individual basis6,7. Over the recent decades, selection of prosthetic valves has become an evolving clinical dilemma for both surgeons and patients, owing to changes in the risk profiles of patients referred for cardiac surgery, advancements in the design and production of new-generation prosthetic valves, the maturation of transcatheter valve replacement, and the emergence of transcatheter valve-in-valve replacement8. Improved durability of modern biologic prostheses and growing experience with the transcatheter valve-in-valve technique have contributed to a substantial increase in the use of surgical bioprostheses in younger patients8–10. For aortic valve replacement (AVR), the recommended age threshold for biological prostheses has decreased from greater than 65 to greater than 50 years in the 2020 American Heart Association/American College of Cardiology (AHA/ACC) guidelines and greater than 60 years in the 2021 European Society of Cardiology and the European Association for Cardio-Thoracic Surgery (ESC/EACTS) guidelines, respectively6,7.
Although end-stage renal failure (ESRD) represents a common comorbidity of valvular heart disease, discussion of prosthetic valve selection in such patients remains scarce as the guidelines are updated7. Mechanical prostheses are generally recommended in patients at risk of accelerated structural valve deterioration (SVD); however, the increased risk of bleeding and decreased life expectancy in the dialysis population have limited the use of mechanical valves in real-world practice6,11–13. Most of the current evidence regarding dialysis patients is reported from retrospective studies with heterogeneity in patient demographics and valve procedures, yielding controversial results12–16.
Material and methods
Study design
Longitudinal data from dialysis patients who underwent primary surgical aortic valve replacement (SAVR) in our country between 1 January 2001 and 31 December 2018, were retrospectively analyzed to study the effect of prosthesis type on long-term outcomes. This study was approved by our Research Ethics Committee on 16 March 2021 (institutional review board approval: 202012072RIND). The research was retrospectively registered at the ResearchRegistry.com. The work has been reported in line with the strengthening the reporting of cohort, cross-sectional and case–control studies in surgery (STROCSS) criteria17 (Supplemental Digital Content 1, http://links.lww.com/JS9/A821).
Patient population
The National Health Insurance in Taiwan is an obligatory, government-operated, single-payer health insurance program launched in 1995, with coverage of 99.9% of Taiwan’s population. The National Health Insurance Research Database (NHIRD) systemically collects clinical and claim data, including deidentified demographics, diagnoses, procedures, and prescriptions for comprehensive reimbursement of medical expenditures and exemplifies a population-level real-world dataset18.
Patients undergoing first-time surgical cardiac valve replacement between 1 January 2001 and 31 December 2018, were identified from the NHIRD. Patients without aortic valve disease, those who received valve replacements at more than one position, those aged less than 18 at the time of surgery, those without records of dialysis within the past year of the index valve replacement, those missing or showing an error in important clinical information, and those who died during the index admission for valve replacement were excluded. A flow diagram of the selection of the study cohort is presented in Figure 1. The definition and reimbursement codes are provided in Supplemental Table 1 (Supplemental Digital Content 2, http://links.lww.com/JS9/A822).
Figure 1.
Flow diagram of the selection and matching of study cohort. Patients who underwent first-time cardiac valve replacement between 2001 and 2018 in the National Health Insurance Research Database were screened for eligibility. A study cohort of 891 dialysis patients who received primary surgical aortic valve replacement was analyzed. Using propensity score matching, the long-term outcome was compared between 243 patients with a bioprosthesis and 243 patients with a mechanical valve.
The baseline characteristics of the included patients were ascertained according to the near-term medical history. Patients were defined as having a disease if there were at least two outpatient or one inpatient diagnoses within 1 year before the index operation, and patients were defined as taking the drug if there were at least two prescription or refill records within 6 months before the index operation. If the patient had visited the emergency room within 24 h before admission, the index operation was defined as emergent surgery. Data of late mortality could be accessed via linking NHIRD to the nationwide cause of death registry within the Health and Welfare Data Center in Taiwan19.
Study outcomes
The primary outcome was all-cause mortality. Secondary outcomes were the composite outcome and individual components of major adverse prosthesis-related events, including death, major bleeding, ischemic stroke, endocarditis, and aortic valve reoperation, each of which was defined as an emergency room visit or hospital admission with related diagnosis codes as the primary diagnosis. The International Classification of Diseases (ICD) codes, the Anatomical Therapeutic Chemical (ATC) codes, and reimbursement codes that we used to define the characteristics and outcomes of procedures are provided in Supplemental Table 2 (Supplemental Digital Content 2, http://links.lww.com/JS9/A822).
Statistical analysis
Descriptive data are reported as the mean with SD or median with interquartile range for continuous variables and as percentages for categorical variables. The balance in patient characteristics between the bioprosthesis group and the mechanical prosthesis group was assessed with the use of standardized mean differences (SMD). An SMD of 0.1 or less indicates an ideal balance, and an SMD of 0.2 or less is considered an acceptable balance20. We used propensity score (PS) matching to limit potential confounding from the retrospective design of this study. Logistic regression, incorporating all baseline covariates described in Table 1, was applied to estimate the PS, the probability that a patient would receive a bioprosthesis. After the PS was assigned, patients in different study groups were matched by 1:1 PS greedy nearest neighbor matching without replacement with a caliper of 0.2 of the SD of the logit of the PS. The distribution of PS matching is provided in Supplemental Figure 1 (Supplemental Digital Content 3, http://links.lww.com/JS9/A823).
