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Ann Thorac Surg 2004;78:1489-1495
© 2004 The Society of Thoracic Surgeons
a Department of Robotic and Minimally Invasive Cardiothoracic Surgery, St. Mary's Hospital, London, United Kingdom
* Address reprint requests to Dr Athanasiou, Robotic and Minimally Invasive Cardiothoracic Surgery, St. Mary's Hospital, 70 St. Olaf's Rd, Fulham, London SW6 7DN, UK
tathan5253{at}aol.com
| Abstract |
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| Introduction |
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Rheumatic heart disease is still the most common worldwide indication for mitral valve replacement, particularly in developing countries. Severe congenital malformation of the mitral valve affecting the subvalvular apparatus or leaflets is another important indication for mitral valve replacement. Patients who undergo stented mitral valve replacements require an organized postoperative anticoagulation program, the cost of which is often unaffordable in many Third World countries. These stented valves have also been associated with early degeneration and calcification, especially in young rheumatic patients [4]. Mitral valve homografts were thought to be the solution, but recent results have raised a question over their durability, especially in young patients [5].
Another approach to mitral valve replacement is the use of an inverted pulmonary autograft in the mitral position (Ross II operation). In 1967 Ross undertook this procedure instead of an aortic homograft. [6]. Encouraging long-term follow-up results of the initial patient series [7] has led to the technique being adopted by Kabbani and colleagues in Syria [8].
We reviewed the worldwide literature that reports on the use of the Ross II procedure. In this paper we present the historical perspectives behind the procedure, short-term and medium-term results, indications, and selection criteria for the operation. By doing this we hope to highlight its advantages and disadvantages.
| Historical Perspectives |
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In 1983 Yacoub and colleagues reported the largest available series of implanted aortic homografts in the mitral position by using the largest available sizes (25 to 30 mm in diameter) and fixing them inside a 35-mm Dacron tube with a collar [10]. In this late development of the operation, he covered the collar with autologous pericardium. This modification created a false floor into the atrium that was used to limit lateral distention of the conduit during systole. As a result the term top hat was born (Fig 2). Freedom from valve degeneration was 97% at 5 years and 48% at 10 years [10, 11].
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| Material and Methods |
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We defined the Ross II procedure as the implantation of a pulmonary autograft in the mitral position. We would like to clarify that studies that reported the implantation of aortic or pulmonary homografts in the mitral position were not included in our review. We considered the top hat to be a technical modification of the operation.
The information extracted from each publication that reported on the Ross II operation was: first author, operating period, type of the study, selection criteria, exclusion criteria, number of patients operated on, early mortality, major in-hospital morbidity, and medium-term follow-up. All studies that reported more than 5 cases are tabulated in Table 1. Care was taken to avoid the inclusion of articles that reported on the same patient population.
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| Results |
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Early Mortality
The procedure was performed in 103 patients with an overall in-hospital mortality of 7 (6.7%). In the first series performed by Ross, a mortality of 1 out of 8 was reported, with intraoperative bleeding as the primary cause [7]. In the second published series by Kabbani, mortality was reported as 4 out of 80, for varying reasons. The first patient suffered a major cerebrovascular event, the second developed acute respiratory distress syndrome, the third encountered intraoperative bleeding, and the fourth patient went into acute renal failure [22]. Finally, in the third series performed by Kumar, 2 patients died intraoperatively, the first was due to pulmonary edema and cardiac failure, and the second was due to intractable ventricular tachyarrhythmia [18]. It is worth noting that when the results from the three case series are combined, intraoperative bleeding was identified as the cause in three out of seven intraoperative deaths.
Perioperative Morbidity
Extraction of perioperative morbidity data was possible from the same three case series [7, 18, 22]. We identified the following nonfatal procedure-related complications among these 98 patients: perioperative myocardial infraction in 2 patients, low cardiac output in 3 patients (2 of which required an intraaortic balloon pump), perioperative bleeding in 3 patients, reexploration for bleeding or postpericardiotomy syndrome in 2 patients, and atrioventricular dissociation that required pacing in 3 patients. It is characteristic that the incidence for each of these complications is lower than 5%. In the two more recent series [18, 22], the length of stay for most patients was about 1 week.
