What’s Known

In most medical centers, biological valves and allografts are the first line of treatment for pulmonary valve replacement. However, the long-term outcomes are not promising.

What’s New

Our intraoperatively created autologous pericardial valve has a trileaflet shape and functions similarly to biological valves. However, due to its native tissue, it is unlikely to have an immune host versus graft reaction similar to biological valves.

Introduction

Despite the acceptable midterm outcomes of the surgical correction of tetralogy of Fallot (TOF), its long-term prognosis is influenced by a gradual increase in pulmonary regurgitation (PR). This gradual increase leads to right ventricular overload, dilatation, and dysfunction, which are the major causes of exercise intolerance, arrhythmia, and death. These events may also occur in less common cases of long-standing PR due to other causes. ^{1 , 2}

Currently, no optimal valve has been established for pulmonary valve replacement (PVR), and an increasing proportion of young patients with previously repaired TOF require repeated procedures due to malfunctioning valves. The use of bioprosthetic valves is preferred due to the absence of bleeding and thrombosis, which are prevalent with mechanical valves. Nonetheless, they are vulnerable to uncontrollable structural valve degeneration (SVD), which is presumed to be enhanced by immunological responses. The evidence suggested that SVD proceeds more rapidly at younger ages, making the youth, as the target population of the present study, prone to accelerated valve destruction. ³ Although various options, such as the construction of valves using synthetic patches, have been proposed, none of them have shown constant success rates.

The present study aimed to introduce a novel, intraoperatively manufactured valve, called the “AAA valve” in this center, referring to the initiatives of the innovator. In this study, we precisely described our novel technique and reviewed the clinical, echocardiographic, and cardiac magnetic resonance imaging (CMR) findings of the patients’ valves.

Patients and Methods

This case series was conducted consecutively on patients who required PVR from September 2018 to March 2021. For all redo PVR patients, the decision to perform PVR was based on their clinical, echocardiographic, and CMR findings, as needed. ⁴ The concomitant procedures included the closure of ventricular or atrial septal defects, tricuspid valve repair, pulmonary artery (PA) repair, and right ventricular remodeling. The study included children, adolescents, and adult patients, as well as cases who had previously undergone surgery to address TOF and non-TOF diseases.

Our novel valve, which comprises native pericardial tissue in a trileaflet configuration inside a small Dacron tube at the pulmonary valve position, has two distinct advantages. First, it eliminates the risk of immunological incompatibility. Second, it has a typical tricuspid shape and function.

All patients underwent regular transthoracic echocardiography every three months after AAA valve insertion, in accordance with established guidelines, using M-mode, two-dimensional, Doppler, and color Doppler techniques. The employed echocardiographic parameters were the AAA valve diameter, z-score, pressure gradient, vena contracta, and vena contracta/annulus diameter ratio. To determine the intensity of PR, the valve annulus/vena contracta ratio was measured, and ratios of <5%, 5-10%, and >10-20% were considered trivial, mild, and mild to moderate, respectively. CMR was performed for five volunteer patients with more than two years of follow-up to evaluate changes in the AAA valve morphology and the function of leaflets in a longer period following the procedure. The quality, shape, and function of the valves were observed, as well as anatomical data, such as geometric height (gH), coaptation height (cH), and effective height (eH).

Surgical Technique

A standard technique was developed for all patients to construct uniform 22-mm trileaflet valves using native pericardium. As the right ventricular outflow tract (RVOT) was opened, and a transannular patch was used in the first operation for the majority of patients, there was no real annulus. Therefore, the valve was created by constructing a trileaflet configuration inside a Dacron tube (length, 20 mm; diameter, 22 mm) (appendix 1: Supplementary video). All operations were performed with a midline sternotomy. After releasing the adhesions, the pericardium was harvested and treated, and the AAA valve was constructed before cardiopulmonary bypass. During the bypass, the constructed valve was then placed and sutured into its position in RVOT. For myocardial protection, the cardioplegic Custodiol solution was utilized (HTK solution; Dr. Franz Köhler Chemie GmbH, Germany).