Table 1.
Baseline characteristics before and after propensity score matching.
| Before matching | After matching | |||||||
|---|---|---|---|---|---|---|---|---|
| Basic characteristics | Biological valve (N=600) | Mechanical valve (N=291) | SMD | P | Biological valve (N=243) | Mechanical valve (N=243) | SMD | P |
| Age | ||||||||
| Mean±SD (year) | 70.14±10.64 | 61.73±13.46 | 0.6933 | <0.0001 | 64.75±11.64 | 65.09±11.35 | −0.0301 | 0.7405 |
| Sex | ||||||||
| Male, N (%) | 336 (56.0%) | 172 (59.1%) | −0.0629 | 0.3797 | 149 (61.3%) | 140 (57.6%) | 0.0755 | 0.4057 |
| Year of surgery, N (%) | ||||||||
| 2001–2004 | 23 (3.8) | 38 (13.1) | −0.3364 | <0.0001 | 7 (2.9) | 29 (11.9) | −0.3510 | <0.0001 |
| 2005–2009 | 81 (13.5) | 64 (22.0%) | −0.2237 | 34 (14.0) | 54 (22.2) | −0.2150 | ||
| 2010–2014 | 188 (31.3) | 99 (34.0) | −0.0573 | 75 (30.9) | 82 (33.7) | −0.0616 | ||
| 2015–2018 | 308 (51.3) | 90 (30.9) | 0.4239 | 127 (52.3) | 78 (32.1) | 0.4171 | ||
| Urgency of surgery | ||||||||
| Emergent surgery, N (%) | 193 (32.2) | 90 (30.9) | 0.0267 | 0.7095 | 79 (32.5) | 74 (30.5) | 0.0443 | 0.6253 |
| Aortic valve etiology, N (%) | ||||||||
| Aortic stenosis | 130 (21.7) | 56 (19.2) | 0.0601 | 0.4040 | 46 (18.9) | 52 (21.4) | −0.0616 | 0.4976 |
| Aortic regurgitation | 53 (8.8%) | 25 (8.6%) | 0.0086 | 0.9045 | 29 (11.9%) | 17 (7.0%) | 0.1693 | 0.0630 |
| Bicuspid aortic valve | 14 (2.3%) | 5 (1.7%) | 0.0437 | 0.5511 | 6 (2.5%) | 3 (1.2%) | 0.0917 | 0.3128 |
| Aortic valve disordera | 439 (73.2%) | 230 (79.0%) | −0.1380 | 0.0574 | 175 (72.0%) | 192 (79.0%) | −0.1632 | 0.0729 |
| Endocarditis | 61 (10.2%) | 40 (13.7%) | −0.1105 | 0.1140 | 35 (14.4%) | 25 (10.3%) | 0.1253 | 0.1679 |
| Concomitant surgical procedure or cardiac intervention during the same admission, N (%) | ||||||||
| Valve repair | 70 (11.7) | 31 (10.7) | 0.0322 | 0.6544 | 34 (14.0) | 25 (10.3) | 0.1136 | 0.2113 |
| CABG | 180 (30.0) | 88 (30.2) | −0.0052 | 0.9415 | 66 (27.2) | 78 (32.1) | −0.1083 | 0.2332 |
| PCI | 35 (5.8) | 12 (4.1) | 0.0787 | 0.2843 | 13 (5.3) | 8 (3.3) | 0.1013 | 0.2647 |
| Comorbidities within the past year, N (%) | ||||||||
| Hypertension | 518 (86.3) | 225 (77.3) | 0.2354 | 0.0007 | 200 (82.3) | 201 (82.7) | −0.0108 | 0.9050 |
| Diabetes mellitus | 283 (47.2%) | 141 (48.5%) | −0.0258 | 0.7183 | 118 (48.6%) | 125 (51.4%) | −0.0576 | 0.5254 |
| Hyperlipidemia | 193 (32.2%) | 98 (33.7%) | −0.0321 | 0.6521 | 80 (32.9%) | 88 (36.2%) | −0.0693 | 0.4454 |
| Coronary artery disease | 411 (68.5%) | 175 (60.1%) | 0.1752 | 0.0136 | 155 (63.8%) | 155 (63.8%) | 0.0000 | 1.0000 |
| Prior myocardial infarction | 130 (21.7%) | 42 (14.4%) | 0.1889 | 0.0103 | 39 (16.0%) | 40 (16.5%) | −0.0112 | 0.9022 |
| Congestive heart failure | 437 (72.8%) | 200 (68.7%) | 0.0904 | 0.2031 | 175 (72.0%) | 168 (69.1%) | 0.0632 | 0.4859 |
| Cerebrovascular disease | 110 (18.3%) | 44 (15.1%) | 0.0862 | 0.2342 | 40 (16.5%) | 40 (16.5%) | 0.0000 | 1.0000 |
| Prior ischemic stroke | 52 (8.7%) | 20 (6.9%) | 0.0670 | 0.3569 | 18 (7.4%) | 17 (7.0%) | 0.0159 | 0.8607 |
