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Ann Thorac Surg 1999;68:1210-1218
© 1999 The Society of Thoracic Surgeons
a Division of Cardiothoracic Surgery, Medical University of South Carolina, Charleston, South Carolina, USA
Address reprint requests to Dr Zellner, Division of Cardiothoracic Surgery, Medical University of South Carolina, 600 MUSC Complex, Suite 409, Charleston, SC 29425
e-mail: zellnejl{at}musc.edu
Presented at the Forty-fifth Annual Meeting of the Southern Thoracic Surgical Association, Orlando, FL, Nov 12–14, 1998.
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Abstract |
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Methods. This report describes long-term experience in 710 adult patients undergoing isolated aortic (AVR) (418) or mitral valve replacements (MVR) (292) with this prosthesis from January 1979 to December 1996.
Results. Ages ranged from 19 to 84 years (54.8 ± 15.1 AVR, 51.8 ± 12.9 MVR; mean ± SD). Male gender predominated in the AVR group (70%) and female gender in the MVR group (62%). One hundred and fifty-seven patients (22%) had associated coronary artery bypass grafting (AVR 27%, MVR 15%). Thirty-day operative mortality was 5.3% (22/418) in the AVR group and 5.1% (15/292) in the MVR group. Follow-up is 96.9% complete and ranges from 1 month to 16.9 years (AVR, 2,376 patient-years, mean 5.7 ± 4.5 years; MVR, 1,868 patient-years, mean 6.4 ± 4.8 years). In the AVR group, 120 late deaths have occurred and actuarial survival was 78.0 ± 2.3%, 58.0 ± 3.2%, and 36.8 ± 4.8%; at 5, 10, and 15 years, respectively. Forty-six patients have sustained 55 thromboembolic (TE) events (2.3%/patient-year). Fifty-one patients had anticoagulant-related bleeding complications (2.7%/patient-year). The mean improvement in New York Heart Association (NYHA) functional class from preoperative to postoperative was 3.0 ± 0.8 to 1.7 ± 0.1 (p < 0.05). In the MVR group, there have been 84 late deaths, and the actuarial survival was 79.3 ± 2.5%, 60.1 ± 3.5%, and 49.3 ± 4.1% at 5, 10, and 15 years, respectively. Fifty-two patients have had 64 TE events (3.5%/patient-year). Twenty-three patients had anticoagulant-related bleeding complications (1.6%/patient-year). The mean improvement in NYHA functional class was from 3.3 ± 0.6 to 1.8 ± 0.1. There were no mechanical failures in either group.
Conclusions. With a follow-up now extending to 17 years, the St. Jude Medical valve continues to be a reliable mechanical prosthesis with low and stable rates of valve-related complications.
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Introduction |
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TopAbstractIntroductionMaterial and methodsResultsCommentReferences |
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Material and methods |
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TopAbstractIntroductionMaterial and methodsResultsCommentReferences |
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Operative techniques were similar to those published in prior reports [1, 2]. Briefly, standard cardiopulmonary bypass was established using a disposable bubble or, more recently, a membrane oxygenator and moderate hypothermia (26°C to 32°C). Cold crystalloid or blood cardioplegia according to surgeon preference was used for myocardial protection. After debridement of the valve annulus, prostheses were secured using interrupted sutures of 2-0 Dacron reinforced with Teflon felt pledgettes. Sutures were carefully placed from above and through the annulus, so that the valve annulus would be everted when the sutures were tied. This technique inserts the prostheses in an "intraannular" position. Beginning in 1988, the subvalvular apparatus of the mitral valve was preserved whenever technically possible. Valve sizes for the two groups ranged from 19 to 33 mm (Fig 2). Heparin administration was started (5,000 U subcutaneously every 6 or 12 hours, depending on surgeon preference) on the first postoperative day and continued until the prothrombin time or, most recently, the International Normalized Ratio (INR) was regulated with the administration of warfarin sodium. Early in our experience, the INR was maintained at 2.5 to 3.5. More recently, we have recommended a target INR of 2.0 for patients who have undergone AVR and 2.0 to 2.5 for MVR. The warfarin dose was regulated by the surgeon during hospitalization and during early follow-up, and thereafter by the referring physician.
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Results |
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Late mortality
Figure 5A illustrates the actuarial survival after AVR at 5, 10, and 15 years. There have been a total of 120 late deaths in this group, and the causes of late mortality are shown in Table 2. Forty-one late deaths were either valve related (24), sudden and unexpected (12) or unknown (5). Seventy-nine late deaths were not valve related. The greatest number of patients (50) died of progressive cardiac failure in spite of proper prosthetic valve function. Eighteen patients died of cancer in this group, and cancer represents the second most frequent cause of non-valve-related mortality after AVR.
