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Eur J Cardiothorac Surg 1998;13:151-159
© 1998 Elsevier Science NL

Multiple mechanical valve replacement surgery comparison of St. Jude Medical and CarboMedics prostheses

Department of Surgery, St. Paul’s Hospital-Heart Centre, Vancouver General Hospital, University of British Columbia, 3100-910 West 10th Avenue, Vancouver V5Z 4E3, Canada

Received 28 July 1997; received in revised form 8 December 1997; accepted 16 December 1997.

Corresponding author. Tel. +1 604 8754141; fax: +1 604 8754036.

	Abstract

Top Abstract Introduction Patient Population Methods and Statistical... Results Discussion References

 
Objective: The experience with the St. Jude Medical (SJM) and CarboMedics (CM) bileaflet mechanical prostheses was evaluated to determine thromboembolic and hemorrhagic complications and predictive risk factors. Methods: From 1989 to 1994, a total of 246 patients had multiple valve replacement (SJM, 140; CM, 106); concomitant procedures 20.3% (50) [coronary artery bypass 10.6% (26)] and 53.7% (132) previous cardiac surgery, primarily valve replacement procedures. The pre-operative variables [coronary artery disease, previous cardiovascular surgery, concomitant procedures, valve lesion (except mitral stenosis), status, atrial fibrillation, and NYHA III/IV] did not distinguish the prosthesis-type (pNS). Results: The prosthesis-type and the pre-operative variables, including atrial fibrillation, were not predictive of overall thromboembolism (TE). The linearized rate of total TE events for overall multiple replacements (MR) was 5.4%/patient-year (minor, 2.52; major 2.85); the total TE for CM and SJM was 5.4%/patient-year, respectively. The 30 day major TE crude rate was 0.82%, while the >30 day major event rate was 2.7%/patient-year. Of the total (major and minor) TE events 100% (3) of 30 days and 72% (29), >30 days had an INR <2.5 at or immediately prior to the event. The thrombosis rate (included in total TE events) was 0.67%/patient-year (4 events, 100% INR <2.5). Of the various TE event categories the prosthesis-types (CM and SJM) were not differentiated (pNS). The freedom, at 5 years, from major/fatal TE, thrombosis and hemorrhage from anticoagulation was 89.3±3.8% for CM and 87.9±3.7% for SJM and, 91.3±3.5% and 89.3±3.7%, respectively, (pNS) exclusive of early events. Conclusions: The performance of the CarboMedics and St. Jude Medical prostheses in multiple valve replacement surgery in this non-randomized prospective study revealed no significant differences in performance with regard to thromboembolic and hemorrhagic complications.

Key Words: Mechanical prostheses • Thromboembolism • Predictive factors and anticoagulation

	Introduction

Top Abstract Introduction Patient Population Methods and Statistical... Results Discussion References

 
The first mechanical prosthesis, the Starr–Edwards caged-ball prosthesis (Baxter Healthcare, Edwards CVS Division, Irvine, CA) was introduced 35 years ago. The developments in mechanical prostheses have incorporated both monoleaflet and bileaflet designs, both formulated with pyrolytic carbon in whole or in part. The two predominant bileaflet mechanical prostheses are the St. Jude Medical (St. Jude Medical, Minneapolis, MN) and the CarboMedics (Sulzer-Carbomedics, Austin, TX). The St. Jude Medical prosthesis was introduced in 1977 and has been the most widely implanted mechanical bileaflet prosthesis. The documentation with the St. Jude Medical prosthesis primarily reveals the 10-year experience [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]. The CarboMedics prosthesis was introduced as an investigational prosthesis in 1986 and received approval to the marketplace in 1993. The CarboMedics prosthesis has an increasing number of published clinical studies [13] [14] [15] [16] [17] [18]. There has been no randomized or non-randomized trials comparing the clinical performance of bileaflet prostheses.