| Peripheral artery disease | 106 (17.7%) | 61 (21.0%) | −0.0836 | 0.2372 | 49 (20.2%) | 49 (20.2%) | 0.0000 | 1.0000 |
| Atrial fibrillation | 106 (17.7%) | 35 (12.0%) | 0.1591 | 0.0305 | 35 (14.4%) | 34 (14.0%) | 0.0118 | 0.8966 |
| Prior major bleeding | 128 (21.3%) | 56 (19.2%) | 0.0520 | 0.4700 | 42 (17.3%) | 47 (19.3%) | −0.0532 | 0.5576 |
| Coagulopathy | 8 (1.3%) | 10 (3.4%) | −0.1382 | 0.0364 | 4 (1.6%) | 4 (1.6%) | 0.0000 | 1.0000 |
| Prior endocarditis | 89 (14.8%) | 59 (20.3%) | −0.1434 | 0.0407 | 47 (19.3%) | 41 (16.9%) | 0.0642 | 0.4797 |
| Chronic pulmonary disease | 185 (30.8%) | 66 (22.7%) | 0.1850 | 0.0112 | 63 (25.9%) | 62 (25.5%) | 0.0094 | 0.9173 |
| Rheumatic disease | 29 (4.8%) | 9 (3.1%) | 0.0893 | 0.2279 | 9 (3.7%) | 9 (3.7%) | 0.0000 | 1.0000 |
| Peptic ulcer | 151 (25.2%) | 74 (25.4%) | −0.0060 | 0.9325 | 62 (25.5%) | 63 (25.9%) | −0.0094 | 0.9173 |
| Renal diseaseb | 435 (72.5%) | 195 (67.0%) | 0.1197 | 0.0913 | 172 (70.8%) | 172 (70.8%) | 0.0000 | 1.0000 |
| End-stage renal diseaseb | 342 (57.0%) | 136 (46.7%) | 0.2065 | 0.0040 | 128 (52.7%) | 125 (51.4%) | 0.0247 | 0.7853 |
| Liver disease | 81 (13.5%) | 47 (16.2%) | −0.0747 | 0.2900 | 41 (16.9%) | 39 (16.0%) | 0.0222 | 0.8067 |
| Cancer | 76 (12.7%) | 22 (7.6%) | 0.1700 | 0.0223 | 17 (7.0%) | 21 (8.6%) | −0.0613 | 0.4991 |
| Osteoporosis | 38 (6.3%) | 17 (5.8%) | 0.0206 | 0.7750 | 15 (6.2%) | 12 (4.9%) | 0.0539 | 0.5525 |
| CCI distribution, N (%) | ||||||||
| Mean (SD) | 4.88±2.33 | 4.39±2.32 | 0.2124 | 0.0030 | 4.65±2.17 | 4.65±2.33 | 0.0000 | 1.0000 |
| 0–1 | 38 (6.4) | 28 (9.6) | −0.1284 | 0.0209 | 17 (7.0) | 19 (7.8) | 0.0035 | 0.5634 |
| 2 | 57 (9.5) | 43 (14.8) | −0.1621 | 23 (9.5) | 31 (12.8) | −0.1049 | ||
| ≥3 | 505 (84.2) | 220 (75.6) | 0.2149 | 203 (83.5) | 193 (79.4) | 0.1061 | ||
| Medication within the past year, N (%) | ||||||||
| Warfarin | 386 (64.3) | 284 (97.6) | −0.9353 | <0.0001 | 155 (63.8) | 238 (97.9) | −0.9639 | <0.0001 |
| NSAID | 443 (73.8) | 229 (78.7) | −0.1144 | 0.1140 | 186 (76.5) | 191 (78.6) | −0.0493 | 0.5866 |
| PPI | 477 (79.5) | 226 (77.7) | 0.0448 | 0.5286 | 194 (79.8) | 194 (79.8) | 0.0000 | 1.0000 |
| H2 blocker | 458 (76.3) | 223 (76.6) | −0.0070 | 0.9215 | 178 (73.3) | 184 (75.7) | −0.0567 | 0.5324 |
| ACEI/ARB | 469 (78.2) | 230 (79.0) | −0.0212 | 0.7668 | 187 (77.0) | 196 (80.7) | −0.0907 | 0.3178 |
| Beta blocker | 506 (84.3) | 241 (82.8) | 0.0409 | 0.5644 | 208 (85.6) | 199 (81.9) | 0.1005 | 0.2685 |
| Statin | 290 (48.3) | 124 (42.6) | 0.1151 | 0.1083 | 110 (45.3) | 111 (45.7) | −0.0083 | 0.9274 |
| Insulin | 472 (78.7) | 232 (79.7) | −0.0261 | 0.7160 | 187 (77.0) | 202 (83.1) | −0.1549 | 0.1370 |
| Other hypoglycemic agent | 229 (38.2) | 117 (40.2) | −0.0418 | 0.5580 | 93 (38.3) | 105 (43.2) | −0.1006 | 0.2679 |
| Distribution of hospital volume of AVR (2001–2011), N (%) | ||||||||
| 1–65 | 90 (15) | 42 (14.4) | 0.0748 | 0.3038 | 39 (16.1) | 32 (13.2) | 0.1870 | 0.1546 |
| 66–1237 | 510 (85.0) | 249 (85.6) | −0.0160 | 204 (84.0) | 211 (86.8) | −0.0816 | ||
Aortic valve disorder denotes mixed stenosis and regurgitation, or ambiguous etiology.
