Operation through a smaller incision makes valve surgery easier on the patient. Because of improved durability, more tissue valves are implanted compared to mechanical valves. The latest development is percutaneous replacement of aortic valves and repair of mitral valves.
Surgery directed at valvular heart conditions dates back almost 80 years when the first efforts were made to relieve mitral valve stenosis. Rheumatic fever was a common disease worldwide and frequently resulted in mitral stenosis. The scarred two-leaflet mitral valve appeared to be an easy target for simple division of the fused valve leaflets along the closure plane of the valve. A few daring attempts by brave surgical pioneers to open the obstructed valve while the heart was beating and pumping blood throughout the body almost always ended in failure and the death of the patient. But occasional by such mitral commissurotomy was successful and, as predicted, when the obstruction to blood flow through the valve was relieved, heart function improved considerably.
Arrival of the heart-lung machine
Despite those rare attempts at direct valve repair, it was not until the heart-lung pump with a blood oxygenator became available that heart valve surgery became widely practised. In the early 1960s, ‘open heart’ surgery became feasible and relatively safe with the development of cardiopulmonary bypass. Surgeons continued to treat the still common condition of mitral stenosis, including many who persisted in using ‘closed heart’ approaches to performing mitral commissurotomy. The major attention in the early days of open heart surgery, however, was directed to the aortic valve which required that the patient be on full cardiopulmonary bypass support in order to work in a bloodless field.
The development of heart valve prostheses
The other requirement for successful treatment of a diseased or deformed aortic valve was a valve substitute, or prosthesis, that could be used to replace the diseased native valve. Heart valve prostheses, both mechanical and those fashioned from biological material and usually derived from pig or cow heart tissue, have undergone multiple iterations over the 50 years of heart valve replacement. Currently available heart valve prostheses represent excellent refinements of earlier devices, but there have been few major innovations in design or manufacture of heart valve prostheses over the past 20 years. Current innovations in heart valve surgery have been directed more toward refinements to the operative approaches and technical aspects of valve surgery itself.
Repair, don’t replace, a leaking mitral valve
Today’s heart valve surgical innovators are a relatively small group of heart surgeons, representing, perhaps, fewer than 20 per cent of practising cardiac surgeons. Although heart valve surgery and surgery for the treatment of congenital heart defects were the most commonly performed procedures during the first two decades of open heart surgery, coronary artery bypass surgery has dominated the field since the late 1970s. Most currently practising heart surgeons are expert coronary bypass surgeons, but their experience with heart valve surgery may be quite limited. This is an especially important consideration today since the most important ‘innovation’ in heart valve surgery over the past two decades has been the successful evolution of mitral valve repair surgery for the treatment of mitral valve insufficiency. In the Western world, with the dramatic decline in rheumatic fever, mitral stenosis is much less common. At the same time, mitral insufficiency, due either to structural deterioration of the valve or secondary to changes in left ventricular geometry from chronic ischemic heart disease, has become a common indication for heart valve surgery.
Structural repair of the leaking mitral valve whenever possible, rather than replacement of the valve with an artificial prosthesis, has been shown to be decidedly better in virtually all important respects, with fewer perioperative deaths and better late outcomes. Some estimate that as many as 80 per cent of leaking mitral valves are amenable to successful repair. Despite compelling outcomes, and data favouring repair rather than replacement, fewer than 50 per cent of patients with mitral valve insufficiency undergo valve repair, but have mitral valve replacement instead. This disappointing statistic has resulted from the fact that many cardiac surgeons have not mastered the technical challenges of valve repair. The clear advantage of mitral repair over replacement with either a mechanical or biological prosthesis has been established by multiple surgical series, making repair rather than replacement mandatory whenever feasible. Since many practising cardiac surgeons are not comfortable attempting mitral valve repair, the referring physician should select for referral of a patient with mitral valve insufficiency only to a surgeon who is capable of and willing to repair the incompetent mitral valve whenever anatomically feasible.
Minimally invasive or limited incision heart operations
The other important innovation in heart valve surgery over the past decade has been the successful development of alternate, and often less invasive, surgical incisions for valve repair or replacement surgery. The standard and most common incisional approach used by heart surgeons over many years is the median sternotomy incision. This operative approach entails a midline incision from the base of the neck to the upper abdominal wall, exposing the sternum which is then completely divided using a bone saw. For most cardiac surgical procedures performed on cardiopulmonary bypass, full exposure of the heart and great vessels within the pericardium and adjacent mediastinum facilitates the necessary operative manoeuvres, provides the surgeon with full exposure of the heart to deal with any unexpected problems, and is in fact necessary to allow for full exposure of the posterior or inferior aspects of the heart. Some negative physiological consequences of a full sternotomy incision, especially when combined with entry into one or both pleural spaces, include respiratory insufficiency, increased post-surgery wound inflammation and greater blood loss.