The purpose of this communication is to document the thromboembolic rate of the bileaflet mechanical prostheses, St. Jude Medical and CarboMedics, in a prospective non-randomized study comparing the experience between the prostheses in multiple valve replacements and to determine predictors of performance.

	Patient Population

Top Abstract Introduction Patient Population Methods and Statistical... Results Discussion References

 
From September 1989, the time of commencement of the University of British Columbia in the United States-Food and Drug Administration CarboMedics investigational study, to June 1994 the CarboMedics (CM) and St. Jude Medical (SJM) prostheses were evaluated in a non-randomized prospective study. The prostheses were implanted, generally, by different surgeons within the teaching hospitals of the University of British Columbia.

Multiple valve replacements were performed in 246 patients (male, 108; female, 138). The mean age of the population was 57.6±13.3 (S.D.) years (range 23–80 years). There were 52.4% NYHA class III and 33.3% class IV patients. The mean follow-up was 2.42±1.70 (S.D.) years, a total of 596.4 years. The median follow-up was 2.32 years. The completeness of follow-up was 99.6%.

The overall patient population comprised 217 (CM, 98; SJM, 119) aortic valve replacements (AVR) and mitral valve replacements (MVR); two (CM, one; SJM, one) AVR and tricuspid valve replacements (TVR); 11 (CM, three; SJM, eight) MVR and TVR; two (SJM, two) AVR and pulmonary valve replacements; 12 (CM, three; SJM, nine) AVR, MVR and TVR; and two (CM, 1; SJM, 1) AVR and MVR and pulmonary valve replacements. The patient population incorporated 12 porcine bioprostheses implanted in the tricuspid and pulmonary positions. There were also three Starr-Edwards prostheses and one Duromedics mechanical prosthesis.

Concomitant procedures were performed in 20.3% (50) of the patients, coronary artery bypass in 10.6% (26) of the patients. Of the multiple population, 53.7% (132) had previous cardiac procedures, primarily valve replacement procedures.

In these multiple replacements (MR) the CM was implanted in 106 patients (male, 49; female, 57) and the SJM in 140 patients (male, 59; female, 81). The mean age of the MR-CM population was 57.0±14.1 (S.D.) years (range 23–78 years) and for SJM, 58.1±12.6 (S.D.) years (range 24–80 years). (pNS) The MR-CM patients were 57.5% NYHA class III and 31.1% class IV, while for SJM patients, 48.6% and 35.0%, respectively (pNS). The mean follow-up for MR-CM was 2.29±1.68 (S.D.) years (total 242.4 years) and for SJM was 2.53±1.72 (S.D.) years (total 354.0 years). The median follow-up was 2.04 years for CM and 2.48 years for SJM. The completeness of follow-up was 100 and 99.3%, respectively.

The patient populations for MR for the CM and SJM groups were essentially the same considering the incidence of coronary artery disease, atrial fibrillation, previous cardiovascular surgery, concomitant procedures, valve pathology and status of procedures (pNS) (Table 1). The incidence of mitral stenosis (CM, 27.3%; SJM, 15.7%) did distinguish the populations (P=0.038).

	Methods and Statistical Analysis

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1. valve thrombosis;
   
2. cerebrovascular accident as occlusive (ischemic) or hemorrhage in origin, in terms of transient ischemic attack (<24 h), reversible ischemic neurological deficit (RIND-minor stroke) (>72 h with complete resolution within 3 weeks), major stroke;
   
3. systemic (non-cerebral) embolism;
   
4. systemic (non-cerebral) bleeding.
   

The information on valve-related complications for this study was obtained by direct contact with patients, family physicians, consultants, hospital health records, and official death registries over a closing interval of 6 months.