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There were 55 thromboembolic events in 46 patients, nine of which were fatal. Six patients had thrombosed valves and 40 patients suffered embolic events. In contrast to our first report, where all thromboembolic events occurred within the first 12 months postoperatively, we have observed a linearized rate of 2.3%/patient-year, in the current long-term series. Freedom from thromboembolic events at 15 years was 73 ± 4.5% (Fig 6). Of the 46 patients in whom thromboembolic events occurred, 12 (26%) were not anticoagulated at the time of the complication.
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MVR group
Operative mortality
A total of 15 patients died in the early postoperative period, yielding a 5.1% operative mortality rate. There was no statistically significant difference in the operative mortality in patients who underwent an isolated MVR (4.4%%) versus combined MVR and coronary artery bypass procedure (9.1% [MVR + CABG], p = 0.2553).
Late mortality
There were 84 late deaths after MVR, and the causes of these deaths are shown in Table 2. Figure 5B illustrates the actuarial survival after MVR at 5, 10, and 15 years. Of the 84 late deaths, 16 were valve related, 6 were sudden and unexpected, and 7 were of unknown causes. The 55 remaining late deaths that occurred were not valve related. The greatest number of patients (38) died of progressive cardiac failure in spite of proper prosthetic valve function. As in the AVR group, cancer was the second most frequent cause of non-valve-related mortality after MVR.
Risk factors affecting long-term survival were analyzed using the Cox proportional hazards model (Table 3). For the MVR group, patient age, NYHA functional class, and the presence of coronary artery disease were independent negative predictors of long-term survival (all p < 0.005), similar to the findings in the AVR group. Gender, valvular lesion, reoperation, and etiology of valvular disease were not predictors of long-term survival.
Valve-related complications
Neither structural failure nor leaflet entrapment was observed. Clinically important hemolysis developed in two patients, and six patients had significant noninfectious paravalvular leaks.
A total of 64 thromboembolic events occurred in 52 patients, nine of which were fatal. Fifty-one patients sustained embolic events and one patient developed valve thrombosis. Freedom from thromboembolic events at 15 years was 59% ± 7.0% (Fig 6). We observed a linearized rate of 3.4%/patient-year in the current long-term series. Six of the 52 patients (11.5%) were not anticoagulated at the time of their thromboembolic event.
Twenty-three patients had 29 events of anticoagulant-related bleeding complications in the current series (1.6%/patient-year). Four patients died as a direct result of this complication. Freedom from anticoagulation-related complications was 88.7% ± 2.3% at 15 years (Fig 7).
Prosthetic valve endocarditis was observed in six patients (six events), yielding a linearized rate of 0.32%/patient-year. Freedom from prosthetic valve endocarditis at 15 years was 93.8% ± 4.1% (Fig 8).
Consequences of morbid events
Eleven of 289 patients underwent reoperation to replace the previously implanted mitral valve prosthesis. Freedom from reoperation at 15 years was 90.1% ± 4.2%, and the linearized rate of reoperation was 0.6%/patient-year (Fig 9). Indications for prosthetic valve replacement in the MVR group included paravalvular leak (6), prosthetic valve endocarditis (3), valvular thrombus (1), and hemolytic anemia (1).
Permanent neurological impairment occurred in 33 of the patients after MVR (Fig 10). Of the anticoagulant-related bleeding events, there were four cerebral hemorrhages, four episodes of cardiac tamponade, eight episodes of gastrointestinal bleeding, and four other internal hemorrhages.
Overall freedom from complication
Figure 12 illustrates the combined overall freedom from all complications during the 15-year follow-up for the MVR group. Overall freedom from all complications was 23.0% at 15 years. When non-valve-related deaths are excluded, the freedom from complications rose to 42.0%.
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Comment |
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TopAbstractIntroductionMaterial and methodsResultsCommentReferences |
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Operative mortality in the current series is similar between the AVR and MVR groups (AVR 5.3%, MVR 5.1%) and is slightly higher than we observed in our earlier series at 5 and 10 years. However, this difference is not significant (p = NS) and compares favorably with other long-term studies of this prosthesis [6, 17–19]. As in our previous studies, we continue to maintain that preoperative patient characteristics, such as age, reoperation, cardiac function, and associated coronary disease, may have greater influence on operative mortality than the type of valve prosthesis implanted. The reported operative mortality in the current series is similar to that of other series of tissue and other commonly used mechanical valves [20, 21].
Similar to other studies, we observed a striking difference between freedom from valve-related death and the long-term survival of our patients [6]. Multivariate analysis demonstrated that the major independent variables significantly impacting long-term outcome in both the AVR and MVR groups were preoperative NYHA class, age at operation, and the presence of coronary artery disease. These results indicate that long-term survival may be significantly related to underlying cardiac function as well as advanced age and coronary artery disease, in addition to valve performance. Indeed, 42% of the late deaths in the AVR group and 45% of the late deaths in the MVR group were secondary to advanced cardiac disease and were not prosthesis related. The 15-year survival of 37% (AVR) and 49% (MVR) again is similar to other studies involving more than 10 years of follow-up [6, 17]. Nakano and associates reported superior 12-year survival (AVR 82%, MVR 87%) compared with the current series; however, the patients in this Asian series were younger (mean age < 50 years), with a high incidence of rheumatic disease (AVR 44%, MVR 81%) and a lower incidence of significant coronary artery disease (1.4% vs 22% in the current series) [20].