Patients with these extensive surgical incisions experience slow recovery and long convalescence. While many surgeons have eschewed the challenge of minimally invasive approaches, complaining that smaller incisions restrict their procedural options and add unnecessary risk for the patient, operations performed through smaller incisions generally result in less discomfort, less blood loss and corresponding reduction in the need for transfusion, more rapid recovery and few wound complications.
The hemi-sternotomy incision
The partial sternotomy approach, sometimes referred to as a hemi-sternotomy incision, represents an important innovation for heart valve surgery. The most common application of a hemi-sternotomy incision in heart valve surgery has been the upper partial sternotomy approach for aortic valve repair or replacement. The sternum is divided from the suprasternal notch and may be carried laterally for a short distance into the 3rd or 4th intercostal space. For an aortic valve procedure, this ‘J’ incision, as it is often referred to, may be directed medially to the left or laterally to the right, depending upon the patient’s unique anatomy. If the mitral valve is the target of procedure, the partial upper sternotomy is generally carried laterally into the 3rd intercostal space. Less commonly used is the lower partial sternotomy incision that some surgeons have employed for mitral valve procedures. The primary disadvantage of the lower partial sternotomy is poor exposure of and access to the ascending aorta for cannulation and cross clamping. If the lower sternotomy approach is used for a mitral valve procedure, arterial access for cardiopulmonary bypass is usually obtained via the femoral artery and the aorta is not cross-clamped. An additional disadvantage of any hemi-sternotomy incision that is carried medially or laterally into an intercostal space is the need to sacrifice the internal mammary artery on that side.
Mitral valve surgery through a right chest wall incision
Although some have used a partial lower sternotomy incision to expose the mitral valve for repair or replacement, the more commonly used ‘less invasive’ incisional approach for a mitral valve procedure is a right lateral thoracotomy incision via the 4th intercostal space. Chest wall muscle sparing and careful rib spreading will minimise chest wall trauma and generally will provide for excellent exposure of the left atrium and mitral valve along with adequate exposure of the ascending aorta. Depending on individual anatomic variations, however, the ascending aorta may not be accessible for cannulation or even cross-clamping from right chest incision. Despite the procedural challenges, the right thoracotomy approach through a small incision has been mastered by many skilled cardiac surgeons and has been shown to be well tolerated by patients as well as hastening postoperative convalescence and full recovery.
Another incisional approach that has been used by some is the right parasternal incision, made over the 2nd to 4th intercostal spaces. It is necessary to incise the corresponding costal cartilage tissue that often resulted in a chest wall defect and lung herniation. For this reason, the right parasternal approach has been largely abandoned. While the upper partial sternotomy can be reliably used for exposure of the aortic or mitral valves, this incision is not suitable if the patient requires concomitant coronary artery bypass grafting.
As is the case with mitral valve repair versus the technically easier mitral valve replacement option, undertaking an aortic or mitral valve procedure through a smaller surgical incision is generally more technically challenging and may, in fact, be riskier. When working on the aortic valve through a partial upper sternotomy, deairing of the left heart chambers may be more difficult, and accessing a tear or disruption on the posterior or lateral aspects of the aorta or adjacent pulmonary artery may be very difficult. Conversion to a full sternotomy incision under such circumstances may be necessary. The dilemma that the surgeon faces when pondering a smaller incision is whether to perform a procedure that will be easier on the patient but technically more challenging for the surgeon. The other important consideration is whether any added risk related to limited surgical field exposure is worth the benefit of the smaller incision and reduced surgical trauma. The referring physician bears some responsibility for determining the appropriateness of the procedure: is surgery indicated and is this the right time for the patient to undergo the operation. The referring doctor must also take into consideration the capability of the surgical team, especially when the procedure involves additional technical challenges related to valve-sparing repairs and smaller incisions.
