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Ann Thorac Surg 1998;66:1684-1691
© 1998 The Society of Thoracic Surgeons

Outcome analysis of 245 CarboMedics and St. Jude valves implanted at the same institution

^a Department of Cardiothoracic Surgery, The New York Hospital-Cornell Medical Center, New York, New York, USA

Accepted for publication May 21, 1998.

Address reprint requests to Dr Rosengart, Department of Cardiothoracic Surgery, The New York Hospital-Cornell Medical Center, 525 East 68th Street, F-2103, New York, NY 10021

	Abstract

Top Footnotes Abstract Introduction Patients and methods Results Comment References

 
Background. Thromboembolism and valve-related death are major complications associated with prosthetic valve implants, but it is difficult to evaluate the relative incidence of these complications based on studies in which the implantation of only one valve is reported from any given institution. We therefore report the outcome of patients implanted at our institution during the same time period with either the recently released CarboMedics (CM) or the St. Jude Medical (SJ) valve prostheses.

Methods. Between October 1994 and January 1996, 245 consecutive patients received either SJ (116 patients) or CM (129 patients) valves at our institution. Follow up of these patients was 99.6% complete, for a total of 318.5 cumulative patient-years (median follow-up, 1.4 years).

Results. The 30-day mortality rates for SJ and CM implants were 3.4% and 3.1%, respectively. Actuarial survival and freedom from valve related mortality rates at 1.5 years for SJ and CM valves were 94% ± 2% versus 86% ± 3% (p = 0.03) and 100% versus 94% ± 2% (p = 0.005), respectively. There was no structural valve failure for either implant, but there were five thrombosed valves in the CM group and none in the SJ group (p = 0.04). All thrombosed valves were mitral (four mitral valve replacement, one aortic and mitral valve replacement). Two of the thrombosed valves were successfully explanted, whereas the three remaining patients died. Freedom from a thromboembolic event in the mitral position at 1.5 years, including thrombosed valves was 97% ± 3% and 83% ± 5% for SJ and CM valves, respectively (p = 0.04).

Conclusions. The results of this study suggest that further evaluation of thromboembolic outcomes after CM compared with SJ valve implantation is warranted.

	Introduction

Top Footnotes Abstract Introduction Patients and methods Results Comment References

 
Durability, physiologic hemodynamic performance, ease of insertion, and freedom from thromboembolic complications are four standards by which all prosthetic heart valves are judged. The ideal prosthetic heart valve should possess all of these qualities, but no prosthetic valve has yet achieved a perfect performance profile as assessed by these criteria.

The St. Jude Medical (SJ) mechanical heart valve prosthesis is a bileaflet low-profile mechanical valve that was introduced in 1977 and approved by the Food and Drug Administration in 1982 [1, 2]. The CarboMedics prosthetic heart valve (CM) was introduced in 1986 and approved by the Food and Drug Administration in 1993 [3, 4]. The CM valve resembles the SJ valve in that it is a pyrolytic carbon bileaflet device, but it possesses several distinguishing design features, including the capacity for rotation of the valve mechanism within the sewing ring [5]. Design goals of the CM valve included pivot flow characteristics that were intended to minimize the incidence of thromboembolism and valve thrombosis by reducing areas of blood stasis within the pivot [5–7]. The CM valve leaflets were designed to translate through an arc of 53°, rather than the 55° to 60° closing arc used in the SJ design, with the intent of reducing the regurgitation characteristically associated with mechanical heart valves. The CM valve lacks pivot guards, providing the CM valve with a somewhat lower profile orifice compared with the SJ valve. As a result, the CM valve leaflets protrude approximately 2 mm farther beyond the orifice in the open position than do the SJ valve leaflets. Finally, the CM sewing ring is coated with carbon to reduce tissue ingrowth that can potentially lead to valve obstruction [5–7].

The present study was undertaken to compare directly the clinical outcomes associated with implantation of the SJ and CM valves, to determine whether any difference exists in the performance of these valves. Conventionally, the difficulty in such an analysis is that it requires comparison of two or more separate studies in which the implantation of only one valve is performed at any given institution. The purpose of the present valve study was to take advantage of an opportunity in which both the SJ and CM valve were implanted at the same institution (The New York Hospital) during the same time period.

