Valve Sparing Aortic Root Replacement with Aortic Valve Re-Implantation

Patient Selection

Introduction

Elective intervention on the aortic root is warranted in two conditions: first, in the presence of critical dilatation of the sinuses of Valsalva (Video 1) as is the case in this patient, and second, in the presence of effacement of the sino-tubular junction accompanied by aneurysmal dilatation of the ascending aorta (Video 2) (different patient). The term “effacement” describes the gradual increase in the intraluminal diameter from the aortic annulus, through the sinuses of Valsalva and into the ascending aorta, without the characteristic tightening plane which defines the transition between the aortic root and the ascending aorta.

Traditionally, the operation of choice has been a total root and ascending aortic replacement, involving a valved conduit and re-implantation of the coronary buttons (modified Bentall Procedure). In younger individuals, the conduit of choice has been a mechanical valved conduit, mandating lifelong anticoagulation, whereas in older individuals or patients with contraindications to anticoagulation, a bioprosthetic valved conduit can be easily constructed in the operating room by sewing a bioprosthetic valve to an appropriately sized vascular graft [1]. In the latter group, cryopreserved homografts or xenografts have also been successfully used.

Preservation of the aortic valve in patients who require root replacement has several distinct practical advantages. In patients who would have normally received a mechanical valve, preserving their own functional aortic valve eliminates the need for anticoagulation while addressing the ascending aortic and sinuses of Valsalva dilatation. In patients who would have received a bioprosthetic valve, it makes the future re-operation easier (explantation of native aortic valve from native left ventricular outflow tract versus explantation of bioprosthesis from vascular graft or even complete root re-operation with coronary arterial button re-reimplantation).

A theoretical advantage of the valve sparing operation is the potential for delay or even complete elimination of the need for re-operation, when compared to the bioprosthetic root group. The mid-term data is very encouraging, and most studies are showing that lack of early significant aortic insufficiency is the major predictor of medium term durability of the reconstruction. Obviously, since the valve sparing operations were introduced in the early 1990s, there is no long term data available yet.

Reimplantation vs. Remodelling

There are currently two main valve sparing root operations that have been described : the aortic valve reimplantation (David I procedure) and the aortic valve remodeling procedure (David II, Yacoub procedure). There are also several variations of both procedures. A comparison of the two and the potential advantages and disadvantages are beyond the scope of this presentation. We feel that both procedures provide excellent functional results, but prefer to perform the re-implantation procedure. The major theoretical advantage of the reimplantation approach is that it provides fixation of the left ventricular outflow tract/aortic annulus, thus making the annulus non susceptible to future dilatation. There is some early and mid-term data suggesting that the remodeling procedure may leave the unsupported annulus more prone to future dilatation, especially in patients with pre-operative aortic insufficiency or the Marfan syndrome.

Anatomic Considerations

In order to be a candidate for this procedure, a patient needs to have dilated sinuses of Valsalva, or effacement of the sinotubular (ST) junction with an ascending aortic aneurysm (or a combination of both). There is no exact size criterion that converts an “observation” patient into an operative candidate. Assuming that the patient is otherwise healthy (which is often the case in patients considered for valve sparing surgery), a dimension of over 5.0cm is an indication for surgery. We are more aggressive with these patients than with the standard ascending aortic aneurysm patients, since we feel that progressive dilatation of the root may lead to interval development of aortic insufficiency, making a valve sparing attempt at that point more likely to fail. In patients with significant hypertension, family history of aneurysmal disease or dissection, the Marfan Syndrome or in patients who had a previously documented significantly smaller dimension, we recommend surgery even at a dimension slightly less than 5.0cm.

Pre-Operative Studies

A CT scan of the chest and abdomen with intravenous contrast is necessary to delineate the thoracic aortic anatomy and help us determine the extent of the operative approach (ascending aorta, arch etc).

A trans-esophageal echocardiogram is also necessary in order to 1) assess the presence and degree of aortic insufficiency, 2) obtain a measurement of the aortic annulus, 3) ST junction, 4) maximal diameter of the sinuses of valsalva and 5) assess the degree of effacement of the ST junction.

