Surgical approach to diseases of the aortic valve and aortic root

Median sternotomy

The median sternotomy is the standard and most common approach for aortic valve and root procedures. The skin incision is vertical and directly overlies the sternum, which is divided from the sternal notch superiorly to the xyphoid process inferiorly. Complete exposure of the aorta and heart allows concomitant procedures such as coronary artery bypass grafting (CABG), multiple-valve procedures, surgical ablation of atrial fibrillation, and left atrial appendage closure. Rigid closure of the divided sternum at the completion of the case with steel wire cerclage is generally well tolerated, although temporary upper-body weight restrictions (i.e., sternal precautions) are required during convalescence.

Minimally invasive approaches

Minimally invasive approaches to AVR include any incision that does not involve a complete median sternotomy, most commonly the upper hemisternotomy and the right anterior thoracotomy. Cosmesis has been the driving factor associated with the development of minimally invasive approaches, and these approaches have not been shown to compromise safety despite longer periods of cardiopulmonary bypass. Potential benefits of a minimally invasive approach include reduction in postoperative bleeding, intensive care unit stay, and hospital length of stay.

Upper hemisternotomy

The upper hemisternotomy is performed through a vertical skin incision 5 to 8 cm below the angle of Louis ( Fig. 14.2 ). The sternotomy is extended into the right third or fourth interspace as a J-shaped incision. Alternatively, the sternum can be divided transversely with a T-shaped incision. Cannulation for cardiopulmonary bypass and cardioplegic arrest can be performed through the incision or through peripheral sites. Exposure of the aortic valve and root is uncompromised, and conduct of the operation is unchanged compared with the median sternotomy approach.

Right anterior thoracotomy

The right anterior thoracotomy is performed through a horizontal skin incision 4 to 7 cm lateral to the sternum ( Fig. 14.3 ). The chest cavity is entered in the second or third interspace, often with division of the right internal thoracic vessels. The lower rib is disconnected from the sternal edge to improve exposure. Cannulation for cardiopulmonary bypass and cardioplegic arrest is performed peripherally. The aortic valve is well visualized, but long-handled instruments are required to complete the valve replacement. No sternal precautions are required for the minithoracotomy approach.

Bioprosthetic valves: Stented

The valve most commonly used to replace the aortic valve is a stented bioprosthetic valve constructed of bovine pericardium ( Fig. 14.4 A) or an actual porcine valve (see Fig. 14.4 B). These valves have several advantages: (1) ease of implantation and the rare occurrence of clinically significant patient-prosthesis mismatch (PPM) due to improving valve hemodynamics; (2) no need for lifelong oral anticoagulation (unless the patient requires it for a different reason); (3) a relatively straightforward future reoperation, if one is necessary; and (4) the potential for a valve-in-valve (VIV) procedure using a transcatheter heart valve for bioprosthetic valve failure. The most important disadvantage to tissue valves is the occurrence of structural valve deterioration (SVD), which is primarily age dependent.

The technical aspects of AVR with a stented bioprosthetic valve are straightforward. The aortic valve can be exposed through a variety of aortotomy incisions (i.e., hockey stick, transverse, or oblique). The aortic valve is excised, and the annulus is completely debrided of calcific plaques, with care taken in the area of the conduction system (below the commissure between the noncoronary and right coronary cusps). Calcific extensions on the aortic root, left ventricular outflow tract, and anterior leaflet of the mitral valve are removed. With adequate debridement of annular calcification, paravalvular leak is rare, and with current-generation bioprostheses, clinically significant PPM is uncommon.

Sutureless valves

The most recent advance in bioprosthetic valve technology is the sutureless or rapid-deployment valve (see Fig. 14.4 C and D, respectively). First implanted in humans in 2005, sutureless valves have a metallic stent frame similar to those seen in transcatheter heart valves. The frames extend beyond the aortic annulus into the left ventricular outflow tract and achieve a seal without the need for complete suturing. Unlike the case with transcatheter valves, complete excision of the native aortic valve is required.

Two valves have been approved for commercial use in the United States and Europe and have shown safety and efficacy ( Table 14.1 ). Benefits include shorter aortic cross-clamp and cardiopulmonary bypass times, which may facilitate minimally invasive approaches and cases of difficult full-sternotomy AVR involving reoperation, delicate aortic wall, concomitant procedures, or small aortic root. A symmetric bicuspid aortic valve (BAV) with two commissures and no raphes (i.e., Sievers type 0) and annular destruction due to complex infectious endocarditis are contraindications for this class of valves. ^,

Use of sutureless and rapid-deployment valves has reduced early postoperative complications, potentially translating into reduced resource consumption such as length of stay and hospital costs. As with all new valve technology, the long-term durability of sutureless valves has not been proved, and equipoise remains regarding the durability in younger patients.

Bioprosthetic valves: Stentless

Stentless bioprosthetic valves made from porcine aortic valves became available in the 1990s (see Fig. 14.4 E) and were followed by stentless bovine pericardial valves (see Fig. 14.4 F). The advantages of this type of valve are (1) improved hemodynamics compared with stented biologic and mechanical valves and (2) the option to replace the entire aortic root, including the aortic valve, for combined valve and aortic disease (using the stentless porcine root). The disadvantages of stentless valves are (1) a more complex operation requiring a full root technique with reimplantation of the coronary ostia ( Fig. 14.5 ), a root inclusion technique, or a subcoronary technique and (2) recent concerns regarding freedom from SVD. The full root technique requires resection of the aortic root in addition to the aortic valve (described later). In the subcoronary and root inclusion techniques, only the aortic valve is excised, and the stentless valve is implanted within the native aortic root. Of these two, the subcoronary technique is more commonly performed ( Fig. 14.6 ).

Typically, two suture lines are required for the stentless porcine valve. The proximal line is a circular suture line at the level of the annulus, and the distal line follows the scallop-shaped leaflet insertion line below the level of the coronary arteries. In some stentless bovine pericardial valves, only a single distal line is required for implantation.

Mechanical valves

Mechanical valves have the advantages of long-term durability and a long track record with designs that have been durable for decades. The major disadvantages are (1) the need for lifelong anticoagulation (i.e., warfarin), (2) a higher risk for thromboembolism compared with bioprosthetic valves, and (3) audible clicking of the normally functioning mechanical valve, which may be troubling to some patients.

The On-X mechanical valve (Cryolife Inc., Austin, TX) was first implanted in 1996 ( Fig. 14.7 ). It has a low rate of adverse clinical events per patient-year, including 0.6% for thromboembolism, 0.4% for bleeding, and 0% for thrombosis when the valve is used in the aortic position.

A randomized clinical trial using the On-X aortic valve, completed in 2014, demonstrated the safety of lower doses of warfarin in AVR patients. The valve was subsequently approved by the U.S. FDA for expanded labeling that allows patients, starting 3 months after AVR, to be maintained at an international normalized ratio (INR) clotting score of 1.5 to 2.0. This approval is reflected in guideline recommendations for the On-X valve (class IIb), rather than the standard target INR of 2.5 recommended for all other mechanical valves (class I).