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Eur J Cardiothorac Surg 2001;20:105-113
© 2001 Elsevier Science NL
Departments of Cardiac Surgery and Paediatric Cardiology, The General Hospital, Southampton, UK
Received 21 October 2000; received in revised form 23 April 2001; accepted 26 April 2001.
Corresponding author. Department of Cardiac Surgery, The General Hospital, Tremona Road, Southampton SO16 6YD, UK. Tel.: +44-23-80796241; fax: +44-23-80798508
e-mail: monro1711{at}aol.com
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Abstract |
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 Top Abstract 1. Introduction2. Patients and methods3. Results4. Discussion5. ConclusionsReferences |
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Key Words: Mechanical mitral valve • Children
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1. Introduction |
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TopAbstract1. Introduction2. Patients and methods3. Results4. Discussion5. ConclusionsReferences |
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The selection of the most appropriate valve substitute in the mitral position has been debated in the past but following the disappointing results produced with bioprostheses [4,5], most surgeons would currently agree that, despite their drawbacks, mechanical valves are the most suitable option [6].
Until 1980, we used biological valves for their merits in avoiding the need for anticoagulation and reducing the risk of thromboembolism. From 1981, having, also, found that they undergo early calcification and degeneration, we have, with occasional exceptions, routinely implanted mechanical valves.
In this paper, we present an analysis of our 20-year experience with the use of mechanical prostheses to replace native irreparable mitral valves in children.
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2. Patients and methods |
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TopAbstract1. Introduction2. Patients and methods3. Results4. Discussion5. ConclusionsReferences |
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During the study period 29 additional children with isolated mitral valve lesions underwent mitral valve repair in our unit. Reparative mitral valve surgery was, also, performed in other children having atrioventricular septal defects and/or other complex congenital abnormalities.
2.1. Aetiology of the disease and indication for valve replacement
The aetiology of the disease was congenital in 37 patients, rheumatic in four, infective in two and Marfan's syndrome in one.
The predominant haemodynamic abnormality necessitating a MVR was mitral regurgitation (MR) in 36 and mitral stenosis (MS) in eight patients.
2.2. Patients with mitral regurgitation
In the patients with MR the disease aetiology was congenital in 31, rheumatic in three, infective in one and Marfan's syndrome in one.
Seventeen of the patients with congenital MR had an atrio-ventricular septal defect (AVSD) which was complete in 15 and partial in two. Of the remaining 14 patients, two had isolated MR and 12 had MR in combination with other problems. These were double outlet right ventricle and ventricular septal defect (VSD) in two, subaortic stenosis in two, tricuspid atresia and VSD in one, interrupted aortic arch with aorto-pulmonary window and subaortic stenosis in one, aortic coarctation and VSD in two, multiple VSDs in two, mitral stenosis in one and aortic coarctation in one patient.
2.3. Patients with mitral stenosis
The disease aetiology in the patients with MS was congenital in six (commissural fusion in four and a parachute mitral valve in two), infective in one and rheumatic in one.
Additional problems were present in five patients, aortic coarctation in three and subaortic stenosis in two.
2.4. Previous operations
Thirty-four patients underwent 66 previous cardiovascular operations shown in Table 1. Thirteen of these patients had one, 10 patients had two, seven patients had three and three patients had four previous cardiovascular procedures.
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2.5. The operation and concomitant procedures
The operations were performed through a median sternotomy using moderately hypothermic cardiopulmonary bypass, established with an ascending aortic and bicaval cannulae. The mitral valve was approached via a transatrial or a direct left atrial approach. Myocardial protection was provided by means of cold crystalloid or blood cardioplegia and topical myocardial cooling.
A bi-leaflet prosthesis was implanted in 42 patients (Carbo-medics in 24, St. Jude Medical in 17 and an On-X in one) and a Bjork–Shiley single-disk valve, early in the series, in two. The mean valve size was 23.8±3.3 mm (range 16–31 mm).
In order to insert a bigger valve, an inverted aortic prosthesis was implanted in eight children by one of the senior authors (J.L.M.). The mean size of the inverted aortic valves was 20.9±2.1 mm (range 16–25 mm). In two patients with severe mitral and aortic stenosis, the annuli were enlarged by incising down through the aortic ring and through the anterior leaflet of the mitral valve. Two mechanical valves, an aortic and a mitral, were then inserted side by side suturing part of the circumference of their sewing cuffs together in a ‘pair of spectacles’-like fashion. The size of the valves in the first patient was 19 and 23 mm and in the second patient it was 21 and 25 mm.
