Introduction
Right ventricular outflow tract and pulmonary artery reconstruction is effective for such congenital heart defects as tetralogy of Fallot, pulmonary atresia with ventricular septal defect / intact ventricular septum, double outlet right ventricle, complex forms of transposition of the great arteries, common truncus arteriosus [1]. Significant progress in surgery of congenital heart defects has led to evolution of valved conduits for right ventricular outflow tract and pulmonary artery reconstructions [2]. However, there is a problem of conduit restenosis followed by right ventricular dysfunction [2, 3]. Solution to this problem is redo surgery with replacement of valved conduit, but each redo surgery increases the risk of complications [3]. An alternative to redo surgery may be transcatheter pulmonary valve implantation into degenerated valve or conduit [4-6]. Selection of patients for this procedure depends on anatomical features of the right ventricular outflow tract and distal pulmonary artery. It is necessary for stable implantation [6].
The purpose of our study was to analyze morphology of right ventricular outflow tract and pulmonary artery using 3D printing with identification of risk factors for each morphological model.
Material and methods
A retrospective study included 350 pediatric patients aged 7-18 years who underwent right ventricular outflow tract and pulmonary artery reconstruction between November 2011 and April 2022.
Reconstruction was performed by using of pulmonary homograft (Cardiostar LLC, St. Petersburg, Russia), transannular repair, transannular repair with a single leaflet, bovine jugular vein (Contegra pulmonary valved conduit; Medtronic, Minneapolis, MN, USA), valved xenopericardial conduit (BioLAB KK/B, Bakulev National Medical Research Center for Cardiovascular Surgery, Moscow, Russia), xenopericardial conduit with porcine aortic valve (AB-Composite, NeoKor, Kemerovo, Russia), xenopericardial valved conduit (Pilon, NeoKor, Kemerovo, Russia). The choice of implanted conduit depended on preferences of surgeons.
The local ethics committee approved the study. Parents of all patients signed an informed consent in accordance with the Declaration of Helsinki.
We included patients who underwent right ventricular outflow tract and pulmonary artery reconstruction and excluded patients weighing less than 25 kg.
3D reconstruction
All patients underwent 320-slice CT of the heart and great vessels with ECG synchronization (Aquilion One, Toshiba Medical Systems Corporation, Japan). Processing of DICOM images was carried out in the specialized program Mimics Research (Materialise Inc., Ann Arbor, Michigan, USA). After import of images, segmentation of pulmonary arteries was performed in a semi-automatic mode.
We controlled correct internal contouring of the vessel and removed uninteresting lobar and segmental arteries, fragments of right ventricular outflow tract. The next stage was export of 3D model of pulmonary arteries to STL format for additive 3D printing.
3D analysis of morphology of right ventricular outflow tract and pulmonary artery
The Mimics software allows rotation and scaling of 3D objects. Thus, we can appreciate 3D anatomy of right ventricular outflow tract and pulmonary artery.
Considering these data, we created morphological classification based on visualization of orifices of pulmonary arteries, proximal, middle and distal parts of pulmonary artery, distal part of right ventricular outflow tract. Six types were distinguished (Fig. 1).
Fig. 1. 3D models of right ventricular outflow tract dysfunctions.
a — type I, b — type II, c — type III, d — type IV, e — type V, f — type VI.
The first type had the shape of a cone (distal narrowing and proximal enlargement of pulmonary artery), type II — pear-shaped (enlargement of the middle and proximal thirds of pulmonary artery and right ventricular outflow tract, unexpanded distal part of pulmonary artery), type III — hourglass shape (enlargement of distal pulmonary artery and right ventricular outflow tract with narrowing of proximal and middle thirds of pulmonary artery), type IV — inverse cone shape (narrowing of right ventricular outflow tract with enlargement of distal pulmonary artery), type V — saccular (isolated dilatation/aneurysm of right ventricular outflow tract with normal dimensions of pulmonary artery), type VI — normal configuration of pulmonary artery and right ventricular outflow tract.
Schematic variants of right ventricular outflow tract dysfunctions are presented in Fig. 2.
Fig. 2. Schemes of right ventricular outflow tract dysfunctions.
a — type I, b —type II, c — type III, d — type IV, e — type V, f — type VI.
Dimensions of various parts of right ventricular outflow tract and pulmonary artery were measured using cardiac surgical sizers.
Statistical analysis
Analysis of data was performed using Stata 14 software for Mac OS (StataCorp LP, College Station, TX, USA). Distribution normality was tested by using of Shapiro-Wilk test. Equality of variances was checked by using of Levene’s test. Qualitative variables are presented as absolute numbers and percentages, quantitative variables — median, 25th and 75th percentiles unless otherwise noted. Regression analysis was used to identify predictors for a binary variable. We used simple and multiple logistic regressions. Proportional hazards regression was used to assess the relationship between one or more continuous or categorical variables until adverse event. Difference were significant at p-value<0.05.
Results
Baseline and demographic characteristics of patients are presented in Table 1.
