Sarah Clark and John Kern
This chapter is a revision and update of that included in the previous editions of the TSRA Review written by Joshua B. Goldberg (2nd edition) and Stephen H. McKellar (1st edition).
Anatomy
The aortic root is a discrete anatomic region that begins at the aortoventricular junction and extends to the sinotubular junction, and it consists of the aortic annulus (also known as the aortoventricular junction), aortic valve cusps, sinuses of Valsalva, and sinotubular junction.
Despite the aortic valve not having a true fibrous annulus, the aortoventricular junction is more commonly known as the aortic annulus; 45% of the aortic root is attached directly to ventricular muscle and 55% is attached to the fibrous skeleton of the heart, specifically the membranous septum and the aortomitral curtain. Within the root lies the aortic valve, typically comprised of three semilunar cusps of differing sizes; however, a standard relationship exists within each cusp that the length of the base of a cusp is always 1.5 times longer than the length of its free margin. This relationship allows adequate coaptation length between the leaflets, providing valve competency. The three leaflets of the aortic valve are named according to their corresponding coronary artery, or lack thereof: left coronary cusp, right coronary cusp, and noncoronary cusp. In general, the noncoronary leaflet is usually slightly larger than the other two leaflets, and the left coronary leaflet tends to be the smallest. Each valve leaflet is scallop-shaped, with the nadir of each cusp delineating the aortoventricular junction. The highest point where two leaflets meet is known as a commissure, and the space beneath that commissure is termed the subcommissural triangle. Within each leaflet cusp are the sinuses of Valsalva, or the dilated pockets of the aortic root. These sinuses provide an essential space for eddy currents to form with closure of the aortic valve leaflets, thus providing valve competency and allowing coronary perfusion during diastole. Finally, immediately distal to each commissure is the sinotubular junction, the junction of the sinuses with the tubular ascending aorta. The diameter of the sinotubular junction tends to be 10-20% smaller than that of the aortic annulus in younger people; however, the elastic fibers of the aortic root dilate over time, causing the diameter of the sinotubular junction to be roughly equal to that of the aortic annulus in older people.
Pathophysiology of root aneurysms
The underlying pathophysiologic process leading to dilation of the aortic root is cystic medial necrosis, which is characterized by degeneration and fragmentation of elastic fibers, loss of smooth muscle cells, and replacement of the degenerated tissue with “cystic” ground substance within the wall of the aorta. This leads to a weakening of the aortic wall, predisposing the aortic root to dilation and dissection.
Aortic root aneurysms typically begin with dilation of the sinuses, and the dilation extends proximally into the aortic annulus and distally into the sinotubular junction. As the sinuses begin to dilate, this pulls the leaflet edges apart, resulting in valve insufficiency. Leaflet cusps can prolapse, thus also leading to aortic valve insufficiency, if the coaptation length of the free leaflet edge is elongated. Most commonly, these pathologic processes are the result of connective tissue abnormalities of the aortic wall, usually associated with genetically mediated connective tissue disorders such as Marfan syndrome, Ehlers-Danlos syndrome type IV, Turner syndrome, or familial thoracic aortic aneurysms. The valvular and tissue abnormalities associated with a bicuspid aortic valve are also known to predispose to aortic root dilatation. Finally, root dilatation can also occur as a result of atherosclerotic or hypertensive degeneration and infectious or inflammatory aortitis.
Presentation and diagnosis of root aneurysms
Patients with aortic root aneurysms are typically asymptomatic, and the pathology is incidentally discovered on CT scans or chest radiographs. They may have vague chest pain; however, severe chest pain in these patients typically indicates dissection or rapid expansion of the aneurysm. As the dilatation progresses, patients develop aortic valve insufficiency which can lead to dyspnea and other symptoms of heart failure. Patients with known genetic connective tissue disorders should be closely followed with serial computed tomography (CT) scans. Those who asymptomatic aneurysms who are being followed with serial imaging should also have aggressive blood pressure management; beta-blockers – with their negative inotropic and chronotropic effects – are known to be particularly useful for decreasing arterial hypertension, and thus, the rate of aneurysm dilation.
Indications for repair
Patients presenting with rupture of aortic root aneurysm or dissection into the aortic root represent a surgical emergency and should be taken to the operating room as soon as possible, provided they are not of prohibitive surgical risk. In patients with incidentally discovered root aneurysms or those being followed with serial imaging, however, the indication for surgical repair is directly related to the size of the aneurysm, as the most important determinant of risk of rupture of these aneurysms is their size.
Because the risk of rupture or dissection increases dramatically when the aneurysm diameter reaches 6 cm, current guidelines recommend elective repair in asymptomatic patients without concurrent cardiac pathology or known connective tissue disorder when aneurysm diameter reaches 5.5 cm (as measured by CT scan) or if the rate of dilatation exceeds 0.5 cm per year. This size cutoff decreases to 5 cm in patients with a bicuspid valve or patients with a family history of aortic dissection or genetically linked aortopathies such as Marfan syndrome; however, in patients with Loeys-Dietz syndrome, repair is recommended at a sinus diameter of 4 cm, as these patients are known to suffer aortic dissections when the aortic diameter is much less than 5.0 cm. In patients undergoing cardiac surgery for other reasons (i.e., coronary artery disease, valvular disease), widespread practice is to repair or replace the aortic root at diameters greater than 4.5 cm. Finally, patients with aortic valve endocarditis may also have extension of the infection and abscess formation within the root, thus necessitating a root replacement.