Pericardial Harvesting

A quadrangular piece (20×82 mm) of the pericardium was required for harvesting. Since most of the patients had undergone previous operations, it was crucial to find a large suitable piece of the pericardium, which was typically available either on the left side or inferiorly attached to the diaphragm. If an appropriate piece of the pericardium was not available, the AAA valve formation would be stopped and conventional mechanical or bio-prosthetic valves would be used, as reported in 20% of scheduled cases.

The fibrous tissue, fat, and areolar tissue were gently removed from both sides of the harvested pericardium using a sharp dissection. The cleaned pericardium was then treated with a 0.625% glutaraldehyde (GA) solution for 10 min, followed by three stages of cleansing in normal saline, each for 6 min. Following treatment, the pericardium should be trimmed to its exact final size. A premade metal template was used to pull over the patch and cut around it (figure 1a). This template and all other specific equipment required for this procedure were designed by an innovative surgeon in our center. Subsequently, Adrian Machine Co. (AAA Valve Set, Adrian Machine Co., Shiraz, Iran) produced the equipment and made it commercially available.

Figure 1. Preparation of the pericardium and the primary steps of valve construction: A) The treated pericardium is cut precisely around the template (20×82 mm). The template is rough to prevent the movement of the pericardium during cutting. B) The tubed pericardial strip is slid over an 18-mm Hegar sizer tip. The Dacron tube is then gently slid over both the sizer and the pericardium. C) The pericardium is inside the Dacron tube and over the Hegar sizer. The edges of both the pericardium and Dacron tube are stitched together at one end with a continuous 5/0 Prolene suture. This suture line denotes the annulus of the new valve.

The length of the pericardial patch was calculated using the tube diameter and the tricuspid structure of the valve. In a 22-mm trileaflet valve, the sum of the free margins of leaflets was almost equal to the annulus circumference (22 π mm). The circumference was multiplied by 1.2 to compensate for the suture lines and provide a firm coaptation. Therefore, the length of the pericardial patch was about 82 mm for the 22-mm Dacron tube.

Construction of the AAA Valve

The two ends of the pericardial strip were sutured together with a 6/0 Prolene suture to construct a tube. This pericardial tube was then placed within a Dacron tube (length, 20 mm; diameter, 22 mm), and its borders were sutured together with a 5/0 running suture at one end to create the annulus. For this purpose, both tubes were placed over an 18-mm Hegar’s dilator, which made suturing much simpler and more regular (figures 1b and 1c). To achieve a lengthy commissural height, the Dacron tube was cut at a length of 20 mm. The commissural height, which was equal to the width of the pericardial patch and the length of the Dacron tube, was 10% shorter than the diameter of the valve itself (22 mm), which made the geometrical height (GH) of the cusps 4 mm longer than that of normal aortic valve cusps (16 mm) (figure 2).

Figure 2. The anatomical shape and characteristics of the AAA valve were compared to the average normal semilunar valve. A) The normal aortic valve and B) the AAA pulmonary valve; cH: Coaptation height; eH: Effective height; gH: Geometric height; STJ: Sinotubular junction

Subsequently, the three commissures of the valve were prepared by stitching two layers of the Dacron tube and the pericardium in three symmetrical straight longitudinal lines along the tubes. The geometry and symmetry of valve leaflets, as the most crucial parts in the valve formation process, were assured by an innovative triangular divider instrument to divide the tube into three equal segments from inside (figure 3a). The pericardium and the Dacron tubes were gently slid over the triangular divider, and symmetry was examined and adjusted by fine movements of the free edge of the pericardium inside the Dacron tube. Then, a commissural suture was performed by suturing the two layers together at the free edges and extending toward the annulus at each specified commissure. The groove designed on the edge of the device blades allowed the suture needle to take the full thickness of both layers while suturing the commissures (figure 3b).

