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Ann Thorac Surg 2003;76:1889-1895
© 2003 The Society of Thoracic Surgeons
a Division of Cardiothoracic Surgery, Department of Surgery, Atlanta, GA, USA
b Division of Pediatric Cardiology, Emory University School of Medicine, Atlanta, Georgia, USA
* Address reprint requests to Dr Kanter, Division of Cardiothoracic Surgery, Emory University School of Medicine, 1365 Clifton Rd, Atlanta, GA 30322, USA
e-mail: kkanter{at}emory.edu
Presented at the Thirty-ninth Annual Meeting of The Society of Thoracic Surgeons, San Diego, CA, Jan 31–Feb 2, 2003.
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Abstract |
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METHODS: From January 1998 to December 2002, 56 patients ages 1.6 to 29.9 years old (mean 11.8 years old) underwent RVOT reconstruction using a Freestyle porcine aortic root. The patients averaged 1.9 prior operations (range 0 to 5) for tetralogy of Fallot ± pulmonary atresia (28 patients), critical pulmonary stenosis (10 patients), Ross procedure (5 patients), pulmonary atresia/intact ventricular septum (4 patients), complete atrioventricular septal defect ± tetralogy of Fallot (4 patients), and others (5 patients). At time of RVOT reconstruction, 42 patients (75%) had additional procedures including the following: tricuspid or mitral repair (24 patients), pulmonary arterioplasty ± Glenn (12 patients), ventricular septal defect closure (5 patients), aortic valve replacement (3 patients), placement of a cardioverter/defibrillator or pacemaker (3 patients), and others (8 patients).
RESULTS: One patient developed mediastinitis; another was treated for Candida endocarditis (his excised homograft unexpectedly grew Candida). All patients are well on follow-up from 2 to 60 months (mean 30 ± 20 months) with no deaths. The patient with endocarditis underwent conduit replacement for recurrent pulmonary stenosis 3.5 years postoperatively. Echocardiography revealed mild or no pulmonary insufficiency in 93%. The calculated mean peak systolic RVOT gradient by echocardiography was 19.7 ± 15.4 mm Hg.
CONCLUSIONS: These data demonstrate excellent results with the Freestyle bioprosthesis for RVOT reconstruction in children. This valve may serve as a readily available alternative to homograft valves in RVOT reconstruction, particularly since early insufficiency seems to be less problematic. Questions of long-term durability and significance of echocardiographic stenosis remain unanswered.
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Introduction |
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Recently, the Medtronic Freestyle porcine aortic root (Medtronic, Minneapolis, MN) was introduced as a stentless valve substitute in the aortic position. We explored the utility of this particular valve for reconstruction of the right ventricular outflow tract in children, which forms the basis of this report.
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Patients and methods |
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| Dr Kanter discloses that he has a financial relationship with Medtronic, Inc.
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From January 1998 to December 2002, 56 patients ages 1.6 to 29.9 years old (mean 11.8 years old) underwent right ventricular outflow tract reconstruction using a Freestyle porcine aortic root. Fifty-five of 56 patients had previous cardiac operations (mean 1.9 operations per patient; range 1–5). The underlying diagnoses are illustrated in Table 1. The most common diagnosis was tetralogy of Fallot, with or without pulmonary atresia or double outlet right ventricle with ventricular septal defect and pulmonary stenosis. Forty-three patients had the Freestyle valve placed as a pulmonary valve replacement, whereas 13 patients had replacement of a valved right ventricular to pulmonary artery conduit. The indications for operation were typically pulmonary insufficiency with right ventricular dilatation or conduit stenosis. The indications for pulmonary valve replacement at our institution have been described previously [1]. At the time of right ventricular outflow tract reconstruction, 42 patients (75%) had additional procedures, which are presented in Table 2. The most common additional operations were tricuspid valve annuloplasty with a De Vega technique [2] or a pulmonary arterioplasty.
