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D.J. WHEATLEY
Department of Cardiac Surgery, University of Glasgow, Scotland, UK
Keywords: coronary artery bypass, CABG, myocardial revascularisation
J.R.Coll.Surg.Edinb., 47 August 2002, 608-612
Since the 1970’s coronary bypass surgery has evolved to become one of the commonest and most successful of all operative procedures. The symptomatic and survival benefit of this surgery is well recognised. However, developments in cardiological interventions, coupled with demographic and lifestyle changes, are altering the patient profile and referral pattern. Coronary surgery at the beginning of the new century frequently involves higher risk patients and more complex surgery as a result of changes in disease presentation and the success of competing cardiological interventional techniques for less extensive disease. Technological advances in endovascular devices are making significant inroads into traditional coronary surgical practice. Surgeons have responded by developing new strategies to maximise effectiveness of coronary surgery and minimise the injury associated with cardiopulmonary bypass. At the same time regulatory and media scrutiny is focussing attention on the cardiac surgeon, further adding to the stresses and complexity of cardiac surgical practice
Surgical bypass of obstructive lesions in the coronary arteries flourished in the last 3 decades of the 20th century as a result of the obvious clinical success of coronary surgery, the seemingly unlimited number of potential patients, and, for many surgeons, its lucrative reward. Angina is abolished for 5 years after surgery in over 80% of those referred for treatment of angina, and at 10 years over 60% are still angina-free.1 Restoration of normal life expectancy has been shown for most patients undergoing surgery for extensive coronary disease or critically located coronary obstructions with normal or mild impairment of left ventricular function. Even when left ventricular function is seriously impaired, survival benefit relative to that seen with drug therapy alone is particularly favourable.1 There are few contra-indications to coronary artery bypass surgery.
Central to the operation is placement of vascular bypass conduits (usually autologous saphenous vein or internal mammary artery, and more recently radial artery) into coronary arteries beyond angiographically demonstrated coronary obstructions. Traditionally, this has been achieved with the aid of cardiopulmonary bypass to allow an immobile, bloodless operative field.
However, at the beginning of the new century a number of developments are challenging the pre-eminence of surgery in the management of coronary disease and adding a note of disquiet to the lives of coronary surgeons.
Figure 1: The surgeon’s magnified view of anastomosis
of a radial artery to distal right coronary artery
In many Western countries, particularly in North America and Western Europe, the overall prevalence of coronary disease is decreasing and the age of patients presenting with manifestations of the disease is increasing, while in Eastern Europe the prevalence is increasing rapidly with onset of manifestations in middle life. Developing countries are having some of the worst aspects of the Western life-style exported to them - eg, cigarettes and unhealthy diets - and widespread coronary disease cannot be far behind.
Improved life-style and diet, anti-platelet drugs, beta-blockade, angiotensin converting enzyme inhibition, and lipid lowering therapy have been shown to have a favourable impact on the clinical manifestations of coronary artery disease. There is widespread acceptance of the need to combine these measures with coronary artery surgery, but whether they will ultimately supplant surgery is still open to question.
Figure 2: Changes in death rates from coronary heart disease, men and women aged 35-74, between 1986 and 1996, in selected countries2
Balloon angioplasty for coronary disease was introduced towards the end of the 1970’s, about ten years after the advent of coronary bypass surgery. For many years balloon angioplasty provided reasonable treatment for simple, short obstructions in one or two coronary arteries, with a risk of restenosis within the first 6 months of some 25 to 30% of cases.
However, technological progress has resulted in intracoronary stents which maintain patency following balloon dilatation and, recently, drug eluting stents have shown promise of solving the problem of early thrombotic stent occlusion and the need for intensive peri-procedural anti-platelet and antithrombotic therapy. Concomitantly, balloon angioplasty and stenting have been applied to more extensive and complex coronary disease. Angioplasty and stenting are now able to achieve revascularisation in a large proportion of patients presenting with symptoms attributable to obstructive coronary artery disease.
In the USA it is estimated that some 587,000 patients had invasive cardiological procedures for treatment of coronary artery disease in 1999, considerably more than the estimated 355,000 patients having coronary surgery in the USA in that year.3 Furthermore, the number of invasive cardiological interventions has risen year by year, while the number of coronary surgical operations appears to have reached a plateau in 1996.
Arterial conduits
Perhaps the biggest drawback to early coronary bypass surgery was the late occlusion of saphenous vein conduits. By 10 years about 50% of venous conduits have been shown to have occluded.1 Although improved handling techniques and postoperative antiplatelet therapy may well improve this occlusion rate, there is wide recognition that arterial conduits are superior to veins in long-term patency. The value of the left internal mammary artery, as a bypass conduit to the left anterior descending artery, has been proven by excellent freedom from atherosclerotic obstruction and long term patency rates of about 95% at 10 years.4 Use of at least one of the internal mammary arteries (usually the left to the anterior descending coronary artery) is almost mandatory nowadays, in view of the clear clinical benefits for late survival and reduction in further coronary events that have been shown.5 Favourable experience with the left internal mammary artery has stimulated a search for other arterial conduits, which have included the right internal mammary artery (often as a free graft), the gastro-epiploic artery (as a pedicled graft) and the inferior epigastric artery (as a free graft). The radial artery has recently been shown to be a practical and effective conduit, with graft patency at 5 years approaching that of the internal mammary artery.6 The extended use of arterial conduits is likely to improve still further the outcomes for coronary surgery.