Figure 3. Construction of commissures: The Dacron tube (outside) and the pericardium (inside) are slid over the designed triangular divider (AAA Valve Set, Adrian Machine, Iran) to divide the circumference into three equal segments. A) A fine adjustment is performed by slightly moving the pericardium to make sure that the segments are symmetrical. B) The commissures are made by suturing the tip of the pericardium to the Dacron tube over the device blade and continuing by oversewing toward the annulus. The needle passes through both layers at full thickness because of the groove on the edge of the blade. The last suture line, which converts the pericardial strip to the pericardial tube, is set at one of the commissures to leave the moving cusps free of the suture line. C) The valve tube is tested by applying mild negative pressure. A 20-mm syringe tube connected to a normal suction device can simply create negative pressure. The geometry and symmetrical coaptation are examined carefully, and fine adjustments are performed if needed. The three commissural sutures are 1 mm apart from the Dacron tube to simplify diastolic closure. D) The valve is positioned in the RVOT and tested after partial coverage by a separate Dacron patch.

Finally, three single commissural stitches, which were 1 mm apart from the Dacron wall, were used to facilitate the closure of cusps during diastole. The valve was ready to be tested by connecting the valve tube to a 20-mL syringe cylinder, attached to a vacuum suction with a mild negative pressure (figure 3c). The geometry, symmetry, central coaptation, and coaptation height (CH) were also investigated. In our experience, the effective height, measured by Schafer’s caliper, was about 14-15 mm in these valves, which provided an adequate coaptation surface with a good reserve if some shortening of the cusps occurred over time. Finally, the AAA valve was ready to be implanted. The treatment of the pericardium took approximately 28 min, and the valve construction was typically carried out in 30-40 min.

Valve Placement in the RVOT

As soon as the valve was prepared, cardiopulmonary bypass was initiated, and the RVOT was opened during cardioplegic arrest. The RVOT was exclusively dilated, and there was enough space for positioning the valve. The valve was then placed in a way that the distal end would be exactly proximal to the PA bifurcation. Commonly, the RVOT and PA wall cover two-thirds of the posterior circumference of the valve, and a separate Dacron patch should cover the remaining anterior one-third. The proximal and distal ends of the valve tube were sutured to the corresponding locations in the RVOT, PA floor, and lateral walls with a 5/0 Prolene suture, sparing the anterior one-third. The sutures were carefully pulled to avoid causing a purse-string effect by pulling the sutures intensively. Next, the anterior Dacron patch was sutured to cover the RVOT with the valve inside.

Suturing was initiated from the distal end of the pulmonary arteriotomy incision and continued on both sides. When the suture lines reached the distal end of the valve, they were folded back, and the distal Dacron tube edge was transversely sutured to the fold. This procedure was repeated once the lateral suture reached the proximal edge of the valved Dacron tube. At this stage, the valve was tested in place by injecting water into the PA (figure 3d).

Subsequently, coaptation was checked, as well as the configuration and symmetry of cusp movements. The procedure was finished by suturing the proximal end of the anterior Dacron patch to the right ventriculotomy incision. To prevent hematomas between the valve and the patch, a small hole might be created in the Dacron on-lay patch. Cardiopulmonary bypass was then terminated as a routine procedure. The patient’s postoperative care was similar to that of other PVR patients, and warfarin was administered for anticoagulation in the first 3 months, followed by long-term aspirin therapy.

Ethical Statement

All the procedures of the present study were performed in line with the ethical standards of the Research Ethics Committee of Shiraz University of Medical Sciences (code: IR.SUMS.MED.REC.1399.510) and were in accordance with the Declaration of Helsinki (1964) and its later amendments. Additionally, written informed consents were obtained from the patients or their legal representatives.

Statistical Analysis

The patient’s demographic, clinical, and paraclinical data were analyzed using IBM SPSS software, version 21.0 (SPSS Inc., Chicago, IL, USA). Continuous demographic characteristics were expressed as range and mean±SD or median and interquartile range (shown in parentheses). Besides, Friedman and Correction Bonferroni post hoc tests were used to compare the average peak pressure gradients and valve stenosis changes during follow-ups. P<0.05 was considered statistically significant.

Results

During this study, surgery was performed on 10 patients, including nine patients with a previous operation (total correction of TOF for seven patients and pulmonary valvectomy for two patients) and one patient with no history of cardiac surgeries.

