Mean normal diameter of pulmonary valve
Tetralogy of Fallot (TOF), primarily named La Maladie Bleue by Louis Arthur Etienne Fallot in 1888, is the clinical description of the physiology created by a combination of anatomic malformations that consists of an interventricular communication, or ventricular septal defect, biventricular connection of the aortic root, which overrides the muscular ventricular septum, obstruction of the right ventricular outflow tract, and right ventricular hypertrophy. This cyanotic malformation belongs to a family of diseases characterized by a similar intracardiac anatomy but highly variable in terms of pulmonary artery anatomy, associated abnormalities, and outcomes; once each component can vary in its severity, with the variation directly affecting the manifestation and management of the disease.
Although the stenosis of the pulmonary trunk and its bifurcation is uncommon, the right and left pulmonary arteries are stenotic to some degree in 30% of infants with Tetralogy of Fallot presenting in the first year of life [1-3].
Based on this premise, here we focus on pulmonary artery anatomy which is one of the most challenging components of Tetralogy of Fallot especially regarding the complexity of its surgical repair and the selection of materials to accomplish such repair. Decision making, timing and techniques for repairing each of these pulmonary artery variants are emphasized in this chapter according to the authors experience and also based on the best evidence in the literature.
2. Morphologic categories of pulmonary artery anatomy in Tetralogy of Fallot
Size and configuration of the pulmonary arteries have been thought to be important determinants of postoperative right ventricular function after complete repair of tetralogy of Fallot. As such, they may affect the result of repair when the pulmonary arteries are hypoplastic or stenotic .
Hypoplasia or narrowness, in the arterial pathways in patients having TOF with pulmonary stenosis is most marked centrally in the RV infundibulum and pulmonary trunk. On average, the RPA and LPA and their branches are not abnormally small. This does not deny the occasional existence of severe narrowing at the origin of the LPA or RPA. Elzenga et al  found juxtaductal proximal stenosis of the LPA in 10% of patients having TOF with pulmonary stenosis; about 90% are free of these severe finding [4, 6].
The nearly infinitely variable spectrum of pulmonary artery obstruction in TOF can be conveniently categorized in a way that is surgically useful because it relates to difficulty in obtaining good relief of the pulmonary stenosis and therefore to surgical techniques and mortality. Because of this great variability in the dimensions of the pulmonary arteries, their careful pre-repair study is very important. In this regard we have didactically separated the pulmonary artery tree into three anatomical segments:
pulmonary trunk bifurcation and;
pulmonary branches (right and left pulmonary arteries).
3. Pulmonary trunk
In TOF, the pulmonary trunk is nearly always smaller than the aorta. Reduction is most marked when there is a diffuse RV outflow hypoplasia. In this case, the pulmonary trunk is less than half the aortic diameter and is short, directed sharply posterior to its bifurcation. It is largely hidden from view at operation by the prominent aorta, which also displaces the origin of the trunk leftward and posteriorly .
When the pulmonary valve is markedly dysplastic, the pulmonary trunk is also stenotic or corseted at its commissural attachments, and it may be very angulated or kinked at this point. This is the usual mechanism of supravalvar narrowing, and it is not associated with wall thickening. Rarely, however, there may be a discrete supravalvar narrowing beyond commissural level with diffuse wall thickening [1, 6].
4. Pulmonary trunk bifurcation
The left pulmonary artery (LPA) is usually a direct continuation of the pulmonary trunk; with the right pulmonary artery (RPA) arising almost at right angles and close to it, but this pattern varies. In TOF is uncommon to have the distal pulmonary trunk and origin of RPA and LPA being moderately or severely narrowed (bifurcation stenosis), and in this situation the bifurcation may have a Y shape  (Fig.1)
5. Right and left pulmonary arteries
Although anomalies of the RPA and LPA are more common in TOF with pulmonary atresia rather than stenosis, Fellows et al found pulmonary artery anomalies in 30% of infants having TOF with pulmonary stenosis presenting in the first year of life [4,8].
The more severe the hypoplasia of the infundibulum and pulmonary trunk, the more severe is the narrowing of the first part of the right and left pulmonary arteries, although the Z values of these structures are usually larger than those of the pulmonary trunk . (Fig.2)
6. Surgical approach over the pulmonary trunk and branches
Pulmonary artery branch stenoses are widely known congenital anomalies especially in children with TOF. Many authors have reported hypoplastic or stenotic pulmonary artery branches to be a major obstacle to successful operative correction of TOF [7,9-13].
In this section we present different techniques and materials that can be used to repair such diseased pulmonary arteries according to their location, size and anatomical configuration.
7. Pulmonary trunk stenosis
In cases of pulmonary trunk stenosis some steps must be followed in order to obtain a successful surgical repair:
Sizing the pulmonary trunk
If the pulmonary valve annulus is hypoplastic, the infundibulotomy incision is extended across the annulus between the valve commissures as far as needed (up to the bifurcation or up to the left or right pulmonary artery). The size of the pulmonary trunk and of the left and right pulmonary arteries is measured by Hegar probes, and then those arteries are calibrated to fit a normal diameter, adjusted to the child's body surface area [14-16].(Table 1)
|Data from Rowlatt et at. 14|
In some patients the distal pulmonary trunk is narrower than the annulus; in these cases the incision is extended into the LPA, which usually continues in the same general direction as the pulmonary trunk and is usually proportionally larger than the distal pulmonary trunk. If the origin of the LPA is proportionally no larger than the distal pulmonary trunk, then the incision and patch reconstruction should be carried into the mid portion of the LPA, which is nearly always wider than the origin [1,4,6].