The valve-related complications and composite indexes of these valve-related complications were evaluated in the time-related manner by actuarial life-table techniques (Cutler–Ederer method). The Wilcoxon–Gehan statistic was used to provide comparison of complication-free curves. Linearized occurrence rates (events per 100 patient-years or percent per patient-year) were utilized specifically for documenting thromboembolic and hemorrhagic complications. The instantaneous hazard functions were determined from combined (CM and SJM) life tables and were demonstrated as bar grafts for thromboembolic and hemorrhagic events and valve-related mortality and reoperation. The predictors of early mortality were determined by stepwise logistic regression, and the predictors of late mortality and thromboembolism by the Cox proportional hazard regression model. The variables evaluated were prosthetic valve type, coronary artery bypass surgery, NYHA IV, age, gender, atrial fibrillation, urgency status and previous valvular surgery. SPSS for MS Windows release 6.1.3 software was used for analysis.

	Results

Top Abstract Introduction Patient Population Methods and Statistical... Results Discussion References

 
The early and late mortality and mortality from valve-related complications are detailed in Table 2 for the overall population (including the 95% confidence limits, CL) and by prostheses types. The early mortality for the total population was 12.2% (30) (CM, 15.1%; SJM, 10.2% pNS). There were three (10%) valve-related deaths while cardiac causes were 40% (12) and non-cardiac causes and surgical causes were 50% (15). The risk factors of early mortality were NYHA IV, and advancing age (Table 3).

The valve-related complications are summarized in Table 4 for overall multiple valve replacement and by prosthesis-type (CM and SJM). The freedom from valve-related mortality, excluding early mortality and sudden unexpected deaths was, at 5 years, 92.6±2.1%. The only risk factor of valve-related mortality was combined thromboembolism and hemorrhage.

View this table: [in this window] [in a new window]   Table 6. Thromboembolic and hemorrhagic events >30 days and 30 days—multiple replacement

The Fig. 1 Fig. 2 illustrate the freedom for MR of thromboembolic and hemorrhagic events overall and exclusive of early events (30 days). The figures show the freedoms from major thromboembolism, and overall major/fatal thromboembolism, thrombosis and hemorrhagic events. The freedom from overall major thromboembolism was, at 5 years, 91.2±2.6% and 92.0±2.6% with exclusion of early events (CM, 94.5±2.8%; SJM, 89.9±3.5%; and exclusion of early events 94.5±2.8% and 91.3±3.4%, respectively) (pNS) ( Fig. 1). The freedom from thrombosis, at 5 years, was 98.5±0.8%. The assessment of overall events ( Fig. 2) revealed 5 year freedom of 87.7±2.9% and 88.5±3.0% with exclusion of early events (CM, 89.3±3.8%; SJM, 87.9±3.7%; and exclusion of early events 91.3±3.5% and 89.3±3.7%, respectively) (pNS).

View larger version (14K): [in this window] [in a new window]   Fig. 1. Multiple valve replacement—freedom from major thromboembolism overall and with exclusion of early events.

View larger version (17K): [in this window] [in a new window]   Fig. 2. Multiple valve replacement—freedom from major/fatal TE, thrombosis and hemorrhage overall and with exclusion of early events.

View larger version (27K): [in this window] [in a new window]   Fig. 3. Multiple valve replacement—hazard function of thromboembolism and hemorrhagic events.

View larger version (23K): [in this window] [in a new window]   Fig. 4. Multiple valve replacement—hazard function of valve-related mortality and reoperation.

There were four episodes of prosthesis thrombosis, 0.68%/patient-year (Table 4Table 6), 1 patient had both a thrombosed tricuspid prosthesis managed by explant surgery and subsequently a fatal thrombosed mitral prosthesis identified at autopsy, both CM prostheses. All these patients occurred out of hospital beyond the 1 month period. One of the patients was managed initially with thrombolytic therapy. A total of 3 patients were managed with reoperation with one fatality. One of these patients, noted above, subsequently died with thrombosis of the mitral prosthesis. The additional patient died without reoperation, thrombosis identified at autopsy. Of the three reoperations, one had explant of the thrombosed tricuspid prosthesis without replacement and one thrombectomy and one valve replacement which resulted in the fatality. The patients were inadequately anticoagulated at the time of the event, three in atrial fibrillation and one in normal sinus rhythm.