In Taiwan, for patients needing regular dialysis, physicians would apply for a catastrophic illness certificate for exemption from co-payments for regular dialysis. We had used the International Classification of Diseases-10 codes registered for a catastrophic illness certificate, which included diagnosis of stage 5 chronic kidney disease and end-stage renal disease, and the reimbursement codes for each dialysis session to identify the patients on regular dialysis within the National Health Insurance Research Database. Therefore, dialysis patients might have either or both the diagnosis of chronic kidney disease and end-stage renal disease. The baseline renal disease was denoted as stage 5 chronic kidney disease.
ACEI, angiotensin converting enzyme inhibitor; ARB, angiotensin receptor blocker; AVR, aortic valve replacement; CABG, coronary artery bypass grafting; CCI, Charlson comorbidity index; NSAID, nonsteroidal anti-inflammatory drug; PCI, percutaneous coronary intervention; PPI, proton-pump inhibitors; SMD, standardized mean differences.
The incidence rates of primary and secondary outcomes were calculated by Poisson regression. The Kaplan–Meier method was used to construct survival curves of overall survival and adverse event-free survival. Long-term mortality was compared between the two types of prostheses within the Cox proportional hazards model. In addition, to address the nonproportional hazards in real-world practice, the restricted mean survival time (RMST) was estimated to describe the average effect of prosthesis choice over a prespecified fixed period20. Subgroup analyses, including stratification by age, sex, urgency of surgery, aortic valve etiology, and Charlson comorbidity index (CCI), of primary and secondary outcomes were performed to explore any possible differential effect of prosthesis choice on long-term outcomes. All the data management and statistical analyses were performed using SAS version 9.4 (SAS Institute Inc.) and R version 4.1.3 (R Foundation).
Theory
This study aims to examine late outcomes in dialysis patients after exclusive aortic valve replacement with mechanical prostheses as compared to bioprostheses using a nationwide population-based cohort.
Results
Study population
A total of 891 dialysis-dependent patients who underwent first-time aortic valve replacement between 2001 and 2018 were identified in the NHIRD, of whom 600 (67.3%) received a biological prosthesis and 291 (32.7%) received a mechanical prosthesis (Fig. 1). Patients in the bioprosthesis group were older (mean age 70.1±10.6 years for bioprosthesis vs. 61.7±13.5 years for mechanical prosthesis, SMD 0.69, P-value <0.0001) and had more comorbidities (mean CCI 4.88±2.33 for bioprosthesis vs. 4.39±2.32 for mechanical prosthesis, SMD 0.21, P=0.003). A remarkably high prevalence of warfarin use in our cohort was observed. Dialysis patients with aortic valve diseases could have multiple comorbidities, for which warfarin might be indicated, for example atrial fibrillation, ischemic stroke, and thromboembolism events. In addition, all records of prescribing warfarin at some time during the year before valve replacement were retrieved, which could involve short-term use of warfarin immediate after vascular access intervention in patients with vascular access occlusion. Up to 30% of the surgeries were emergent operations, and concomitant coronary artery bypass grafting was performed in 30% of patients, which did not differ between the two groups. Bioprostheses have been increasingly used in more recent cardiac surgeries (P-value <0.0001). Operative mortality during the index admission was 8.1% for bioprosthesis and 7.9% for mechanical valve (P=0.0213).
Using 1:1 propensity score matching, 243 matched pairs of patients with biological valves and mechanical valves were analyzed. Apart from more patients taking warfarin before surgery in the mechanical valve group (63.8% for bioprostheses vs. 97.9% for mechanical prostheses, SMD −0.96, P-value <0.0001) and half of the bioprostheses having been implanted during the most contemporary surgical era (52.3% for bioprostheses vs. 32.1% for mechanical prostheses, SMD 0.42, P-value <0.0001), the matched groups were properly balanced (Supplemental Fig. 1, Supplemental Digital Content 3, http://links.lww.com/JS9/A823). The characteristics of the unmatched and matched cohorts are shown in Table 1.
