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Ann Thorac Surg 1999;68:2169-2172
© 1999 The Society of Thoracic Surgeons

Original Articles: Cardiovascular

Are older patients with mechanical heart valves at increased risk?

Roy G. Masters, MDa, Lloyd C. Semelhago, MDa, Andrew L. Pipe, MDa, Wilbert J. Keon, MDa

a Division of Cardiac Surgery, University of Ottawa Heart Institute, Ottawa, Ontario, Canada

Address reprint requests to Dr Masters, Division of Cardiac Surgery, University of Ottawa Heart Institute, 40 Ruskin St, Ottawa, ON, Canada K1Y-4W7


   Abstract
Top
 Abstract
Introduction
 Material and methods
 Results
 Comment
 References
 
Background. Controversy exists regarding the use of mechanical valves in older patients. Many authorities believe that the use of anticoagulants in the elderly is associated with an increased risk of warfarin-related complications. Therefore, we compared the results with mechanical valves in older patients to a cohort of younger patients.

Methods. Aortic (AVR) or mitral valve replacement (MVR) with a mechanical valve was performed in 1,245 consecutive patients who were followed prospectively. They were grouped by age (group 1, <= 65 years; group 2, > 65 years). The study groups consisted of AVR (group 1, 459 patients; group 2, 323 patients) MVR (group 1, 313 patients; group 2, 150 patients).

Results. The average age for the groups was: AVR (group 1, 51 years; group 2, 70 years; p = 0.03) and MVR (group 1, 53 years; group 2, 70 years; p = 0.03). For AVR the incidence of thromboembolism was 0.050 (group 1) and 0.038 (group 2) (p = 0.37) and the actuarial freedom from thromboembolism was 83.0% ± 3.0% and 86.5% ± 1.0%, respectively (p = 0.13). The incidence of bleeding after AVR was 0.021 for group 1 and 0.028 for group 2 (p = 0.49). For MVR the incidence of thromboembolism was 0.059 for group 1 and 0.051 for group 2 (p = 0.75) and the actuarial freedom from thromboembolism was 78.8% ± 3.0% and 75.4% ± 8.7%, respectively (p = 0.71). The incidence of bleeding after MVR was 0.020 for group 1 and 0.027 for group 2 (p = 0.62).

Conclusions. Mechanical valves perform well in selected older patients with no increased risk of bleeding or thromboembolism.


   Introduction
Top
 Abstract
 Introduction
Material and methods
 Results
 Comment
 References
 
With the exponential growth of the geriatric population in North America, the number of older patients referred for open heart operations during the past decade has markedly increased [1]. Although the use of bioprosthetic valves for heart valve replacement in the elderly is well established, controversy surrounds the use of mechanical valves in these patients. Whether their benefits of superior structural integrity with very low reoperation rates outweighs the risks of anticoagulant-related complications is moot. This debate is fueled by the purported increased susceptibility of the elderly to complications of anticoagulants, both embolic and hemorrhagic [2]. In this study we compared the long-term results of elderly patients with mechanical valves to a younger cohort to assess the relative risk of anticoagulant-related complications in the elderly.


   Material and methods
Top
 Abstract
 Introduction
 Material and methods
Results
 Comment
 References
 
From January 1985 to December 1996 inclusive, 1,245 consecutive patients underwent isolated aortic valve replacement (AVR) or mitral valve replacement (MVR) using a mechanical valve at the University of Ottawa Heart Institute. Aortic valve replacement was performed in 782 patients, of which 320 used the St. Jude Medical valve (St. Jude Medical, St. Paul, MN), 296 used the Medtronic-Hall valve (Medtronic Inc, Minneapolis, MN), and 166 used the Carbomedics valve (Sulzer Medica, Austin, TX). Mitral valve replacement was performed in 463 patients, with the St. Jude Medical valve being used in 144, the Medtronic-Hall valve in 242, and the Carbomedics valve in 77.

The choice of valve was at the surgeon’s discretion; however, the surgical technique and follow-up were similar for all patients. The operative technique included cardiopulmonary bypass with moderate hypothermia, topical cooling with cold saline solution, and antegrade cold crystalloid cardioplegia. The implantation technique consisted of interrupted horizontal mattress sutures reinforced with Teflon pledgets.