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The native pulmonary valve and proximal pulmonary trunk or the old right ventricular pulmonary artery conduit was excised in its entirety. If necessary, the proximal branch pulmonary arteries were enlarged either with autologous or bovine pericardium (11 patients) or had placement of an intraoperative stent (1 patient). The Freestyle valve was trimmed and then beveled distally. An end-to-end anastomosis between the distal Freestyle valve and the distal pulmonary trunk or the proximal pulmonary bifurcation was performed using continuous polypropylene suture. The posterior row of the proximal Freestyle valve was now anastomosed to the leading edge of the right ventricular outflow tract, again using continuous polypropylene suture technique. Typically it was necessary to place a hood of autologous or bovine pericardium between the right ventricular outflow tract and the anterior wall of the proximal Freestyle valve. This was necessary because the Freestyle root was somewhat short in length. An effort was made to tilt the valve plane more parallel with the pulmonary arteries in order to avoid compression of the valve with sternal closure. The valve sizes implanted are illustrated in Figure 1.
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Patient Follow-Up
All patients had periodic follow-up by his or her referring cardiologist. Routine echocardiograms were obtained when clinically indicated and the results reviewed for this study. No patient had routine postoperative cardiac catheterization. Routine anticoagulation or antiplatelet therapy was not used.
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Results |
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One patient developed postoperative mediastinitis, which was treated with muscle flap closure. Another patient developed Candida endocarditis. His excised homograft unexpectedly grew Candida from a culture taken in the operating room. Despite these two complications, all patients are well on follow-up from 2 to 60 months (mean 30 ± 20 months) with no late deaths. Only 1 patient has required reoperation. This was the patient who developed Candida endocarditis. He required conduit replacement for recurrent conduit stenosis 3.5 years postoperatively. The remaining patients are asymptomatic.
The most recent echocardiogram reveals that 51 of 55 remaining patients (93%) have no or mild pulmonary insufficiency (Table 3). The peak instantaneous systolic gradient as calculated by Doppler analysis plotted against the time interval from operation to echocardiographic examination is illustrated in Figure 2. The average peak instantaneous systolic gradient measured by Doppler echocardiography was 19.7 ± 15.4 mm Hg (median = 18 mm Hg). It does not appear that the gradient increases with time, although the average follow-up in this study was only 2.5 years. Although the majority of the patients had a widely patent pulmonary valve or conduit on two-dimensional imaging, there almost always was increased velocity across the outflow tract (Fig 2). In only 1 patient was this increased velocity felt to be of clinical importance. None of the patients has had a postoperative cardiac catheterization. The echocardiographic gradient on the most recent echocardiogram is also plotted against the age of the patient at time of Freestyle valve implantation in Figure 3. Younger children do not appear to have higher postoperative gradients in the follow-up period compared with older children. Furthermore, there were no statistically different differences in measured gradients between the different valve sizes.
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Comment |
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Experience with mechanical valves is limited and the results have been particularly disappointing with a high incidence of valve thrombosis [3–5]. For years, stented xenograft valves were the only widely available valve substitute for this clinical situation. Over time, it became clear that these valves were prone to premature deterioration and calcification [6] with actuarial freedom from reoperation at 5 years as low as 37% [7].
In view of the disappointing results with the stented xenograft valve, when homograft valves became widely available they became the valve substitute of choice and remain the "gold standard" at the present time against which other valves are to be compared. However, homograft valves also were found to deteriorate with time. Various series have reported actuarial freedom from reoperation at 5 years ranging from 74% to 85% [8–10], and freedom from reoperation at 10 years ranging from 54% to 69% [6, 8–10].
In view of the limited longevity of homografts, as well as the lack of uniform availability of required sizes, many groups have investigated substitutes other than homograft valves. Schlichter and his colleagues [11, 12] in Argentina have constructed a cleverly designed autologous pericardial valve for this use in children. Although they saw a freedom from reintervention at 5 years of 92% and at 10 years of 76%, they discovered that, in fact, the valvular portion of the conduit had disappeared by 6 months after operation. Effectively, therefore, all of the patients had free pulmonary insufficiency within a short time of implantation of the valve. This, of course, is a major drawback to the use of this valve in this patient set.