Fifteen concomitant procedures were performed in 13 patients, including aortic valve replacement (AVR) in six and a composite graft-valve aortic root replacement for Marfan's syndrome in one (Table 2).
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Patients were seen regularly by the paediatric cardiologists. Echocardiography was performed before discharge from the hospital and during each outpatient visit.
Data on the patients preoperative clinical features, operations, postoperative course, late events and survival were obtained through a detailed review of hospital medical records. Additional information was sought from the referring physicians, family doctors and/or the patients families.
The mean follow up for the hospital survivors was 6.4±4.8 years, ranging from 1 month to 18.1 years, with a total of 213 patient years. Follow up was complete.
2.7. Definitions and statistics
Operative mortality includes death within 30 days following the mitral valve replacement. Continuous data are presented as means (±standard deviation) and categorical variables as percentages. Means were compared with unpaired t-test and proportions with 
2 or Fishers exact test as appropriate. The prediction of freedom from death and other events (±standard error from the mean) was calculated with the Kaplan–Meier product limit method and the resulting curves compared with the log-rank test. In these calculations included were the operative deaths and other untoward events (i.e. thromboembolism, endocarditis, re-operation) occurring early postoperatively, before patient-discharge from the hospital. A P value of less than 0.05 was considered significant. Analysis was done with the statistical package SPSS PC (version 8.0) (Chicago, IL, 60611).
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3. Results |
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TopAbstract1. Introduction2. Patients and methods3. Results4. Discussion5. ConclusionsReferences |
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Operative mortality for children aged under 5 years was 22% (5 out of 23) and it was 4.8% (1 out of 21) for the older children (P=0.2).
Operative mortality for the children having an AVSD was 19% (3 out of 16) and for the remaining patients this was 11% (3 out of 27) (P=0.6).
Operative mortality was reduced significantly over the study period. Before 1990 it was 31% (5 out of 16 children with a mean age 7±4.5 years) and thereafter it was 3.6% (1 out of 27 children with a mean age of 6.8±4.7 years), (P=0.02). This reduction was more pronounced among the youngest, aged less than 1 or 5 years, children (Table 3).
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The other three operative fatalities occurred in children who had previously undergone surgery for complex congenital conditions. The first patient had repair of an interrupted aortic arch with aorto-pulmonary window, resection of subaortic stenosis and a homograft AVR. The second had resection of a subaortic stenosis, mitral valvotomy and a tissue MVR and the third had had a Fontan procedure for tricuspid atresia. All three presented, on this occasion, in poor condition and underwent emergency surgery, the first two a double valve replacement (AVR & MVR) and the third one a MVR. One patient could not be weaned from bypass and two died 8 and 12 days postoperatively from multiple organ failure.
3.2. Early postoperative complications
Eleven additional patients (26%) experienced severe early postoperative complications. These were low cardiac output syndrome due the narrowing of the outflow of the tricuspid valve by the newly inserted mitral prosthesis in one, myocardial ischaemia attributed to the pressure exerted by the mitral prosthetic valve on the circumflex artery in one, early Staphylococcal prosthetic valve endocarditis in one, mitral valve thrombosis in one, complete heart block requiring insertion of a permanent pacemaker in two, transient complete heart block in one, persistent hypotension in two, difficulty in weaning from the ventilator in one, recurrent laryngeal nerve palsy in one and pericardial effusion requiring re-sternotomy for drainage in one patient.
Echocardiography performed before discharge from the hospital has demonstrated satisfactory prosthetic mitral valve function in all cases.
3.3. Valve or anticoagulation treatment-related events
Seven patients experienced valve or anticoagulation treatment-related events. Two patients developed prosthetic valve endocarditis (PVE). The first had early PVE and the second had two episodes of late PVE and a paravalvular leak. Ten-year freedom from PVE was 97.3±2.7% and the linearized rate was 0.9% per patient year.
Two patients sustained thromboembolic events. One had early prosthetic valve thrombosis and the other one, a transplant candidate with poorly contracting left ventricle, had a late thromboembolic event, despite her INR being 4.2, resulting in left hemiparesis from which she made a slow recovery. Ten-year freedom from thromboembolism was 92.8±5.3% (0.9% per patient year).