Follow-up Data
Two recent series report on short-term and medium-term functional status after the Ross II operation. In the first [18], the 8 survivors were in New York Heart Association (NYHA) functional class I, with excellent autograft and homograft function at a follow-up of 2 to 20 months (mean 9 months). In the second report [22], echocardiographic follow-up confirmed excellent function of the pulmonary autograft in the mitral position with freedom of mitral stenosis and mitral regurgitation being 97% and 94%, respectively, at up to 36 months of follow-up (mean 25 months). Sixty-two patients remained in New York Heart Association functional class I-II during the follow-up period.
In the initial Ross series [7], 1 patient died 3.5 years after the operation. Mitral valve replacement for subacute bacterial endocarditis was required in 2 patients and for ruptured pulmonary autograft cusp in 1 patient. No late deaths or pulmonary autograft failure were reported in the series performed by Kumar [18]. In the largest and most recently published series by Kabbani [22], nine late deaths were reported. Of these 3 patients had subacute bacterial endocarditis, 1 had a paravalvular leak requiring reoperation, 1 patient developed delayed tamponade due to excessive anticoagulation, 2 patients died from undetermined causes, and 2 from causes unrelated to the procedure. In the same series, 2 patients developed progressive pulmonary xenograft stenosis during the follow-up period.
The late mortality for the procedure was 9% (10/103). Subacute bacterial endocarditis was identified as the most common cause of mortality or requirement for mitral replacement in the medium-term to long-term follow-up period. It is important to emphasize that long-term follow-up data for the Ross II procedure is fragmented and therefore has not yet been adequately evaluated.
| Surgical technique |
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The drawback of this modification is that it leaves the conduit uncovered in the left atrium, increasing the risk of thromboembolism because of exposure of blood in the left atrium to foreign material. This is particularly relevant in patients with atrial fibrillation, who are already prone to thromboembolic disease. In these patients a concomitant ablative procedure should be undertaken to complete the long-term benefits of the operation. In Kumar's modification, the stent from the thick Teflon (DuPont, Wilmington, DE) felt does not come in contact with the blood stream, and therefore this does not carry the previously mentioned thromboembolic risk. The shape and size of the Teflon felt can be fashioned on the table according to the autograft itself. The autograft sinuses are intact, and they are free to billow during valve closure.
In patients with congenital stenosis, the Dacron tube does not allow the annulus of the mitral valve to grow with the child. To counter this, Kabbani has described leaving the Dacron tube slit open along one or both sides. At this stage it is important to appreciate the tube and autograft do not need to be the same size (a 25-mm autograft can be inserted in a 28-mm Dacron tube). A "loose fit" will allow the new mitral substitute to function in a more physiologic way, with the autograft sinuses allowed to expand during systole. The impact of these technical modifications on the long-term outcome have yet to be addressed in the literature.
Our review identified three complications that could be directly attributed to the surgical technique. The first was autograft stenosis resulting from kinking of the Dacron tube in 5 consecutive patients early on in the relevant series [20, 22]. This was caused by the use a softer variety of Dacron as well as inadequate removal of the posterior subvalvular apparatus. The second was rupture of the pericardial collar that required reoperation in 2 patients in the early series of Kabbani [22]. The third was a disruption of the proximal suture line in one of the series by Kumar and colleagues [18].
An important finding is that all of these technical failures occurred early on in the relevant published series and had a significant impact in mortality. It therefore highlights the learning curve associated with this operation, which can be applied to each of the steps that comprise this procedure, namely, removal of the pulmonary autograft, construction of the new mitral valve, and the implantation technique.
