The status and future directions of cardiac surgery

Any speculations or predictions about the future of cardiac surgery must first reflect carefully upon its past. Over the last 50 or so years of its relatively nascent history, cardiac surgery, along with its practitioners, has evolved rapidly. Prior to the 1950s, most of cardiothoracic procedures have dealt with the pulmonary complications of tuberculosis with occasional closed heart procedures for valvular stenosis.

The development and first clinical use of the cardiopulmonary bypass (CPB) machine by Gibbon in 1953 [1], marked the beginning of a new era, in which intracardiac, as well as coronary and ascending aortic pathology were now readily accessible to surgical treatment. This ‘golden era’ of cardiac surgery witnessed the development of a plethora of new techniques to treat a variety of structural cardiac diseases, including congenital defects in newborns and infants, and the late valvular consequences of rheumatic disease in adults. Over the last 20–30 years, with the virtual eradication of rheumatic fever in the developed world, cardiac surgeons have focused their efforts on the treatment of ischemic coronary disease, degenerative valve disease and heart failure. Significant improvements in anesthesia and critical care, combined with refinements in surgical techniques and related technologies have led to significant reductions in the morbidity and mortality resulting from open heart surgery. More recently, cardiothoracic surgeons and the procedures they perform have been the focus of great scrutiny, particularly in North America, leading to rigorous quality evaluation and consequently, to quality improvement.

Despite the significant and consistent progress in the surgical treatment of cardiac disease, challenges facing the specialty are perhaps more formidable today than ever before. In the last 10–15 years, parallel improvements in medical therapy and percutaneous techniques to treat cardiovascular disease have helped to prolong the life of the patients and treat the symptoms of cardiac disease. As a result, patients referred for surgical treatment are invariably older, have greater comorbidities and more advanced disease. While mortality rates from uncomplicated coronary and valve procedures remain low, there is increasingly greater emphasis on reducing the morbidity associated with cardiac surgical procedures.

The CPB machine is used for most life-saving cardiac surgical procedures, and it inevitably contributes to the morbidity of the procedure. Exposure to CPB leads to an inflammatory response, derangement of the coagulation system, reduction in platelet function, renal and splanchnic complications, and possible neurologic injury. In an effort to avoid the deleterious consequences of coronary artery bypass and cardioplegic arrest, some surgeons have proposed the use of off-pump coronary artery bypass (OPCAB) surgery. It has been established that performance of off-pump surgery requires some new skills that are associated with a learning curve. A large body of published literature attests to the ability of surgeons, with appropriate training and skills, to perform OPCAB in a safe manner with results similar to conventional on-pump surgery. Despite the tremendous early enthusiasm for this approach, the proposed benefits of OPCAB have not been borne out in large studies. These proposed benefits include a reduced need for blood transfusions, decreased postoperative atrial fibrillation, reduced renal injury, decreased incidence of stroke and neurocognitive deficits, reduced postoperative hospital and intensive care unit stay and cost. However, clinical trials to date have not clearly demonstrated major clinical benefits of OPCAB as reflected in a recently published American Heart Association consensus statement [2]. Future well-conducted, large, multicenter, randomized trials may eventually be required to definitively evaluate the benefits of OPCAB versus conventional coronary bypass surgery.

Various adjunctive strategies have also been evaluated to reduce the detrimental effects of CPB, for example, the use of coated CPB circuits, ultrafiltration, systemic anti-inflammatory drugs and aprotinin. Although some of these strategies have demonstrated clear benefits, others have been unable to do so. In particular, aprotinin, a serine protease inhibitor, has been demonstrated to reduce bleeding, decrease the need for blood transfusions and diminish the inflammatory response to CPB.

A major source of morbidity following cardiac operations is the midline incision and sternotomy required for the vast majority of procedures. Various approaches have been suggested to provide minimally invasive access to the heart and the pericardial space. These include left-anterior mini-thoracotomy and sub-xiphoid incisions for single vessel left-anterior descending artery bypass, hemisternotomy for certain valvular procedures and right mini-thoracotomy for isolated mitral valve repairs. Although a reduction in incision size can be associated with decreased pain and improved cosmesis, randomized trials are required to demonstrate whether these approaches provide substantial benefits over conventional approaches while retaining long-term efficacy.

The need for relatively large incisions in cardiac operations is due to the requirement for direct visual, as well as manual access to the heart. Recent technological developments in video-assisted and robotic surgery have facilitated the development of port-access or closed-chest approaches. These approaches are a novel attempt to achieve the excellent long-term results of surgery while minimizing the morbidity of large incisions. These techniques and technologies are currently in their infancy and limited by long operative times, high cost, significant learning curves, and the small subset of patients in whom they can be applied. However, future technological improvements may enable more widespread application of these techniques.