Two patients bled after tooth extraction requiring blood transfusion. Ten-year freedom from bleeding was 97.7±2.3% (0.9% per patient year).
Paravalvular leak occurred in two patients, in one of them, mentioned above, following repeat MVR for PVE in another unit. Ten-year freedom from paravalvular leak was 97.2±2.7% (0.9% per patient year).
Kaplan–Meier 10-year freedom from any of these events (PVE, thromboembolism, bleeding and paravalvular leak) was 85±6.5% (3.7% per patient year) (Fig. 1) .
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The remaining four patients had late mitral valve-related re-operations. The first patient underwent two repeat MVRs for PVE in another unit and repair of a paravalvular leak in our unit and the second patient had repair of a paravalvular leak. The third had re-resection of a subaortic stenosis followed by two AVRs and two repeat MVRs to insert bigger size valves. The fourth patient had a repeat MVR to insert, also, a bigger size mitral valve. These two patients were the only ones to have a repeat MVR to replace an outgrown mitral prosthesis. Two patients had re-operations unrelated to the mitral prosthesis. Both had a normally functioning mitral prosthesis and received a heart transplant. One had rheumatic heart disease and the other had congenital mitral stenosis and MR with severe endocardial fibroelastosis.
Ten-year freedom from re-operation related to the mitral valve was 75±9.8% (3.7% per patient year) and from re-operation due to any cause it was 64±11% (4.3% per patient year) (Fig. 2) .
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Overall, Kaplan–Meier, 5 and 10-year survival was 81±6% and 78±7.1% and for the hospital survivors this was 90.3±5.4% and 90.3±5.4% (Fig. 3) .
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4. Discussion |
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TopAbstract1. Introduction2. Patients and methods3. Results4. Discussion5. ConclusionsReferences |
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Owing to their good durability, availability and haemodynamic performance, mechanical valves are the most preferred mitral valve substitute in children. Conclusive evidence supporting the superiority of any particular type of mechanical prosthesis in children is lacking and our preference in using bileaflet mechanical valves (in 42 out of 44 children) reflects our practice in the adult population over the same period.
The special anatomical features, the severe associated defects and the frequently compromised haemodynamic condition of some children, particularly infants, can render MVR a challenging and hazardous procedure. The overall operative mortality of 14% (11% for isolated MVR and 29% for MVR plus AVR) compares favourably with previous reports [3–8]. The 22% mortality for infants and children aged less than 5 years was relatively high but not dissimilar to early mortality rates of 17, 28, 35 and 36%, respectively, as previously reported for these age groups from major paediatric centres in Europe and USA [3,6–8]. The operative death rate in children older than 5 years was low, at 4.8%, with the only death occurring in a patient with complex congenital problems undergoing an emergency AVR and MVR.
Our operative mortality has decreased from 31% (5 out of 16) in the 80s to 3.7% (1 out of 28) in the 90s. Gratifyingly, this was the result of a dramatic reduction in the mortality between infants and children aged less than 5 years. From 1990, none of the six infants died early and the only early death among the 16 children aged under 5 occurred in a 3-year-old male following, again, an emergency repeat AVR and MVR.
Others [1,2,9,10] have recently reported mortality rates between 0 and 5% following mitral valve repair and/or replacement in infants and young children. Combined with these reports, our most recent experience suggests that mitral valve surgery (repair or replacement) in the first years of life is becoming increasingly safer. This is likely to reflect the improvements made in all aspects of peri-operative care of the paediatric surgical patients overtime.
As discussed earlier, with the exception of two children, we have used low profile bileaflet valves. Their haemodynamic performance has been good and the valve-related complication rate low. The thromboembolic rate in this series (0.9% per patient year) compares with previously reported rates of 0.7–2% per patient year [6,8,11]. Milano et al. [12], however, described a thromboembolic rate of 4% per patient year for mechanical MVR and 0.7% for MVR with bioprosthetic valves, reminding us that the use of bioprostheses may reduce but does not eliminate the risk of thromboembolism.