Long-term mortality and major adverse prosthesis-related events
Before matching, all-cause mortality was 22.5 events per 100 patient-years in the bioprosthesis group and 13.7 events per 100 patient-years in the mechanical prosthesis group [hazard ratio (HR) 1.63, 95% CI: 1.53–1.74]. The RMST at 10 years was 7.21 years in the bioprosthesis group and 8.03 years in the mechanical prosthesis group (RMST difference −0.82 years, 95% CI: −0.96 to −0.68 years). Bioprosthesis was associated with an increased risk of aortic valve reoperation (HR 1.78, 95% CI: 1.23–2.57) and a decreased risk of endocarditis (HR 0.87, 95% CI: 0.79–0.95). No significant difference between the two prostheses regarding the risk of thromboembolism or bleeding events was observed (Table 2).
Table 2.
Primary and secondary outcomes in unmatched and matched dialysis-dependent cohorts.
| Before matching | After matching | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Biological valve (N=600) | Mechanical valve (N=291) | Biological valve (N=243) | Mechanical valve (N=243) | |||||||
| Event No. | Event rateb | Event No. | Event rateb | HR (95% CI)a | Event No. | Event rateb | Event No. | Event rateb | HR (95% CI)a | |
| All-cause mortality | 374 | 22.54 | 173 | 13.7 | 1.63 (1.53–1.74) | 141 | 19.17 | 152 | 15.81 | 1.11 (0.88–1.40) |
| Major adverse event | 489 | 50.94 | 249 | 43.95 | 1.03 (0.99–1.08) | 197 | 50.77 | 210 | 45.52 | 1.03 (0.84–1.25) |
| Aortic valve reoperation | 6 | 0.36 | 2 | 0.16 | 1.78 (1.23–2.57) | 4 | 0.55 | 1 | 0.10 | 6.06 (0.62–59.1) |
| Major bleeding | 246 | 21.54 | 146 | 20.42 | 0.95 (0.90–1.01) | 110 | 22.20 | 123 | 22.12 | 0.96 (0.74–1.24) |
| Ischemic stroke | 84 | 5.62 | 41 | 3.65 | 1.05 (0.97–1.15) | 34 | 5.18 | 33 | 3.88 | 1.25 (0.77–2.04) |
| Endocarditis | 95 | 6.56 | 66 | 6.58 | 0.87 (0.79–0.95) | 53 | 8.83 | 47 | 5.84 | 1.36 (0.91–2.02) |
Mechanical as ref.
Per 100 person-year.
HR, hazard ratio.
After PS matching, there was no significant difference in all-cause mortality or incidence of major adverse prosthesis-related events between bioprostheses and mechanical prostheses (Table 2). All-cause mortality was 19.2 per 100 patient-years in the bioprosthesis group and 15.8 per 100 patient-years in the mechanical prosthesis group (HR 1.11, 95% CI: 0.88–1.40). The long-term overall survival and adverse event-free survival of the matched cohorts are displayed in Figures 2A and 2B. The RMST at 10 years was 4.44 years (95% CI: 3.92–4.97 years) in the bioprosthesis group, compared with 4.93 years (95% CI: 4.40–5.47 years) in the mechanical prosthesis group (RMST difference −0.49 year, 95% CI: −1.24 to 0.26 year, P=0.3879). The incidence of major adverse prosthesis-related events was 50.8 events per 100 person-years in the bioprosthesis group and 45.5 events per 100 person-years in the mechanical prosthesis group (HR 1.03, 95% CI: 0.84–1.25). The adverse event-free survival over the 10-year follow-up was 2.11 years (95% CI: 1.72–2.49 years) in the bioprosthesis group and 2.15 years (95% CI: 1.79–2.52 years) in the mechanical prosthesis group (RMST difference −0.05 year, 95% CI: −0.58–0.49 year, P-value=0.8068). Major bleeding was the most frequent adverse event after valve replacement in dialysis patients (22.2 events per 100 person-years for bioprostheses vs. 22.1 events per 100 person-years for mechanical prostheses, HR 0.96, 95% CI: 0.74–1.24). The incidence of aortic valve reoperation was low in both groups (0.55 events per 100 person-years for bioprostheses vs. 0.10 events per 100 person-years for mechanical prostheses, HR 6.06, 95% CI: 0.62–59.1).
Figure 2.
(A) Long-term survival among propensity-matched dialysis patients. The overall survival and estimated restricted mean survival time after primary surgical aortic valve replacement are depicted and compared between the two types of prosthetic valves. The group of patients who received a mechanical valve was the reference group. The numbers of patients at risk are included below each graph. (B) Major adverse event-free survival among propensity-matched dialysis patients. The major adverse event-free survival and estimated major adverse event-free survival days after primary surgical aortic valve replacement are depicted and compared between the two types of prosthetic valves. The group of patients who received a mechanical valve was the reference group. The numbers of patients at risk are included below each graph. RMST, restricted mean survival time; RMTL, restricted mean time lost.