Transesophageal echocardiography (TOE) should be undertaken preoperatively and intraoperatively to measure the size of the pulmonary autograft and the left atrium, evaluate the valve function, and to identify any clots in the left atrium. The important role of intraoperative TOE for the Ross II procedure has been highlighted in the biggest published study report on the procedure [22]. TOE was used in this study to identify graft stenosis in 5 patients and flail pericardial collar in 2 patients, all of whom required surgical re-intervention.
| Comment |
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Ever since the beginnings of mitral surgery, severe pulmonary hypertension and poor left ventricular function have been important risk factors for adverse outcome following mitral valve replacement [24, 25]. This risk is even higher when the right ventricular outflow tract also requires reconstruction during the procedure. For these reasons patients on whom the Ross II procedure is performed must be carefully selected, and those with significant aortic disease, endocarditis, severe pulmonary hypertension (> 80 mm Hg), severe mitral calcification, and severe left ventricular dysfunction should be excluded. Also previous cardiac surgery and pericarditis identified during the operation make harvesting the pulmonary autograft very difficult, and these patients should not be considered for the procedure.
Indications for the Ross II operation include women of childbearing age with mitral valve disease not suitable for mitral valve repair, young patients with contraindication to coagulation, and patients with unrepairable rheumatic mitral valves, especially in developing countries where anticoagulation is not preferable because of its cost and social implications. The operation can also be considered in pediatric patients with congenital mitral valve disease, who otherwise face life-long anticoagulation, and pregnant women who require mitral valve replacement.
Many attempts have been made to identify an ideal mitral valve substitute by seeking to take advantage of the features of autologous (fascia lata) or homologous tissue (human mitral homografts, aortic homografts, pulmonary homografts). A few surgeons have used fascia lata to reconstruct a thee-leaflet valve on a rigid frame, but the failure rate during the first 14 months after implantation has been significant. The use of mitral homografts to replace the mitral valve were successfully reintroduced by Acar and others [2628], but notably, this has been abandoned even by its promoters because of reports of inferior durability compared with other tissue valves [5].
The encouraging performance of the aortic homograft in the aortic position and the fact that upside down aortic valves can be used for mitral valve replacement motivated surgeons to start using inverted stented aortic and pulmonary homografts to replace the mitral valve [29, 30]. It has become evident that homografts (especially pulmonary) in the mitral position deteriorate earlier than when in the aortic position. Also, mounting of the homografts in a rigid stent or ring is associated with inferior durability [31]. The explanations for homograft failure include physiologic factors responsible for the vulnerability of the homograft under the high left ventricular closing pressure, factors related to the preservation technique, the additional negative feature of the rigid stent or mounting ring, and finally, the obstruction and systolic turbulence in the left ventricular outflow tract caused by the struts.
Young patients and pregnant women comprise a patient group in whom the results of mitral valve replacement with stented valves are not satisfactory [4, 32]. An adverse outcome after mitral valve replacement is also common in the young child. It has been reported that mitral valve homograft implantation is a safe and reproducible technique, but it does not provide durable results and should not be used in young patients. Similarly, other studies have identified young age as a risk factor for an early homograft structural deterioration (degeneration). Cumulative rates for freedom from reoperation for any cause in different age groups suggest careful selection and indications in homograft implantation in the younger patients [33]. Other reports emphasize the use of autografts in pregnancy [34, 35]. In pregnant patients, structural changes have been found at 5 years after placement of the mitral valve bioprosthesis. This may be attributed to the natural course of the bioprosthesis and thus may be independent of any direct effects of pregnancy [32].
More recently, implantation of bovine quadrileaflet stentless xenograft valves in the mitral position has been reported as another option. The implantation technique for this bovine quadrileaflet stentless xenograft mitral valve is more demanding, but the prosthesis is a promising alternative to conventional biologic mitral valve replacement. Midterm results after stentless mitral valve implantation are promising. Preservation of the annuloventricular continuity leads to stable left ventricular function and when combined with ablation therapy, to physiologic hemodynamics. Long-term durability however, remains unproven [36, 37].
