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Asian Cardiovasc Thorac Ann 2006;14:189-194
© 2006 Asia Publishing EXchange Ltd

ORIGINAL CONTRIBUTIONS

Late Mortality and Morbidity in Elderly Patients with Mechanical Heart Valves

Sadanari Sawaki, MD, Akihiko Usui, MD, Tomonobu Abe, MD, Masaharu Yoshikawa, MD, Toshiaki Akita, MD, Yuichi Ueda, MD

Department of Cardiothoracic Surgery, Graduate School of Medicine, Nagoya University, Nagoya, Japan

For reprint information contact: Sadanari Sawaki, MD Tel: 81 52 744 2375 Fax: 81 52 744 2383 Email: sawasada{at}med.nagoya-u.ac.jp, Department of Cardiothoracic Surgery, Graduate School of Medicine, Nagoya University, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 PATIENTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
A retrospective study was performed in patients under and over 65 years old implanted with a mechanical valve, to compare late mortality and morbidity. Of 381 patients who underwent mechanical valve replacement at Nagoya University in the 1990s, 357 (11 hospital deaths and 13 lost to follow-up; 96.4% follow-up rate) were followed up for 7.9 ± 3.3 years (2,811 patient-years). They were divided into two groups either side of 65 years of age at operation. The young and elderly patient groups contained 275 and 82 patients, respectively. The survival rate in the young group was 96.1% (95% confidence interval, 93.7%–98.5%) at 5 years and 92.0% (95% confidence interval, 88.3%–95.7%) at 10 years, which was significantly better than 88.0% (95% confidence interval, 80.6%–95.4%) at 5 years and 73.8% (95% confidence interval, 66.2%–85.4%) at 10 years in the elderly group. The two groups did not differ significantly in the incidence of thromboembolic events, bleeding events, endocarditis, or reoperation. We are also encouraged by the fact that mechanical valves are not a risk factor for late mortality or morbidity, even in elderly patients.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
PATIENTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Selection of prosthetic valve type is a major concern in heart valve surgery. Mechanical valves provide better durability but require careful anticoagulant therapy, whereas bioprostheses have limited durability. Improper management of anticoagulant therapy carries the risk of thromboembolism or bleeding complications. The ACC/AHA guidelines propose that bioprosthetic valves be used in patients who have few thromboembolic risks, are over 65 years old needing aortic valve replacement (AVR), or over 70 years old undergoing mitral valve replacement (MVR).1 However, improved living standards and progress in medicine has since prolonged life expectancy, and it is unclear whether bioprosthetic valves last long enough relative to the current life expectancy of patients. An increasing number of patients over 65 years old are given mechanical heart valves. It is possible that a mechanical valve is a risk factor for late mortality or morbidity in elderly patients. This should be clarified to confirm the suitability of the ACC/AHA guidelines for Japanese patients. To this end, we performed a retrospective comparative study of patients under and over 65 years of age given a mechanical heart valve.


   PATIENTS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 PATIENTS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Mechanical valves were implanted in the aortic and/or mitral position in 381 patients at Nagoya University Hospital between January 1990 and December 1999. The overall hospital mortality was 2.9% (11/381). A survey by questionnaire was carried out by mail or telephone to all 370 survivors; any events were confirmed by clinical records or by inquiries to follow-up institutes or general physicians. Thirteen patients were lost to follow-up; the follow-up rate was 96.4%. The study group comprised 357 patients, the total follow-up was 2,811 patient-years, and the mean follow-up period was 7.9 ± 3.3 years. To compare late mortality and morbidity after mechanical valve implantation, we divided the patients into 275 who were < 65 years of age at operation (young group) and 82 who underwent valve replacement at > 65 years of age (elderly group). The demographic data for both groups are given in Table 1Go. The total follow-up was 2,253 patient-years in the young group, and 557 patient-years in the elderly group. In the elderly group, the proportion who had undergone a previous operation was slightly lower (the most common previous operation in the young group was open mitral commissurotomy for rheumatic mitral stenosis), body surface area was smaller, left ventricular ejection fraction was slightly better, and the mean follow-up period was shorter than in the young group. There were no significant differences in the other parameters studied.


