(1)
Department of General surgery, Fuwai Hospital, Beijing, China
9.1 General Considerations
9.1.1 The Cardiac Skeleton
The fibrous skeleton of the heart, namely, the cardiac skeleton, is a framework supporting all of the chambers of the heart. Cardiac surgery involving the chambers of the heart and the aortic root also involves the cardiac skeleton (Fig. 9.1). The cardiac skeleton is composed of the left and right AV valve rings and the aortic annulus and consists of four bands of dense connective tissue. The cardiac valve leaflet and the myocardium are accreted to the cardiac skeleton, so as to maintain the shapes of the chambers of the heart and the three-dimensional structure (Fig. 9.2). The aortic annulus is in the central portion of the cardiac skeleton and adjoins the PV ring with the loose connective tissue.
The core of the cardiac skeleton is composed of the central fibrous triangle (body) and the left fibrous triangle (Fig. 9.3). The central fibrous triangle is the site at which the aortic annulus, the mitral ring, and the tricuspid annulus meet; it is fibrous and cartilaginous. The membranous interventricular septum lies in its front and at its end is the Todaro tendon, running from the interatrial septum inferiorly and to the right to the inferomedial part of the IVC valve. The atrioventricular band passes through the central fibrous body, following the lower margin of the membranous interventricular septum into the ventricular (Fig. 9.4).
The left fibrous trigone is the site at which the left aortic and the mitral annuli meet. Its lateral end adjoins the left coronary artery (Fig. 9.5).
9.1.2 The Aortic Root
The aortic root may be defined generally as a supra-coronary aorta inside the pericardium – the AV with its crown-shaped annulus, interleaflet triangles, sinotubular ridge, and sinus of Valsalva. For practical purposes, the aortic root should be between the aortic annulus and the sinotubular ridge, concluding at the sinus of Valsalva and left and right coronary artery ostia (Fig. 9.6).
Because the aortic root is the central part of the heart, the aortic annulus is the important part of the supporting frames of the heart. All cardiac surgery should refer to the aortic root; therefore, the topography of the aortic root is very important for the surgery.
The sinus of the Valsalva refers to the expanded portions of the aortic root confined proximally by the concave attachments of each cusp and named accordingly (right, left, and noncoronary). Part of the wall of the right sinus of Valsalva is the myocardium of the ventricular septum. The base of the sinus of Valsalva is imbedded in other tissues, increasing the difficulty for exposing it during surgery on the aortic root. It is surrounded by the left and right atria, and the atrial septum faces the middle of the noncoronary sinus of Valsalva. The right sinus of Valsalva adjoins to the RA, and its front adjoins to the major pulmonary artery. These imbedding contact surfaces are connected by the loose connective tissue, which could be divided by blunt dissection. The right sinus of Valsalva straddles the infundibular septum and adjoins the RVOT (Fig. 9.7).
The ostia of the left and right coronary arteries originate from the posterior left sinus and the upper portion of the anterior sinus of Valsalva, respectively (Fig. 9.8). It is difficult to stop bleeding of the anastomosis between the left coronary artery and a vascular prosthesis because this anastomosis is covered by the vascular prosthesis after the heart rebeats, rending it difficult to expose. Traction on the vascular prosthesis aiming to expose the anastomosis may result in more bleeding. The ostium of the RCA lies superficially, but the incision of the aortic root is too low to impair it. After the sinus of Valsalva is opened, one can find the ostia of the coronary arteries, the AV, the aortic annular, and the position of the sinus of Valsalva in its adjoining relationship (Figs. 9.8 and 9.9). An AV device includes a cusp of the aorta, an aortic annular, and a subvalve structure.
The AV ring is not a completely uniform fiber cable; the bottom of the right coronary cusp is attached at the septum muscle. The bottom of the left coronary cusp and the noncoronary cusp is connected with the anterior leaflet of the MV. The connecting wires form the last half of the aortic annulus. It includes the right fibrous triangle, with the triangular and left fibrous triangle, and is a very dense and solid part. The aortic annulus shows a wave type to form the upper edge of the LVOT.
The AV presents the three half-moon leaves and is attached to a wave-type aortic ring. The structure is different from the atrioventricular valve, having no accompanying chordae tendineae and relying mainly on the aortic sinus tension among the three leaflets to the free edge of the ventricular diastolic to prevent insufficiency. The free margin of the valve lies at the same level, and the basal adhesion is in a wave-like valve ring (Fig. 9.10).