Warfarin sodium was started within 24 to 48 hours of the operation. During the initial years the prothrombin time was used to monitor the level of anticoagulation with a target prothrombin time ratio of 1.5 to 2.0. Most recently, the international normalized ratio (INR) has been used to monitor the level of anticoagulation with a target of 2.5 to 3.5 [3]. Regulation of the INR after discharge from the hospital was by the patient’s family physician or cardiologist after initial stabilization by the surgeon.

All patients who undergo valve replacement are registered with the Valve Clinic of the Ottawa Heart Institute and survivors are evaluated annually. For patients having AVR there were 2,137 patient-years of follow-up and for those having MVR there were 1,140. For the purpose of this study, patients were divided into two groups according to their age at the time of operation. Group 1 patients were 65 years old or less and group 2 patients were more than 65 years of age.

Data are presented in accordance with the Guidelines for Reporting Morbidity and Mortality After Cardiac Valvular Operations [4]. We also further defined bleeding as major if it resulted in hospitalization, transfusion, permanent injury, or death. All other episodes of bleeding were defined as minor. Comparisons between the preoperative characteristics of the patient groups were made using the {chi}2 test or Fisher’s exact test where appropriate for discrete variables and analysis of variance for continuous variables. The relative frequency of morbid events is expressed as the incidence (percent per patient-year) and as the actuarial probability. The actuarial estimates were calculated by means of the life-table technique with the SPSS statistical data analysis software (SPSS Inc, Chicago, IL) and are reported with 95% confidence limits. All results were considered statistically significant at the less than 0.05 level.


   Results
Top
 Abstract
 Introduction
 Material and methods
 Results
Comment
 References
 
Among the AVR patients there were 459 patients in group 1 and 323 patients in group 2 with 1,457 and 680 patient-years of follow-up, respectively. Table 1 shows the preoperative characteristics of these two groups. The mean age was 51.4 years for group 1 and 70.0 years for group 2. The two groups were otherwise similiar except that the older patients had a higher incidence of concomitant coronary artery bypass grafting (p = 0.001). Among the AVR patients, 2.3% (18 of 782) were in atrial fibrillation preoperatively.


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  		Table 1. Preoperative Characteristics of Patients Having Aortic Valve Replacement and Mitral Valve Replacement

 
Among the MVR patients there were 313 patients in group 1 and 150 in group 2 with 889 and 251 patient-years of follow-up, respectively. Table 1 shows the preoperative characteristics of these two groups. The mean age was 52.9 years for group 1 and 70.3 years for group 2. Again the two groups were similiar except for the higher incidence of coronary artery bypass grafting among the older patients (p = 0.001). Among the MVR patients, 19.7% (91 of 463) were in atrial fibrillation preoperatively.

The overall hospital mortality for the patients having AVR was 3.8% and for those having MVR it was 8.2% (p = 0.001). For the AVR patients the mortality was 2.7% for group 1 (12 of 459) and 5.5% for group 2 (18 of 323) (p = 0.05). For the MVR patients the mortality was 7.3% for group 1 (23 of 313) and 10.0% for group 2 (15 of 150) (p = 0.36).

Table 2 shows the relative incidence of bleeding complications for patients having AVR and MVR. After AVR, in group 1, there were 32 bleeding episodes in 28 patients, of which 23 were minor and 9 were major. In group 2, there were 19 bleeding episodes in 17 patients of which 18 were considered minor and 1 was considered major. After MVR, in group 1, there were 18 bleeding episodes in 14 patients of which 13 were considered minor and 5 were major. In group 2, there were 7 bleeding episodes in 7 patients, 6 of which were considered minor and 1 considered major.


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  		Table 2. Incidence of Thromboembolic and Bleeding Complications after Aortic Valve Replacement and Mitral Valve Replacement

 
For both AVR and MVR the incidence of all bleeding events was not statistically different between the two age groups. When considered separately the incidence of major bleeding, the most seri ous complication, was also not statistically different between groups. Figures 1 and 2 , respectively, show the actuarial probability of freedom from bleeding for AVR and MVR. At 5 years the probability estimate for AVR was 92.2% ± 3% for group 1 and 88.1% ± 3% for group 2 (p = 0.34). For MVR the probability estimate at 5 years was 92.6% ± 2% for group 1 and 86.8% ± 5% for group 2 (p = 0.29).



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  		Fig 1. Actuarial freedom from bleeding after aortic valve replacement.

 


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  		Fig 2. Actuarial freedom from bleeding after mitral valve replacement.