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  		Table 1. Preoperative Demographics of 357 Patients Undergoing Aortic and/or Mitral Valve Replacement
 
The standard operative procedure was performed via median sternotomy under cardiopulmonary bypass with mild hypothermia, ascending aortic crossclamping, and intermittent cold blood cardioplegia. The mean duration of the operation was 390 ± 158 min, cardiopulmonary bypass was 186 ± 64 min, and the aortic crossclamp time was 117 ± 41 min. Anticoagulant therapy with warfarin began after the chest drains were removed. The warfarin dosage was adjusted to maintain the prothrombin time-international normalized ratio (PT-INR) at 1.8–2.2 for AVR and 2.0–2.5 for MVR. Operative procedures are shown in Table 2Go. During the 1990s, several types of mechanical valve were implanted (Table 3Go).


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  		Table 2. Operative Procedures
 

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  		Table 3. Mechanical Valves Implanted in 357 Patients
 
Data were evaluated using StatView J5.0 statistical software (SAS Institute, Cary, NC, USA). The Kaplan-Meier method was used for statistical analysis. Confidence intervals (CI) were set at 95%. Late mortality or morbidity was expressed as a linearized rate and by the actuarial survival curve. Linearized occurrence rates were calculated by dividing the observed number of occurrences of a particular event by the total number of years of patient follow-up. The log-rank test (Mantel-Cox) was used for comparison of the survival or event-free curves. A p-value less than 0.05 was considered significant. The Cox proportional hazard model was applied to show the relative risks for any significance.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 PATIENTS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Late mortality during the follow-up period was 17 (6.2%) in the young group and 16 (19.5%) in the elderly group. The causes of death are shown in Table 4Go. The actuarial survival rates were 96.1% (95% CI, 93.7%–98.5%) at 5 years and 92.0% (95% CI, 88.3%–95.7%) at 10 years in the young group, and 88.0% (95% CI, 80.6%–95.4%) at 5 years and 73.8% (95% CI, 66.2%–85.4%) at 10 years in the elderly group ( p < 0.0001). There were significant differences in the survival curves between the groups ( p < 0.0001; Figure 1Go). Age over 65 years was a significant prognostic factor for late mortality ( p = 0.0002, odds ratio = 3.67).


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  		Table 4. Causes of Death
 

Figure 1
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  		Figure 1. Kaplan-Meier survival curve.

 
Morbidity is shown in Table 5Go. Freedom from thromboembolic events was 93.8% (95% CI, 90.9%–96.7%) at 5 years and 85.1% (95% CI, 80.0%–90.2%) at 10 years in the young group, and 93.7% (95% CI, 88.4%–99.0%) at 5 years and 91.8% (95% CI, 85.3%–98.3%) at 10 years in the elderly group ( p = 0.6; Figure 2Go). The linearized rate of thromboembolism was 1.5%/patient-year in the young group and 1.1%/patient-year in the elderly group. Two patients in the young group and one in the elderly group were hospitalized because of massive nasal bleeding. The freedom from bleeding events was 98.5% (95% CI, 96.9%–100.1%) at 5 years and 93.5% (95% CI, 90.0%–97.4%) at 10 years in the young group, and 97.4% (95% CI, 93.9%–100.9%) at 5 years and 95.5% (95% CI, 90.4%–100.6%) at 10 years in the elderly group ( p = 0.8; Figure 3Go). The linearized rate of bleeding events was 0.5%/patient-year in each group.


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  		Table 5. Morbidity in 357 Patients
 

Figure 2
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  		Figure 2. Freedom from thromboembolism.

 

Figure 3
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  		Figure 3. Freedom from bleeding events.