A coronary angiogram is also obtained regardless of the age of the patient. This is mainly done in order to assess the anatomy of the right coronary artery, in case this needs to be grafted separately (ostial calcifications or post-reimplantation kinking and RV failure). Obviously, in older individuals, it also reveals occult coronary artery disease.

Operative Steps

The patient is placed supine on the operating table. A left arterial line is placed (in case the right axillary artery needs to be used for arterial cannulation) and a Swan-Ganz catheter is placed through a right internal jugular approach. The valve and aortic root are inspected utilizing TEE. We look for presence of aortic insufficiency, bicuspid/tricuspid aortic valve, size of annulus and sinotubular junction as well as maximal size of sinuses of Valsalva.

A standard sternotomy is performed. The arterial cannulation site can be the distal ascending aorta or the right axillary artery, depending on the extent of the ascending aortic resection. In cases of a distinct root aneurysm with a normal proximal ascending aorta, we do not perform an open distal anastomosis with circulatory arrest (Video 1). If the ascending aorta is aneurysmal but tapers to a normal caliber toward the arch, we always perform an open distal anastomosis.

Venous Drainage is provided using a single, two stage cannula, unless further work is required with the mitral or tricuspid valves.

The heart is arrested in diastole using 750cc of antegrade cold blood hyperkalemic cardioplegia. Arrest is maintained throughout the case using cold blood retrograde cardioplegia delivered through a coronary sinus catheter.

The aorta is first transected proximal to the cross clamp. The right and left coronary buttons are dissected out, using scissors for the aortic layer and electrocautery for the underlying tissues (Video 3).

The aortic valve is then inspected, assessing the thickness and coaptation of the leaflets and looking for leaflet fenestrations. This is the final check before deciding whether the valve will be preserved or removed. The aortic annulus is then sized, taking extra caution not to injure the aortic valve leaflets during insertion of the sizer.

The next step is unique to this procedure (not necessary in a “button” Bentall). It involves separation of the right ventricular fibers from the left ventricular outflow tract, at the level of the right commissure. This is mandatory in order to facilitate placement of the subannular stitches later in the procedure. Special care needs to be taken in order to avoid entry into the right ventricular cavity which is very hard to repair, given the lack of any epicardial layer at that level (Video 4).

A series of sub-annular stitches (2-0 Ethibond) are then placed in horizontal mattress fashion, with pledgets on the ventricular side. The stitches then exit outside the aorta at the junction of the aorta and the LVOT. We place one such stitch in each corner and three in each commissure, for a total of twelve. The aortic valve leaflets should never be handled with the forceps’ teeth during placement of these stitches. They should simply be pushed to the side with closed forceps. Also, care needs to be taken to place the sub-annular stitches very accurately around the junction of the right and non-coronary aortic leaflets, in order to avoid injury to the conduction system. (Video 5).

We then bring an appropriately sized vascular graft to the field. We use a modification of Svensson’s guidelines to size the graft [2]. In brief, we use a graft of at least 28mm in females and 30mm in males, which should always be at least 5mm bigger in diameter than the size of the aortic annulus. Prior to passing the annular stitches through the graft, we slightly bevel the one third of the graft that will correspond to the right cusp by cutting a curved segment with a maximal diameter of three or four graft divisions. This helps the graft sit more upright in the chest, instead of being directed toward the right. The sub-annular stitches are then passed through the graft (Video 6).

The subannular stitches are then tied, thus securing the graft around the aortic annulus. A Hagar’s dilator is passed through the valve before tying the stitches, in order to control the new size of the aortic annulus. The size of the Hagar’s dilator (and size of the aortic annulus) is determined based on the body surface area of the patient. We have been sizing patients with a BSA up to 2.0m2 to an aortic annulus of 21mm. If the BSA is over 2.0m2, we size them at 23mm. If the patients’ original annular size is less than the calculated numbers, we do not undersize them at all (Video 7).