Avoidance of long-term anticoagulation with the Ross II procedure has benefits for pregnant women, young patients, and patients in developing countries [3840]. Data have shown that anticoagulation with low-molecular-weight heparin alone is neither safe nor effective in preventing thromboembolic events after mechanical heart valve replacement. Thromboembolic prophylaxis of pregnant women with mechanical heart valves is best achieved with oral anticoagulation, although this carries an increased the risk of fetal embryopathy. Substituting oral anticoagulation with heparin between 6 and 12 weeks of gestation reduces the fetopathic effects but increases the risk of thromboembolic complications. Low-dose heparin use is definitely inadequate, and the use of adjusted-dose heparin warrants aggressive monitoring and appropriate dose adjustment [39, 40]. Large prospective trials to determine the best regimen for these women are not available.
The management of young patients with valvular heart disease is a difficult problem in developing countries [41, 42], almost all of these being of rheumatic etiology. In developing countries these patients are young, geographically dispersed, and socioeconomically deprived. Hospital attendance is erratic, and compliance with conventional anticoagulation is difficult. The function of mechanical heart valves is critically dependent upon adequate anticoagulation. Fixed-dose warfarin is associated with an increase in thromboembolic events, but no significant increase in mortality or hemorrhagic events, and thus may be an acceptable option where conventional anticoagulation is impracticable. The difficulty of adequate anticoagulation in a population where compliance is erratic and often nonexistent has previously been identified [43].
Mitral valve replacement with the Ross II procedure has advantages over other surgical options. It should be noted, however, that the structure of the replaced mitral valve cannot be compared with a normal mitral valve or a mitral homograft. The main advantages of the procedure are that the new valve is composed of living tissue, is competent, and anticoagulation with warfarin is required for only 3 months. The valve and its mountings are fully flexible, creating a physiologic structure that does not interfere with valve function. The valve lies only in the left atrium and for this reason does not impede the ejection of the left ventricle. Other advantages are that partial or total preservation of the mitral valve apparatus is possible and the procedure is suitable for young candidates.
The main disadvantage of the procedure is that its application requires the sacrifice of the right ventricular outflow. The operation is more technically difficult than standard mitral valve replacements, and there is concern about failure of two valves rather than one in the long-term. We should bear in mind that although the overall in-hospital mortality and morbidity were not increased with the Ross II procedure, fatal complications did occur and were closely related to the learning curve. Myocardial injury-related complications can occur as a result of the excision of the autograft (septal artery injury) and conduction disturbances or obstruction of pulmonary veins because of the suturing of the collar into the left atrium. Technically difficult reoperation and prolonged cardiopulmonary bypass time should both also be considered as disadvantages of the Ross II procedure.
Future development of the procedure
The Ross II is not a static procedure. Although the Ross I operation provided excellent results in all age groups, the complication of right ventricular outflow tract stenosis has not been seen in patients older than 50 years undergoing this procedure. This implies that it offers superior results for aortic valve disease in middle aged and older patients [44]. It follows, therefore, that the Ross II procedure may benefit the elderly patient in whom anticoagulation is associated with significant adverse events. Ablation procedures for chronic atrial fibrillation can be combined with the Ross II procedure to remove the need for anticoagulation in patients with mitral valve disease. Also, any long-term outcomes after the reconstruction of the right ventricular outflow tract can be improved with the use of CryoValve SynerGraft valves (CryoLife Inc, Kennesaw, GA) [45].
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The efficacy of the procedure has not yet been proven, and further evaluation of long-term follow-up is required. From the evidence available thus far, it seems that the procedure is a valuable alternative in low-risk young patients where the durability and complication rate of other available options (mitral homografts, mechanical and bioprosthetic valves) are still not satisfactory.
| Acknowledgments |
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| References |
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This article has been cited by other articles:
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T. Gudbjartsson, T. Absi, and S. Aranki Mitral Valve Replacement Card. Surg. Adult, January 1, 2008; 3(2008): 1031 - 1068. [Full Text] |
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S. Kabbani, H. Jamil, F. Nabhani, A. Hamoud, K. Katan, N. Sabbagh, A. Koudsi, L. Kabbani, and G. Hamed Analysis of 92 mitral pulmonary autograft replacement (Ross II) operations. J. Thorac. Cardiovasc. Surg., October 1, 2007; 134(4): 902 - 908.e7. [Abstract] [Full Text] [PDF] |
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