Subgroup analysis of the matched cohort
In the subgroup analysis stratified by age, as might be anticipated, the long-term survival decreased with increasing age for both types of prostheses (Fig. 3A). When different boundaries-of-age subgroups (50 and 60 years) were tested, we observed a similar trend favoring mechanical prostheses in the lower age-bounded subgroup (Supplemental Table 3, Supplemental Digital Content 2, http://links.lww.com/JS9/A822). There was a statistically significant difference in the estimated average survival time across 10 years of follow-up between the two prostheses in patients younger than 50 years [RMST at 10 years: 5.25 (95% CI: 4.25–6.25) years for bioprosthesis vs. 7.24 (95% CI: 6.33–8.14) years for mechanical prosthesis, RMST difference −1.99 years, 95% CI: −3.34 to −0.64, Figure 3A). The sex, urgency of surgery, aortic valve disease etiology, and CCI did not significantly affect the impact of prosthesis choice on long-term overall survival or major adverse prosthesis-related events (Supplemental Tables 4–7, Supplemental Digital Content 2, http://links.lww.com/JS9/A822). The long-term overall survival of the matched cohorts aged less than 50 years is displayed in Figure 3B.
Figure 3.
(A) Subgroup analysis stratified by age. A 2-year survival gain in favor of mechanical prostheses was identified in dialysis patients younger than 50 years. (B) Long-term survival among propensity-matched dialysis patients younger than 50 years. The overall survival in patients younger than 50 years after primary surgical aortic valve replacement is depicted and compared between the two types of prosthetic valves. The group of patients who received a mechanical valve was the reference group. The numbers of patients at risk are included below each graph. EST, estimate; RMST, restricted mean survival time.
Discussion
Our nationwide population-based study represents one of the largest published cohorts of dialysis patients who underwent a first-time single SAVR. In parallel with previous studies, patients on dialysis had poor late survival and a high incidence of prosthesis-related adverse events after valve replacement surgery. Bleeding was the most frequently reported adverse event, while only a small number of patients received aortic valve reoperation. These outcomes did not significantly differ between patients with bioprostheses and patients with mechanical prostheses. However, in the subgroup analysis, a long-term survival benefit of mechanical prostheses over bioprostheses in patients younger than 50 years was identified.
Guidelines for prosthesis selection in the dialysis population
The guidelines for prosthesis choice in valve replacement have evolved remarkably from the early recommendations toward a more liberal discussion between patient and surgeon with the introduction of a widening gray zone of age threshold in which either valve is considered reasonable8. In dialysis patients, mechanical valves were initially preferred due to concern for accelerated calcific structural deterioration of biological valves in patients with abnormal metabolism of calcium and phosphate21. However, lifelong anticoagulation in dialysis patients could be associated with an exponential increase in the risk of major bleeding22. Subsequent observational studies in the dialysis population found no differences in terms of mid-term survival between bioprostheses and mechanical valves, and the risk of reoperation for SVD of bioprostheses was relatively low14,23. The AHA/ACC guideline has made no explicit recommendation on prosthesis selection in dialysis patients since 20067,24,25. In contrast, the ESC/EACTS recommended bioprosthetic valves in dialysis patients in its 2007 and 2012 guidelines because patients’ life expectancy was lower than valve durability26,27. While there is no specific discussion for dialysis patients in the 2017 guideline, the latest 2021 guideline gives a class I recommendation for mechanical valves in dialysis patients due to the risk of accelerated SVD without reviewing supporting evidence5,6,28. Currently, debate over the optimal prosthetic valve for the dialysis population remains, and more evidence might be needed to guide the selection of either prosthetic valve as in the nondialysis population20.
Evidence of prosthetic valve selection in dialysis patients undergoing AVR
Few studies have investigated the long-term impact of prosthesis type in exclusive aortic valve replacement in dialysis patients. The group from Emory University found that long-term survival did not differ by prosthesis type in their isolated AVR patients (N=100)29. Okada et al.11 reported outcomes of their valve selection criteria (bioprostheses for all patients older than 65–70 years) in 89 dialysis patients, with a 5-year survival of 45% in the elderly group (≥70 years), 73% in the middle-age group (from 65 to 69 years), and 75% in the young group (<65 years). In a recent multi-institutional retrospective study, Nakatsu et al.30 reported no significant differences in adjusted rates of intermediate-term survival, bleeding events, and any reoperation between bioprosthetic valves and mechanical valves in 491 patients on hemodialysis. From Sweden’s nationwide cardiac surgery registry, Perrotta et al.31 observed that the type of valve prosthesis was not associated with an adjusted risk of late mortality and adverse events in 335 patients with end-stage renal disease.
In our study, 891 dialysis-dependent patients undergoing first-time single SAVR were analyzed, and late outcomes were compared between 243 ideally matched pairs of patients with biological valves and mechanical valves. Before matching, substantial heterogeneity in patient characteristics between the two groups was noted. Determining prosthesis choice in patients with comorbidities could be multifactorial; therefore, we used PS matching to account for this bias inherent to retrospective studies. After matching, there was a similar distribution of PSs within the two groups (Supplemental Fig. 1, Supplemental Digital Content 3, http://links.lww.com/JS9/A823).
Through conforming to the strict inclusion rules of patients on regular dialysis with a catastrophic illness certificate, we aim to focus on the long-term impact of dialysis on the late outcomes after aortic valve replacement. Diabetes mellitus, chronic glomerulonephritis, hypertension, and chronic interstitial nephritis were reported to be the major underlying renal diseases of ESRD. Regular use of Chinese herbal drugs is also a well-established risk factor for renal failure in Taiwan. Successful renal transplantation can ameliorate many of the problems associated with chronic dialysis. However, the easy accessibility of dialysis therapy and low mortality rate in dialysis patients had resulted in a low transplantation rate in Taiwan32,33. Thus, we expected the proportion of patients with transient or permanent renal recovery after aortic valve replacement would be low in this study.