 
Table 2 shows the incidence of thromboembolic events for the two groups of patients having AVR and MVR. After AVR, in group 1, there were 73 thromboembolic events in 61 patients. These included 47 transient ischemic attacks, 18 cerebrovascular accidents, 4 peripheral emboli, and 4 myocardial infarctions. In group 2, there were 26 events in 21 patients including 13 transient ischemic attacks, 10 cerebrovascular accidents, 1 peripheral embolism, and 2 myocardial infarctions. After MVR, in group 1, there were 53 thromboembolic events in 40 patients including 35 transient ischemic attacks, 15 cerebrovascular accidents, 1 peripheral embolism, and 2 myocardial infarctions. In group 2, there were 13 events in 11 patients including 9 transient ischemic attacks, 3 cerebrovascular accidents, and 1 peripheral embolism. For both AVR and MVR the incidence of all thromboembolic events was not statistically different between the two age groups. When considered separately, the incidence of stroke, the most serious thromboembolic complication, was also not statist ically different between groups. Figures 3 and 4 , respectively, show the actuarial probability of freedom from thromboembolism for AVR and MVR. At 5 years the probability estimate for AVR was 82.0% ± 3% for group 1 and 86.5% ± 1% for group 2 (p = 0.13). For MVR, the probability estimate at 5 years was 78.8% ± 3% for group 1 and 75.4% ± 8.7% for group 2 (p = 0.71).



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  		Fig 3. Actuarial freedom from thromboembolism after aortic valve replacement.

 


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  		Fig 4. Actuarial freedom from thromboembolism after mitral valve replacement.

 

   Comment
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
References
 
The number of elderly patients presenting for open heart operation is growing as the average age of the general population increases [1]. For those who require heart valve replacement the prosthesis of choice remains somewhat controversial. Biologic valves offer the advantage of not requiring long-term anticoagulation with warfarin, whereas mechanical valves offer the advantage of superior durability. Whether the risk of anticoagulant-related complications with mechanical valves outweighs the benefits in older patients is moot. This debate is fueled by the purported increased susceptibility of the elderly to the complications of anticoagulants, both embolic and hemorrhagic [2].

To hopefully facilitate this discussion we compared the long-term morbidity with mechanical valves for AVR or MVR in older patients to a younger cohort to assess the relative risk of anticoagulant-related complications in the elderly. Although not a randomized trial our patients were all followed prospectively on an annual basis in a Valve Clinic in a single center. Nevertheless, our results suggest that older patients are not at increased risk with mechanical valves and warfarin, at least within a target INR range of 2.5 to 3.5. However, there was likely selection bias when choosing which of the older patients were offered a mechanical valve. Those older patients implanted with a mechanical valve were undoubtedly in relatively good health.

A number of previous studies have attempted to assess the risk of bleeding with the use of anticoagulants in the elderly. Although some studies found that the frequency of bleeding during warfarin therapy is higher in older patients, other investigators disagree.

In one study of 565 patients taking warfain for a variety of indications it was found that age 65 years or more was an independent risk factor for bleeding [5]. The cumulative incidence of bleeding at 48 months was 13% in those less than 65 years and 35% in those 65 years or older. In that study, however, the target INR was not specified and the rates of bleeding appear excessive compared with what we report this study. In another study of 1,608 patients with mechanical valves and warfarin, an increased risk of bleeding with age was also noted [6]. The incidence of bleeding was 2.5% per patient-year for patients less than 50 years of age, 2.8% for patients 50 to 69 years, and 5.6% for patients more than 70 years of age. In that study, however, the target INR range was 3.6 to 4.8, a level that is beyond the current recommendations [3]. Two consecutive reports of 1,100 patients on warfarin by the Stroke Prevention in Atrial Fibrillation investigators showed that advancing age was a risk factor for bleeding [7, 8]. In the latest of these reports the overall incidence of major bleeding was 1.7% for patients 75 years or younger and 4.2% for patients more than 75 years of age. In the Stroke Prevention in Atrial Fibrillation studies, however, the target range of INR was up to 4.5. Of particular importance, these researchers found that in older patients the risk of bleeding increased with the intensity of anticoagulation. In those patients more than 75 years, in whom the INR was less than 3, the rate of major bleeding was only 2.7% per patient-year, a rate similar to that of their young patients, whereas for those elderly patients with an INR more than 3, the rate was 9.0% per patient-year. Finally, in a multivariable analysis of 6,512 patients on warfarin for a variety of indications it was reported that age and INR were risk factors for bleeding [9]. However, as with many of the other studies the target range for INR in that study was up to 4.5.

