Ann Thorac Surg 2001;71:1181-1187
© 2001 The Society of Thoracic Surgeons
Original article: cardiovascular
Intermediate-term results with 1,019 Carbomedics aortic valves
Hui-Hua Li, MDa,
Joar Hahn, MDb,
Paul Urbanski, MDb,
Marius Torka, MDb,
Gary L. Grunkemeier, PhDa,
Robert W. Hacker, MDb
a Herz- und Gefaessklinik, Bad Neustadt, Germany
b Providence Health System, Portland, Oregon, USA
Accepted for publication September 15, 2000.
Address reprint requests to Dr Li, 9155 SW Barnes Rd, #33, Portland, OR 97225
e-mail: huihuali{at}msn.com
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Abstract
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Background. A retrospective study was conducted to evaluate the intermediate-term outcome in patients with the Carbomedics aortic valve prosthesis.
Methods. The study included 1,019 primary valve replacements between 1989 and 1997. Seventy-two percent of patients were men; mean (standard deviation) age was 61 (10) years. The preoperative New York Heart Association functional class was III or IV in 70% of patients. Follow-up at 9 years was 99.6% complete, comprising 2,730 patient-years (mean, 2.7 years).
Results. Patient survival, including operative deaths, was 80% at 7 years. The linearized death rate was 2.9%/year. Statistically significant risk factors for mortality were diabetes, pure valve insufficiency, advanced age at operation, and advanced preoperative functional class. Linearized rates were thrombosis, 0.1%/year; thromboembolism, 1.0%/year; hemorrhage, 1.7%/year; endocarditis, 0.1%/year; paravalvular leak, 0.1%/year; reoperation, 0.1%/year; and all events, 3.0%/year. The 7-year estimates of freedom from complications were thrombosis, 99%; thromboembolism, 93%; hemorrhage, 89%; endocarditis, 99%; paravalvular leak, 99.7%; reoperation, 99%; and all events, 82%. No structural valve failure was observed.
Conclusions. The low incidence of valve-related complications favors the continued use of the Carbomedics valve in the aortic position.
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Introduction
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Clinical use of the Carbomedics (CM) heart valve prosthesis (Carbomedics, Inc, Austin, TX) began in 1986, and we began using the valve in 1989. To date, we have the largest reported number of CM aortic valves implanted per single institution worldwide. Our follow-up extends to 10 years and is 99.6% complete. This report describes the results we have attained during 10 years of using the CM aortic valve.
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Material and methods
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Patients
From February 1989 to December 1997, 1,019 patients underwent isolated aortic valve replacement (AVR) with a CM valve at the Herz- und Gefaessklinik Bad Neustadt, Germany. There were 285 (28%) women and 734 (72%) men with a mean age (standard deviation) of 61 (10) years (range, 14 to 86 years). Patients were included whether the operation was done on an elective or emergency basis. Patients who had a preexisting or concomitant valve replacement in another position were excluded. There was no definite age limit for using mechanical prostheses, although we recommended it primarily to patients less than 70 years of age. Table 1 summarizes the demographic data for these patients. Thirty-three patients (3%) had a previous AVR. The preoperative New York Heart Association functional class was III or IV in 70%. A mixture of valve stenosis and valve insufficiency was found in 56%, stenosis alone in 27%, and insufficiency alone in 14% (3% had previous AVR).
Operative data are shown in Table 2. Valve sizes of 21 mm, 23 mm, and 25 mm were used most frequently. Additional coronary artery bypass grafting was performed in 32% of patients.
Surgical technique
The operation was performed through a standard median sternotomy. The ascending aorta and inferior vena cava were cannulated for establishing extracorporeal circulation. A left atrial vent was then placed. Under moderate systemic hypothermia and after topical cooling, the ascending aorta was cross-clamped. In ischemic cardiac arrest, the ascending aorta was incised transversely. The aortic valve cusps were excised and the valve prosthesis implanted with felt-pledgeted 2-0 mattress sutures. The pledgets were usually positioned according to the size of annulus, which is subannular for small prosthetic valves and mostly supraannular for valve sizes 25 mm and larger. The aortotomy was closed with a running 4-0 monofilament suture. In the case of concomitant myocardial revascularization, the distal anastomoses of the venous grafts were done after cross-clamping of the aorta before the AVR. The proximal anastomoses were performed after declamping of the aorta on the beating heart under partial extracorporeal circulation. After discontinuation of extracorporeal circulation and decannulation, the sternum was closed with wires.