 
Cardiac re-operation was required in 14 patients in the young group and one in the elderly group. Re-operation at the same valve position was performed in 7 patients in the young group only; 3 had perivalvular leakage, 2 had prosthetic valve endocarditis, and 2 required the Bentall procedure after developing a pseudoaneurysm (Table 5Go). The 5-year freedom from re-operation was 97.8% (95% CI, 96.0%–99.6%) in the young group and 100% in the elderly group. The linearized rate of re-operation was 0.3%/patient-year in the young group and 0% in the elderly group. Four patients in the young group and 2 in the elderly group were diagnosed with endocarditis. Two in the young group underwent a further valve replacement. One patient in the elderly group died despite treatment. The other 3 were treated medically and survived without complications. The 5-year freedom from endocarditis was 98.9% (95% CI, 97.7%–100.1%) in the young group and 98.8% (95% CI, 92.3%–101.3%) in the elderly group ( p = 0.5). The linearized rates of endocarditis for the young and elderly were 0.2%/patient-year and 0.4%/patient-year, which were not significantly different.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 PATIENTS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Hospital mortality was 2.9% in the 381 patients who underwent mechanical valve replacement in our institute, which is lower than previously reported rates (4.0%–8.3%).2–8 Hospital mortality has been improving year by year. This cohort underwent valve replacement in the 1990s and the 10-year survival rate was 93.0% in the young group and 73.1% in the elderly group. Although hospital mortality was excluded, 10-year survival exceeding 90% in the young group is better than reported survival rates.2–5,8,9 The young group had a significantly better survival rate than the elderly group; however, the 2004 annual survey of life expectancy reported by the Japanese Ministry of Health, Labor and Welfare revealed that the 5-year survival rate of 68-year-olds (equal to the mean age of the elderly group at operation) was 89.6% for Japanese males, and 95.5% for females. Hence the 5-year survival rate of 88.0% in our elderly group is excellent. The Ministry also announced that the average length of life was 78.6 years for males and 85.6 years for females; the latter is the longest in the world. The life expectancy of 68-year-old Japanese males is 16.0 years and that of females is 20.7 years, and the statistics are still improving. Therefore, the long-term durability of prosthetic valves will become more important.

We also looked at mortality and morbidity for each operative procedure and noted that the survival rate of elderly patients after AVR was relatively low (Figure 4Go). This cohort included patients with aortic stenosis who may have a worse prognosis. Nevertheless, no significant differences were found. There is concern about thromboembolic or bleeding complications in patients with mechanical heart valves, and the risk may increase with age. In this study, advanced age was not found to be a risk factor for thromboembolism. More than a third of thromboembolic episodes were transient ischemic attacks, which occurred at a similar rate to those of previous reports (0.5%–4.4%/patient-year).2–7,10–16 Blood vessels in the elderly may be more tortuous and have more arteriosclerotic changes. Thus, elderly patients are expected to suffer more thromboembolic events than young patients, but there was no significant increase in the thromboembolism rate in the elderly group in this study. Cannegieter and colleagues10 found that the risk of thromboembolism was small among patients aged 50 years or less (0.1%/patient-year). The incidence increased with advancing age: 0.8%/patient-year for 50 to 69-year olds, and 1.1%/patient-year for those aged 70 years or more. The same study also investigated several PT-INR levels and reported that the risk of ischemic or hemorrhagic complications was least when the PT-INR was in the range 2.0–2.9. However, another study found that the risk of thromboembolism for elderly patients (≥ 70 years) with a St. Jude Medical aortic valve prothesis was 0.7%/patient-year for a PT-INR of 1.8–2.5.11 Thus, aging may not be an important risk factor for thromboembolism after mechanical valve replacement under good PT-INR control. We believe that our equal thromboembolism rates for elderly and young patients were due to careful control of anticoagulation. Previous reports suggested that the incidence of thromboembolic or bleeding events depends strongly on control of anticoagulant therapy.1,10–12,15–18 The PT-INR levels we adopted (1.8–2.2 for AVR and 2.0–2.5 for MVR) are lower than those recommended in the ACC/AHA guidelines.1 There is a tendency in Japan to control patients at lower PT-INR levels, probably because of concern over bleeding complications. In fact, the Japanese literature recommends a lower level of warfarin than in Western countries.15,16,19


Figure 4
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  		Figure 4. Survival curve for each operative procedure.