	Patients and methods

Top Footnotes Abstract Introduction Patients and methods Results Comment References

 
Patient population
Between October 1994 and January 1996, 245 consecutive patients received either a SJ or CM prosthesis at The New York Hospital. These 245 patients constitute the study population and represent all patients receiving mechanical valve implants at our institution during this time period. Of these patients, 129 received CM valve implants and 116 patients received SJ valve implants. Valve selection was based on surgeon preference. One patient had a double valve replacement with one valve of each type implanted and was excluded from analysis, as were two children.

Operative technique
All patients were operated on through a median sternotomy and with standard cardiopulmonary bypass technique using a disposable membrane oxygenator (Capiox Sx, Terumo, Inc, Tokyo, Japan). Myocardial protection consisted of systemic hypothermia (28°C), topical cooling with iced saline or slush, and intermittent antegrade blood cardioplegia with or without retrograde cardioplegia delivered into the aortic root, coronary ostia, or coronary sinus, as appropriate. In the cases in which coronary artery bypass grafting was performed, the distal saphenous vein graft anastomoses were usually completed before valve replacement and proximal anastomoses were performed thereafter. Standard surgical techniques of valve replacement were used. Valves were secured with pledgeted horizontal mattress sutures using 2-0 braided, nonabsorbable suture thread.

Guidelines for anticoagulant therapy
Warfarin therapy was initiated on postoperative day 1 unless contraindicated. Heparin infusion was begun in patients in whom warfarin therapy was not instituted by postoperative day 2 and was maintained until daily warfarin therapy resulted in a prothrombin time of 1.5 to 2.5 times control or in an international normalized ratio of approximately 2.5 to 3.5. After hospital discharge, the referring physician was responsible for the control of anticoagulant therapy. The guidelines for anticoagulant therapy were the same for both SJ and CM valves.

Follow up
One-time follow up data were obtained by telephone interview with all living patients, or with the patient’s family in the case of death. Complications reported by the patients were verified by contacting the private physician or obtaining medical records of hospitalization outside of New York Hospital. Death certificates were obtained and examined where the cause of death was unknown. Follow up was 99.6% complete with 1 patient lost to follow up, for a total of 318.5 cumulative patient-years and a median follow up of 1.4 years.

Definitions
Definitions of morbidity and mortality were based on the guidelines established for reporting these events by the Society of Thoracic Surgeons and The American Association for Thoracic Surgery [8]. Early mortality was based on the time from start of the operation to within 30 days postoperatively. A thromboembolic event was defined as any embolic event that occurred in the absence of infection after the patient had awakened from anesthesia. All thrombosed prostheses were included under this category and were also described separately. Valve-related death in this series is death caused by valve thrombosis, embolism, a bleeding event, or operated valvular endocarditis and also includes sudden or unexplained deaths as recommended by Edmunds and associates [8].

Statistical analysis
Continuous data were compared using the Levene test for equality of variances and unpaired t tests. Categoric data were compared between groups using ² or Fisher exact test as appropriate. Univariate analysis was performed to identify the variables that are associated with morbidity and mortality in this population. Although the importance of a multivariate analysis to adjust for differences between groups in this type of study is recognized, there were an insufficient number of events, especially when stratified by valve position, to allow meaningful performance of such an analysis.

Estimated survival and event-free curves at 1.5 years were calculated by the Kaplan-Meier method, and groups were compared by the log rank test statistic to compare the survival distributions. All statistical analysis was done in SPSS (version 6.1.1, SPSS Inc, Chicago, IL).

	Results

Top Footnotes Abstract Introduction Patients and methods Results Comment References

 
Study group characteristics
The SJ (116 patients) and CM (129 patients) groups possessed similar characteristics in terms of preoperative parameters, with a few exceptions (Table 1). Specifically, patients receiving CM implants had a lower ejection fraction and more commonly demonstrated NYHA Class IV symptoms than did SJ patients. Patients receiving SJ mitral valve implants weighed less and had a smaller body surface area compared with patients receiving CM mitral valve implants. There were more men and a higher incidence of coronary artery disease and atrial fibrillation in the CM mitral group compared with the SJ mitral group, although these differences were not statistically significant. The origin and nature of native valve abnormalities was similar in the SJ and CM groups (Table 2).