Definitions
For definitions of mortality and morbidity, standard guidelines were used [1]. Early event refers to any event within the first 30 postoperative days. Late event refers to occurrences at all subsequent times.
Anticoagulant therapy
Anticoagulant therapy was started with phenprocoumon on the third postoperative day. The international normalized ratio (INR) should reach therapeutic levels on the sixth or seventh postoperative day.
Follow-up
For the purpose of this study, patients or their relatives were contacted by telephone. In the case of late complications, written documents were requested from physicians or hospitals.
Statistical analysis
All analyses were performed using SPSS version 9.0 (SPSS, Inc, Chicago, IL). Early events were expressed in percentage form. Late event rates were estimated as percent per year. Actuarial analyses, including both early and late events were calculated using the Kaplan-Meier method for survival and freedom from reoperation [2], and the Cutler-Ederer method for other events [3]. The 5% level of statistical significance was used. Cox’s proportional hazard model was used to assess the relationship between various risk factors and patient survival [4].
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Results
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Early mortality
Sixteen (1.5%) patients died within the first 30 postoperative days. The cause of death was valve related in 2 patients, cardiac related in 9, and noncardiac related in 5 patients.
Follow-up
Follow-up information is summarized in Table 3. The total cumulative follow-up was 2,730 patient-years (mean, 2.7; maximum, 9.3). With follow-up to 1998, only 6 patients were lost (0.4%).
Late mortality
There were 80 late deaths (2.9%/year): 33 (1.2%/year) were valve related, 19 (0.7%/year) were due to cardiac causes, and 26 (1.0%/year) were due to noncardiac causes (Table 4). Patient survival (standard error), including operative mortality, was 87% (2%) and 80% (3%) at 5 and 7 years, respectively (Fig 1).
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Fig 1. Patient survival after aortic valve replacement. Numbers above horizontal axis indicate the numbers of patients at risk.
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Multivariable analysis was performed using Cox’s proportional hazard method to assess the relationship of various risk factors with survival. The factors examined were age at operation, gender, previous myocardial infarction, previous AVR, preoperative functional class, smoking history, diabetes, obesity, hypertension, hypercholesterolemia, aortic valve disease, prosthetic valve size, orifice area index, concomitant coronary artery bypass grafting, and number of grafts. Significant risk predictors of reduced patient survival were (in decreasing order of significance) diabetes, pure valve insufficiency, advanced age at operation, and high preoperative functional class (Table 5). Concomitant coronary artery bypass grafting was not found to be a significant risk factor for reduced late survival. Univariate analysis using the Kaplan-Meier method shows that coronary artery bypass grafting is a risk factor (Fig 2), but it was not found to be significant. There was also no significant difference in survival between patients with small (19 to 21 mm) and large (> 21 mm) valves (Fig 3).
Complications
Table 6 contains the early percentages and late rates and Kaplan-Meier estimates for all valve complications.
Valve thrombosis was observed in 2 patients, both in the third postoperative year. The linearized rate for valve thrombosis was 0.1%/year and the actuarial estimate of freedom from thrombosis was 99% (0.5%) at 7 years. One patient was involved in a road-traffic accident. Because of a subdural hematoma, anticoagulation was discontinued for some time. After partial valve thrombosis was diagnosed echocardiographically, anticoagulation was resumed and valve function returned to normal. The other patient received dental treatment during which her anticoagulation was discontinued. Although she was given low molecular weight heparin, a partial valve thrombosis developed. Valve function returned to normal when anticoagulation was resumed. Both patients survived.
Thromboembolism was detected in 42 patients, of which 16 (1.5%) had an event during the first postoperative month. Twenty-six patients (1.0%/year) had a late thromboembolic episode. The actuarial estimate of freedom from thromboembolism was 94% (1%) and 93% (2%) at 5 and 7 years, respectively (Fig 4).