 
Previous comparisons of mechanical and bioprosthetic valves found no clear difference in the thromboembolic rates.4,8,14 However, significant increases in bioprosthesis deterioration were found in young patients, and there was a higher rate of bleeding events in patients with a mechanical valve, especially when anticoagulant therapy was targeted at higher values of PT-INR.4,7,8,14 Elderly patients given a bioprosthesis without anticoagulant therapy have similar rates of thromboembolism to those with a mechanical valve taking warfarin.4,7,13,14 Furthermore, previous reports found no significant difference between the types of mechanical valve.5,9,12,17 The rate of bleeding complications was the same for each group in this study. Complications such as major bleeding that influence or are directly related to death were much lower than the rates in previous reports (0.5%–8.5%/ patient-year).2,3,6,8,14–16,18 This may be a consequence of our lower levels of warfarin. There were no significant differences between the groups in the incidence of perivalvular infective endocarditis, which was similar to previous reports (0.0%–1.6%/patient-year).8,15,17 We routinely performed a dental check in all patients requiring valve surgery. This might partly explain our reduced incidence of infective endocarditis. Although there was no significant difference, re-operation was performed more often in young patients. The reason is unclear, but some elderly patients might refuse a re-operation because of advanced age.

We recognize some limitations in the present work, which was a retrospective follow-up study on a limited number of patients. The study included both AVR and MVR, with 5 different mechanical valves. Dementia and other characteristics particular to elderly patients must be considered. However, little information has been available regarding the late mortality or morbidity of elderly patients with a mechanical heart valve. It is hoped that this study will assist in decisions about valve surgery in the elderly. It seems that mechanical heart valves may be selected for AVR and MVR in the elderly as they show similar clinical performance to bioprosthetic valves. We are also encouraged to find that mechanical valves are not a risk factor for late mortality or morbidity as patients given a mechanical valve become older.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 PATIENTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Bonow RO, Carabello B, DeLeon AC Jr, Edmunds LH Jr, Fedderly BJ, Freed MD, et al. ACC/AHA guidelines for the management of patients with valvular heart disease. A report of the American College of Cardiology/American Heart Association. Task Force on Practice Guidelines (Committee on Management of Patients with Valvular Heart Disease). J Am Coll Cardiol 1998;32:1486–588.[Free Full Text]

  2. Kvidal P, Bergstrom R, Malm T, Stahle E. Long-term follow-up of morbidity and mortality after aortic valve replacement with a mechanical valve prosthesis. Eur Heart J 2000;21:1099–111.[Abstract/Free Full Text]

  3. Fiane AE, Geiran OR, Svennevig JL. Up to eight years’ follow-up of 997 patients receiving the CarboMedics prosthetic heart valve. Ann Thorac Surg 1998;66:443–8.[Abstract/Free Full Text]

  4. Hammermeister KE, Sethi GK, Henderson WG, Oprian C, Kim T, Rahimtoola S. A comparison of outcomes in men 11 years after heart-valve replacement with a mechanical valve or bioprosthesis. Veterans Affairs Cooperative Study on Valvular Heart Disease. N Engl J Med 1993;328:1289–96.[Abstract/Free Full Text]

  5. Edmunds LH Jr, Clark RE, Cohn LH, Grunkemeier GL, Miller DC, Weisel RD. Guidelines for reporting morbidity and mortality after cardiac valvular operations. Ann Thorac Surg 1996;62:932–5.[Abstract/Free Full Text]

