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J Thorac Cardiovasc Surg 2003;126:358-364
© 2003 The American Association for Thoracic Surgery
Surgery for acquired cardiovascular disease |
a Department of Cardiovascular Surgery, National Cardiovascular Center, Osaka, Japan,
b Department of Cardiology, National Cardiovascular Center, Osaka, Japan
c Department of Public Health, Kitasato University, Kanagawa, Japan
Read at the Eighty-second Annual Meeting of The American Association for Thoracic Surgery, Washington, DC, May 5-8, 2002.
Received for publication June 3, 2002; revisions received July 8, 2002; revisions received January 15, 2003; accepted for publication February 18, 2003.
* Address for reprints: Ko Bando, MD, Department of Cardiovascular Surgery, National Cardiovascular Center, 5-7-1, Fujishirodai, Suita, Osaka 565-8565, Japan
kobando{at}hsp.ncvc.go.jp
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Abstract |
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METHODS: Early and late mortality and stroke were assessed. Potential predictors of mortality and stroke were entered into a Cox proportional hazards model. Actuarial survival and freedom from stroke were determined by a log-rank test.
RESULTS: Mitral valve replacement was performed in 812 patients. Concomitant procedures included left atrial appendage closure in 493 (61%) patients, tricuspid annuloplasty-replacement in 348 (43%) patients, maze procedure in 185 (23%) patients, plication of the left atrium in 148 (18%) patients, and other procedures in 151 (19%) patients. Five-year actuarial survival was 91.1% ± 2.3%. Freedom from stroke at 8 years was significantly better in patients with sinus rhythm versus atrial fibrillation (P < .001). Ninety-nine percent of patients with mitral valve replacement combined with a maze procedure were free from stroke, whereas only 89% of patients with mitral valve replacement alone were free from stroke at 8 years after surgical intervention. Seventy-two patients had late stroke; sixty-five patients (90%) were in atrial fibrillation, and 47 (65%) patients had the left atrial appendage closed. Multivariate analysis showed that late atrial fibrillation (odds ratio, 3.39; 95% confidence interval, 1.72-6.67; P = .0001) and omission of the maze procedure (odds ratio, 3.40; 95% confidence interval, 1.14-10.14; P = .003) were the significant risk factors for late stroke.
CONCLUSIONS: Persistent atrial fibrillation was the most significant risk factor for late stroke after mechanical mitral valve replacement. Restoration of sinus rhythm with a maze procedure nearly eliminated the risk of late stroke, whereas neither closure of the left atrial appendage nor therapeutic anticoagulation prevented this complication.
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Despite improvements in valve design, stroke remains a serious complication after heart valve replacement. It is generally agreed that lifelong anticoagulant therapy is indicated in all patients with mechanical valves. Recent studies indicate that major systemic embolism still occurs at a rate of 2% to 3% per year after mechanical mitral valve replacement (MVR), despite anticoagulation.1-3 We and others recently demonstrated that maintaining sinus rhythm by using the Cox maze procedure reduced the incidence of late stroke.4-6 However, the risk for late stroke after mechanical valve replacement remains to be determined.
The purpose of the study was to elucidate the risks for early and late mortality and stroke after mechanical MVR in a single center over a 24-year period.
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Patients and methods |
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Definitions
Stroke was defined as cerebral thromboembolism diagnosed by a neurologist and confirmed by means of a computed tomographic scan. Transient ischemic attacks were not counted as strokes in this study. Valve thrombosis was defined as impairment of the valve function by the deposition of thrombus demonstrated at operation or autopsy. Bleeding includes intracranial bleeding, spinal bleeding, and major extracranial bleeding. Intracranial and spinal bleeding were defined as a neurologic deficit of sudden or subacute onset confirmed by means of computed tomographic scanning, surgical investigation, or autopsy. Major extracranial bleeding was defined as an acute bleeding event that led to death or hospital admission or treatment of bleeding; bleeding that led to hospital admission for diagnostic procedures only was not considered major. Bleeding caused by trauma was also excluded. We also excluded all complications that occurred during hospitalization for a different reason because other diseases, interventions, and diagnostic procedures might affect the risk of complications far more than the intensity of the anticoagulant therapy.7,8
Patients
Demographic data and preoperative cardiac information are given in Table 1.
With respect to preoperative heart rhythm, 78% of patients had chronic atrial fibrillation. In May 1992, the Cox maze procedure was introduced. Between May 1992 and December 1994, the Cox maze III procedure was the procedure primarily performed. A modified maze III procedure (Kosakai maze) was performed until May 1998. The cryo-maze procedure was used thereafter. Details of these procedures have been previously described.6,9 Five hundred thirty-three (66%) patients had St Jude Medical valves (St Jude Medical, Inc, St Paul, Minn). The remaining patients had a variety of valves including CarboMedics (n = 125; Sulzer Carbomedics, Inc, Austin, Tex), Björk-Shiley (n = 70, in our early experience; Shiley, Inc, Irvine, Calif), ATS (n = 47; ATS Medical, Inc, Minneapolis, Minn), Omniscience (n = 29; Medical Inc, Inver Grove Heights, Minn), and other valves (n = 8). All valves were placed in the antianatomic position.