Measuring the patch
Generally, a transannular patch should not be placed when the Z value is larger than -3. Otherwise, the incision is carried across the annulus, the pulmonary valve excised, and the patch inserted.
The length of the patch can be determined by measuring length of the incision from the RV to the pulmonary artery, and its maximum width is determined visually by holding the edges of the incision open at valve level and judging the size of the roof required to create a new pulmonary annulus whose diameter is no larger than three fourths the diameter of the ascending aorta [4,17] (Fig. 3).
Alternatively a Hegar dilator can be placed through the divided annulus and the width of the patch required to complete the roof over it measured. Usually, the patch is about 50mm long and 15mm wide at its center. Both ends are cut almost transversely to create a blunt patch. When a transannular patch is used, a major consideration is the distal extent of the incision in the pulmonary trunk, because this must be into an area of distinctly greater diameter than that of the annulus, which is usually the narrowest area [4,17] (Fig. 4)
Selecting the patch
The transannular patch may be of glutaraldehyde-treated or untreated pericardium. Glutaraldehyde-treated pericardium is advantageous because it facilitates precise sizing of the patch, and when properly trimmed, its convexity is ensured, as is a relatively square cut of its distal end. Thus, when it is inserted, it forms a roof that is convex in all directions relieving the transpulmonary gradient. Although technically more demanding; untreated, especially pedicled pericardium has the potential advantage of growing as the child grows [9,10,17,18].
Inserting the patch
The patch is positioned using continuous 5-0 polypropylene sutures, commencing at the distal end of the incision. The suture is mattressed at the end and over and over elsewhere, placing the first two or three throws along each side before pulling the pericardial patch into position as the suture is tightened. Suturing is continued down each side to annulus level; then the reminder of the right ventriculotomy is closed by incorporating the pericardial patch into it with continuous sutures. Deep bites of muscle are taken down each side and at the angle  (Fig 5).
Untratead pedicled pericardium
Preparation and tailoring of the pericardial flap:
The broadly based pericardial flaps are tailored before cardiopulmonary bypass begins. The pericardial sac is usually opened transversely in the midline near the diaphragm. The incision is extended along the diaphragm toward both phrenic nerves and then goes cephalad, parallelling the right phrenic nerve closely, until the flap can be rotated in front of the pulmonary arterial segment needed to be repaired. The pericardium usually remained normally attached on the left side with the left phrenic nerve along its base [18,19] (Fig. 6).
Inserting the pedicled pericardium patch
After incising the anterior aspect of the pulmonary trunk, pulmonary valve ring and right ventricular outflow tract, the valve ring is measured using Hegar dilator according to the body surface area as previously described, then the suture of the pericardium is begun at the lateral edge by implanting the patch on a tile-shaped using 6-0 polydioxanone thread throughout the suture.
Using a valved patch
If it is anticipated that a too large transannular patch will be required, a monocusp may be attached to the pericardial roofing patch to prevent increasing postoperative pulmonary regurgitation. The cusp diameter is fashioned somewhat larger than the planned roofed RV outflow. It is cut more or less circular and sutured to the patch when the latter suturing from distally reaches the valve annulus. Numerous materials, such as polytetrafluoroethylene, porcine heterografts, allografts and others can also be used to repair the pulmonary trunk in this situation [21,22](Fig.8).
If the surgeon’s preference is for a monocusp allograft and, considering that only one cusp will be used and that the size of aortic or pulmonary cusps in adults can vary by only a few millimeters, a graft between 17mm and 23mm in diameter is chosen according to the ring size based on the body surface area as it has already been described above  (Fig.9).
Technique of implantation: after inspecting the graft, one of the larger cusps is selected. Then, the graft is cut to fit a segment of the aortic or pulmonary wall that is distal to this cusp. Using a Nº 5-0 polypropylene suture, the procedure is done in such way that the cusp edge can be at the same level of the edges of the native pulmonary valve  (Fig 10).