In this unit experience, PVE after implantation of mechanical valves in children has been uncommon. None of the 56 patients having an AVR between 1974 and 1999 acquired prosthetic valve infection [13]. The two patients who developed endocarditis in the present series were treated with repeat mechanical valve replacement. One made an uneventful recovery and the other required further re-interventions. We have previously reported low operative mortality and satisfactory late survival, but a high re-operation rate following surgery for infected heart valves in children [14].
Small annular sizes in the aortic position can be adequately managed with several aortic root enlargement manoeuvres and an adult-size prosthesis can usually be implanted [13]. A small mitral annulus cannot be enlarged and other techniques need to be employed. Supra-annular valve placement is one of the options and excellent [3] and poor results [15] following its use in small numbers of patients have been achieved. We used this technique only in one of our patients who died early.
Our preference is to use an inverted aortic prosthesis as this facilitates the implantation of usually a one size bigger valve. Six of the eight children receiving these prostheses remain well without having a re-operation at a mean follow up of 4.7±3.4 years (range 2 months–6 years). The other two patients required repeat MVR to replace their outgrown prostheses. The first had initially a 16 mm valve and 6 years later had a further MVR with a 21 mm valve. The second patient had originally a 19 mm valve and required two further MVRs, the first 6 years later with a 23 mm valve and the second in another 8 years with a 27 mm valve. The ability of the mitral annulus to grow, despite the implantation of a valve, allowing the insertion of a larger prosthesis at subsequent MVRs has been well-documented [16].
A difficult situation is a child with severe aortic and mitral annular stenosis requiring AVR and MVR. In two such patients we have divided the annular tissues at the point of the aorto-mitral continuity and inserted two valves in a ‘pair of spectacles’ like fashion. One of them died early but the second patient remains well free from repeat valve replacement 8 years later.
The 10-year freedom from a mitral valve-related re-operation of 75% (64% for any type of re-operation) was acceptable. Considerably higher or similar re-operation rates, depending on the age of the patients included and the type of prostheses used, following MVR in children have been described in previous studies [3,6,8,11]. Re-operation for replacement of an outgrown prosthesis was uncommon but, unexpectedly, two patients required early re-operations for the management of major complications caused by the insertion of oversized prostheses. Kadoba et al. [3] reported on 25 infants having a MVR with nine early deaths, five of which were due to the obstruction of the left ventricular outflow tract by the high profile tissue valves used in the 70s and 80s. Our two cases show that severe obstructive phenomena can occur with the low profile valves currently in use and extreme care in order to select an appropriately sized valve size should be exercised.
It has been suggested that modern low profile bileaflet valves are less thrombogenic and no anticoagulant needs to be prescribed [17], but such a policy resulted in a high incidence of severe thromboembolic events in one series [18]. We feel that the administration of Sodium Warfarin following the insertion of a mechanical valve in any position is essential if catastrophic complications are to be avoided. We appreciate the inconvenience and potential hazards associated with it but our experience with the use of anticoagulants after mechanical AVR and/or MVR indicates that provided adequate monitoring and follow up facilities are available, Warfarin in the paediatric age group is well tolerated [13].
The management of anticoagulation during pregnancy remains a problem. Warfarin may cause embryopathy and nervous system damage. The administration of long-term subcutaneous Heparin may provoke bleeding and its efficacy in preventing arterial thromboembolism is not established [19]. Sbarouni and Oakley [20] have in their survey across the major European specialist centres found that Warfarin treatment was safe and effective whereas subcutaneous Heparin was associated with more thromboembolic and bleeding complications. The outcome of pregnancy between women having mechanical and bioprosthetic implants was similar, but more than one third of the bioprostheses had to be replaced during or soon after pregnancy [20]. We do not have a strict policy as to the management of the anticoagulation in the childbearing women and believe that this should be best individualized to each patient circumstances.
The 10-year survival of 78% for all patients and 90.3% for those surviving their initial operation was encouraging. Ten-year survival rates reported from other centres range from 50–76% [6,8,11,12,21]. However, as these series cover a wide time-span, include patients of different ages and utilised a host of valve substitutes, comparisons should be undertaken cautiously.
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5. Conclusions |
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TopAbstract1. Introduction2. Patients and methods3. Results4. Discussion5. ConclusionsReferences |
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Acknowledgments |
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Footnotes |
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References |
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TopAbstract1. Introduction2. Patients and methods3. Results4. Discussion5. ConclusionsReferences |
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