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Ann Thorac Surg 2002;73:871-880
© 2002 The Society of Thoracic Surgeons
a Department of Surgery, Division of Cardiothoracic Surgery, Indiana University School of Medicine, Indianapolis, Indiana, USA
* Address reprint requests to Dr Turrentine, Section of Cardiothoracic Surgery, 545 Barnhill Dr, EM 215, Indianapolis, IN 46202, USA
e-mail: mturren{at}iupui.edu
Presented at the Thirty-sixth Annual Meeting of The Society of Thoracic Surgeons, Fort Lauderdale, FL, Jan 31–Feb 2, 2000.
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Abstract |
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Methods. From June 1990 through June 1999, 158 patients underwent either PTFE MO RVOT reconstruction (n = 115 patients; 120 implants) or nonvalved transannular repair (TA) repairs (n = 43 patients; 5 subsequent MO implants) at our institution. Standard MO construction techniques and TA repairs were utilized. Intraoperative, postoperative, and echocardiographic data with a mean interval of 2.6 years (range 6 months to 8 years) were used in retrospective fashion to compare clinical outcomes. In addition, PTFE monocusp valves beyond 6 months post-implant underwent echocardiographic analysis of MO function and durability.
Results. There were 4 early (MO-3, TA-1) and no late deaths. Overall, perioperative complications were not significantly different between MO and TA groups, nor were total hospitalization days (9.1 versus 10.7, p = 0.24). However, a significant difference in intensive care unit (ICU) utilization (3.6 versus 5.8 days, p = 0.03) favored MO patients. Patients with tetralogy of Fallot (TOF) and ventricular septal defect/pulmonary atresia (VSD/PA) undergoing the MO implant demonstrated a trend toward improved survival (p = 0.08) when compared to TA repairs. Intraoperative PI was graded mild in the MO group and moderate-severe in the TA group (p = 0.003). Progressive MO regurgitation occurred (mild-moderate) but remained significantly less than the transannular patch repairs (p < 0.05).
Conclusions. Utilization of a PTFE MO valve prevents short-term and significantly reduces midterm PI. It is inexpensive, easy to construct, and demonstrates no evidence of stenosis, calcification, or embolization. Despite longer cardiopulmonary bypass and ischemic times, it reduces ICU stay and, in both TOF and VSD/PA patients, decreases operative morbidity and mortality.
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Introduction |
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This was very much consistent with the experience at our institution. Patients undergoing a TAP repair, in contrast to those with valve-sparing procedures, were believed to exhibit a greater degree of early perioperative morbidity manifest by right ventricle (RV) dysfunction, low cardiac output, and inotrope dependence translating into prolonged ventilation requirements and intensive care unit (ICU) admissions. As a result, interest evolved around creating a competent post-repair RVOT in these patients. Animal studies in our laboratory confirmed previous reports that a competent monocusp valve could be constructed in the RVOT [7]. This led to our clinical use of a 0.1-mm polytetrafluoroethylene (PTFE) monocusp valve in hopes of improving early postoperative RV function in patients not amenable to pulmonary valve (PV)-sparing TOF repairs. Early results were encouraging and, within 4 months, the technique was all but universally adopted in this patient population. With ratification of the merits using this technique in TOF patients, it was then broadly applied to a variety of cardiac defects with RVOTO provided there was ample surface area allowing coaptation and closure of the RVOT by a mobile monocusp valve (MO) leaflet.
The purpose of this article was to review our experience and demonstrate the versatility of using the PTFE monocusp reconstruction technique in a variety of cardiac defects associated with RVOTO. The study also compares the clinical outcomes of TOF and ventricular septal defect/pulmonary atresia (VSD/PA) patients with MO implants with those undergoing TAP procedures. In addition, midterm characteristics and function of the PTFE membrane utilized as a monocusp pulmonary valve are reviewed.