Figure 3a: Isolated short stenosis in right coronary artery Figure 3b: Angioplasty stent deployment Figure 3c: Restored lumen
Recognition of the injury of cardiopulmonary bypass
It has long been recognised that cardiopulmonary bypass, by exposing the patient’s blood to the foreign surfaces of the pump-oxygenator circuit, induces a whole body inflammatory response, reflected in fluid retention and temporary impairment of function of the lungs, kidneys and brain.7 Temporary coagulation defects are another consequence of cardiopulmonary bypass. Although modern extracorporeal equipment minimises these injurious effects, there has been a move to avoid the use of cardiopulmonary bypass altogether. Anastomosis of conduits to the distal coronary arteries is possible while the heart is beating and supporting the circulation. “Beating heart” surgery requires careful positioning of the heart, stabilisation of the target coronary artery with special retractors, local occlusion of the artery to keep blood out of the operative field, and the possible use of local intra-coronary shunts to maintain a level of distal myocardial perfusion during construction of the anastomosis.
The aim of coronary surgery is the construction of strategically placed bypass routes from a systemic pressure inflow source to the distal coronary arteries beyond angiographically demonstrated, haemodynamically significant coronary obstructions. The conditions under which the anastomoses are constructed are probably less important than the precision and completeness of revascularisation - whether by use of cardiopulmonary bypass with cardioplegic arrest giving a flaccid, immobile, bloodless heart, or by careful positioning of the beating heart with local stabilisation of the target vessel. Few randomised assessments of the two techniques have been undertaken. One such trial is reported from Bristol, and shows reduction in blood loss and transfusion requirement for the “beating heart” group, but little difference in neurological outcome.8,9 Beating heart surgery is gaining in popularity, with some centres reporting 70% or more of their patients being managed in this way. Currently in the USA, some 25% of coronary artery surgery is undertaken as a “beating heart” procedure.
Other developments intended to minimise the injury of access for coronary artery surgery have focussed on minimal access through limited thoracotomy, often with the aid of videoscopic display, and even with the introduction of robotic systems for remote control of instruments inserted through minimal access ports.10 Cardiopulmonary bypass can be used as an adjunct to such minimal access surgery without sternotomy, using jugular and femoral vessel cannulation. However, such procedures are still in their infancy, are time-consuming, very expensive and not in widespread use.11 A further contribution to improving-safety of coronary surgery is awareness of the dangers of atheroembolism from the ascending aorta. Minimal handling of the aorta, and use of epi-aortic ultrasound scanning to identify loose atheroma has been advocated, though it is not yet widely available.
Figure 4a: Total occlusion of right coronary artery
Figure 4b: Following proximal angioplasty,
Figure 4c: Following successive dilations
- a candidate for surgery in earlier
years
distal vessel appears
poor
and proximal stenting, good lumen is restored
The financial cost of coronary surgery is considerable. The cost of a coronary operation in the National Health Service is variously estimated as between £6,000 and £10,000, and the shortage of resources for this surgery has been a constant source of difficulty for those trying to meet demand for this treatment. In the USA, there is also careful scrutiny of costs and increasing pressure for cost containment, with many US surgeons having seen a real fall in income as a result.
Coronary artery surgery is well suited for outcome monitoring. The procedures are relatively uniform and are performed in large numbers. Large databases have been developed, allowing identification of risk factors for death or other adverse outcomes.12 Though originally intended as a tool for stimulating-best practice and improving clinical decision-making, the databases have inadvertently provided a means for regulatory bodies to scrutinise individual surgeons’ outcomes. Coronary surgery has been in the vanguard of such scrutiny. In New York State and Pennsylvania the operative mortality (observed and expected) for coronary surgery for each individual cardiac surgeon has been freely available to the public for a number of years. In January 2002, the UK Department of Health published its response to the report of the public inquiry into children’s heart surgery in Bristol. Among its intentions for future action is the requirement for publication, by April 2004, of 30-day mortality rates for the previous two years for every cardiac surgeon in England and Wales.13
While no one would dispute the need for careful audit of outcomes to ensure uniform best practice, the identification of individual surgeons is likely to engender unease. Outcomes depend on more than just the actions of the surgeon - many others are crucially involved in the provision of this demanding surgery. Furthermore, the increasing age and prevalence of co-morbidity of patients presenting for coronary surgery are likely to make mortality and adverse outcomes more frequent in future. In spite of assurances that risk stratification will make comparisons fair, many surgeons will feel apprehensive and defensive, with the risk that higher risk patients will be turned down for surgery that could have been beneficial in spite of increased initial hazard. It is in those higher risk surgical patients with extensive coronary disease and impaired left ventricular function that relative survival benefit is greatest for surgery, as compared with medical therapy.
At a time when less complex coronary disease rarely gets beyond the interventional cardiologist and surgical referrals offer an increasing challenge, life for the cardiac surgeon is becoming less attractive. Just how great the challenge from interventional cardiology is, cannot be easily assessed at this time of rapid evolution. In spite of the surge in interventional cardiological procedures in the USA, surgery continues at a rate that well exceeds that of any other country.
The attention paid by regulatory bodies and the media to cardiac surgeons is likely to spread to all fields of medicine, and appropriate responses will be a matter for the entire medical profession. With careful documentation of surgical practice and outcome, increased regulation should not inhibit effective and rational surgery.
Technical advances in the fields of surgery and interventional cardiology, together with improved understanding of their respective roles seem likely to ensure a future for coronary surgery for some considerable time to come. More importantly, the technological and therapeutic advances which have so profoundly transformed the management of coronary heart disease in the last decades of the 20th century promise even greater benefit for those still vulnerable to coronary artery disease in the 21st century.
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Copyright: 12 March 2002
Correspondence :Professor D.J. Wheatley, University Department of Cardiac Surgery, Royal Infirmary, 10 Alexandra Parade, Glasgow G31 2ER