More isolated CM mitral valves (n = 54) were implanted than isolated SJ mitral valves (n = 38), and the total number CM mitral valves implanted (n = 74) was greater than the total number of SJ mitral valves implanted (n = 52). There was no difference between the SJ and CM groups in the size of the implanted valves. Differences also existed in the distribution of valve type implanted by each individual surgeon (Table 3). Perioperative characteristics, including cardiopulmonary bypass and aortic cross-clamp time were otherwise generally similar for the two groups (Table 3). The incidence of concomitant coronary artery bypass grafting, although occurring at a higher percentage in the CM group for both isolated AVR and isolated MVR, was not significantly different.

View larger version (17K): [in this window] [in a new window]   Fig 1. Survival from all causes of death for patients with St. Jude valves (SJ) compared with CarboMedic valves (CM) at 1.5 years.

View larger version (18K): [in this window] [in a new window]   Fig 2. Survival from valve-related death for patients with St. Jude valves (SJ) compared with CarboMedic valves (CM) at 1.5 years.

View larger version (13K): [in this window] [in a new window]   Fig 3. (A) Survival from valve-related death for patients with St. Jude valves (SJ) compared with CarboMedic valves (CM) in isolated aortic valve replacement at 1.5 years. (B) Survival from valve-related death for patients with SJ compared with CM valves in isolated mitral valve replacement at 1.5 years.

The actuarial freedom from any thromboembolic event for SJ and CM in all positions at 1.5 years was 94% ± 2% and 89% ± 3% (p = 0.1), respectively. When stratified by valve position, the freedom from thromboembolic event curves demonstrated a significantly greater incidence for isolated CM MVR compared with SJ mitral implants (97% ± 3% and 83% ± 5%, respectively [p = 0.04] at 1.5 years) (Fig 4). The freedom from thromboembolic event curves were not significantly different, however, for isolated AVR or AVR and MVR combined patients (not shown). Factors significantly associated with thromboembolism in the mitral position by univariate analysis included both CM valve (p = 0.03) and surgeon 3 (p = 0.03), who predominantly used the CM valve (Table 5).

View larger version (19K): [in this window] [in a new window]   Fig 4. Freedom from a thromboembolic event in patients with St. Jude valves (SJ) compared with CarboMedic valves (CM) in isolated mitral valve replacement at 1.5 years.

Bleeding events
A total of six bleeding events (one early, five late) occurred in the SJ group, compared with eight bleeding events (four early, four late) in the CM group. Actuarial freedom from a bleeding event for SJ and CM was 95% ± 2% and 93% ± 2%, respectively (p = 0.75). The incidence of bleeding events for SJ and CM implants was not significantly different when analyzed by implant position. Univariate analysis revealed several preoperative variables to be associated with a bleeding event (Table 5).

Other complications
Two late paravalvular leaks occurred in the SJ group. Both of these resulted in reoperation for repair of the leak. Two CM valves, both aortic, demonstrated a paravalvular leak on echocardiogram but did not require reoperation. Two early and no late cases of endocarditis were identified postoperatively in the SJ group. No early and four late cases of endocarditis were identified on follow-up in the CM group. There were no cases of prosthesis dysfunction in either group.

	Comment

Top Footnotes Abstract Introduction Patients and methods Results Comment References

 
The present study represents one of few studies in which a side-by-side comparison was made of two different valves implanted at the same institution during the same time period. The overall performance profile of the two valves was similar, as was their performance in the aortic position. There was no difference in early mortality rates between the groups, which suggests a similar operative risk profile for these two patient groups. The increased late mortality rate for CM compared with SJ patients can most likely be explained by the increased incidence of coronary artery disease and decreased left ventricular function in the CM patients compared with SJ patients.

