Asian Cardiovasc Thorac Ann 2000;8:121-126
© 2000 Asia Publishing EXchange Pte Ltd
Bioprostheses and Mechanical Prostheses Predictors of Performance
WR Eric Jamieson, MD,
Eva Germann, MSc,
Guy J Fradet, MD,
Samuel V Lichtenstein, MD,
Robert T Miyagishima, MD
Department of Surgery
Faculty of Medicine
University of British Columbia
Vancouver, British Columbia, Canada
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For reprint information contact: WR Eric Jamieson, MD Tel: 1 604 806 8383 Fax: 1 604 806 8384 St. Paul's Hospital, 1081 Burrard St., 331–332 Burrard Building, Vancouver, BC V6Z 1Y6, Canada.
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Abstract
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From 1975 to 1995, 4200 patients had bioprosthetic valve replacements (2240 aortic, 1607 mitral, 353 multiple) and 2038 had mechanical valve replacements (747 aortic, 928 mitral, 363 multiple). Freedom from major thromboembolism or both major thromboembolism and hemorrhage for aortic and mitral valve replacement at 15 years was significantly greater for bioprostheses than mechanical prostheses. Freedom from valve-related mortality and reoperation for both aortic and mitral valve replacements was the same for bioprostheses and mechanical prostheses. Advancing age increased overall mortality (all positions), valve-related mortality (aortic, mitral), major thromboembolism (aortic), thromboembolism and hemorrhage (aortic, mitral) but decreased reoperation (all positions). Coronary artery bypass grafting increased overall mortality (aortic, mitral) but not valve-related mortality, and it decreased reoperation rate (aortic, mitral). Overall mortality was not influenced by valve type in aortic or multiple valve replacement but it was decreased by bioprostheses in mitral valve replacement. Valve type did not influence valve-related mortality (all positions). Mechanical valves decreased reoperation only for aortic valve replacement but they increased major thromboembolism with and without hemorrhage for both aortic and mitral replacements. There is support for bioprostheses in aortic valve replacement and mechanical prostheses in mitral valve replacement but for neither in multiple valve replacements.
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Introduction
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The last quarter century has afforded a choice between heterograft and mechanical prostheses. Throughout this period, there have been advances in tissue preservation and stent designs for bioprostheses (BP) and valvular designs and materials for mechanical prostheses (MP). Major thromboembolism (TE), prosthesis thrombosis, and anticoagulant-related hemorrhage remain the predominant complications of MP, while structural valve deterioration necessitating reoperation is the main complication of BP. The choice of suitable prosthetic type must be made by attending cardiologists, cardiac surgeons, and their patients, with the aim of minimizing the risks of permanent impairment, mortality, and reoperation. BP provide the opportunity to avoid long-term anticoagulant management. BP have been identified as the choice for the elderly, especially for aortic valve replacement in patients aged 65 years or older. The influence of age on structural valve deterioration of BP and the necessity of reoperation have been well documented by the authors and other investigators.1–19 There has been limited documentation of other patient-related variables or confounders, either singly or in combination, that affect life expectancy or relate to permanent impairment.1–19 The purpose of this report is to evaluate clinical performance by valve type, age, and coronary artery disease, as factors in the selection of BP and MP.
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Patients and Methods
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A population of 6238 patients who had cardiac valve replacement procedures was evaluated to determine the predictors of survival and valve-related complications and composites of complications. The patients underwent implantation between 1975 and 1995 with follow-up completed during a 9-month closing interval in 1996. The follow-up evaluation incorporated interviews with all patients and review of hospital records, consultation reports, autopsy records, operative and pathology records of explanted valves, vital statistics evaluation of death records and reports from family physicians. The completion of follow-up for the various prostheses populations ranged between 95% and 99%. There were 4200 patients with BP and 2038 with MP. BP consisted of porcine bioprostheses: Carpentier-Edwards Standard, Carpentier-Edwards SupraAnnular (Baxter Healthcare Corp., Irvine, CA, USA), and Medtronic Intact (Medtronic, Inc., Minneapolis, MN, USA). The MP group received bileaflet prostheses: St. Jude Medical (St. Jude Medical, Inc., St. Paul, MN, USA) and Carbomedics (Sulzer Carbomedics, Inc., Austin, TX, USA).