The mean age of the patients at the time of surgery was 16.20±5.81 years, and the mean interval since the last surgery was 11.62±6.03 years. The mean and median follow-up duration were 32.30±13.64 and 33 (20.50) months, respectively (table 1), with a follow-up index of 1 (0.11).

There was no valve thrombosis, and none of the patients required re-intervention. The participants’ operative and postoperative hemodynamic data are summarized in table 1.

The mean bypass time was 73.9 min, and the aortic cross-clamp time was 58.5 min. The mean duration of the AAA valve creation was 73 min, including 28 min of GA treatment. Table 2 presents the echocardiographic findings early after surgery and two years later.

All patients exhibited none to mild PR early after surgery and no to mild progression during follow-up. The early postoperative degree of AAA valve regurgitation was none/trivial in five cases and mild in five cases (table 2). Eight patients (90%) had none to mild pulmonary stenosis (PS) early after surgery, with no progression during the follow-up period.

Patient no. 5 developed mild to moderate PS early after surgery and showed no progression during the follow-up (figure 4). In this patient, echocardiography revealed mild motion restrictions of the cusps and partial stenosis at the supravalvar level. It was unclear whether this was due to technical problems or the unlikely early degeneration.

Figure 4. The comparison of the average peak pressure gradient of the AAA valves in three follow-up sessions: 1 to 6 months after surgery, 1 to 2 years after surgery, and the last follow-up. F/U: Follow-up

Patient number 9 in table 2 died in the second month after surgery as a result of a non-cardiac disease, although having a satisfactory AAA valve performance.

According to figure 4 and Friedman test results, a significant difference was observed between the average peak pressure gradient of the three measured times (P=0.045). According to the correction Bonferroni post hoc test, this difference was due to the significant difference between the average peak pressure gradient of 3-4 years (28.33±9.96) with the average peak pressure gradient of 1-2 years (25.49±10.23) and 1-6 months (23.94±11.21). However, there was no significant difference between the average peak pressure gradient of 1-6 months and the average peak pressure gradient of 1-2 years (P=0.289).

According to table 2 and Friedman’s test results, a significant difference was observed between the average tricuspid annular plane systolic excursion (TAPSE) of the three measured times (P=0.002). Bonferroni’s corrected post hoc test revealed that this difference was due to the significant difference between the average TAPSE for 3-4 years (19.59±3.39) and the average TAPSE for 1-6 months (16.08±2.73) (P=0.001). However, there was no significant difference between the average TAPSE of 1-6 months (16.08±2.73) and the average TAPSE of 1-2 years (17.97±3.30). Furthermore, there was no statistically significant difference between the average TAPSE between 1-2 years and 3-4 years (P=0.124).

CMR was performed for five volunteer patients with a follow-up period of more than 24 months to better evaluate the changes in the structure and function of the AAA valves (table 3, figures 2, 5, and 6).

Figure 5. The figure shows the cardiac magnetic resonance imaging of the AAA valve.

Figure 6. The final in vitro shape of the AAA valve is illustrated.

The mean pressure gradient estimated by CMR was 19.69±10.95 in these five patients, which was lower than that estimated by echocardiography at the same time (25.60±19.30 mmHg). CMR-reported regurgitation was classified as trivial in three cases, mild in one case, and mild to moderate in one case, which was almost identical to the echocardiographic findings. The anatomic parameters on CMR were compatible with the technical values of AAA valve formation, as the mean gH was 19.6 mm, the mean cH was 10.2 mm, and the mean eH was 14.5 mm.

Discussion

The selection of a valve type for PVR following the repair of congenital heart defects, especially TOF, is still challenging. This study utilized a novel technique to construct a valve inside a short Dacron tube. The valve was subsequently placed into the pulmonary valve position. This study used a Dacron tube (22 mm in diameter), which could be employed for most children and young adults without valve-patient mismatch. In this study, a valve was developed using the patient’s tissue during the operation. This valve, which was made by a simple and quick method, has a trileaflet function similar to biological valves; nevertheless, it is unlikely to have an immunological host against graft reaction.