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Material and methods |
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For more specific comparative analysis, patients in each cohort were partitioned into three subgroups based on similar RVOT features, operative risk, and associated comorbidity unique to the individual to the individual diagnostic groups (Fig 1). This was intended to limit patient variability and allow better comparative analysis of outcomes. TOF and PA/VSD patients were paired together (subgroup 1) because of similarity in both the RVOT anatomy and expected perioperative clinical course. Reoperation for RVOT conduit obstruction or insufficiency following previous repair (subgroup 2) included both valved and nonvalved grafts or patches (Table 1). Monocusp conduits replaced in the course of subsequent elective or staged cardiac procedures were also included in this group. By definition, to be classified in the third group (Subgroup 3), the defect had to exhibit either atypical RVOT morphology or present with a combination of defects demonstrating significantly different expected morbidity or mortality from either of the other two groups. Unfortunately, only Subgroup 1 provided a suitable size TAP cohort for statistical analysis.
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Data were collected retrospectively by chart review and, when necessary, patient or family interview(s). Information consisted of intraoperative and postoperative clinical as well as echocardiographic data. Echocardiography data, derived by continuous-wave Doppler flowmetry, were recorded from serial studies and used to assess postoperative pulmonary insufficiency. Evaluation of the MO valve’s competency and relief of pulmonary outflow tract obstruction included time after operation, RV systolic pressure, RV-PA gradient, tricuspid regurgitation, and pulmonary insufficiency. Echocardiographic assessment of the MO valve was reported only for patients beyond 6 months postimplant and PI was assigned numerical values (mild [1], moderate [2], severe [3]) for analysis. Echo follow up was complete in 65% of patients (102/158). This included 70% of the MO group (80/115) and 51% of the TAP group (22/43). Multivariate statistical analysis was performed using Microsoft Excel.
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Results |
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Of the TAP patients entered into the study, 5 (11.6%) underwent reoperation and placement of an MO valve either for complications related to RVOT stenosis or insufficiency, or elective conversion in subsequent operations for other cardiac pathology associated with PI. Five (4.3%) MO repair patients have undergone reoperation for staged procedures (2 patients), resection of an RV muscle bundle (2 patients), and closure of a residual VSD associated with MO PI in the remaining patient.
Clinical and echocardiographic follow-up was complete in 65% of patients (102 of 158). Echo data was available for a mean follow-up time of 2.6 years in the MO group (80 of 115; 70%) and 2.7 years in the TAP group (22 of 43; 51%). RV systolic pressures, RV-PA gradients, and the presence of tricuspid insufficiency (TR) were not statistically different between cohorts. There was a significant difference (p < 0.05) in the incidence of pulmonary insufficiency with only mild-moderate RVOT regurgitant flow in MO patients. Midterm postoperative echocardiography demonstrated mobile MO leaflets in 85% of patients (68 of 80) and reduced mobility in 15% (12 of 80). There was no RVOT obstruction or known thromboembolism related to the MO valve.
Subgroup 1: TOF—PA with VSD (Table 3)
When comparing patients with some form of simple PA/PS and VSD (including TOF), the study and control groups were matched with respect to patient demographics and preoperative hemodynamics. CPB (159.5 versus 123.1 minutes, p < 0.05) and aortic cross-clamp time (95.5 versus 64.8 min, p < 0.05) were significantly longer in the MO group. Unlike the overall group, MO patients in this subgroup also had a significantly increased ischemic time compared to those undergoing TAP repair (78.1 versus 58.8 minutes, p < 0.05). However, the ICU length of stay was significantly less in the MO group (3.9 versus 5.8 days). Their total hospitalization was also shorter by at least 1 day (9.8 versus 10.9 days) but was not statistically significant. All TAP patients requiring ECMO support, or exhibiting operative mortality, were in this subgroup. No patient in this MO cohort required perioperative ECMO support or died.
