Ann Thorac Surg 1998;66:280-284
© 1998 The Society of Thoracic Surgeons
How to Do It
Implantation technique of aortic homograft root: emphasis on matching the host root to the graft
William F. Northrup, III, MDa,
Vibhu R. Kshettry, MDa
a Cardiac Surgical Associates, PA, Minneapolis, Minnesota, USA
Accepted for publication March 4, 1998.
Address reprint requests to Dr Kshettry, 920 E 28th St, Suite 420, Minneapolis, MN 55407
e-mail: (vkshettry{at}csa-heart.com)
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Abstract
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The technique of homograft aortic root replacement in our practice has evolved as our experience has increased. This technique is described and illustrated. In most cases, aortic annuli are reduced by using various suture techniques to match the homograft. This allows for a successful implantation of a normal-sized aortic homograft root in a patient with a diseased aortic valve and annular dilatation.
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Introduction
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Aortic valve replacement using an aortic homograft or pulmonary autograft has a growing appeal to patients and surgeons because it provides a long-lasting valve without the inconvenience, expense, and potential hazard of anticoagulation that may be associated with mechanical prosthetic valves [1]. Although these grafts were introduced clinically more than three decades ago [2, 3], a resurgence of interest has recently occurred in their use for replacement of the diseased aortic valve in selected patients [4].
The insufficient commercial availability of aortic homografts in large diameters and the more complex surgical implantation techniques that they require have limited the use of homograft tissue for aortic valve replacement. In addition, there is a prevalent assumption that a substantial mismatch between the host aortic annulus and homograft precludes implantation. However, many aortic annuli are dilated as a result of disease and not because of their original dimensions. Therefore, correspondingly large homografts are not required in these cases. Still, the host root in such cases must be tailored to match the graft annulus for aortic valve homografts to function properly. We present a technique of aortic root replacement with a homograft that circumvents the problem of annulus mismatch.
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Technique
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After a median sternotomy, standard techniques are used to establish cardiopulmonary bypass. The myocardium is preserved with blood cardioplegia delivered via the retrograde route. The ascending aorta is cross-clamped with a soft-jaw clamp below the innominate artery take-off. The aorta is transected 1.0 cm distal to the aortic commissures. Traction sutures are placed above each commissure and coronary ostium to provide proper orientation and radial retraction. The aortic valve leaflets are then excised. Anatomic landmarks of the host aortic root are identified (Fig 1). Next the locations of the host coronary ostia are noted (Fig 2).
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Fig 1. Anatomic landmarks of left ventricular outflow tract and aortic root. (a) Surgeon’s view of the aortic root from the right side. (b) Opened aortic root. (c) Approximately 55% of the left ventricular outflow tract is fibrous and 45% is muscular.
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Fig 2. Measurement of coronary distance above the horizontal plane of annulus and intercoronary distance across left/right commissure. These measurements are taken as a guide for selecting the proper site of the host coronary ostia implantation in the homograft. The surgeon should not be committed to using the homograft coronary ostia if they are not in location corresponding to those of the host.
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Host coronary ostia "buttons" are prepared using most of the sinus wall. The plane immediately behind the aortic sinus is relatively avascular and easily developed with blunt dissection. Mobilization of coronary arteries is avoided. Only the buttons themselves are mobilized from the surrounding aveolar tissue. Both coronary arteries are "implanted where they lie" in the host.
The host aortic annulus is sized with a cylindric valve sizer. If the diameter of the host annulus is more than 2 mm greater than the diameter of the homograft, a reduction annuloplasty of the host is required. The final host aortic annulus diameter should be only 1 to 2 mm larger than the graft to ensure that the graft is seated within rather than above the left ventricular outflow tract. Diameter reduction is related to the degree of circumferential reduction according to a 3:1 mathematical relationship (
) (ie, for every 3 mm of plication around the linear plane of the circumference, a 1 mm reduction in diameter is achieved). Five priority zones in the host annulus are suggested for reduction annuloplasty in descending order (Figs 3–5):
- Non/left interleaflet triangle
- Left/right interleaflet triangle
- Right/non-interleaflet triangle
- Aortic/mitral curtain
- Muscular septum
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Fig 3. Priority zone 1 (non/left interleaflet triangle): reduction annuloplasty with figure-of-8 suture. Ten- to 15-mm plication can be achieved without distorting adjacent structures.