Recently, another alternative to the use of homograft valves for the right ventricular outflow tract in children has been the use of stentless xenograft valved conduits. Early experiences with the gluteraldehyde-treated stentless pulmonary xenograft Tissuemed valve (Tissuemed Ltd, Swellington, Leeds, UK) have been disappointing with a high incidence of conduit stenosis [13, 14] and a freedom from reoperation at 27 months of only 25% [15]. The Shelhigh No-React porcine pulmonary conduit (Shelhigh, Inc, Millburn, NJ), a different stentless xenograft valved conduit, has had variable results. Marianeschi and colleagues [16] reported 2 of 23 operative survivors requiring conduit replacement within 2 years of implantation. Pearl and his colleagues [17] reported an actuarial conduit failure at 12 months of 72%. The results with a third type stentless xenograft valve, the SJM Biocor (St. Jude Medical, Belo Horizonte, Brazil), were more promising with an 83% freedom from reoperation at 5 years [18].
The Medtronic Freestyle stentless porcine aortic root is a newer generation stentless valve. It is gluteraldehyde-fixed using zero pressure fixation. Importantly, it is treated with an antimineralization agent, alpha amino oleic acid (AOA), which has been demonstrated to reduce cusp calcification in animals [19]. The Freestyle valve has been reported to have excellent hemodynamic characteristics when used as an aortic valve replacement [20–22]. In spite of evidence that the Freestyle valve deteriorates quickly in growing pigs [23], others have adopted the use of the Freestyle valve for reconstruction of the right ventricular outflow tract in limited series with short but promising follow-up [24, 25].
With these studies in mind, because of its availability and the promise of delayed calcification in children due to the use of AOA, we used the Freestyle valve in 56 children as described in this report. Because, in the United States, the smallest commercially available Freestyle valve is 19 mm, we were unable to implant this valve in infants (we currently use cryopreserved homograft valves in smaller patients for whom a Freestyle valve would be too large). Nonetheless, we were able to use the valve in 22 children under the age of 10, including 12 patients under 5 years old (Fig 1) who were as young as 1.6 years old. Furthermore, in this series, the Freestyle valve was basically used in children undergoing cardiac reoperation (only 1 child who had undergone balloon valvuloplasty for critical pulmonary stenosis as an infant did not have a previous sternotomy). With the current emphasis in most busy congenital heart centers toward early total repair, valved reconstruction of the right ventricular outflow tract during primary repair of the heart defects are at a younger age and smaller size. With the lack of sizes smaller than 19 mm, the Freestyle valve has not been appropriate in these infants. Basically, we have reserved the use of the Freestyle valve for older children who are undergoing reoperation. In the future, if smaller sizes become available, we will most like extend the use of the Freestyle valve to infants undergoing primary repair of their heart defects, particularly since it has become increasingly more difficult to obtain appropriate sizes of smaller cryopreserved homografts.
An important characteristic of a valve for use in the right ventricular outflow tract in children is ease of implantation. Because the Freestyle valve is a porcine aortic root fixed with gluteraldehyde, it is somewhat thick and stiff to work with, particularly when compared with a pulmonary homograft. On the other hand, the small strip of Dacron cloth attached as a sewing ring at the proximal end of the valve facilitates the proximal anastomosis to the right ventricular outflow tract. It also tends to reduce the risk of mechanical distortion of the valve itself with the subsequent early development of significant pulmonary insufficiency. In our series we have found it useful to add a roof of autologous or bovine pericardium anteriorly from the right ventricle to the proximal Freestyle valve. This maneuver both adds length to the conduit as well as tilting the valve itself more posteriorly in the chest to avoid distortion with sternal closure.
As with any implanted heart valve, hemodynamic performance is important. In our study we found that 93% of patients on follow-up had mild or less pulmonary insufficiency (Table 3). This compares favorably with the homograft valve. A previous study from our institution revealed that homograft valves had a 28% incidence of moderate or severe pulmonary insufficiency on echocardiographic follow-up [1]. Albert and his colleagues [26] reported a similar incidence of pulmonary insufficiency.