Of the 4200 patients with BP, aortic valve replacement (AVR) was performed in 2240, mitral valve replacement (MVR) in 1607, and multiple valve replacements (MR) in 353. Of the patients with MP, AVR was performed in 747, MVR in 928, and MR in 363. The mean age of the BP population was 63.1 ± 13 years (range, 8 to 89 years) and for the MP population, it was 58.1 ± 12.6 years (range, 13 to 91 years). Coronary artery bypass grafting (CABG) was performed in 31.5% (1321) of the BP group and in 23.3% (474) of the MP group. Total follow-up in the BP population was 27,521.6 patient-years (AVR 15,273.9, MVR 10,174.8, and MR 2071.9 patient-years); in the MP population, it was 5158.8 patient-years (AVR 1892.5, MVR 2293.1, and MR 973.2 patient-years). The mean follow-up was 6.5 ± 4.6 years in the BP group and 2.5 ± 1.97 years in the MP group. The patient population is further differentiated in Table 1
. The groups and valve positions are detailed with regard to major thromboembolic and hemorrhagic events, reoperation, and valve-related mortality.
The risk factors evaluated as predictors of performance were advancing age assessed by age groups (< 60, 61–69, and 
70 years), valve type (MP or BP), and coronary artery disease as reflected in CABG. The freedom from complications (major TE and hemorrhage) and from composites of complications (valve-related reoperation and valve-related mortality) was derived by actuarial life analysis and significance (p < 0.05) by the WilcoxonGehan statistic. Risk factors were assessed by the Cox proportional hazard regression analysis as predictors (odds ratio, p < 0.05) of influence on overall mortality and freedom from major TE and hemorrhage, valve-related reoperation, and valve-related mortality. The definitions of the valve-related complications are in accordance with the guidelines for reporting morbidity and mortality after cardiac valvular operations.20
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Results
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Freedom from major TE and freedom from both major TE and hemorrhage is demonstrated in Figures 1 to 3. For AVR, the freedom from major TE at 15 years for BP was less than for MP (p < 0.05), but the freedom from both major TE and hemorrhage at 15 years was greater for BP than for MP. For MVR, the freedom from major TE at 15 years was greater for BP than for MP and the freedom from both major TE and hemorrhage at 15 years was also greater for BP than for MP. For MR, there were no significant differences in these parameters at 15 years. The freedom from valve-related reoperation and from valve-related mortality is illustrated in Figures 4 to 6. There were no statistically significant differences between the two types of prosthesis in terms of these parameters at 15 years.
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Figure 1. Freedom from major thromboembolism, and major thromboembolism and hemorrhage after aortic valve replacement. BP = bioprostheses, MP = mechanical prostheses, SE = standard error, TE = thromboembolism.
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Figure 2. Freedom from major thromboembolism, and major thromboembolism and hemorrhage after mitral valve replacement. Abbreviations as in Figure 1 .
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Figure 3. Freedom from major thromboembolism, and major thromboembolism and hemorrhage after multiple valve replacement. pNS = not significant, other abbreviations as in Figure 1.
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The predictors of overall mortality are demonstrated in Figures 7 to 9. Advancing age significantly increased overall mortality for AVR, MVR, and MR. The overall mortality was greater for MP than BP but this was not significant. MP decreased overall mortality for MVR and MR but the decrease was significant only for MVR. Overall mortality was increased by coronary artery disease in AVR and MVR (p < 0.05), and not significantly in MR. Valve-related mortality predictors are illustrated in Figures 7 to 9. Age was a significant predictor of valve-related mortality in AVR and MVR but not in MR. Valve type was not a predictor of valve-related mortality. Coronary artery disease did not significantly influence valve-related mortality. Advancing age increased major TE for AVR but not for MVR and MR. MP was a significant predictor of major TE in AVR and MVR but not MR. Coronary artery disease significantly increased major TE only for MR. The predictors of major TE and hemorrhage (Figures 7 to 9) were the same as for TE alone, except that the addition of advanced age increased TE and hemorrhage in MVR (p < 0.05). Advancing age significantly decreased the reoperation rate for all valve positions. Mechanical valves decreased valve-related reoperation significantly for AVR but not for MVR and MR. Coronary artery disease decreased valve-related reoperation significantly for AVR and MVR.