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Fig 4. Priority zone 2 (left/right interleaflet triangle): reduction annuloplasty using mattress compression suture.
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Fig 5. Priority zone 3 (right/non-interleaflet triangle): deep sutures are avoided because of risk of injury to conduction tissue. This site for reduction annuloplasty is rarely used. Also shown are priority zone 4 (aortic–mitral curtain) and priority zone 5 (muscular septum and free wall).
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The amount of tissue plicated along the circumference of the aortic annulus is equal to the interval within the loop of the suture (ie, a 10-mm interval of tissue incorporated accomplishes a 10-mm plication). Large plications in the range of 10 to 15 mm can be accomplished in non/left and left/right interleaflet triangle using figure-of-8 sutures without distorting adjacent structures. For plications between 5 and 10 mm, simple horizontal mattress compression sutures along the fibrous or muscular left ventricular outflow tract can provide additional annular reduction if required.
The homograft is prepared and trimmed, leaving a 3 mm cuff of tissue below the annulus. The three commissures are identified and marked with 6-0 monofilament suture placed inside out just above the commissure, creating an external reference point. With gentle lateral traction to simulate a distended root, the distance between each commissure (between the external marks) is measured and recorded. This allows a precise measurement of each of the sinuses and the circumference and diameter of the graft at the plane of the sinotubular junction. The lateral dimension of each sinus allows for accurate placement of pilot sutures in the host annulus to mark the vertical plane of the commissures, the nadir of the sinuses, and selection site of coronary ostia implantation in the graft without distortion. It is interesting to note that sinuses in the host and the graft are frequently asymmetric.
Using the measurement of the host coronary ostia, holes are fashioned in the homograft with an aortic punch. If the homograft coronary ostia cannot be used, coronary stumps are oversewn with 6-0 monofilament suture. A 1-cm-wide strip of pericardium measuring 
cm longer than the external circumference dimension of the graft annulus is obtained and kept aside for later use.
With the aid of tissue valve sizer with the three-pointed "Mercedes" star, three pilot commissure sutures of 4-0 Cardionyl (Peters, Paris, France) are placed in the host annulus to mark the location of the vertical plane of the graft commissures. Cardionyl suture is used because it is slightly elastic and has not coil memory. The non/left commissure suture is placed in the annulus first to facilitate the location of the implantation of the left coronary ostium. It is important to be certain that this first pilot suture is precisely placed, because the remainder of the host-graft relationship depends on its accuracy.
The three commissure sutures are the first to be placed in the graft. The remaining interrupted sutures are then placed in each corresponding sinus of host and graft, filling in from commissure to the middle pilot suture on each side, placing the middle suture through the graft last. Special care is taken while passing sutures through the graft, avoiding injury to the aortic cusps. This sequence is repeated for each of the two remaining sinuses. Minor mismatch between the host and graft annulus can be corrected by taking slightly wider intervals in the host rather than the graft (Fig 6). The graft is parachuted to achieve proper seating. The prepared pericardial strip is passed within each suture loop, then the sutures are tied and cut (Fig 7). Next the coronary buttons are sutured to the graft with a running 5-0 Cardionyl (Peters, Paris, France) (Fig 8).
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Fig 6. Correction of minor mismatch between host graft annulus by taking wider (2- 3-mm) intervals in the host annulus. This results in circumferential plication of the annulus when sutures are tied. (a = 1- 2-mm suture interval in the graft annulus; b = 2- 3-mm suture interval in recipient annulus; c = circumferential plication of recipient annulus.)
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Fig 7. One end of the pericardial strip is anchored by passing a suture through it. The pericardial strip is passed within each suture loop evenly distributed, and the sutures are securely tied and cut. This buttressing strip of pericardium aids in hemostasis and prevents any late dilatation of the annulus.
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Fig 8. Coronary button anastomosis. The suture line is placed around the edge of coronary ostia, incorporating surrounding aortic tissue. The host aortic sinus wall outside the suture line with its broad surface of coaptation against the graft serves as its own buttress to facilitate hemostasis—an endobutton buttress. The distal suture line is reinforced with a pericardial strip.