Figure 5 shows the influence of age on freedom from thromboembolism. In patients aged 60 years or less, 97 (2%) were free from thromboembolism at both 5 and 7 years. In patients more than 60 years, these rates were 92 (2%) and 89 (3%) at 5 and 7 years, respectively (p = 0.002).
Fifty-two patients (1.7%/year) had anticoagulant-related hemorrhage. At 5 and 7 years, 92 (2%) and 89 (2%) of patients were free of anticoagulant-related hemorrhage (Fig 6).
No early and four late (0.1%/year) prosthetic valve endocarditis episodes were recorded. The actuarial estimate of freedom from endocarditis was 99 (0.2%) at 7 years.
Paravalvular leak leading to reoperation was observed in 3 patients (0.1%/year). The actuarial estimate of freedom from paravalvular leak was 99.7% (0.1)% at 7 years.
No structural valve degeneration was observed.
Four patients (0.1%/year) underwent valve-related reoperation. Three were performed for paravalvular leak and one for endocarditis. The actuarial estimate of freedom from reoperation was 99% (2%) at 7 years.
The linearized rate of any valve-related morbidity or mortality was 3.0%/year. The actuarial estimate of freedom from any valve-related morbidity or mortality was 86% (2%) and 82% (3%) at 5 and 7 years (Fig 7).
Functional class
The postoperative New York Heart Association classification at the most recent follow-up was III or IV in 6% of patients. Compared to the preoperative New York Heart Association class, 845 patients (83%) showed improvement, 139 (14%) were unchanged, and 29 patients (3%) were worse. New York Heart Association classification change by follow-up interval is illustrated in Figure 8. The rate of improvement in patients with advanced New York Heart Association functional class status preoperatively remained stable with time.
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Comment
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This study was undertaken to define the intermediate-term outcome in patients with the CM aortic valve prosthesis. To date, we have the largest reported number of CM aortic valves implanted per single institution worldwide. Our follow-up extends to 10 years and is 99.6% complete.
Potential limitations
Data collection
Patients or their relatives were retrospectively contacted by telephone for the purpose of this study. This method of data collection may underestimate the true number of adverse events.
INR data
The INR target range was not available for the early years of the study, as INR was not known in those years. In Germany, we used the so-called "Quick" value, which had different target ranges depending on the method of analysis. To compare our results with other studies, we devised Figure 9, examining the rates of thromboembolism plus thrombosis versus bleeding, which we believe is a natural index of anticoagulation intensity, and a possible surrogate for the unknown target INR.
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Fig 9. Plot of complication rates for St. Jude or Carbomedics aortic valve series taken from the data in Table 7. Each circle represents one series. The height of the circle is the thromboembolism (TE) plus thrombosis (TS) rate, the horizontal axis represents the hemorrhage rate, and the area of the circle is proportional to the valve-years in the series. Codes inside the symbols correspond to the reference numbers in Table 7. (PS = present series.)
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The CM mitral valve
The mitral valve experience using the CM valve was not reported in this study, however, because most of the mitral valves are being repaired, and the number of CM valves in the remaining patients is small, especially as different prostheses were used for replacement.
Clinical implications
Valve thrombosis is considered to be one of the most serious complications of mechanical prostheses and usually leads to death or reoperation. Although it has not been shown conclusively that mechanical valves differ with regard to the risk of thromboembolism, the hypothesis has been formed that valvular thrombosis serves as a basis for distinguishing valves of varying thrombogenicity [5, 6]. Some investigators [7] allege that the CM valve has a higher risk of thrombosis than the St. Jude valve and suggest better anticoagulant control is required, whereas other researchers [8] are not of the same opinion. However, follow-up in both of these studies was relatively short and the aortic and mitral valve results were grouped together.