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Subgroup 2: conduit replacement (Table 4)
Patients in this group underwent monocusp valve insertion as a replacement of RVOT conduits (n = 23), previous transannular patches (n = 5), or MO repairs (n = 5). With exception of the MO patients in whom the reoperations have been previously described, all operations were due to recurrent RVOT obstruction or insufficiency associated with RV hypertrophy or dilatation. Unfortunately, because of having only 1 patient in the control group, no meaningful statistical evaluation could be performed. However, the resultant residual RVOT gradient and monocusp function is very similar to Subgroup 1 MO patients. Mean echo follow-up was only 1.8 years but the monocusp valve retained good function resulting in only mild-moderate PI, and there was no evidence of MO stenosis. No deaths occurred in this subgroup.
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PTFE monocusp function and durability
Virtually all PTFE monocusps were competent during the perioperative period (Fig 3).
Pulmonary stenosis or obstruction did not occur during the study period, and monocusp dehiscence was not observed (Fig 4).
However, there was a notable dissimilarity between the study subgroups with regard to progressive PI (Fig 5A). Both Subgroup 1 and Subgroup 2 patients exhibited preservation of monocusp function with only mild progressive PI throughout the observation period. Subgroup 3 had a higher degree of PI over time and approached moderate-to-severe levels, which was significantly different from Subgroup 1 (p < 0.05) but not Subgroup 2. No significant differences between diagnostic groups were noted in Subgroup 3 as all trended toward early progressive PI, perhaps with the exception of the TOF/Other group (Fig 5B).
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Comment |
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As a result, many reports have described methods of creating a competent pulmonary valve in the RVOT as a means of ameliorating this pathophysiologic process and enhancing early recovery of the RV, albeit with mixed clinical results [5, 13–18]. In 1967, the use of a cusp-bearing homograft patch was first described but unfortunately its use in children almost uniformly requires reintervention for structural valve failure or RVOT, often within a few years [14, 15]. Homograft tissue has limitations in that it is expensive and not readily available in all locations. This led some innovative surgeons to create methods of constructing a simple monocusp pulmonary valve from autogenous and prosthetic material. Techniques utilizing fresh autologous and gluteraldehyde-treated homograft pericardium, tensor fascia lata, xenograft pericardium, and silastic membrane were reported [19–25]. Unfortunately, these materials were fraught with early degeneration, and in some cases caused PS leading to variable clinical results and interest.
In 1993, Yamagishi and Kurosawa [26] and Oku and colleagues [27] independently introduced PTFE as a readily available material with good characteristics for monocusp valve construction when compared with the other materials. Our animal studies suggested that 0.1-mm PTFE material functioned as well as, or better than, fresh or gluteraldehyde-treated pericardium. Initial clinical application of this technique in TOF patients resulted in apparent improvement of perioperative RV function and the technique rapidly gained favor. It was then adopted in a wide range of RVOT obstructive and insufficiency defects.
Although our interest in the MO valve was for short-term postischemic recovery of the RV, ultimately, the durability of any style repair is likely to impact mid- to late-term patient outcomes. Chronic RV volume overload can lead to ventricular dilatation and reduced exercise tolerance, and appears to correlate with the degree of PI. Our own data with transannular repair TOF patients demonstrates a significant decline in right ventricular ejection fraction within 10 years of surgery from a baseline right ventricular ejection fraction of 0.52 to 0.45 (p < 0.01). At last follow up, 7 of those patients (33%) had an right ventricular ejection fraction of less than 0.42 (greater than 2 SD less than our laboratory normal) [28]. Echocardiographic analysis (unpublished) in a well-matched group of 17 TOF patients at our institution undergoing PTFE MO reconstruction demonstrates a normalization of RV size, function, and wall thickness at a mean follow-up of 26 months. These findings were consistent with our observation that MO patients, whose clinical courses were remarkably similar to those undergoing valve-sparing repairs, exhibited less complicated postoperative recovery when compared with those undergoing TA repairs.