The magnitude of the transvalvular gradient is also an important consideration when evaluating the hemodynamics of valves for right ventricular outflow tract reconstruction. In this series the average peak systolic right ventricular outflow tract gradient calculated by Doppler echocardiography was 19.7 ± 15.4 mm Hg (Fig 2). This compares with an average peak echocardiographic gradient of 15.3 ± 5.2 mm Hg at 3-year follow-up of Freestyle valves implanted in the aortic position (19-mm valves were excluded) in a study by Baur and associates [20]. This value corresponded to a calculated echocardiographic mean gradient of 5.1 ± 3.5 mm Hg. It has been demonstrated that the peak instantaneous systolic gradient calculated by Doppler echocardiography overestimates the "true" gradient measured at cardiac catheterization [27]. Echocardiographically, the mean transvalvular gradient rather than the peak systolic gradient more closely corresponds to the systolic gradient found at cardiac catheterization. Although we did not calculate the mean echocardiographic gradient in the majority of our postoperative echocardiographic studies, one may extrapolate, from Baur's data, the presumed average mean gradient across the Freestyle valves in the pulmonary position is less than 10 mm Hg. Because none of our patients had postoperative cardiac catheterization, this is only an assumption.
It is reassuring that, to date, only 1 patient has required valve or conduit replacement. This patient had evidence of an indolent Candida infection at the time of Freestyle implantation. His excised stnotic homograft unexpectedly grew Candida. Candida endocarditis developed in the patient postoperatively, which was treated. He eventually required a pulmonary valve re-replacement 3.5 years postoperatively (his fourth pulmonary valve replacement). Only one of the remaining patients in our series has a clinically significant gradient despite the echocardiographic findings. Of course, with an average follow-up of only 30 months, it is too early to make a definitive statement about these gradients. We cannot yet determine if the hope with the Freestyle valve of delayed onset of calcification and restenosis is real when the valve is implanted in the pulmonary position.
Additionally, the Freestyle valve does have the desirable characteristic of low thrombogenicity, which allowed us to forego the use of anticoagulation or antiplatelet agents in this series without evidence of thromboembolic complications. The cost of this valve, at least in our institution, is similar to that of other bioprosthetic and mechanical valves, and slightly less than homograft valves, which in the current era can be of some consideration.
In all, we have found that the Freestyle porcine aortic root can be implanted in the pulmonary position in children with good clinical results. Operative and late mortality in our series was zero. There was only 1 patient who required conduit replacement. On follow-up of 2.5 years, there appears to be reasonable hemodynamic function of the valve. Due to the natural history of other valves used for this indication, long-term follow-up of these patients is mandatory. The appropriate time frame for determining the usefulness of a successful valve in this position is in the order of 10 years.
In the future, however, there are other valves on the horizon that may also be substitutes for the homograft valve. There are some promising results using a bovine jugular vein as a valved conduit with promising short-term results [15, 28]. There was even a report of successful percutaneous placement of this valve in 7 children and 1 adult [29]. Other potential valve replacements on the horizon are synthetic polyurethane valves [30] and decellularized homograft valves (Synergraft; CryoLife, Inc, Kennesaw, GA) [31]. Clearly, as time goes on, we will be able to determine if the Freestyle porcine valve (or any of the previously mentioned valves) will have satisfactory durability and hemodynamic performance to supplant homograft valves in reconstruction of the right ventricular outflow tract in children.
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Discussion |
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TopAbstractIntroductionPatients and methodsResultsCommentDiscussionReferences |
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I have one general question. For homografts, it appears that durability and longevity of the homograft in the right ventricle to pulmonary artery (RV-to-PA) position is favorable in the setting of orthotopic implantation, as in a Ross procedure, for example, as compared with the durability when it's used as an extracardiac conduit. I was a little bit unclear. It seemed that you used this in a sort of a hybrid mode with some of the characteristics of an extracardiac conduit, using the ascending aorta of the root to anastomose directly to the pulmonary artery confluence, but trying to put the valve in an orthotopic site with a proximal extension. Have I pictured that right? And is it more of an orthotopic implantation or more of an extracardiac conduit, and do you think that will have any bearing on its long-term durability?