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The distal ascending aorta is tailored to match the graft and anastomosed end-to-end with a running 3-0 Cardionyl suture. After standard deairing techniques, the aortic clamp is released. After the patient is weaned from cardiopulmonary bypass and satisfactory hemodynamics and hemostasis are achieved, a strip of pericardium is placed around the distal suture line. This provides hemostasis and support to prevent late dilatation of the distal suture line. The sternotomy is then closed in a standard manner.
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Comment
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The anatomy of the aortic root is complex [5]. Although the aortic valve does not have a true annulus as the mitral valve does, surgeons use the term "aortic annulus" to describe the ventriculoaortic junction. There is a discrepancy between the anatomic and hemodynamic ventricular-aortic junction because of the semilunar attachments of the leaflets. The horizontal plane of the anatomic ventriculoaortic junction occurs just distal to the nadir of the aortic sinuses, so that a small amount of ventricle is actually present within the base of each sinus. Similarly, the interleaflet triangles between the top of the commissures and the plane of the anatomic ventriculoaortic junction represent the aortic wall below the annulus. The entire cylinder forming the aortic root and supporting the valve leaflets can be considered to represent a ring. The reduction of the annulus is done in the horizontal plane of this imaginary ring just below the level of the anatomic ventriculoaortic junction, except in the area of the conduction system in the base of the right/non-interleaflet triangle.
The diameter of the normal aortic annulus in adults varies depending upon the individual size. In a study by Cryolife Inc (Cryolife Inc; personal communications, 1997) of 2,180 normal adults (810 women and 1,370 men) for those with a body surface area of 1.5 to 1.6 m2, the mean diameter of the aortic annulus was 20.1 ± 1.8 mm in women and 20.2 ± 1.9 mm in men. For those with a body surface area of 2.0 to 2.1 m2, the mean diameter of the aortic annulus was 21.7 ± 1.4 mm in women and 23.1 ± 1.7 mm in men. Many large host aortic annuli are secondarily large because of disease and not because of original dimensions. These annuli require reduction annuloplasty rather than corresponding large aortic homografts.
Many surgical techniques have been described to facilitate implantation of an aortic homograft [6–8]. It is of paramount importance that efforts be directed at ensuring that the homograft maintains its original dimension. All revisions are made in the host annulus and not in the graft. We have successfully used this technique in 30 homograft aortic root replacements where host annulus diameters have been reduced up to 15 mm to match the graft with excellent postoperative graft function.
The potential clinical and hemodynamic advantages of aortic homograft versus conventional mechanical or xenograft valve prostheses are now being recognized. Successful implantation and functioning of the aortic homograft root requires careful attention to technical details.
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References
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- Petterson G. Surgical treatment of aortic valve disease in the nineties with special emphasis on the use of pulmonary autograft (the Ross operation). Ann Chir Gynaecol 1995;84:251-259.[Medline]
- Ross D.N. Homograft replacement of aortic valve. Lancet 1962;2:487.[Medline]
- Ross D.N. Replacement of the aortic and mitral valves with a pulmonary autograft. Lancet 1967;2:956-958.[Medline]
- Santini F., Dyke C., Edwards S., et al. Pulmonary autograft versus homograft replacement of the aortic valve: a prospective randomized trial. J Thorac Cardiovasc Surg 1997;113:894-900.[Abstract/Free Full Text]
- Anderson R.H., Devine W.A., Ho S.Y., Smith A., McKay R. The myth of the aortic annulus: the anatomy of the subaortic outflow tract. Ann Thorac Surg 1991;52:640-646.[Abstract]
- Elkins R.C., Knott-Craig C.V., Howell C.E. Pulmonary autografts in patients with aortic annulus dysplasia. Ann Thorac Surg 1996;61:1141-1145.[Abstract/Free Full Text]
- O’Brien M.F. Allograft aortic root replacement: standardization and simplification of technique. Ann Thorac Surg 1995;60:592-594.
- Doty D.B. Aortic valve replacement with homograft and autograft. Semin Thorac Cardiovasc Surg 1996;8:249-258.[Medline]
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Abstract
Introduction