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Statistical methods
Survival and freedom from mortality, atrial fibrillation, and stroke were estimated by using the Kaplan-Meier method. Survivorship curves were compared with a log-rank test. The risks for death, recurrence of atrial fibrillation, and stroke were analyzed by using both univariate analysis and multivariate analysis with a Cox proportional hazards model.
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Results |
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Incidence of stroke after surgical intervention
Seventy-two patients had a late stroke; 65 (90%) patients were in atrial fibrillation, and 47 (65%) patients had the left atrial appendage closed. Irrespective of preoperative rhythm (either in sinus rhythm or atrial fibrillation), closure of the left atrial appendage did not have a significant effect on the incidence of stroke, even in patients undergoing MVR alone. At the time of their stroke, 63 (86%) patients had an INR of greater than 1.8. Nine patients had stopped warfarin for minor operations or dental care; their INR was less than 1.5.
Freedom from stroke 15 years after surgical intervention was 90.7% ± 6.5% in patients with regular rhythm compared with 73.8% ± 6.9% in patients with chronic atrial fibrillation (P < .0001, Figure 3). Freedom from stroke 8 years after surgical intervention was 98.7% ± 2.3% in patients who underwent a concomitant maze procedure compared with 88.7% ± 2.6% in patients who underwent MVR alone (P = .033, Figure 4). Three (6.5%) of the 46 patients with an unsuccessful maze procedure had a stroke late after surgical intervention.
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Discussion |
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TopAbstractPatients and methodsResultsDiscussionDiscussionReferences |
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The current retrospective study confirms that mechanical MVR resulted in excellent 15-year survival (85%, Figure 1). Furthermore, the only risk factors for late mortality were preoperative New York Heart Association class IV and older age (>65 years, Table 4).
This study also confirms that greater than 25% of patients with chronic atrial fibrillation had a stroke during the same 15-year period (Figure 3). Because 78% of the patients who underwent MVR were in atrial fibrillation preoperatively (Table 1), restoration of sinus rhythm after surgical intervention was a critical factor in preventing strokes after mechanical MVR (Figure 3). The use of the maze procedure is a logical strategy to prevent late strokes after MVR with mechanical prostheses.
In the present study a maze procedure combined with MVR resulted in 98.7% freedom from stroke, whereas only 89% of the patients undergoing MVR alone were free from stroke 8 years after surgical intervention.
Moreover, chronic atrial fibrillation and the omission of a maze procedure were the 2 major predictors of late stroke after mechanical MVR. These results indicate that an adjunct maze procedure nearly eliminated the risk of late stroke after MVR with mechanical prostheses.
Among 185 patients who underwent a concomitant maze procedure, 3 patients had a stroke, but all of these patients were in atrial fibrillation at the time of their strokes. Moreover, none had left atrial contraction, which was confirmed by the absence of the a-wave on echocardiography. Patients with a failed maze procedure might have a risk for late stroke similar to that of patients with atrial fibrillation. The radial approach or new radiofrequency techniques preserve a more physiologic atrial transport function.14,15 Further study is necessary to elucidate the role of left atrial contraction in eliminating left atrial thrombus.16
In addition to maintaining sinus rhythm by using a maze procedure, closure of the left atrial appendage or reducing the size of an enlarged left atrium might also be expected to reduce the incidence of late stroke. In this study neither closure of the left atrial appendage nor plication of the left atrium prevented late stroke. However, more than 90% of patients with a combined maze procedure had the left atrial appendage closed, and the cutting and sewing in the original maze procedure could certainly have reduced the size of the left atrium. Differentiation of these factors might be difficult.