	Discussion

Top Abstract Introduction Patient Population Methods and Statistical... Results Discussion References

 
Thromboembolism, including thrombosis, and anticoagulant hemorrhage remain the major valve-related complications of mechanical prostheses. The purpose of this study is to evaluate the thromboembolic and hemorrhagic complications of the St. Jude Medical and CarboMedics mechanical prostheses in multiple valve replacement. The St. Jude Medical prosthesis has received documentation of clinical performance to 10 years [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]. The CarboMedics prosthesis has an increasing number of publishing clinical studies [13] [14] [15] [16] [17] [18]. There has been no randomized or non-randomized trials comparing the clinical performance of the two bileaflet prostheses. The University of British Columbia commenced utilization of the CarboMedics prosthesis in September 1989 as part of the multicentre investigational study. The experience with the CarboMedics and St. Jude Medical prostheses between September 1989 and June 1994 inclusive formulates the patient population of this study. The study was conducted as a non-randomized prospective evaluation. The study, although early, revealed no significant difference in the clinical performance of the two prostheses in multiple replacements. The prostheses were not differentiated with regard to the incidence of overall thromboembolism.

The current knowledge of mechanical protheses has been derived primarily from recent reports on the clinical performance of individual prostheses [13] [1] [2] [14] [15] [16] [3] [17] [4] [5] [6] [7] [8] [9] [10] [11] [21] [22] [12] [18]. There have been only two randomized trials, of significance, both comparing the performance of the St. Jude Medical prosthesis to the Medtronic-Hall monoleaflet prosthesis [23] [24]. The major concern with randomized reports has been the wide variation of reported results on thromboembolic events [23] [25] [24] [26]. There remains extensive inconsistency of clarification of definition, for most reports do not differentiate between major and minor events and do not indicate the standard of reporting. For multiple valve replacement with mechanical prostheses the incidence of thromboembolic rates have ranged between 0.3 and 6.6%/patient-year [13] [14] [15] [16] [4] [6] [10] [11] [12]. Smith and coauthors [12] have reported the incidence of thromboembolic events to be 0.3%/patient-year for double valve replacement for the St. Jude Medical prosthesis. On the other hand, Horstkotte and colleagues [4] have reported unexpected findings with the St. Jude Medical prosthesis with an incidence of 6.62%/patient-year for double valve replacements. These authors when considering only first or most serious of several events, documented incidence of 5.40%/patient-year for double valve replacement. Ibrahim et al. [6] have also reported high total thromboembolic rates with the St. Jude Medical prosthesis, 5.0%/patient-year for multiple valve replacements. Several reports document only events that occur beyond the early 30 day interval and consequently provide an unfair assessment of patient morbidity and mortality [2] [14] [15] [3] [4] [7]. Jegaden and investigators [8], on the other hand, have expressed concern over the occurrence of major thromboembolism during the early postoperative period, often when anticoagulation has yet to be adequately controlled. There also is limited information provided on the level of anticoagulation at the time of both thromboembolic and hemorrhagic events. The extent of patient follow-up and depth of evaluation, as well as the adequacy of anticoagulation management are likely contributing factors to the wide range of reported events.

This report attempts to alleviate some of these concerns by reporting total overall events, events occurring <30 days, events occurring 30 days and classifying events as major (reversible and permanent), minor, fatal and thrombotic occlusion. The study has documented the adequacy of anticoagulation at the time of event occurrence. An INR level of 2.5 was considered as the minimal level of adequacy of anticoagulant management. The study did not determine the anticoagulant status of patients who did not have a thromboembolic event, or at times remote of an event.