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Figure 7. Predictors of performance after aortic valve replacement. BP = bioprostheses, CABG = coronary artery bypass grafting, MP = mechanical prostheses.
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Discussion
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Cardiovascular surgeons, cardiologists, and patients will continue to have the choice of bioprostheses or mechanical prostheses for cardiac valve replacement. The choice of prosthesis for the individual patient has depended on the clinical status of the patient, the confidence of the surgeon in the prosthesis, and the risk of valve-related complications. The literature has provided extensive documentation on individual prostheses, combinations of prostheses, and nonrandomized assessments of BP and MP, but few randomized trials. Randomized clinical trials such as the Veterans Administration Study on Valvular Heart Disease and the Edinburgh Heart Valve Trial have provided several conclusions, the majority were known from nonrandomized studies.2,3 Hemorrhagic complications from anticoagulation are the predominant complications in mechanical valve populations. The rates of TE and prosthetic endocarditis from the randomized trials are the same for BP and MP. Porcine bioprostheses fail more frequently in the mitral position than in the aortic position, 5 or more years after implantation. The freedom from death, reoperation, major embolism, and endocarditis was less with porcine bioprostheses, especially in the mitral position.
The influence of patient-related variables on valve-related complications has had minimal evaluation.1–19 Age as a patient-related variable has received the most attention.4–13 In 1988, Jamieson and colleagues4 demonstrated increasing freedom from structural valve deterioration for both AVR and MVR with each decade of age at implantation. The study also determined a greater freedom from structural failure with AVR than MVR. In the same year, Pupello and colleagues5 documented a trend of more freedom from structural failure for patients 70 years of age than those of 55 to 69 years. Jamieson and colleagues6 reported again in 1991 that age was a predictor of structural valve deterioration but that structural failure had little influence on valve-related mortality and permanent impairment. Also in 1991, the authors confirmed that mitral position as well as age were predictors of structural valve deterioration.7
Bioprostheses in the elderly have received considerable attention since 1988. Burr and colleagues9 summarized the status of porcine bioprostheses in the elderly. Freedom from structural valve deterioration at 10 years was 98% for AVR and 79% for MVR. Freedom for AVR at 10 years for the 65 to 69 years age group was 95%, and for those aged 70 to 74 years, it was 99%. Freedom from structural failure at 10 years after MVR for 65 to 69-year-olds was 70% and it was 90% for 70 to 74-year-olds. Freedom from structural valve deterioration necessitating reoperation for patients 75 years was over 96% for AVR and over 94% for MVR. We have always been of the opinion that if structural failure was increasing, it had not advanced so as to necessitate reoperation or to contribute to mortality.
Assessment of freedom from major TE with and without hemorrhage for both AVR and MVR revealed a significant difference over 15 years in favor of bioprostheses. The major difference occurred in the first 10 years rather than in the last 5 years. The most clinically relevant differences occurred in the assessment of MVR over the total 15 years. The actuarial incidence of major TE with MP was twice that of BP, while that of major hemorrhage was the same. Freedom from valve-related mortality and reoperation did not achieve statistical significance because of an inadequate number of MP patients at risk in the last 5 years of evaluation but the results must be considered clinically relevant. The overall mortality was influenced significantly by advancing age and concomitant CABG. Age increased overall mortality for AVR, MVR, and MR. CABG increased overall mortality for AVR and MVR but not for MR. Valve type only influenced overall mortality for MVR with BP.
Several investigators have evaluated the risk factors for overall mortality in valve replacement. Advancing age has been consistently identified as a risk factor in various populations.10–12 Hwang and colleagues13 reported that late mortality was the same for MP and BP in AVR. Concomitant CABG also adversely affected survival.14 Gehlot and colleagues15 found CABG to be a predictor of long-term survival after AVR in those 80 years of age. In 1995, Jamieson and colleagues1 reported that CABG decreased survival in BP and MP groups. In the same study, AVR with MP and MR with either BP or MP (both without CABG) improved the overall survival. The predictors of major TE were advancing age for both AVR and MVR with MP. For MR only, CABG was a significant predictor of major TE. When major TE and hemorrhage were assessed together, the predictors were advancing age and MP for AVR and MVR. CABG was not a predictor in AVR or MVR but it was the only predictor of major TE and hemorrhage for MR.