RMST analysis has been validated as an alternative to the HR for studying clinical cardiovascular research, especially for patients with limited life expectancy34–36. The poor long-term survival after cardiac valve replacement in dialysis patients was demonstrated in that across 10 years of follow-up, patients survived an average of 4.44 years in the bioprosthesis group and 4.93 years in the mechanical prosthesis group, with a statistically nonsignificant RMST difference of −0.49 years between groups (95% CI: −1.24–0.26 years).
Although the small number of aortic valve reoperations in our study decreased the statistical power to make an effective comparison between the two prostheses, the reported incidence was comparable to that of prior studies, and there seemed to be more aortic valve reoperations in the bioprosthesis group (0.55 per 100 person-years in the bioprosthesis group vs. 0.10 per 100 person-years in the mechanical valve group, HR 6.06, 95% CI: 0.62–59.1)30,31.
As suggested in a previous large series, the decreased survival and low reoperation rate after valve replacement support the use of bioprostheses for most dialysis patients12,13,31. To define the small portion of dialysis patients who could benefit from the increased durability of a mechanical valve, Manghelli et al.13 concluded that only young dialysis patients (aged 30 or 40 years) without diabetes or New York Heart Association functional classification III or IV symptoms might survive long enough to justify placement of a mechanical valve. In our subgroup analysis stratifying patients based on age, we identified a survival benefit of mechanical prostheses over bioprostheses in patients younger than 50 years, a subset accounting for 29.2% (N=71) and 31.3% (N=76) of dialysis patients in the bioprosthesis group and mechanical prosthesis group, respectively. Due to the improved durability of modern bioprostheses, we expected that only a longer life expectancy could possibly justify using a mechanical valve in dialysis patients. Subgroup analyses stratified by different boundaries of age had been conducted in our study. A cut-off age at 50 identified a small but clinically meaningful group of patients (around 30% of the matched cohort), in whom a statistically significant difference in the estimated average survival time between the two prostheses was demonstrated. There was no such difference in RMST between the two prostheses with a cut-off age at 60. Compared to the old dialysis population, the estimated survival time was increased in the young dialysis population, especially for patients in the mechanical prosthesis group. For the dialysis population younger than 50 years, patients who received a mechanical prosthesis survived 2 years longer over 10 years of follow-up than patients who received a bioprosthesis (RMST at 10 years: 5.25 years for bioprosthesis, 7.24 years for mechanical prosthesis, RMST difference −1.99 years, 95% CI: −3.34 to −0.64). With RMST analysis, the clinical significance could be explicitly interpreted to help guide prosthesis selection for both surgeons and dialysis patients.
Compared with bioprostheses, mechanical valves are characterized by improved durability but the mandatory use of lifelong anticoagulant. The choice of prosthetic valve is often determined by balancing the risks of bleeding and reoperation. Mechanical valves are recommended for patients with a longer life expectancy and without impermissive cost from bleeding. In agreement with prior studies, we had demonstrated a survival benefit of mechanical valves in young patients, which diminished in their older counterparts13. SVD and the associated reoperation had been implicated as one of the underlying causes of the difference in mortality between mechanical valves and bioprostheses20. For young patients, who are more immunologically active, it has been observed that SVD tends to develop earlier with a bioprosthesis, and the bleeding risk with a mechanical valve would be outweighed by the durability advantage20,37. In young patients on dialysis, the impact of durability might be more pronounced. Although there was no significant difference in the reoperation rates between two prostheses in our study, as suggested by the low incidences of reoperation in both groups, redo cardiac surgeries could be deferred due to the perceived high surgical risks in dialysis patients. Using a bioprosthesis in patients under the age of 50 might hint a significant burden of preoperative comorbidities. We had used PS matching to balance the differences in baseline characteristics, but there could be residual confounders underlying the impaired survival in patients receiving a bioprosthesis.
There was no significant difference in the RMST between the two prostheses in patients older than 50 years (RMST at 10 years: 4.11 (95% CI: 3.50–4.72) years for bioprosthesis vs. 3.92 (95% CI: 3.33–4.51) years for mechanical prosthesis, RMST difference 0.19 years, 95% CI: −0.66–1.04, Fig. 3A). From our analysis, no definitive conclusions could be drawn on the issue of beneficial prosthesis in patients aged over 50 years. Yet, considering the reduced estimated survival, a bioprosthesis is deemed a reasonable choice.