Heart valve repair and replacement performed without surgery
The most important current innovation in heart valve surgery has been the development of transcatheter techniques for repair or replacement of heart valves. Just as has been the case with percutaneous transcatheter treatment of coronary artery disease, catheter delivery of valve prostheses for valve replacement is now a reality. In addition, percutaneous catheter techniques have been developed to reduce mitral valve insufficiency. To treat aortic valve stenosis, two transcatheter devices have been implanted successfully in hundreds of patients with excellent results in terms of safety and efficacy. Both are bioprostheses mounted on a balloon catheter. In the more common approach, the catheter is threaded into place in the aortic root retrograde through the aorta via a trans-femoral or iliac artery insertion site. Alternately, the catheter with the collapsed valve prosthesis is inserted through the left ventricular apex into the aortic root. The balloon is then inflated, compressing the native aortic valve, followed by deployment and expansion of the valve prosthesis snugly into place in the aortic annulus.
For transcatheter mitral valve repair, two options have been used successfully over the past several years. The technique referred to as transcatheter mitral annuloplasty involves insertion of a semi-rigid device into the coronary sinus directly adjacent to the posterior aspect of the mitral valve. With successful sizing of this annuloplasty device, the dilated posterior mitral annulus is compressed or shortened by the device, reducing the dilation of the annulus and rendering the valve more functional and less insufficient. The other technique involves apical septal puncture and placement of a catheter into the left atrium. Using fluoroscopic and echocardiographic imaging of the valve leaflets, a clip is deployed in such a way as to attach the central leading edges of both mitral leaflets. With this technique, a billowing and incompetent mitral valve is converted from a single leaking orifice to a more effectively closing double-orifice valve.
While many patients have been successfully treated with transcatheter mitral repair devices or have had transcatheter aortic valve replacement, the longterm durability, especially of the mitral repairs, remains to be demonstrated. Regardless, these innovations have been transforming. In the case of transcatheter aortic valve replacement, many people in need of relief from progressive aortic stenosis who may not have tolerated surgical valve replacement have, and will be, successfully treated. As we have experienced with percutaneous stent therapy for obstructive coronary artery disease, the availability of percutaneous techniques for heart valve disease will greatly increase the number of those benefitting for heart valve therapy. It is remarkable to reflect on the progress in heart valve surgery over the past 80 years. Who could have predicted the success of heart valve surgery or the development of transcatheter heart valve repair and replacement!
Technical innovations in handling diseased valves
1. Preferential repair of a leaking mitral valve instead of replacement with a prosthesis
2. Valve-sparing replacement of a dilated or dissecting aneurysm of the ascending aorta instead of replacement
3. Routine repair of a leaking tricuspid valve rather than valve replacement with a prosthesis
4. Repair of selected leaking tricuspid and bicuspid aortic valves instead of replacement with a prosthesis
5. Direct-vision commissurotomy of stenotic mitral valves
Innovative operative approaches in heart valve surgery
• Greater use of smaller incisions to expose the valve (“limited incision” or “minimally invasive” heart valve surgery)
• Upper or lower “hemi-sternotomy” approaches for isolated aortic or mitral valve procedures instead the traditional full median sternotomy incision
• Right lateral thoracotomy approach to the mitral valve
• Increasing use of peripheral cannulation (femoral or iliac artery, internal jugular and/or femoral vein) for cardiopulmonary support when using a very small chest incision to expose the targeted area of the heart
• Use of full Port Access approach for mitral valve repair via a 10cm or smaller right thoracotomy incision, including femoral or iliac artery cannulation and internal jugular and/or femoral vein cannulation to establish cardiopulmonary bypass support, use of a percutaneous endo-clamp catheter to arrest the heart, remote and magnified visualisation of the surgical site, and use of elongated surgical instruments including scalpel, scissors, suture needle driver and knot tying tools, all of which allow for extra-thoracic instrumentation of the valve repair.
Trends and improvements in heart valve prostheses
• Improved durability of bioprostheses (tissue valve substitutes), resulting from improvements in harvest, preservation and production techniques
• With improved durability of bioprostheses, the proportion of mechanical valve prostheses implanted is declining compared to use of bioprostheses
• Availability of multiple mitral valve annuloplasty rings for varied anatomical conditions for use in mitral valve repair
• Recent availability of self-monitoring devices for prothrombin time calculation greatly facilitates daily warfarin dosing for patients with mechanical heart valve prostheses.
Timothy J Gardner is a noted heart surgeon and leader in cardiovascular medicine in the US. He is Medical Director of Christiana Care’s Center for Heart & Vascular Health. He was chief of the Division of Cardiothoracic Surgery for the University of Pennsylvania Health System from 1993-2003. He has lectured extensively both nationally and abroad and he is the author of nearly 200 scientific papers and has edited or contributed to many texts on cardiac surgery.