The only cases of prosthetic valve thrombosis in our study were limited to CM valves in the mitral position, yielding a statistically significant association of this complication with CM valve implantation. The freedom from thromboembolic complication rate, which includes valve thrombosis, was also higher for the CM valve compared with the SJ valve in the mitral position. Although it is difficult to compare the current study examining two valves implanted at the same institution and previous one-valve studies [9–21], the difference in thromboembolic complications demonstrated by the CM valve compared with the SJ valve in the mitral position in the present study warrants further examination.

Risk analysis
There are several possible explanations for the increased CM mitral valve thromboembolic rate compared with that of the SJ mitral valve. The first is that the results of our short-term study are not representative of long-term valve performance, and differences between the two valves may equalize with longer follow up. Another explanation for differences between the SJ and CM thromboembolic complication rates is that our results may reflect an increased thromboembolic potential specific to our patients, including the anticoagulation practices of the referring cardiologist. However, no difference exists in the bleeding complication rate between the CM and SJ groups, which suggests that anticoagulation practices were similar for the SJ and CM groups.

Because our study was not a prospective randomized trial, it is possible, however, that the pattern of patient selection in our study resulted in CM patients who were at increased risk for thromboembolic complications compared with SJ patients. For example, aside from CM valve implantation, atrial fibrillation was also associated by univariate analysis with valve thrombosis in our study. Similarly, both heart failure and coronary artery disease occurred in a greater percentage of CM compared with the SJ mitral implant patients. Although these differences were not statistically significant, a predilection for left ventricular thrombus formation and aortic atherosclerotic disease are two obvious mechanisms by which these risk factors might have contributed to the significant increase in thromboembolic complications in the CM implant group. Unfortunately, because of the study population size and the few number of adverse events, our inability to perform a meaningful multivariate analysis to appropriately adjust for these risks in our SJ and CM populations leaves this issue unresolved.

One possible source of the unequal distribution of potential risk variables in this study was that several surgeons implanted more of one valve in the mitral position than the other. Surgeon 3, for example, predominately implanted CM mitral valves, and also demonstrated a significantly greater thromboembolic complication rate than did the other implanting surgeons. The preoperative characteristics of the patients referred to surgeon 3, the practices of surgeon 3, or the referring physicians that managed anticoagulant therapy in these patients might have predisposed these patients to thromboembolic complications.

Potential mechanisms and solutions
If an increased thromboembolic risk did exist for the CM valve, it would not be unexpected for this complication to be more prevalent in the mitral position, given the generally increased incidence of this complication in the mitral position compared with aortic valve implants. Design features of the CM valve and native mitral valve anatomy that theoretically could enhance thromboembolic potential include use of a biocompatible sewing ring that could paradoxically encourage pannus ingrowth, a valve opening profile that could affect "washout" of stagnant flow areas where thrombus could form, and pivot guard configuration and valve sizing that could allow impingment of the ventricular wall or subvalvular apparatus on the valve mechanism, thereby interfering with normal valve opening. Depending on which, if any, of these theoretic mechanisms might be relevant, potential remedies might include the use of better anticoagulant regimens (especially during the early postoperative period), more aggressive resection of the native valve or subvalvular apparatus, and more appropriate sizing of the valve prosthesis, and these putative mechanisms will be investigated.

The results of this study suggest that further evaluation of thromboembolic outcomes after CM valve implantation is warranted. Definitive resolution of this question must be based only on a more extensive, prospective randomized trial, in which risk-adjusted comparisons with multivariate analysis can be performed.

	Footnotes

Top Footnotes Abstract Introduction Patients and methods Results Comment References

 
Dr Rosengart has received funding from St. Jude Medical and from Sulzer CarboMedics.

	References

Top Footnotes Abstract Introduction Patients and methods Results Comment References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Todd K. Rosengart Samuel J. Lang Wilson Ko Nasser Altorki Karl H. Krieger O. Wayne Isom Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Rosengart, T. K. Articles by Isom, O. W. Search for Related Content PubMed PubMed Citation Articles by Rosengart, T. K. Articles by Isom, O. W.