In this report, the overall results suggest a clinical improvement in early perioperative outcome as judged by length of ICU stay and a trend toward decreasing need for ECMO support. The use and duration of inotropic agents, length of ventilation, and other morbidity variables are not specifically analyzed. Although earlier extubation has evolved in our overall practice, limitations on patient transfer from the ICU remained; the resultant length of stay reflected an indirect measure of these parameters relating to patient recovery and stability, as the care model exhibited little variance throughout the study period.
In contradistinction to some reports in the literature, our study suggests a beneficial effect of RVOT reconstruction with a PTFE MO valve. This appears most pronounced in Subgroup 1 patients (TOF and VSD/PA). When compared with the TAP control population, these MO patients did not require ECMO support and no deaths were observed. The control populations in Subgroups 2 and 3 were small and did not allow similar analytical evaluations. However, our data suggest that the PTFE MO functional characteristics observed with patients undergoing conduit replacements were similar to that of Subgroup 1 patients. The major exception is in Subgroup 3 patients in whom a more complex RVOT exists and this, in turn, might account for the decreased performance of the MO valve in the subset.
Assuming the PTFE monocusp is treated biologically the same, regardless of the cardiac defect, differences in function and durability appear to be the result of technical challenges imposed by the outflow tract into which it is constructed. In contradistinction to Nistal and associates [29], we found no calcification in the membrane but rather a well-vascularized layer of nonobstructive fibrocollagenous tissue incorporated within the PTFE with focal areas of endothelialization. As a result, the MO valve integrates with the RVOT patch to a variable degree. Fibrocollagenous incorporation of the monocusp leaflet is likely the cause of the observed progressive PI but, interestingly, there is no associated development of a thick obstructive peel or thrombus resulting in PS. In addition, we have not experienced MO valve structural disruption or embolization in any patient.
The PTFE material appears to retain a degree of functional durability, particularly in Subgroups 1 and 2, beyond the early postoperative period translating into favorable remodeling of the RV, at least in TOF patients. What remains unknown is how long the MO valve will remain functional and thus sustain this normalization of RV structure and function. Additionally, it remains unknown what impact, if any, there is on exercise functional capacity.
Previous reports in the literature suggesting inconclusive perioperative function and clinical benefit of a MO valve may reflect the challenges of free-hand construction or the material chosen for valve construction. In our series, reconstruction of the RVOT with a PTFE MO valve has proven to be a simple and reproducible technique demonstrating excellent early postoperative function with minimal PI. In addition, our results suggest a degree of early clinical benefit in patients reconstructed with an MO valve when compared with TAP repairs, particularly in those with TOF or VSD/PA. Unexpectedly, the PTFE MO valve has also been found to retain a moderate degree of competency at midterm follow-up in this group, as well as in those individuals undergoing replacement of a previous RV-PA conduit. As a result, we favor its use in these groups of patients. However, growth of the RVOT or eventual fibrocollagenous incorporation of the leaflet will likely limit mid- to long-term function. So, at this time, and with this technique, the PTFE monocusp should only be expected to retain adequate function in the short-to-midterm perioperative period.
Other patient groups with complex RVOTO deserve further consideration and, in some cases, might be better served with an alternative technique. For patients undergoing complete repairs in defects exhibiting an absent or anatomically distorted RVOT (ie, TOF/APV), significant peripheral pulmonary stenosis, or severe pulmonary hypertension, use of a biologic valve (or conduit), is our procedure of choice.
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Discussion |
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I have two questions, Dr Turrentine. The first question is: Do you think that your selection of the Gore-Tex monocusp has changed your cutoff for when you accept a pulmonary valve stenosis in a tetralogy patient? In other words, are you finding yourself using this more frequently now that you are happy with it and, say, not preserving a valve that you might have preserved 5 to 6 years ago? I guess one way to get a handle on that is, if you know, in what percentage of your tetralogy patients are you preserving the pulmonary valve?
The second question is: Are you impressed enough with this technique to apply the technology to, say, a patient that is undergoing a Ross operation and, instead of putting a homograft in, put in some sort of a Gore-Tex tube with a monocusp within it?