Another barrier to port-access and closed-chest coronary surgery is the need to perform suture-based microvascular coronary anastomoses that can be cumbersome through small incisions. A variety of anastomotic devices are currently in various stages of development and clinical application. Some employ nitinol clips and pins that eliminate knot tying, while others use biological glue or even magnets to bind the two vessels together [3,4]. The ultimate goal of these techniques is to eliminate the need for sutures and enable delivery through small incisions or ports. As these technologies evolve, they will facilitate the evolution of minimal access cardiac surgery.

Recent advances in endovascular technology combined with success in the treatment of coronary disease has opened the doors for percutaneous valvular interventions. To date, the vast majority of percutaneous valve repair and replacement technologies are in the preclinical development phase with some early Phase I and II studies in patients who are not surgical candidates. Devices have been developed for mitral annular reduction, edge-to-edge repair of the mitral valve, as well as antegrade and retrograde approaches to aortic valve replacement. Although these technologies are attractive for use in patients who are currently not candidates for surgery, their safety and long-term efficacy will need to be clearly established before routine use in patients currently treated with open procedures. There is some debate as to whether surgeons or interventional cardiologists will be the primary deliverers of these new technologies. A collaborative approach will probably facilitate the development and optimal implementation of these technologies in the right populations while protecting the best interests of the patients who they are meant to serve [5].

Surgical treatment of cardiac arrhythmias initially began with ablation of aberrant pathways involved in Wolff–Parkinson–White Syndrome. Since then, surgeons have successfully performed ablation procedures for ventricular and atrial arrhythmias. The development of the Cox–Maze procedure opened the doors to the treatment of atrial fibrillation, which is a commonly occurring arrhythmia with detrimental consequences that are just being realized. Although the complexity of the original Maze procedure hampered its widespread adaptation, newer energy sources that have now replaced the cut-and-sew method of ablation have increased its accessibility. In many cardiac surgical centers, endocardial atrial ablation procedures are routinely being performed concomitantly with mitral valvular surgery to treat atrial fibrillation without significantly increasing the morbidity of the operation. However, the future of atrial fibrillation surgery will likely involve a minimally invasive epicardial approach, without the need for CPB, for the performance of lone atrial fibrillation surgery, which has the potential of impacting a large number of people.

Improvements in the medical, percutaneous and surgical treatment of ischemic cardiac disease now allow patients to survive longer than ever following manifestations of their coronary disease. As a result of this and the aging population, there will continue to be an increasingly large number of individuals with heart failure in developed and developing countries [6]. Although excellent results can now be achieved with cardiac transplantation, a limited and deminishing supply of donors allows only a small number of patients to benefit from this life-saving therapy. Ventricular assist devices have demonstrated their important role as a bridge to transplantation. However, high rates of thromboembolic and bleeding complications combined with high cost and bulky composition make them unattractive as destination therapy for the treatment of end-stage heart failure. Newer generation devices that are smaller, provide nonpulsatile flow and assist rather than replace the ventricle are currently in various stages of development. Technological improvements in this area will have the potential for affecting a large number of patients with end-stage heart failure in the future.

In contrast to the mechanical solutions that surgeons have traditionally provided, an emerging area with great therapeutic potential is the use of cellular therapies for heart failure and end-stage coronary disease. Scientific advances have enhanced our understanding of endogenous processes of vascular and myocyte growth and repair that may be harnessed in the future to provide tailored therapies for patients. The biology of the complex interactions between the various components involved is far from being fully elucidated. Yet some of these therapies have entered the clinical realm and have shown some promise, for example, the administration of angiogenic factors using protein- and gene-based delivery mechanisms, as well as bone marrow and skeletal muscle-derived progenitor cells. Although significant limitations and many unanswered questions remain, these therapies may provide a new treatment paradigm for patients with end-stage cardiac disease.

Cardiac surgery has been, and will continue to be a rapidly evolving discipline. Its progress and development has always been married to technological developments in the biomedical sciences, which are moving at a rapid pace. In the near future, changes in the field will be driven by the need to reduce the morbidity of cardiac surgery through improvements in CPB and related technologies, and greater emphasis on minimally invasive and endovascular approaches. New frontiers for the specialty may include the treatment of lone atrial fibrillation and cellular and mechanical therapies for heart failure. Although it is difficult to predict what procedures cardiac surgeons will be performing 50 years from now, it is very likely that they will be significantly different from the practice of cardiac surgery today.

Conflict of interest

Frank Sellke is on the speaker’s bureau for Bayer Corporation.