Thromboembolism remains a major complication after mechanical valve replacement. The linearized rate of thromboembolic complications in this series (AVR 2.3%/patient-year, MVR 3.4%/patient-year) is slightly higher than in our 10-year follow-up report. This may reflect the increasing average age of the patients in the current series and the prevalence of significant cardiovascular disease. In addition, patients in this study were contacted prospectively at yearly intervals and would be more likely to recall an adverse event than patients, reported in other series, who were contacted only once in follow-up. Still, this incidence of thromboembolism is comparable with other series of St. Jude Medical valves (0.8%–3.5%/patient-year) [4, 5, 18, 22, 23]. These thromboembolic rates are also comparable with the composite rates for other mechanical valves and tissue valves [24, 25].
The incidence of anticoagulant-related bleeding complications has again decreased in the current series compared with our two previous reports [1, 2]. In the AVR group, the linearized rate of anticoagulant-related complications was 2.7%/patient-year, and in the MVR group was 1.6%/patient-year. This represents a substantial reduction in anticoagulant-related bleeding events compared with our original 5-year study (AVR 6.9%/patient-year, MVR 2.4%/patient-year) and a modest reduction compared with our 10-year report (AVR 3.5%/patient-year, MVR 2.2%/patient-year). Patients undergoing AVR were, on the average, older than those patients who underwent MVR (AVR 54.8 years vs. MVR 51.8 years). Further, the median age of those patients who experienced anticoagulant-related bleeding after AVR was significantly older than observed in the MVR group (AVR 62, MVR 54; p < 0.05). Thus, the higher incidence of anticoagulant-related bleeding events observed after AVR may reflect the older age of the patients in that group. Other large series have also observed a higher incidence of anticoagulant-related bleeding after AVR compared with patients who underwent MVR [5]. We, like others, have been favorably impressed with the low thromboembolic rate of the St. Jude Medical prosthesis and have gradually lowered our target prothrombin time ratio (INR) from 2.5 to 3.5 to 2.0 to 2.5 [2, 4–6, 17–19].
The incidence of prosthetic valve endocarditis was quite low (AVR 1.0%/patient-year, MVR 0.3%/patient-year) and is similar to other series [1–6, 17–19]. There was nearly complete freedom from acquiring endocarditis beyond 5 years for both aortic and mitral valve prostheses in this study. This is similar to our earlier findings [2]. It has been speculated that the valve design, increased probability of prosthetic valve sterilization, and early incorporation of the cloth sewing ring by tissue ingrowth may offer some protection from bacterial invasion [2, 3]. This complication, however, carried a substantial mortality in this study (40%) despite aggressive medical and surgical intervention.
The NYHA functional status of surviving patients who underwent valve replacement with the St. Jude Medical mechanical prosthesis significantly improved when compared with the NYHA status prior to surgery. Whereas more than 80% of patients in group I and II were in NYHA class III or IV preoperatively, more than 80% achieved class I or II postoperatively. Furthermore, this functional profile (NYHA class I and II vs NYHA class III and IV) was maintained at 5, 10, or 15 years after operation. Thus, functional improvements appeared to be sustained over the course of this 15-year study and may be partly attributable to the favorable hemodynamics of the St. Jude Medical prosthesis.
In our 10-year follow-up, we observed that freedom from valve-related complications was 35.1% for aortic and 50.3% for mitral valves [2]. Our impression, at that time, was that overall performance of the St. Jude Medical valve was excellent; however, patients who undergo prosthetic valve replacement do not have a normal outlook compared with the general population. Rather, these patients have substituted their original disease (native valve) for a new one (prosthetic valve) with lower, but definite morbidity. Examination of the current 15-year data in Figures 11 and 12 support that observation: after prosthetic valve replacement, only 41.5% (AVR group) and 42.0% (MVR group) of patients remain free of valve-related complications.
Results from this and other studies suggest that overall long-term survival after prosthetic valve replacement may be strongly influenced by what preexisting comorbidities the patient brings to the operating room [6]. As more elderly patients with more comorbidities undergo valve replacement, the importance of valve-related factors will continue to diminish relative to patient-related factors. The current investigation has demonstrated that there is significant and sustained improvement in NYHA functional class after valve replacement. However, valve-related complications will always impose substantial costs on patients undergoing prosthetic valve replacement.
In summary, this series of patients undergoing AVR and MVR with the St. Jude Medical mechanical prosthesis with follow-up now extending beyond 15 years confirms the excellent performance of this valve, as documented in our earlier reports. In addition, the excellent durability and total absence of mechanical structural failure makes the St. Jude Medical heart valve prosthesis our prosthesis of choice for any patient undergoing mechanical prosthetic valve replacement.
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Footnotes |
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References |
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