The valve and its corresponding aortic wall constitute an upwardly opening bag-shaped depression, called the aortic sinus. The three leaflets are identical with regard to size, location, and other characteristics; the free edges contact each other, and the free edge of the leaflet midpoint locally thickened free limbal nodule formation often [this is not clear]. During the left ventricular ejection, the AV opens. The valve is attached to the sinus. During left ventricular diastole, the AV closes, with the valve leaflet contacting the free edge in order to prevent the backward flow of blood.
The tissue beneath the AV is the LVOT, around which are (Figs. 9.11, 9.12, 9.13, 9.14, 9.15, 9.16, 9.18, and 9.19):
1.
The anterior wall, composed of the muscle structure of the ventricular septum, which lies under the left and right aortic valves.
2.
Fibrous triangle between the noncoronary ring and the left coronary ring; it stretches with the anterior leaflet of the MV, continuing a screen shape, which forms the posterior wall.
3.
Below the leaflet of the left coronary; a valve there may be a ventricular free wall myocardium, which is of little clinical significance.
4.
Below the junction of the right coronary and noncoronary leaflets is the membranous septum. It is a thin membrane-like tissue. The scope is very small, but it is in the central part of the fibrous skeleton of the heart, and its surrounding anatomy is complex and is of considerable surgical significance.
9.2 Surgical Significance
9.2.1 Incision of the Aortic Root
The anterior wall and the right diagonal back are dissociated, so the incision can be made there. For thick tissue, the surgeon should choose the anterior wall; for thin tissue, the surgeon should choose the right diagonal back. The right diagonal back incision starts from the upper left and extends to the right bottom. Sometimes, the aortic artery can be traversed for a clearer view. If the aortic artery is not fully grown, it is widened with a patch. An incorrect incision leads to a more difficult operation; the bleeding around the aortic ring should be prevented (Fig. 9.27).
9.2.2 Aortic Valve Plasty
The juncture adhesion should be treated as a commissural incision, but the leaflet cannot be repaired. The plasty of a loose and prolapse leaflet is not ideal. A single leaflet could be repaired. The constriction is suitable for an enlarged aortic ring, but the method used for a normal leaflet with a wave-like ring is different. The aortic regurgitation is the main complication after operation (Fig. 9.20).
9.2.3 Aortic Valve Replacement
Mechanical valves have a level suture edge, whereas bioprosthetic ones have a wave-like suture edge; neither of them can match with the aortic ring, and close attention should be paid to them. Sometimes, the root is too thin to plant a valve, so the aortic artery must be widened. We choose different patterns according to the extent of the expansion (Figs. 9.21 and 9.22).
9.2.4 Stenosis (Figs. 9.28, 9.29, 9.30, and 9.31)
9.2.4.1 Moderate Stenosis
The root incision should be extended to the back sinus, and the root should be widened by a tricuspid patch, the bottom of which should be parallel with the ring.
9.2.4.2 Severe Stenosis
The root incision should be extended to the juncture between the left sinus and the back sinus, the ring to the base of the anterior leaflet of the MV should be cut off, and a combined incision of the aortic artery and the LA should be made. Simultaneously, the aortic ring should be widened sufficiently. The key point is divergence of the aortic ring, the base of the anterior leaflet of the MV, and the lower limb of the anterior wall of the LA. After the aortic and mitral valves are replaced, the anterior leaflet of the MV should be repaired, the incision of the LA should be sutured, and the aortic root should be widened by a patch. The Ross-Konno procedure, which involves cutting off the right sinus, extends to the ventricular septum. It also involves part of the anterior wall of the RV, avoiding the RCA. After AV repair is completed, a three-vane patch is used to repair the ventricular septum, the wall of the RV, and the incision of the aortic artery (Figs. 9.39 and 9.40).
9.2.5 Aortic Root Dilatation and Aneurysm
We define dilatation as a diameter of the base of the aortic ring >25 mm, diameter of sinotubular junction >30 mm, and diameter of aortic artery > 50 mm, which can be considered as an aneurysm and should be treated surgically. We classify the operations as replacement and plasty.
The root replacement includes replacement of the AV and the ascending aortic artery and transplantation of the coronary.
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