Again, I enjoyed your presentation very much.
DR TURRENTINE: Thank you for your kind remarks, Dr Backer.
I am very aggressive with sparing the pulmonary valve. Although I do not have the specific numbers, I think we are in the high 40% range of pulmonary-sparing procedures. My tendency is that if I get within 1 mm of a minus one zero value following a valvotomy, I will save the valve. Generally, I found, post-bypass, the gradient is somewhere less than 20 mm Hg. If it is higher than that, certainly if greater than 25 to 30 mm Hg, I will convert it to a monocusp. I have gotten away, more times than not, in saving the valve.
For the Ross procedure, I personally would stick with a homograft for the primary reconstruction at this point. We do have at least 1 patient that has been converted to a monocusp valve following degeneration of a pulmonary homograft. He developed pulmonary stenosis and was converted to a monocusp implant as described here.
DR SHUNJI SANO (Okayama, Japan): I congratulate you on your result.
I and many of the Japanese surgeons, now use the Gore-Tex monocusp patch to reconstruct the RV outflow tract, mainly because we cannot get homograft in Japan. We used to use a lot of different materials, but at present we believe that the Gore-Tex monocusp, the same one you use, would be the best material so far.
However, if my understanding is correct, you anastomosed the Gore-Tex monocusp directly to the right ventriclar myocardium. We make a monocusp patch to anastomose the Gore-Tex monocusp to either pericardial patch, Gore-Tex patch, or Dacron patch. This monocusp patch is used to reconstruct the RV outflow tract to the pulmonary artery. This makes the pulmonary valve, Gore-Tex monocusp, to place in the suitable position.
My first question is: If you anastomose the monocusp to the RV directly, then the monocusp may drop into the right ventricle, and not sit in a suitable pulmonary valve position; in this case, how can you manage?
The second question is: If you use the monocusp patch directly to the RV, then how do you create a suitable size of the right ventricular outflow tract, and how do you determine the size of the monocusp?
DR TURRENTINE: Thank you for your questions. Technically, one of the reasons we have not favored primary construction of the monocusp/outflow patch is the reported variable results with that technique. We thought that we could get more consistent results with conforming the monocusp to the RVOT. I think in the construction you have to complement what septum is there. And if you can leave some retained posterior leaflet to also have a little coaptation effect, that is helpful.
What we do is open up the right ventricular outflow tract as wide as possible and then put traction sutures at the annulus. In patients with pulmonary atresia, once you excise the atretic valve plate pulmonary valve, the annulus will open quite a little bit. You do have to do some tailoring of the muscle in the subannular region, but it opens up very much like a patient with pulmonary stenosis.
Then the monocusp has to be fit to the RVOT. There is a limit as to how much monocusp material you can place, but you have to be sure that you get a big enough opening that you will not create stenosis, and that has not been a problem with this technique. We think that constructing the monocusp in this fashion allows us to create one that complements the septum and the outflow tract, and this may be why we are seeing a high degree of competence, at least early on. But I think it is also critical to point out that we think this functions primarily by coaptation against the septum, and only secondarily with any retained leaflet tissue. So if you do not have decent septum to work with, you either have to move the monocusp up higher into the main pulmonary artery or do an alternative technique. Thank you.
DR CARLOS J. TROCONIS (Caracas, Venezuela): I would like to congratulate the authors for these results.
I have a brief comment about our results in Venezuela when we received older patients, about 3 to 5 years of age, usually in our public hospital. For many years, we used, as a routine in those babies, a transannular patch, but made in the OR with pericardium, with monocusp, or bovine pericardium and monocusp with porcine valve. We no longer use this technique because we found out, 2 years after, that all these monocusps in the pericardium or bovine disappear. And in using Gore-Tex patch, we will have some neointima formation and will create a pseudo-obstruction or a stenosis later on, after 2 years. So we are using the monocusp with pericardial patch just for the initial postop care because these patients do not tolerate well the PI, and with a less compliant right ventricle.
Thank you.
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