Although biological valves and allografts are the first choice for PVR in most medical centers, the long-term outcomes are not promising enough. In a study on 227 patients, the rates of freedom from reintervention and SVD were 94% and 74% in a mean follow-up of five years, respectively. ⁵ Moreover, a meta-analysis of studies on 3,118 patients with PVR found that nearly 5% of patients required another PVR within five years. ¹ As indicated in the majority of studies, the overall outcomes of biological valves and allografts were not significantly different. Nevertheless, younger age and a smaller valve size were associated with an increased risk of valve re-intervention. ^{6 , 7}

Additionally, in a mixed population of children and adults undergoing different types of PVR, the rate of freedom from valve replacement was estimated at 81%, 58%, and 41% within 5, 10, and 15 years, respectively. ⁸ Furthermore, long-term immunological rejection of foreign organic tissue might result in limited durability of these valves. ^{3 , 9} Although mechanical valves have the advantage of long-term durability, the risk of thrombosis and complications of lifelong high-dose anticoagulation make them less appropriate, particularly in the pulmonary valve position. Sadeghpour and colleagues found that 18% of patients (n=38) with metallic PVR showed prosthesis malfunction, two of whom underwent redo PVR after a median follow-up of one year. ¹⁰ Furthermore, more than 20% of the patients developed moderate or severe PS or PR, ¹¹ while none of our patients experienced more than moderate PS or PR.

The higher rates of early biological valve degeneration and SVD at younger ages raise major concerns, as adolescents account for the vast majority of TOF patients who require PVR. Tissue engineering for the decellularization of xenografts has recently been used to improve the remodeling of xenogenic heart valves. A study on porcine heart valves for the biocompatibility assessment of valves, implanted in the orthotopic pulmonary valve position of young pigs, showed a small thrombus and calcification in the leaflets 3 months after placement. ¹² Another study, conducted on three leaflet valves with a decellularized pericardial patch placed in the aortic valve of three juvenile sheep, showed minimal PR and minimal calcification of the leaflets 6 months after placement. ¹³ However, further animal and human studies are required to assess these valves.

Generally, the material used for valve construction is of paramount importance. The untreated autologous pericardium has been used for various valve repairs and constructions; nonetheless, scarring, shrinkage, and retraction of the pericardial tissue are some of the challenges faced with this procedure. Treatment with GA improves the biomechanical properties of the autologous pericardium, which becomes stiffer and stronger and shows increased resistance to proteolytic degradation compared to non-treated pericardium through the formation of a collagen crosslink. However, in a study of 98 patients with TOF, who underwent surgical repair with fresh autologous untreated pericardium, it was found that only 12.5% of the patients had more than mild PS after a 57-month follow-up period. ¹⁴

For many years, GA-treated autologous pericardium has been used in various valve repair or construction techniques. The results are favorably comparable to or even better than those of biological valves. In this regard, Xiaohong Liu reported freedom from fibroelastic degeneration in 80% of patients (n=15) over an 11-year follow-up. ¹⁵ Histopathological analysis indicated the presence of a thin endothelial layer on the GA-treated pericardial leaflets. Besides, the presence of elastic bonds in the pericardial cusps, which are generally observed in the aortic valve tissue, suggested that the pericardium transplants might adapt to new environmental demands. However, some evidence suggested that myofibroblasts and osteoblasts in the pericardial tissue could serve as a source for fibrosis or calcification.

In 2005, Halees conducted a 16-year follow-up of GA-treated autologous pericardium for aortic valve reconstruction and reported that the rate of freedom from reoperation was 72% in 10 years and 45% in 16 years. ¹⁶ Additionally, Chan and others reported excellent durability for up to 6.5 years, with 100% freedom from SVD in 11 patients. There was no calcification on the CT scans or histological findings of four explanted valves. ¹⁷ The most encouraging outcomes of GA-treated autologous pericardium were reported by Ozaki in 2011, who described a new aortic valve replacement technique using GA-treated pericardial tricuspid valves. ¹⁸ In 2018, another study on 850 cases of aortic valve replacement in a mean follow-up of 53 months found that the incidence of reoperation and recurrent moderate aortic regurgitation was 4.2% and 7.3%, respectively. ¹⁹ These promising results encouraged us to use GA-treated autologous pericardium to construct a valve for PVR patients. The mean age of the patients in studies by Halees and Ozaki was 30 and 71 years, respectively, which differed from the age range of our patient population. However, there were no long-term data available regarding the durability of pericardial valves in younger patients.