8. Left pulmonary artery stenosis
As postulated by Kalangos et al  only one of the pulmonary artery branches has the same anatomical direction as the main stem of the PA, either the right or the left pulmonary artery. This particular feature is important because it can directly affect the surgical outcome; therefore, the patch enlargement technique must be performed in accordance to the anatomy of the pulmonary arch in each individual case (Fig. 11)
In most of the cases a single transannular patch enlargement extending into the LPA is sufficient to repair stenosis of the origin of the LPA when it has the same axis as the main PA (Fig. 12)
As the LPA is usually an extension of the pulmonary trunk, isololated stenosis at origin of LPA is uncommon. In these uncommon situations in which a transannular patch is not needed, an incision is made across the stenosis in the origin of the LPA and a rectangular patch of pericardium is trimmed and sewn in to place using Nº 6-0 polypropylene sutures [4,23] (Fig. 14)
9. Right pulmonary artery stenosis
After mobilizing the aorta, the pulmonary trunk and the left and right pulmonary branches, the origin of the RPA is disconnected from the pulmonary trunk. Lateral incisions are made to enlarge the orifice in the side of the pulmonary trunk. The RPA is incised from its narrow orifice back into its wide portion. A rectangular piece of pericardium is trimmed and sewn to the RPA to make a markedly enlarged proximal RPA. The proximal end of the reconstructed RPA is then sutured to the enlarged orifice in the side of the pulmonary trunk using Nº 6-0 polypropylene sutures and closely placed sutures, while taking care to avoid any purse- string effect [4,23] (Fig.15)
Another alternative is to suture the posterior edge of the opened RPA to the back wall of the opened pulmonary trunk. A rectangular piece of pericardium is then sewn to the remaining opening to widen it further; however, this technique is more demanding and may generate tension on the anastomosis.
As shown in the figure above, the aortic transection facilitates exposure of the distal main PA, confluence and branches up to the hilum, especially in patients with difficult anatomy and sternal re-entry. This maneuver is recommended in patients requiring exposure of the main PA, its bifurcation, and branches during surgery for congenital heart disease, especially if adequate exposure is critical for successful repair (Fig. 17).
10. Bifurcation stenosis of the pulmonary trunk
Bifurcation stenosis is characterized by both LPA and RPA ostia stenosis to a similar degree and over a short distance (<15 mm) with the distal pulmonary trunk similarly narrowed making the bifurcation more Y shape than usual. However, repair of bifurcation stenosis is indicated only when the stenosis is severe [1,4,6,7,16].
The first option for infants is repair rather than replacement; however, in children age 5 years or older, the optimal procedure may be to replace the pulmonary valve, trunk, bifurcation, and proximal RPA and LPA with a pulmonary allograft [22,26,27].
Selecting the graft:
A 22- to 25-mm-diameter allograft can provide a good hemodynamic result in this complex situation. There is a trend towards the RVOT enlargement using a homologous and decellularized allograft putting forward a theoretical attempt of a graft with greater durability potential than those currently available. Decellularized grafts may be related to a lower immune response when compared with cryopreserved grafts [22, 27-32].(Fig. 18)
11. Surgical technique
Repair (for children < 5 years old)
The aortopulmonary septum is dissected and the ascending aorta is freed completely from the main PA and its branches, and then mobilized. A resection of the anterior aspect of the entire bifurcation is performed in a Y-shape fashion. The defect is repaired with a Y-shaped patch (pericardium, PTFE or allograft) using 6-0 or 7-0 absorbable sutures. (Fig. 19)
Replacement (for children ≥ 5 years old)
The entire ascending aorta is completely freed from its posterior connections and from pulmonary trunk and its bifurcation. At this time, the ascending aorta may be divided if required . The superior vena cava is completely mobilized and the RPA and LPA are dissected to the point where the first branch is visualized and subsequently transected beyond the narrow areas. A vertical ventriculotomy is carried across the annulus into the pulmonary trunk which is ultimately transected.
A 22- to 25-mm-diameter allograft can provide a good hemodynamic result in this complex situation.
Distal anastomoses are made first with continuous Nº 5-0 or 6-0 polypropylene suture. The proximal conduit anastomosis is made by commencing the suturing posteriorly where the allograft is opposed to the superior margin of the ventriculotomy using an Nº 4-0 polypropylene suture. The suture line is continued from the midline along both sides around about half the circumference of the conduit, and the sutures are held. A patch of pericardium 2 to 5 mm larger than the diameter of the allograft valve annulus is cut to an approximate semilunar shape and sutured into place to complete the anterior half of the anastomosis serving as a roof on the ventriculotomy incision and preventing the graft distortion. [4,22,32] (Fig. 20)
12. Special remarks
Isolated LPA and RPA stenosis in TOF requires distinct surgical repair otherwise a residual stenosis or arterial kinking may occur.
Replacement of the entire pulmonary bifurcation must be reserved for children 5 years of age and over with severe bifurcation stenosis for whom allograft insertion seems to be the best option.
Decellularized allograft for patching and also as a conduit is a promising alternative for reconstruction of the pulmonary trunk and its branches in TOF
If a conduit insertion is required, care must be taken to position it nearly in the same position as a normal pulmonary artery by directing it toward the patient`s left shoulder as it come off the right ventriculotomy in order to prevent compression by the sternum.
Although the growth potential of pedicled pericardium has not been clearly demonstrated, it is a very attractive alternative for enlargement of small pulmonary arteries or the RVOT in TOF or pulmonary atresia because it maintains its native vascular and neural supply which may avoid further reoperations to replace the pulmonary arterial trunk with an extracardiac conduit after growth of the child.
Postoperative RV/LV ratio ≥ 0.9 indicates residual obstruction either muscular or arterial, which must be promptly surgically removed or ameliorated by percutaneous balloon dilatation, if possible.
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