Repair techniques
Surgical management of aortic root pathologies can be classified into two broad categories: root replacement with valve replacement [which includes root replacement with a pulmonary autograft otherwise known as a Ross procedure and root replacement with a stentless porcine root replacement (Freestyle valve)] and aortic valve-sparing root replacement. Deciding which is the most suitable procedure for a given patient depends on the patient’s age, underlying diagnosis, and the condition of the aortic valve. With all of these repair techniques, patients undergo central aortic and venous cannulation, unless the distal extent of the aneurysmal aorta precludes central aortic cannulation. In those cases, an 8 mm Dacron graft can be sewn to the right axillary artery and directly cannulated, thus allowing work on the arch and antegrade cerebral perfusion during deep hypothermic circulatory arrest, if necessary. Cardioplegia for cardiac arrest and subsequent myocardial protection is administered via retrograde cannulation of the coronary sinus and intermittently through intermittent direct cannulation of the coronary ostia. Finally, a left ventricular vent is placed in the right superior pulmonary vein to maintain left ventricular decompression.
In many patients with aortic root aneurysms, the aortic valve is morphologically normal or competent without flow-limiting calcification. In this subgroup of patients, a valve-sparing root replacement is an attractive option to prevent future structural valve deterioration or annular dilatation that can occur following root replacement with a composite valve graft. There are a variety of modifications to the valve-sparing root replacement, and the two most widely used techniques are the remodeling and the reimplantation techniques. The remodeling technique introduced by Yacoub reduces the aortic root and recreates neosinuses of Valsalva with a Dacron tube graft but does not address the aortic annulus. The reimplantation technique introduced by Dr. Tirone David is the most widely used technique. This “David” technique begins with transection of the aorta at the sinotubular junction, and right and left coronary buttons are excised. The residual aorta is trimmed, leaving approximately 8 mm of native aorta. Next, dissection of the root proceeds with separation of the root from the pulmonary artery, right ventricular outflow tract, and the left atrium, ideally continuing below the level of the aortic annulus. Aortic valve leaflet height is essential to maintaining valve competency; thus, graft sizing is of paramount importance. This can be easily estimated with a Hegar dilator placed across the valve that fits comfortably within the outflow tract. Then, 5 mm (2.5 mm on either side of the outflow tract) and 6 mm (to allow for billowing of the graft) are added to the dilator number; this usually results in a graft size varying from 32–38 mm. Alternatively, a Valsalva graft with premade sinuses can be used. Next, horizontal mattress sutures are placed circumferentially in the subannular plane at the level of the basal ring, and these sutures are placed through the previously sized Dacron graft. When that is completed, the graft is parachuted into position with the valve and all aortic layers within the lumen of the graft. The Hegar dilator that was used to size the annulus is placed across the annulus, and the three subcommissural sutures are tied first, thus slightly plicating the graft under each commissure and narrowing the valvular subcommissural angle, which is essential to achieving valve competence. Additional horizontal mattress sutures are placed from inside to out at the tops of the valve commissures to anchor the commissures and ensure adequate leaflet coaptation along their free margins, and these sutures are used to suture the aortic cuff to the distal end of the graft in a running fashion. The coronary buttons are then reimplanted, and the distal aortic-graft anastomosis is completed.
Although the aortic valve can be spared in many patients with moderate or even severe aortic insufficiency, a functional and durable valve repair is unlikely in patients with significant aortic valve pathology or calcification. In its modern iteration, the aortic valve and root are replaced with a composite valve graft (modified or button Bentall). The aneurysmal tissue of the root and the aortic valve leaflets are resected, and coronary buttons are harvested for reimplantation. A Dacron conduit containing a mechanical or bioprosthetic valve (bio-Bentall) is sutured intra-annularly, with oversizing of the graft to recreate the aortic sinuses or with use of a graft of prefabricated sinuses (Valsalva graft). Openings in the graft are created for coronary reimplantation, and each coronary button is anastomosed to the graft. The graft is then trimmed to size, and the distal anastomosis is sutured.
Valve-sparing root replacement and root replacement have been demonstrated as equivalent, and among patients undergoing valve-sparing root replacement, the reimplantation technique is associated with a reduced rate of reintervention compared with the remodeling technique.
Suggested Readings
- Cohen RG, Elsayed RS, and Bowdish ME. Surgery for Diseases of the Aortic Root. Cardiol Clin. 2017. 35:321-329.
- Ikonomidis JS. Valve-Sparing Aortic Root Replacement – “T. David V” Method. Op Tech Thor Cardiovasc Surg. 10:281-296.
- Kouchoukos NT, Haynes M, Baker JN. The Button Bentall Procedure. Op Tech Thor Cardiovasc Surg. 2019. 23:50-61.