The type of valve was determined by others to be a predictor of major thromboembolic and hemorrhagic complications.16,17 Jamieson and colleagues1 found that bioprostheses with or without CABG, decreased events after AVR but not after MVR. Heras and colleagues16 showed that the risk of TE was predominant in MVR with advancing age. Holper and colleagues17 showed that thromboembolic and hemorrhagic complications were 3 times more prevalent with MP than BP. Tyers and colleagues18 reporting on reoperative surgery in 1995, identified repeat surgery as a factor in the greater prevalence of thrombotic complications with MP over BP.
Valve-related mortality was only influenced by advancing age, and only for AVR and MVR. CABG did not influence valve-related mortality for AVR, MVR or MR. Valve type did not predict valve-related mortality. Jamieson and colleagues1 noted in 1995, that CABG was not a predictor of valve-related mortality for AVR and MVR. This latter study evaluated different populations with the MP comprising both monoleaflet and bileaflet prostheses. Hammond and colleagues19 also showed that valve-related mortality was the same for BP and MP.
The factors that decreased valve-related reoperation for AVR were advancing age, MP, and CABG. For MVR, advancing age and CABG were predictive of decreasing valve-related reoperation, while for MR, only advancing age was significant. Valve type was not a predictor of either increasing or decreasing reoperation rate for either MVR or MR. This finding may be related to the higher paravalvular leak rate requiring reoperation with MP and the lack of adequate numbers of MP at the extended intervals when BP fail to a greater degree. In 1995, Jamieson and colleagues1 reported that BP with concomitant CABG (and not without CABG) decreased valve-related reoperation for both AVR and MVR. The influence of advancing age and CABG is, no doubt, related to decreased longevity due to these factors and specifically to lack of time for BP structural failure.
Several conclusions can be drawn from this study, providing indications for BP and MP utilization by valve position. Advancing age increased overall mortality, valve-related mortality, and major TE both with and without hemorrhage, but it decreased reoperation. CABG, indicative of accompanying coronary artery disease, increased overall mortality but not valve-related mortality, and decreased valve-related reoperation. Valve type did not influence overall mortality for aortic and multiple replacements but BP decreased overall mortality in MVR. Valve type did not influence valve-related mortality for all positions. MP decreased valve-related reoperation but only for AVR, and increased major TE and TE plus hemorrhage for both AVR and MVR.
From this study and previous reports by the authors, there are reasons to support the use of BP for AVR due to their lack of influence on both overall and valve-related mortality, as well as the extensive morbidity caused by MP from major TE. This conclusion could be interpreted to mean that the use of biological substitutes only (pulmonary autografts, allografts, stentless and stented heterograft prostheses) should be considered for AVR. There are reasons to support use of MP for MVR when reconstruction is not feasible. Neither valve type was predictive of valve-related mortality but the negative influence of MP in MVR on overall mortality may be offset by increased major TE and hemorrhage. Other factors such as atrial fibrillation contribute to the support for MP. Our previous documentation8,9 and the current study support the use of BP for MVR in the elderly or when factors such as coronary artery disease are anticipated to reduce longevity. The indications for prostheses type, especially for MVR, requires further evaluation of comorbidity risk factors. The conclusions of this comparative study have the limitation of shorter follow-up for MP than BP, but the majority of complications with mechanical prostheses occur early and bioprostheses complications occur late.
Presented at the VII International Symposium on Cardiac Bioprostheses, Barcelona, Spain, June 13–15, 1997.
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Acknowledgments
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We extend appreciation to our clinical research staff: Joan MacNab, Florence Chan, Charmaine Henderson, and Heidar Sadeghi for database management and patient follow-up.
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References
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[Abstract]
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Abstract
Introduction