The overall thromboembolic rate, considering both major and minor events, for multiple replacements was 5.4%/patient-year. These results are comparable to the reported results by Horstkotte et al. [4] and Ibrahim et al. [6] with the St. Jude Medical prosthesis. These results are at variance to the literature for the St. Jude Medical prosthesis, the range from other reports was 0.3–3.2%/patient-year for multiple replacements [9] [10] [11] [12]. The results with the CarboMedics prosthesis was 0.3–3.10%/patient-year for multiple replacements [13] [15] [16]. This wide ranging reporting of thromboembolic rates must be related to the detailed nature of evaluation and possibly the extent of anticoagulation.

The most important aspect of thromboembolism is the rates of major events, as well as, hemorrhagic events. The major event rate in the present series of combined St. Jude Medical and CarboMedics prostheses is 2.85%/patient-year for multiple replacements. The 30 day minor event rate was 2.52%/patient-year. The reports by Horstkotte and Ibrahim and colleagues [4] [6] range from 1.5–1.6%/patient-year for multiple replacements. The incidence of anticoagulant hemorrhage in these reports has shown less variation. The major hemorrhagic rate in the authors combined series is 1.34%/patient-year for multiple valve replacement. The hemorrhagic rates for the series of St. Jude Medical prostheses by Horstkotte and Ibrahim and colleagues [4] [6] ranges from 1.9–2.1%/patient-year for multiple replacements. These apparent differences may explain the higher major event rates in the authors series. The inadequacy of anticoagulation in our series of overall thromboembolic events may also be a contributing factor; 100% and 72% for multiple replacements <30 days and 30 days, respectively.

The prostheses thrombosis rates for our combined series was 0.68%/patient-year for multiple replacements. The thrombosis rate, reported by Orszulak and coauthors [22] for Björk–Shiley standard and concave-convex prostheses was 0.27%/patient-year. Aagaard et al. [13]. reported a CarboMedics rate of 0.3%/patient-year. Nitter-Hauge et al. [21]. documented the thrombosis rate for the Medtronic-Hall monoleaflet prosthesis at 0.2%/patient-year for multiple replacements. The rate of prosthesis thrombosis with the St. Jude Medical and the Björk–Shiley Monostrut has been reported as low [1] [24] [6] [8] [9] [10] [11] [22] [12]. In the authors series of the four multiple replacement events in 3 patients, 1 patient had both tricuspid and mitral thrombosis. The tricuspid thrombosis was managed with explantation and no replacement while the mitral thrombosis resulted in mortality. There were three successful reoperations and one additional fatality. Of the total four thrombosed prostheses, all four had INR levels of >2.5 at or immediately prior to the event.

The fatality rate from thromboembolism has been infrequently reported. The rate in the authors combined series was 0.50%/patient-year for multiple replacements. The reported fatality rates for multiple replacements is 0.2–0.7%/patient-year [1] [6] [10] [11] [12].

Sudden unexpected death has been considered to be a valve-related mortality [27]. In our series the incidence of sudden unexpected death was 0.17%/patient-year for multiple valve replacement. The incidence of sudden death with the St. Jude Medical prosthesis ranges from 0.06–0.9%/patient-year for multiple replacement [1] [8] [10] [11]. Butchart [27] reported it was illogical to attribute all sudden deaths to the prosthesis in the absence of an autopsy.

The authors study revealed no influence of prosthesis type on overall thromboembolism but late major TE rates were high (2.7%/patient-year for multiple replacements) and higher including early events <30 days. The thrombosis rates were high, as well as in other reported series [1] [6] [8] [11] [12]. The commencement of anticoagulation, at our hospitals, on the 3rd to 4th day without heparinization may be less than optimal. The long-term management of anticoagulation by numerous family physicians and internists may require reconsideration and possibly home anticoagulation management [28] [29] [30]. Irrespective of these concerns our results parallel the embolic rates confirmed with well conducted studies of Horstkotte and Ibrahim and colleagues [4] [6]. The concluding comment is that mechanical prostheses in multiple replacement carry a high risk of embolic and hemorrhagic complications but the performance is not different with the CarboMedics and St. Jude Medical prostheses.

	References

Top Abstract Introduction Patient Population Methods and Statistical... Results Discussion References

 

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