Prosthesis selection of dialysis patients in the era of transcatheter aortic valve replacement (TAVR)
For patients with a high or prohibitive risk in SAVR, TAVR is an effective treatment. Although TAVR is considered an appealing alternative to SAVR in the dialysis population, randomized controlled trials of TAVR in ESRD are lacking. Findings from large registries showed comparable short-term outcome between SAVR and TAVR38. However, long-term survival remains poor39. Compared to the surgical bioprosthesis, limited data about the crimping effect on valve durability is another concern with TAVR. Currently, robust durability data for TAVR extend to only approximately 5 years in the nondialysis population7. With considerable progress in the care of patients with ESRD as well as population aging, patients on dialysis are expected to have a longer life expectancy2,40. As a result, the potential consequence of SVD of a surgical or transcatheter bioprosthesis in dialysis patients should be carefully addressed16.
Study limitations
This study was subject to the bias inherent in retrospective observational studies. Because both groups had similar operative mortality (bioprosthesis 8.1%, mechanical valve 7.9%, P-value =0.0213) and we hope to study the long-term durability of prosthetic aortic valve in ESRD, we followed the patients after the index admission of valve replacement. Although we used PS matching to balance patient characteristics between the two types of prostheses, there may have been residual uncontrolled confounders. To increase statistical power for overall comparisons, we did not separate the dialysis population according to the duration of dialysis, the modality of dialysis, quality for dialysis and the etiology of the renal disease. Coding errors could have occurred within an administrative database. However, expert boards of the NHI program strictly review the process of medical coding to guarantee accurate claim payments. Important clinical information was lacking with the NHIRD, for example frailty, ejection fraction, international normalized ratio, and echocardiographic findings, which limited in-depth evaluation about the incidence of SVD and the definite cause of aortic valve reoperation or cardiac death.
Conclusion
This study compared the long-term outcomes associated with two types of valve prostheses from one of the largest cohorts of dialysis patients who underwent first-time single SAVR. Despite an overall decreased life expectancy after valve replacement surgery compared to the nondialysis population, there could be a 2-year survival gain in favor of a mechanical prosthesis in dialysis patients who underwent a first-time SAVR under the age of 50. For those aged over 50 years, bioprosthesis is a reasonable choice.
Ethical approval
This study was approved by the Research Ethics Committee of National Taiwan University Hospital, Taipei, Taiwan on 16 March 2021 (institutional review board approval: 202012072RIND).
Consent
The IRB has approved a request to waive the documentation of informed consent due to the minimal risks to the participants in our retrospective observational study.
Sources of funding
This study was funded by a grant from Edwards Lifesciences. The sponsors had no role in the study design and conduct of the study, collection, management, analysis, and interpretation of the data, preparation, review, or approval of the manuscript, and decision to submit the manuscript for publication.
Author contribution
H.-Y.F.: data curation, writing – original draft, and writing – review and editing; T.-C.W.: data curation, formal analysis, methodology; C.-H.W.: conceptualization, methodology, and supervision; N.-K.C.: data curation, conceptualization, methodology, and supervision; I.-H.W.: conceptualization, data curation, methodology, and supervision; R.-B.H.: conceptualization, investigation, supervision, writing – review and editing; S.-C.H.: conceptualization, data curation, supervision; H.-Y.Y.: conceptualization, data curation, methodology, and supervision; Y.-S.C.: conceptualization, investigation, supervision; N.-H.C.: conceptualization, data curation, formal analysis, investigation, methodology, supervision, writing – original draft, and writing – review and editing.
Conflicts of interest disclosure
The authors have declared no conflicts of interest.
Research registration unique identifying number (UIN)
Name of the registry: Research Registry.
Unique identifying number or registration ID: researchregistry9051.
Hyperlink to your specific registration (must be publicly accessible and will be checked): https://www.researchregistry.com/.
Guarantor
Nai-Hsin Chi. Department of Surgery, National Taiwan University Hospital, No. 8, Chung-Shan S Road, Taipei 65082, Taiwan. Tel: +886 2 23123456, fax: +886 2 23956934. E-mail: chinaihsin@gmail.com.
Data availability statement
Because the National Health Insurance Research Database (NHIRD) in this study encompasses a broad spectrum of sensitive medical information from a nationwide cohort, raw data would remain confidential and would not be shared.
Provenance and peer review
None.
Supplementary Material
Acknowledgements
The authors thank the staff at the Seventh Core Laboratory, Department of Medical Research, National Taiwan University Hospital. The study data source is the Health and Welfare Data Science Center, Ministry of Health and Welfare (HWDC, MOHM). The authors acknowledge the statistical assistance provided by the Health Data Research Center, National Taiwan University. The authors would especially like to thank Hsuan Chiu for preparing the tables.
Footnotes
Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.
Supplemental Digital Content is available for this article. Direct URL citations are provided in the HTML and PDF versions of this article on the journal's website, www.lww.com/international-journal-of-surgery.
Published online 31 July 2023
Contributor Information
Hsun-Yi Fu, Email: b95401026@ntu.edu.tw.
Ting-Chuan Wang, Email: tcwang0360@gmail.com.
Chih-Hsien Wang, Email: wchemail@ntu.edu.tw.
Nai-Kuan Chou, Email: nickchou@ntu.edu.tw.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
Because the National Health Insurance Research Database (NHIRD) in this study encompasses a broad spectrum of sensitive medical information from a nationwide cohort, raw data would remain confidential and would not be shared.