Table 1. Baseline and demographic characteristics of patients
|
Variable |
Value |
|
Age, years |
12 [10; 15] |
|
Weight, kg |
34 [28; 45] |
|
Male, n (%) |
239 (68.2) |
|
Primary diagnosis, n (%): |
|
|
TF |
78 (22.3) |
|
PAA with VSD |
72 (20.6) |
|
DORV |
17 (4.9) |
|
PAA with intact IVS |
9 (2.6) |
|
CTA |
66 (18.9) |
|
Complex TGA |
52 (14.9) |
|
CTGA |
10 (2.8) |
|
PVS |
17 (4.8) |
|
Lesion of RVOT and AV |
29 (8.2) |
|
Type of conduit or pulmonary artery repair, n (%): |
|
|
Transannular repair |
46 (13.1) |
|
Transannular repair with single leaflet |
32 (9.2) |
|
Homograft |
87 (24.9) |
|
Xenopericardial conduit |
52 (14.8) |
|
Contegra conduit |
122 (34.8) |
|
Xenopericardial conduit with porcine aortic root |
9 (2.6) |
|
Other xenopericardial conduits |
2 (0.6) |
Note. TF — tetralogy of Fallot, PAA with VSD — pulmonary artery atresia with ventricular septal defect, DORV — double outlet right ventricle, PAA with intact IVS — pulmonary artery atresia with intact interventricular septum, CTA — common truncus arteriosus, TGA — transposition of the great arteries, CTGA — corrected transposition of the great arteries, PVS — pulmonary valve stenosis, RVOT — right ventricular outflow tract, AV — aortic valve.
— Type I occurred in 54 (15.5%) patients. The risk factor for “cone type” morphology was Contegra conduit that increased the risk of distal stenosis by 22.3 times (OR 22.3, 95% CI 4.8; 78, p=0.01);
— Type II occurred in 24 (6.8%) patients. The risk factor for pear-shaped morphology was pulmonary homograft that increased the risk of trunk dilatation by 2.3 times (OR 2.3, 95% CI 1.4; 8.6, p=0.034);
— Type III occurred in 87 (24.8%) patients. The risk factor for hourglass morphology was xenopericardial conduit that increased the risk of proximal stenosis by 5.1 times (OR 5.1, 95% CI 1.8; 12.7, p=0.001);
— Type IV occurred in 51 (14.6%) patients. The risk factor for inverse cone morphology was transannular repair with a single leaflet that increased the risk of muscular stenosis by 1.2 times (OR 1.2, 95% CI 1.1; 1.9, p=0.04);
— Type V occurred in 21 (6%) patients. The risk factor for saccular morphology was xenopericardial conduit with porcine aortic root that increased the risk of aneurysms by 2.2 times (OR 2.2, 95% CI 1.5; 3.7, p=0.035);
— Type VI occurred in 113 (32.3%) patients. Normal configuration was more common after transannular repair without a single leaflet (OR 1.8, 95% CI 1.3; 2.5, p=0.045) and implantation of pulmonary allograft (OR 3.1, 95% CI 2.3; 8.9, p=0.001).
Sizes of various conduits are presented in Table 2.
Table 2. Sizes of various conduits
|
Conduit |
Distal third of the conduit, mm |
Middle third of the conduit, mm |
Proximal third of the conduit, mm |
Distal RVOT, mm |
Pulmonary artery angulation, ° |
|
I |
15.5 [12; 22] |
18.5 [15; 24] |
22 [19; 27] |
23.5 [20; 34] |
109 [97; 130] |
|
II |
20 [19; 23.5] |
23.5 [21.5; 29] |
29.5 [25; 35] |
23.5 [21.5; 24] |
110 [92; 121] |
|
III |
22 [18; 27] |
20 [16; 23] |
16 [11.5; 22] |
20 [16; 24.5] |
100 [95; 121] |
|
IV |
27 [25; 29] |
25 [23; 26] |
21 [19; 24] |
16 [14; 18] |
110 [90; 120] |
|
V |
26 [23; 29] |
25 [22; 28] |
25.8 [22; 29] |
32.2 [29; 36] |
99.5 [92; 115] |
|
VI |
21 [16.5; 28] |
21 [17; 25] |
23 [21; 28] |
23 [18; 31] |
120 [105; 124] |
Discussion
Despite great advances in cardiac surgery, we still do not have an ideal conduit for right ventricular outflow tract reconstruction [2]. Currently, no conduit has ideal parameters [2, 6]. As a result of degenerative processes, original properties of the conduit are lost, and its functions are impaired. It is especially true for small valved conduits (≤16 mm) in infants and young children [7]. In addition, standard surgical approaches for critical congenital heart diseases have shifted to earlier stages. Therefore, the demand for small-diameter conduits is constantly growing [8, 9].
Cryopreserved pulmonary homograft has long been considered as the gold standard for right ventricular outflow tract reconstruction [2, 9]. However, alternative conduits for right ventricular outflow tract reconstruction appeared due to some problems typical for pulmonary homograft (high cost, difficult storage, immune response and deficit of small conduits). These conduits are porcine aortic root xenoconduit, bovine jugular vein conduit, xenopericardial conduit, Dacron and PTFE conduits [2, 6]. Alternative materials solved the problem of small conduits without affecting the function and durability of the conduit [2, 10, 11].