This study was also designed to examine the effect of anticoagulation on the incidence of late stroke. Among 72 patients who had a late stroke, 63 had an INR considered therapeutic (1.8-2.8) in the Japanese population (Figure 5).11,12 Thus therapeutic anticoagulation with warfarin alone is insufficient to prevent late strokes after mechanical MVR, especially in patients with chronic atrial fibrillation. This was a significantly lower target level compared with the American Heart Association/American College of Cardiology guidelines,7 the recommendations of the American College of Chest Physicians,17 and several European studies.18 However, recent studies from Japan indicate that maintaining an INR level between 1.8 and 2.8 results in lower bleeding and stroke rates compared with studies in the United States or Europe.11,12 Accordingly, the guidelines of the Japanese Circulation Society recommend a target INR of 1.8 to 3.0 for patients after MVR with bileaflet mechanical valves.19 The overall linearized risk of stroke in this study was only 0.02 per year in patients with atrial fibrillation and 0.004 per year in patients with regular rhythm. Moreover, the majority of patients who had major bleeding had INRs between 2.0 and 3.3 at the time of their events. Thus setting a higher INR might increase bleeding in our population. A prospective randomized study to determine the optimal anticoagulation regimen (eg, warfarin alone vs warfarin plus antiplatelet agents) is necessary.3,8,18,20
The major limitation of our study is that it was not randomized. The maze procedure was performed only after 1992, and therefore the follow-up period in the group undergoing MVR alone versus those undergoing MVR plus the maze procedure was different. The follow-up period for the group undergoing MVR plus the maze procedure (mean, 4.45 patient-years; range, 0.5-12.4 patient-years; total, 828 patient years) was significantly shorter compared with that of the group undergoing MVR alone (range, 0.5-22.9 patient-years; total, 5035 patient-years; P < .0001). Thus the significantly higher freedom from stroke in the maze procedure group might be related to a shorter observation period. However, our recent study regarding the impact of a maze procedure with mitral valve repair and replacement since 1992 indicated that the addition of a maze procedure significantly reduced the incidence of stroke between the groups during a comparable follow-up period.6 In addition to this, the decision for or against an adjunctive maze procedure reflected each surgeon’s experience. Regarding anticoagulant therapy, the INR was known at the time of a stroke or major bleeding event, but baseline INR was only partly taken into account in this study. Thus the role of compliance as a cause of instability in oral anticoagulant therapy was not fully investigated.20
In conclusion, persistent atrial fibrillation was the most significant risk factor for early and late stroke after mechanical MVR. Restoration of sinus rhythm with the maze procedure nearly eliminated the risk of late stroke, whereas neither closure of the left atrial appendage nor therapeutic anticoagulation prevented this complication. Continuing efforts to define the optimal oral anticoagulant therapy to minimize the chances of stroke and bleeding are still necessary.
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Discussion |
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Dr Bando. Thank you very much, Dr Akins, for your excellent questions. Regarding the type of valves, among these 812 patients, 533 patients had a St Jude mechanical valve, and the remaining valves include the CarboMedics valve in 125 patients and, recently, the ATS valve in 47 patients. Earlier in our experience, the Björk-Shiley valve was used in 70 patients, and the Omniscience valve was used in 23 patients. We did analyze the type of valves as potential predictors in univariate and multivariate analyses, and these were entered into a Cox proportional hazards model, but none of the valve types came out as a risk factor for either late mortality or late stroke.
Dr Akins. My second question focuses on the effect of obliteration of the left atrial appendage on late stroke. The authors include in their statistical analysis of this part of the study patients who had a concomitant maze procedure. Wouldn’t it be better to eliminate the maze patients and analyze only patients who had a MVR with or without obliteration of the left atrial appendage?
Dr Bando. That is a very excellent point, Dr Akins. Removing 185 patients, we have 627 patients undergoing MVR alone, and if you compared those patients with or without closure of the left atrial appendage, actually half of them, 320, have the left atrial appendage closed, whereas the remaining 307 patients had the left atrial appendage left open. Of those, there are 69 strokes we have so far. Again, 43 patients had the left atrial appendage closed, and the remaining 26 were left open. Therefore, looking at those data in this subset of the whole group, there is no difference and no positive effect on the prevention of late stroke.
Dr Akins. In contrast to the program book abstract, the manuscript states that of the 72 patients who had a late stroke, 62 had an INR of only greater than 1.8 and not 2.3. In fact, half of the patients who had a stroke had an INR of 2.2 or less, a level that would be quite low for North American patients with a mechanical mitral valve, particularly those with persistent atrial fibrillation. Have you changed your target INR levels for these patients?
Dr Bando. Actually not, because the second to last slide shows that if the target level is coming out over 3, we are going to have more and more patients with major bleeding, and in our society with the Japanese circulation, we are about to make guidelines of what would be an adequate target level, and it ends up to be between 2 to 3 or 1.8 to 2.8.
Dr Akins. I question using patients going back 25 years as a cohort against which to compare patients having concomitant maze operations since 1992. Earlier patients might have had substantially different operations, prostheses, and other risk factors for stroke. Indeed, earlier year of operation is a significant predictor of late stroke. How do you think the addition of this early surgical group has really added to the strength of your study?
Dr Bando. That is a good point. The observation period is totally different for the maze group studied since 1992 and those patients operated on before that, close to 24 years. Numerous changes have happened in our institution. First, we used the bioprosthetic valve, the Ionescu-Shiley valve, extensively for all generations between 1980 and 1984 and then changed to using the Carpentier-Edwards bioprosthetic valve, but only for patients over 70 years old. Otherwise, we all use mechanical valves. That is the major change. And also, even after 1992, we used 3 different maze techniques. That might have an effect on the results. I agree with you.
Dr Akins. There is no doubt that patients with atrial fibrillation, even those without mitral valve disease, have a greater risk of stroke and are best treated with long-term anticoagulation. Although my bias is to agree with the authors’ premise that maintenance of sinus rhythm in addition to anticoagulation for mechanical mitral prostheses might yield better neurologic outcomes, I am not convinced that adding this earlier surgical group has made this study prove that point.
Dr Bando. That is a very good point, and that is the primary reason we are going to do a prospective randomized study to try to find out what would be the best anticoagulation strategy comparing warfarin versus warfarin plus aspirin, and we are going to start that pretty soon. Appendix figure
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