Other studies have not found an increased risk of bleeding with anticoagulation in the elderly. In two such studies of 480 and 213 patients taking warfarin it was found that the risk of bleeding was unrelated to age [10, 11]. Neither of these two studies actually assessed the risk of bleeding as a function of age but rather simply compared the average age of those who bled to those who did not. Finally, a 1996 study followed 2,376 patients who were receiving warfarin of which 719 patients were 60 to 69 years of age and 432 patients were 70 to 79 years of age [12]. Using multivariable analyses, these investigators found that the risk of minor or serious bleeding did not increase with age, but it did increase with the intensity of anticoagulation.

The low rate of hemorrhagic complications in the elderly that we report is corroborated by the 1996 report by Arom and colleagues [1]. Using St. Jude mechanical valves in 796 patients 70 years of age or older, they noted the incidence of hemorrhage to only be 0.4% ± 0.12% for AVR and 0.78% ± 0.32% for MVR. They attributed these low rates to a reduced intensity of anticoagulation with the target INR being 1.8 to 2.5 for AVR and 2.5 to 3.2 for MVR. Despite this reduced level of anticoagulation the incidence of thromboembolism also remained low in that study.

We believe these studies and the results reported in this study suggest that mechanical valves can be used safely in older patients. Careful patient selection before the implantation of a mechanical valve, which commits the patient to lifelong warfarin, is even more important in the elderly.


   References
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
 References
 

  1. Arom K.V., Emery R.W., Nicoloff D.M., Petersen R.J. Anticoagulant related complications in elderly patients with St. Jude mechanical valve prostheses. J Heart Valve Dis 1996;5:505-510.[Medline]
  2. Jamieson W.R.E. Mechanical and bioprosthetic aortic valve replacement. In: Edmunds L.H., Jr, ed. Cardiac surgery in the adult. New York: McGraw-Hill, 1997:859-909.
  3. Stein P.D., Alpert J.S., Copeland J., Dalen J.E., Goldman S., Turpie A.G.G. Antithrombotic therapy in patients with mechanical and biological prosthetic heart valves. Chest 1992;102(suppl):445-454.
  4. Edmunds L.H., Jr, Clark R.E., Cohn L.H., Miller D.C., Weisel R.D. Guidelines for reporting morbidity and mortality after cardiac valvular operations. Ann Thorac Surg 1996;62:932-935.[Abstract/Free Full Text]
  5. Landefeld C.S., Goldman L. Major bleeding in outpatients treated with warfarin. Am J Med 1989;87:144-152.[Medline]
  6. Cannegieter S.C., Rosenthal F.R., Wintzen A.R., van der Meer F.J., Vandenbroucke J.P., Briet E. Optimal oral anticoagulant therapy in patients with mechanical heart valves. N Engl J Med 1996;333:11-17.[Abstract/Free Full Text]
  7. Stroke Prevention in Atrial Fibrillation Investigators. Bleeding during antithrombotic therapy in patients with atrial fibrillation. Arch Intern Med 1996;156:409-416.[Abstract/Free Full Text]
  8. Stroke Prevention in Atrial Fibrillation Investigators. Warfarin versus aspirin for prevention of thromboembolism in atrial fibrillation. Lancet 1994;343:687-691.[Medline]
  9. Van der Meer F.J., Rosendaal F.R., Vandenbroucke J.P., Briet E. Bleeding complications in oral anticoagulant therapy. An analysis of risk factors. Arch Intern Med 1993;153:1557-1562.[Abstract/Free Full Text]
  10. Forfar J.C. A 7-year analysis of haemorrhage in patients on long-term anticoagulant treatment. Br Heart J 1979;42:128-132.[Free Full Text]
  11. Lundstrom T., Ryden L. Haemorrhagic and thromboembolic complications in patients with atrial fibrillation on anticoagulant prophylaxis. J Intern Med 1989;225:137-142.[Medline]
  12. Fihn S.D., Callahan C.M., Martin D.C., McDonell M.B., Henikoff J.G., White R.H. The risk for and severity of bleeding complications in elderly patients treated with warfarin. Ann Intern Med 1996;124:970-979.[Abstract/Free Full Text]
Accepted for publication May 11, 1999.




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