In the present study, we found no evidence of calcification, shrinkage, or fibrosis in the AAA valves after treating 10 patients. However, some degree of motion restriction occurred in one of our patients since the early postoperative period, resulting in moderate PS. It might be concluded that the GA-treated pericardium was effective and acceptable for constructing a valve in the majority of patients, at least in the short to midterm follow-up. Although Baird and colleagues applied Ozaki’s technique for pulmonary valve reconstruction for a 16-month-old patient, ²⁰ this technique might not be applicable for older patients with a previous transannular patch, chronic PR, and aneurysmal dilatation of RVOT.

The AAA valve was designed as a trileaflet valve because a valve with three leaflets provides the best hemodynamics and the longest durability. As skillfully represented by Ozaki, tricuspidization is the ideal technique for valve reconstruction. ²¹ The cusps in a trileaflet valve have a larger total coaptation surface in diastole than in bicuspid valves. On the other hand, the bicuspid anatomy prevents the full opening of the valve in systole, as the valve circumference is larger than the sum of two leaflet edges. In a tricuspid valve, the total free-edge length approximates its circumference (2r×3=2 πr), while in a bicuspid valve, the length of the cusps is shorter than its circumference (2r×2<2 πr). Therefore, the trileaflet valve has a totally circular opening, whereas a bicuspid valve has an elliptical opening.

In this study, the AAA valve was designed to secure CH and effective height (EH) above normal levels to achieve optimal hemodynamics and durability. It is well-established that the GH and EH of repaired aortic valves were significantly correlated with clinical parameters and aortic valve insufficiency. ^{22 , 23} The GH of the constructed AAA valve and the EH measured by Schafer’s caliper during surgery was much higher than the average acceptable height (9 mm). The mean CH measured on CMR was significantly longer than the average normal value (4 mm). This geometric design, with longer GH, CH, and EH might guarantee ideal hemodynamics and provide the reserve cusp tissue if certain cusp retractions occur in the long term. The CMR results showed that this valve configuration was maintained during the follow-up.

Another important point in the AAA valve construction is that the valve formation procedure is performed before cardiopulmonary bypass. Therefore, it does not significantly increase the bypass time. In the present study, we attempted to standardize this technique and make it simpler, faster, and more reproducible. Tools specifically designed for this purpose make valve construction simpler and faster. Since all of these tools are reusable, avoiding the use of commercial valves makes the procedure cost-effective.

Although the developed procedure could be performed for the majority of patients, the availability of adequate pericardium might limit the AAA valve formation. The limited number of patients and the short follow-up period were the main limitations of the present study, and conclusions could only be reached after a longer follow-up with a larger group of patients.

Conclusion

The AAA valve provided satisfactory short- to midterm functional outcomes in the studied patients. Therefore, it might be considered a suitable alternative for patients who require PVR. Nevertheless, a longer follow-up of a larger sample size is required to establish a definite conclusion.

Supplementary video

Acknowledgment

The authors would like to thank Shiraz University of Medical Sciences, Shiraz, Iran, for non-financial support.

Authors’ Contribution

AAA: Conceptualization, design, surgical management; KJ and ME: Writing, project administration; GA: Design and writing; HA and HA: Echocardiography; MS, RH, and MA: Investigation; EN: Investigation and revising of the manuscript; MK: Cardiac MRI. All authors reviewed the manuscript. All authors have read and approved the final manuscript and agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Conflict of Interest

The authors did not receive any direct or indirect financial payment for the research and are not the owners of any related company. Moreover, they had no financial relationship with the device-producing company.

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