Our experience with the CM device demonstrates that excellent freedom from thrombosis can be achieved with adequate anticoagulation. Our low thrombosis rate (0.1%/year) is within the range of reports for the St. Jude valve. Thrombosis was identified in 2 patients. Both were related to inadequate anticoagulation and resolved completely when anticoagulation was resumed. Table 7 [9–18] compares the linearized complication rates in other series of CM and St. Jude aortic valves. The series included are those published since 1990 containing a minimum of 1,000 patient-years of follow-up. Articles without separate data on thromboembolism and bleeding events were excluded. In these studies, the CM valve is comparable to the St. Jude valve in terms of valve thrombosis. The weighted average (90% confidence interval) for the CM valve, including our series, is 0.03%/year (0.01 to 0.08%/year) and the St. Jude valve is 0.1%/year (0.08 to 0.15%/year).
Our linearized and actuarial rates of thromboembolism are favorable to that found in other series (Table 7). The risk of thromboembolism remains approximately constant during the entire follow-up period. However, elderly patients (> 60 years) had an increased risk of thromboembolism. Many studies have documented a relatively high risk of embolic events soon after operation [19]. In our series, 38% (16 patients) of the thromboemboli occurred during the first month and 28% (12 patients) occurred between the first and eighth postoperative day. This suggests that a more intensive anticoagulation protocol could be considered in the first month. Episodes of atrial fibrillation occurred during the early postoperative period in 12 of 16 patients with early thromboembolic events. This exceeds the incidence of atrial fibrillation in the entire group (75% versus 32%). Therefore, it may be sufficient to intensify the anticoagulation regime by administering heparin as soon as atrial fibrillation develops in the patient.
Anticoagulant-related hemorrhage is both the most common complication in our series and the most common cause of valve-related deaths. Comparison of our findings with other studies is difficult because of variations in the therapeutic ranges and differences in the technique of measuring prothrombin time [20]. Although our hemorrhage rate of 1.7%/year is relatively high compared with the low rate of thromboembolism and thrombosis, it is identical to that in North America as a whole where a target INR of 2.5 was aimed at [18]. However, anticoagulation during follow-up is managed by the patient’s physician rather than the surgeon who, therefore, can do little to influence it.
The optimal anticoagulation regimen for patients with the CM valve remains unclear. Current guidelines recommend a target INR of 2.5 for the second-generation bileaflet valve after AVR [7]. With this target level, the North American experience reported a thromboembolism rate of 1.1%/year and a hemorrhage rate of 1.7%/year in 603 patients with a CM aortic valve for a follow-up to 5 years [18]. A similar incidence of thromboembolism and hemorrhage was found in the long-term results of Rodler and associates [17] with a target INR of 1.8 to 2.8 and the use of an antiplatelet agent. Aagaard and colleagues [21] reported a high incidence of hemorrhage with a target INR range between 3.0 to 4.0. Therefore, they have decided to decrease the target INR to 2.5 to 3.0 in patients without additional risk factors. The early results with this new regime are encouraging but continued follow-up is warranted.
The relationship between thromboembolic and hemorrhage rates from Table 7 was examined (Fig 9). Our thromboembolism plus thrombosis rate is very similar to that of the other series, although our hemorrhage rate exceeds the average (symbol PS in the graph). We failed to demonstrate the inverse relationship between thromboembolism plus thrombosis rate and hemorrhage rate that has been suggested for a hypothetical patient with a mechanical valve [5, 22]. Instead, there was an almost significant (p = 0.08) direct relationship, according to a linear regression analysis weighted by patient-years. This may be attributed to variations such as different patient demographics and patient follow-up, which could mask an underlying inverse correlation. Alternatively, if a prosthetic valve truly has a low degree of thrombogenicity, it may be impossible to detect significant changes in thrombogenic incidence relative to the changes in hemorrhage incidence (a natural index of anticoagulation intensity). Conversely, the suggestion that a direct relationship between thrombogenic and hemorrhage complications may exist implies the importance of other factors in determining thrombogenic and hemorrhage complication rates. For example, anticoagulation variability reflects overall difficulty of anticoagulation control. Such variability may predispose to both thrombogenic and anticoagulant complications. In conclusion, the low incidence of valve-related complications favors the continued use of this valve in the aortic position.
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Acknowledgments
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This study was supported financially by a research grant from Carbomedics, Inc.
We thank Bianca Rieger, who did all the work on our database, for compiling and extracting the necessary data, and Cindy L. Fessler and Stuart M. Robertson for reviewing the manuscript.
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Abstract
Introduction