The three commissures are then resuspended using 4-0 Prolene suture with a pledget on the endoluminal side in horizontal mattress fashion. These stitches exit the graft 6-7mm apart. The reason for this difference is to reduce the effective diameter of the neo-sinotubular junction and create three artificial bulges corresponding to the neo-sinuses. It is crucial to be very accurate both with the height of resuspension of each commissure, as well as with the distance between each resuspension, in order to avoid distortion of the aortic valve leaflet positioning. Remember that the three resuspension points are not necessarily perfectly symmetrical (120o). Their exact relationship should be established during initial inspection of the aortic valve, prior to separation of the coronary buttons (Video 8).

A preliminary view of the resuspended valve can be obtained at this point. Any corrections of the height of the commissural resuspension or adjustments of the distances between each resuspension point should be performed at this stage. A preliminary water test combined with visual inspection of the valve should give a good hint as to whether this will be a successful re-implantation (Video 9).

Re-implantation of the valve is performed using 4-0 polypropelene suture material. This is the only hemostatic layer of the root reconstruction and should be performed with utmost precision. The commissural resuspension stitches are utilized for this suture line, which is performed in “in-and-out” fashion (Video 10). Once this layer is completed, the valve is once again tested with a saline infusion of the root. If the result is not satisfactory at this point, the three valve leaflets can be resected and the valve replaced with the prosthesis of choice. We have had to do this once, and we found it easier to place the pledgets of the horizontal mattress stitches on the ventricular side (supra-annular AVR).

Coronary button re-implantation is performed in standard fashion, utilizing 5-0 polypropelene suture material, after an appropriate size hole is made on the side of the graft using the ophthalmic electrocautery. A mental note of the position of the buttons relative to the commissures (especially the right button) should be taken before the buttons are mobilized, in order to facilitate the choice of the exact point of re-implantation. We have found that adequate mobilization helps in preventing kinking or stretching after re-implantation.

It has also been our practice to re-implant the right coronary button after the distal anastomosis is performed (open or clamped). This maneuver further facilitates with the choice of the exact location of the reimplantation spot on the Hemashield graft.

After standard de-airing techniques, the clamp is removed and the heart is reperfused.

We always perform a TEE after termination of cardiopulmonary bypass, to assess any presence of aortic insufficiency as well as evaluate the symmetry of the reconstruction. The following video clip demonstrates the pre- and post-operative echo appearance of the aortic root (Video 11)

Post-operative care

Patients are usually extubated within 12 hours from their arrival to the ICU. The standard post- open heart surgery protocols are followed in terms of ulcer protection, early mobilization and physical therapy. Antibiotic prophylaxis is continued for 48 hours. Chest tubes are kept for 72 hours to allow for drainage from the graft “sweating”. A trans-thoracic echocardiogram is obtained prior to discharge.

Tips & Pitfalls

Take a good look at the left and right coronary ostia before cutting them off the sinuses of Valsalva.  Make sure you evaluate their asymmetry relative to their surrounding commissures. This will help with reimplanting them at the right spot, thus avoiding tension or kinking.

Mobilize the coronary buttons extensively. This will make them more flexible and easier to reimplant, while making the proximal portion of the main coronary arteries less likely to kink after re-implantation and pressurization.

The aortic valve commissures rarely form an equilateral (60o) triangle. They usually form an isosceles triangle, (two sides equal and one side slightly bigger or slightly smaller). Evaluate this relationship before taking the root apart, and try to recreate it when resuspending the valve.

Make sure you don’t puncture the right ventricle when mobilizing its fibers off the left ventricular outflow tract. It is VERY DIFFICULT to repair…

Don’t burn your 4-0 prolene resuspension suture line when burning the holes for the coronary buttons.

Do not accept a sub-standard result after your initial water test. The operation can be converted to a valved-conduit reconstruction fairly easily mid-way through the procedure. Remember that a button Bentall is an excellent operation with a superb long term track record.

References

1. Hilgenberg AD, Mora BN Composite aortic root replacement with a bovine pericardial valve conduit. Ann Thorac Surg 2003;75:1338-1339.

2. Svensson, LG Sizing for Modified David’s reimplantation procedure.
Ann Thorac Surg 2003;76:1751-1753.