Definitions and Procedural Elements of Cardiac Surgery
Cardiac surgery is one element of the specialty of cardiothoracic surgery. The other major element is general thoracic surgery, primarily addressing intrathoracic malignancies in adults. Included in cardiac surgery are: revascularization of the myocardium (heart muscle) by performance of bypasses around obstructions in the coronary arteries, using a variety of conduits (arteries are preferred); correction of valvular lesions by repair techniques or by replacement of the valves with substitutes (biologic or mechanical); combined procedures to address coexisting or etiologically related lesions of the arteries and valves; correction, usually by total repair, less often by palliation of pediatric congenital heart lesions of all the cardiac structures; control and/or correction of arrhythmias from simple conduction abnormalities to repetitive, life-threatening rhythms (sudden death); and heart replacement, currently done with transplants but with some promise of the use of devices to augment or replace heart function in the future in patients with advanced heart failure. Currently, coronary artery bypass graft (CABG) is the most frequently performed surgery, comprising 80% of cardiac surgery cases in a variety of institutional settings, most often in community hospitals.
Cardiac surgery can be done by either "closed" or "open" technique, that is without or with heart-lung machines that permit blood to continue normal flow through the heart or to be diverted so that the heart can be placed at rest (arrested) while the most delicate aspects of the surgery are performed. If the surgery is done without diverting the blood, this is often termed "off-pump." When the blood is diverted and the heart is arrested, the circulation of the rest of the body and the oxygenation of the blood are functions that are maintained by the heart-lung machine. In either event special equipment is necessary to accomplish the surgery. Two significant claims for off-pump surgery are that heart function is better maintained and that the incidence of cardiovascular and other blood abnormalities are reduced by avoiding use of the pump. Notwithstanding, it must be appreciated that when the chambers of the heart have to be entered or heart function is significantly abnormal, a pump has to be used. Whether a pump is used or not, the classic incisional approach to the heart is through the breastbone (a median sternotomy incision).
More recently, a variety of minimally invasive incisions, some of which were commonly used early in cardiac surgery, are being reintroduced. What is different now is that technologic innovations using light sources within the chest cavity, video devices to facilitate and magnify what is being done and a variety of new instruments are essential to the successful conduct of these lesser invasive procedures. As a result of these changes, many cardiac surgeons are having to learn surgical techniques that were not in use during their residency training in cardiothoracic surgery. Thus, there is the potential for a generational disconnect between younger and middle to older aged practitioners. Finally, robotic techniques of surgery are just emerging from the laboratory.
One of the most important aspects of heart surgery involves how the heart is managed, if a heart-lung machine is used and heart function is suspended. There are two aspects to cardiac functional preservation: using temperature (cold) to minimize metabolic need and using special biochemical solutions to suspend all electrical function/activity of the heart muscle. If this preservation is not done perfectly, heart function can be difficult to resume and cardiac function, once restored, can be significantly compromised. From consideration of these issues, it is clear that the conduct of anesthesia and the monitoring and support of cardiac function are integral to the successful conduct of cardiac operations.
What should be evident from these considerations is that cardiac surgery needs, for consistently successful performance, to be conducted in a highly controlled environment, with a well developed infrastructure and disciplined teams. To achieve optimal outcomes consistently, such teams need to work together on a regular basis and the members of the team have to represent a variety of specialty capabilities, from the laboratory to nursing, engineering and technology to cardiology, imaging, anesthesia and surgery professionals. Over the next 5-10 years, research and development will continue in a number of areas: minimally invasive approaches; instrument development, including robotics; cardiac assist devices; transplants; improved cardiopulmonary bypass methods; and informatics. Databases are essential to collect the large number of observations over time necessary to assess the significance of innovations, and to address and reduce variability of outcomes.
Patient Populations and the Indications for Cardiac Surgery
Currently, the indications for cardiac surgery are driven by the high incidence of coronary atherosclerosis. Given that this process is age related, the need for those services is greater in the age cohorts 60-70 and 70-80 years. In these populations there is compelling evidence that risk-adjusted determinants of both morbidity and mortality have increased, due to increasing age and increasing incidences of co-morbidities (hypertension, diabetes, peripheral vascular disease). Age related indications are such that the aging of the population into the 80-90 and over 90 years cohorts has been accompanied by increasing intervention at these ages. Postoperative mortality and morbidity in such therapeutic undertakings are greater than in younger patients but very acceptable; and symptomatic status, ability to live independently and longevity are appropriate anticipated clinical outcomes. There is nothing in future projections to suggest that this trend to surgically treat older patients, including the eldest of the elderly, will change over the next 5 years. In fact, the percentage of such patients presenting for surgery has the potential to create a subspecialty of geriatric cardiac surgery.
Concerning the indications for cardiac surgery, what cardiac surgeons currently consider to be the classic indications (triple vessel disease with ventricular dysfunction, left main disease (obstruction) of more than 50%, etc.) will probably not change. The literature documents some substitution of PTCA for cardiac surgery in certain areas that have traditionally been the province of surgeons alone: triple-vessel disease and left main disease, for example, although this is an area of some controversy and disagreement. Discussion of whether diabetes mellitus in patients with double vessel disease or in those with single vessel disease characterized by obstruction of dominant vessels creates the circumstances for performing bypasses, especially with arterial conduits, will continue. It is not known at this time whether current patient populations who have had prior angioplasty and/or stent insertions will in the long run have recurrent problems that necessitate a different therapeutic approach. If so, progressive disease states may be present that necessitate CABG.
It is also not clear what effects the development of new technologies, especially catheter-based, will have in directly approaching obstructive plaques with the intent to remove them (endarterectory). Nor is it apparent that potential genetic therapies will be able to generate an environment of angiogenesis (generation of a new arterial vessel) that could preclude current revascularization therapies. Transmyocardial laser revascularization (TMR) is also not yet a proven method for producing angiogenesis. This involves using a laser beam to create channels in areas of the heart that are not receiving enough blood flow from the coronary arteries.
How Patient Management Will Change the Treatment of CAD
Those who control the referral mechanisms will continue to frame indications for the basic diagnostic interventions. With the current dynamics of performing catheter-based therapeutic interventions in association with the diagnostic procedure ("ad hoc" angioplasty, for example), cardiologists will, as technologic innovations proceed, have increasing influence over what happens to patients with coronary artery disease. There are two possible counterbalances that could come into existence. The first will occur if diagnostic catheter based interventions are separated from the therapeutic intervention, as in the development of diagnostic capabilities with MRI. In this instance, therapeutic decisions would be "audited" and the indications for surgery may change. This could result from the need for a clinical review between diagnostic and therapeutic interventions that returns control of the patient back to the primary physician. The second counterbalance will occur if surgeons begin to develop skills in catheter-based therapeutic interventions. This strategy would position the surgeon as the "full service" provider. Because the surgeon/interventionist would be paid regardless of the service provided, some feel that the decision as to what is best done would be made on clinical grounds without regard to economic incentives.