DR KANTER: For the majority of the patients it was orthotopic. However, in the patients who had a previous right ventricular to pulmonary artery conduits with a right ventriculotomy, we placed it at the old right ventriculotomy site, so it was an extracardiac position. For more than three-quarters of our patients it was in an orthotopic position. We found that an extension hood was necessary to prevent it from being compressed because the valve is short.
DR WILLIAM M. NOVICK (Memphis, TN): With regards to the size valve that you implanted in these children and the stenosis that was noted on some of your children, did you correlate the Z-value for the overimplantation size with the gradients in any of those children? That's one. Two, from your echocardiographic analysis, were you able, to determine whether or not those children that seemingly displayed a gradient manifested any annular shrinkage?
We have used this valve exclusively in our International Ross patients and have similar results to yours, excellent hemodynamic performance, but have noticed some annular shrinkage in these children over time, now almost at 4 years, and the same gradients that seemed to have developed in your group.
DR KANTER: We did not specifically look at the annular shrinkage, so I cannot comment on that. As far as Z-value is concerned, we always try to oversize the valve. So at no point did we put in a valve that was actually appropriate for the patient. It was always oversized, unless they were adult-sized, in which case it was the appropriate size. So the Z-score for these valves would always be positive, one or two standard deviations from the normal, in hopes of preventing the child from outgrowing the valve.
DR JACOBS: Kirk, have you used any of these for aortic root reconstruction in children, and what are your thoughts with respect to calcification and durability and applicability in that setting?
DR KANTER: Well, as with other congenital centers, we prefer the Ross procedure. If the pulmonary valve is not available, then we will use a homograft, or if the family desires a mechanical valve. So it's uncommon that we would use a Freestyle valve. We have only used one Freestyle valve in the aortic position, and that went well, but we can't really make conclusions based on 1 patient.
DR PEDRO J. DEL NIDO (Boston, MA): Kirk, just to follow up on the calcification issue, because that has been the objection to using porcine or bovine valves, have you looked for calcification by plain roentgenogram or fluoroscopy in these patients?
DR KANTER: No, we don't typically look for calcification in the outpatient setting. The one valve that was excised was not calcified. Supposedly one of the advantages of this valve is the alpha amino oleic acid (AOA) treatment, which retards calcification, but time will tell if that's true or not.
DR DEL NIDO: I think that will be important information as you follow these kids long-term because calcification continues to be a nagging issue. The other question is, in a center like yours with experience in magnetic resonance imaging (MRI), what do you see is the role of MRI in both the short-term and long-term management of these patients. In other words, decisions about size of valve, which patients have aneurysms, whether the indications are regurgitation versus conduit stenosis?
DR KANTER: In our institution, we use the MRI as the trigger as to whether or not to operate in children with predominantly pulmonary insufficiency. If the right ventricular volume to left ventricular volume ratio is greater than 2, then that's our indication for operation. A lesser indication is the development of tricuspid regurgitation, presumably reflecting right ventricular dilatation. For pulmonary stenosis we use gradients, but because we're suspicious of the gradients we get on echocardiogram, we often confirm that with a cardiac catheterization.
DR JACOBS: With the exception of the neonates for whom you found this inapplicable because of size limitations, what percentage of your right ventricular outflow tract valved reconstructions during this time period is represented by this patient cohort?
DR KANTER: Early on in our experience we used it less commonly, particularly with children who required pulmonary artery work, because the pulmonary homograft lends itself so well to enlarging the branch pulmonary arteries. As we have the high incidence of early pulmonary insufficiency in homografts, we have started using it more and more, and now for an appropriately-sized child, it has been 100%.
DR JACOBS: Thank you.
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