Conduit dysfunction is currently an unresolved problem in cardiac surgery [3]. Different dysfunctions (stenosis, insufficiency or combined lesion) require various interventions. Thus, many cardiac surgical centers prefer minimally invasive transcatheter pulmonary artery replacement instead of open reconstruction for pulmonary valve insufficiency due to lower risk of complications [4, 5, 12]. However, there are no clear criteria for transcatheter valve implantation in patients with combined lesions or stenosis of pulmonary artery. Therefore, many surgeons prefer open replacement of conduits [2–4, 6].
3D printing technologies successfully create a prototype of the heart or a part of the heart. This approach provides excellent visualization and understanding of defect anatomy [13, 14]. Visual anatomy allows planning the intervention for each patient [15, 16]. Thanks to 3D printing technology, we have divided all conduit dysfunctions and reconstructions of right ventricular outflow tract and pulmonary artery into 6 types depending on anatomy. The first type had cone shape and was characterized by narrowing of distal pulmonary artery. The only risk factor for this dysfunction was Contegra® xenoconduit (Medtronic Inc., Minneapolis, MN, USA). Various studies are devoted to frequent distal stenoses and proximal enlargement after implantation of this conduit. The main causes of stenosis are distal narrowing of pulmonary arteries, mismatch between the conduit and pulmonary artery dimension, erroneous surgical technique, local immune reaction and thrombosis of the conduit [2, 17, 18]. Transcatheter surgery is usually ineffective for this dysfunction, so most authors prefer open reconstructive surgery with conduit replacement [6].
The second type had a pear-shaped shape and was characterized by dilatation of distal right ventricular outflow tract, as well as proximal and middle thirds of pulmonary artery with intact distal third. This type was typical for cryopreserved pulmonary homograft that increased the risk of type II dysfunction by 2.3 times. The main feature of cryopreserved pulmonary homograft is elastic wall of the conduit, so even small peripheral stenosis can lead to dilatation of the homograft [2, 19]. Conduit enlargement often leads to severe pulmonary valve regurgitation and right ventricular dysfunction that is a direct indication for surgery [3, 4]. Redo replacement by homograft leads to a worse result, and replacement with another conduit may affect long-term function of the conduit [6]. The optimal solution may be self-opening transcatheter valve that can reduce the risk of reconstructive surgery and eliminate pulmonary regurgitation [5].
The third type had hourglass shape with narrowing of the middle or proximal third and normal or dilated distal third of pulmonary artery and distal part of right ventricular outflow tract. In our study, the only risk factor for hourglass conduit dysfunction was xenopericardial conduit. Xenoconduits have certain advantages over other conduits: low price, low risk of thrombosis, natural biological structure with high elastic properties. Despite the widespread use of these conduits in surgery for congenital diseases, postoperative results are suboptimal due to early valve and conduit calcification that can lead to type III dysfunction [2, 7, 19]. Treatment of this dysfunction can be carried out via open replacement of conduit and transcatheter valve implantation after preliminary stenting [5, 12].
The fourth type of conduit dysfunction (inverse cone) was characterized by narrowing of right ventricular outflow tract with enlargement of distal pulmonary artery. This dysfunction was common after transannular repair with a single leaflet. In our opinion, calcification of a single leaflet leads to narrowing of right ventricular outflow tract, and stenotic blood flow contributes to enlargement of distal pulmonary artery. As with hourglass variant, there is no definite consensus regarding the treatment of such patients [20, 21]. Surgical strategy should be individual for each patient [6]. Surgeons prefer conduit replacement with partial infundibulectomy [21]. At the same time, endovascular implantation of self-opening transcatheter valve is possible in case of mild calcification [22].
The fifth type of conduit dysfunction (saccular) was characterized by isolated aneurysm of right ventricular outflow tract. In our study, this type was common in patients with xenopericardial conduit containing porcine aortic root. However, there were aneurysms after implantation of cryopreserved pulmonary homograft and Contegra xenoconduit. According to some authors, right ventricular outflow tract aneurysms are more common after previous balloon angioplasty [6, 14]. In our study, we confirm these data. Most patients with right ventricular outflow tract aneurysms underwent previous balloon dilatation of the conduit. Surgical strategy for right ventricular outflow tract aneurysms consists solely in aneurysm excision and conduit replacement [21].
The sixth type was characterized by normal anatomy of pulmonary artery and right ventricular outflow tract with severe pulmonary valve regurgitation. Transcatheter technologies are preferred in these patients [22].
Conclusion
3D analysis of right ventricular outflow tract and pulmonary artery is useful for choosing treatment strategy and minimizing complications associated with implantation of conduit or transcatheter valve.
Financing
The article was supported by the grant 21-75-10041 of the Russian Science Foundation (“Research by scientific groups led by young scientists” of the presidential program of research projects implemented by leading scientists, including young scientists).
Conflict of interest
The authors declare no conflicts of interest.