  6. Remadi JP, Baron O, Tribouilloy C, Roussel JC, Al-Habasch O, Despins P, et al. Bivalvular mechanical mitral-aortic valve replacement in 254 patients: long-term results—a 22-year follow-up. Ann Thorac Surg 2003;76:487–92.[Abstract/Free Full Text]

  7. Jamieson WR, Janusz MT, Burr LH, Ling H, Miyagishima RT, Germann E. Carpentier-Edwards supraannular porcine bioprosthesis: second-generation prosthesis in aortic valve replacement. Ann Thorac Surg 2001;71(5 Suppl):S224–7.[Abstract/Free Full Text]

  8. Oxenham H, Bloomfield P, Wheatley DJ, Lee RJ, Cunningham J, Prescott RJ, et al. Twenty year comparison of a Bjork-Shiley mechanical heart valve with porcine bioprostheses. Heart 2003;89:715–21.[Abstract/Free Full Text]

  9. Murday AJ, Hochstitzky A, Mansfield J, Miles J, Taylor B, Whitley E, et al. A prospective controlled trial of St. Jude versus Starr Edwards aortic and mitral valve prostheses. Ann Thorac Surg 2003;76:66–74.[Abstract/Free Full Text]

  10. Cannegieter SC, Rosendaal FR, Wintzen AR, van der Meer FJ, Vandenbroucke JP, Briet E. Optimal oral anticoagulant therapy in patients with mechanical heart valves. N Engl J Med 1995;333:11–7.[Abstract/Free Full Text]

  11. Arom KV, Emery RW, Nicoloff DM, Petersen RJ. Anticoagulant related complications in elderly patients with St. Jude mechanical valve prostheses. J Heart Valve Dis 1996;5:505–10.[Medline]

  12. Pengo V, Barbero F, Banzato A, Garelli E, Noventa F, Biasiolo A, et al. A comparison of a moderate with moderate-high intensity oral anticoagulant treatment in patients with mechanical heart valve prostheses. Thromb Haemost 1997;77:839–44.[Medline]

  13. Mistiaen W, Van Cauwelaert P, Muylaert P, Sys SU, Harrisson F, Bortier H. Thromboembolic events after aortic valve replacement in elderly patients with a Carpentier-Edwards Perimount pericardial bioprosthesis. J Thorac Cardiovasc Surg 2004;127:1166–70.[Abstract/Free Full Text]

  14. Khan SS, Trento A, DeRobertis M, Kass RM, Sandhu M, Czer LS, et al. Twenty-year comparison of tissue and mechanical valve replacement. J Thorac Cardiovasc Surg 2001;122:257–69.[Abstract/Free Full Text]

  15. Soga Y, Okabayashi H, Nishida T, Enomoto S, Shimada I, Miyamoto TA, et al. Up to 8-year follow-up of valve replacement with carbomedics valve. Ann Thorac Surg 2002;73:474–9.[Abstract/Free Full Text]

  16. Matsuyama K, Matsumoto M, Sugita T, Nishizawa J, Yoshida K, Tokuda Y, et al. Anticoagulant therapy in Japanese patients with mechanical mitral valves. Circ J 2002;66:668–70.[Medline]

  17. Akins CW. Results with mechanical cardiac valvular prostheses. Ann Thorac Surg 1995;60:1836–44.[Abstract/Free Full Text]

  18. Koertke H, Minami K, Boethig D, Breymann T, Seifert D, Wagner O, et al. INR self-management permits lower anticoagulation levels after mechanical heart valve replacement. Circulation 2003;108 Suppl I:II75–8.

  19. Kitamura M, Koyanagi H, Kawada S, Hosoda Y, Kurosawa H, Takeuchi Y, et al. Optimum anticoagulation control after bileaflet mechanical valve replacement: a prospective multi-institutional study. Kyobu Geka 1999;52:1001–4.[Medline]




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