The modern era of myocardial revascularization was started in the sixties by the studies of Favaloro and Ellis (Cleveland Clinic) and Johnson (New York University) (I). The development of the myocardial protectìon techniques enabled the diffusion of the myocardial revascularization surgery from the seventies. It became the elective therapeutic option in coronary arteriosclerotic disease. In the history of medicine seldom a surgical intervention was so effective and reached so a broad employ. The indicatious and surgical techniques are iri constant evolution. The advent of percutaneous coronary angioplasty contributed to modify radically in the recent years the patients' population subjected to myocardial revascularization surgery. Generally, persons undergoing this surgery are older subjects with a greater involvement of coronary arteries and, often, with a reduced ventricular function. The purpose of the present paper is to summarize the present situation and the evolutive trends of coronary surgical revascularization.

Surgical indications

Stable angina

When myocardial revascularìzation surgery entered the clinical practice in 1967, there was no medical therapy capable to improve the survival of patients with coronaroscerosis. Therefore, the aortocoronary by-pass surgery reached a fast and broad diffusion. However, in the seventies, with the introduction of new medical therapies, the need was felt of performing randomized prospective studies to compare medical treatment with surgical intervention. Three randomized prospective studies,

Fig. 1: dati non modificati della sopravvivenza a 10 anni per i pazienti con malattia dei tre vasi in funzione del tipo di condotto usato (AMI versus graft venoso) nella serie della Cleveland Clinic  Unadjasted raw survival data for patients with three vessels disease who were selected for coronary grafting with and without IMA use in the Cleveland Clinic series

similar in the size of the test population and the statistical methods employed, have played a fundamental role in identifying the indications to surgery in patients with stable angina. There are: 1) Veterans Administration Cooperative Study, carried out on a population of 686 patients; 2) The European Coronary Surgery Study, including 767 patients; 3) The National Heart, Blood and Lung Institute, CASS Study, with 780 patients (2,3,4). However, it is appropriate to point out that about 15 years have elapsed from these studies. During this period, many surgical and pharmacological innovations deeply modified the treatment of patients with stable angina.

A detailed analysis of these studies and of their implications goes beyond the scope of this article. We invite the interested reader to read the study published by Califf et al. (5). Data presented in these studìes and the most recent literature demonstrate a remarkable clinical improvement and a greater exercise toterance in patients operated on of aorto-coronary by-pass. Therefore, patients whose angina cannot be controlled by medical therapy and who have a coronary anatomy suitable to surgery can be subjected to surgery. However, two important questions remain controversial: 1) which is the correct therapeutic approach to patients with significant stenosis of coronary arteries and poor or absent symptomatology? 2) Which is the role of coronary angioplasty in relationship to surgery? For patients wiih poor symptomatology or with a good pharmacologic control of symptoms, the surgical indication should be based on three points: 1) improvement of survival; 2) prevention of myocardial infarction; 3) preservation of ventricular function. The available randomized studies demonstrate a superiority of surgery to medical therapy concerning the prevention of myocardial infarction and the preservation of ventricular function. The same prospective studies show an improvement of far survival in high-risk patients categories. These are: 1) patients with stenosis of the common trunk over 50%; 2) patients with significant stenosis of the three main branches and reduced left ventricular function; 3) patients with non-invasive indicators of high risk (hypertension, hypercholesterolemia, silent ischemia). The presence of conflicting data in the above mentioned randomized studies, leaves open the controversy about patients with three-vessels dìsease and normal left ventricular function and subjects with two-vessel disease. However, the results presented by the Europears Coronary Surgery Studya and theanalysis of data from Duke University (6), in our opinion, enable to state that the probability of obtaining a prolongation of survival ís particutarly real for the following categories of patients: 1) presence af Three-vessel Disease; 2) Two-vessel Disease with involvement of the anterior descending and with a wide risk myocardial area especially in the event of exercise-test ischemia.

Unstable angina

The greater difficulty in the revision of the efficacy af surgery is the broad range of definitions used for this category of patients. However, it is a general opinion that the diagnosis of unstable angina should be characterized by the presence of the folowing signs and symptoms: 1) sudden onset of symptom at rest in subjects without previous history of coronarosclerosis; 2) enhancements or modifications in the symptomatology of patienis with coronarosclerosis and stable symptomatology; 3) recurrence of ischemic symptoms within four weeks after an acute myocardial infarction. Two randomized

Fig. 2: Dati non modificati della sopravvivenza a 10 anni per quattro sottogruppi con o senza AMI nella serie della Cleveland Clinic  Unadjusted survival data for four subgroups who had coronary revascularization with and without IMA in the Cleveland Clinic series

prospective studies compared the medical therapy versus surgery in patients with unstable angina. They are: 1) The National Cooperative Study including 288 patients and carried out from 1972 to 1976; 2) The Veterans Cooperative Study, with a population of 486 patients, performed from 1976 to 1982 (7,8). In both studies, the interpretation of longterm data is made more complex by the fast passage from medical therapy to surgery (36% at 30 months in the National Cooperative Study and 34% at 2 years iu the Veterans Administration Cooperative Study). The efficacy of surgery in improving the symptomatology is similar to the one obtained in patienis with stable angina. In the National Cooperative Study group, only 14% of patients with diffuse arteriosclerotic disease and unstable angina exhibited at one year a significant symptomatology (New York Heart Association Class Ill vs IV). Rahimtoola et al. observed that 6l % of 282 patients operated an for unstable angina from 1970 to 1982 had no symptoms at 10 years (9). None of the two randomized studies demonstrated a protective effect of the revascularization surgery of myocardial infarction. Differing from what occurs in patients with stable angina, myocardialrevascularization surgery in patients with unstable angina or in cardiogenic shock exerts a proteciive effect on myocardial function (10, 11, 12). The hospital surgical death-rate for this category of patìents is 3%. The favourable effect on the far survival ìn surgery in patients with unstable angina and ejection fraction <50% is particularly obvious (13). Therefore, the need of performing surgery in patients with unstable angina is evident, when there is no indication to coronary angioplasty.

Coronary percutaneous angioplasty and surgical intervention

Gruentzig et al. introduced in 7971 coronary percutaneous angioplasty. The advent of this new method deeply changed therapy of coronarosclerosis. However, in the lìierature no randomized prospective studies are mentioned, which compare the results of percutaneous angioplasty in relationship with those obtained with surgery or medical therapy. The indications to angioplasty are in steady evolution. They are mostly influenced by the experience of the Center in which the method is performed. Death-rate ranges from 1% in patìents with a single dilated stenosis to 3% in patients with

Fig. 3: Incidenza di reinterventi nei pazienti con o senza AMI nella serie della Cleveland Clinic  Reoperation rates versus postoperative years for patiens who had vein grafts only compared with patiens who had at least one IMA graft

three-vessel disease. In 20% of patients, the recurrence of stenosis is observed wìthin 6 to 12 months. However, this can be dilated again with an exceltent potential of success. The incidence of peri-procedural complications is a function of the experience of the team performing angioplasty and ranges from 1 % to 56%. In patients with three-vessel disease, an incomplete revascularization is obtained in 70% of cases (14). Besides the number of concerned vessels, the results of coronary angioplasty are influenced by the type of stenosis (15). The single stenoses of length lower than 1 cm sited in easily accessible paris of the vessel and without calcification (type A) are surely easier to be dilated, while the injuries longer than 2 cm localized in parts difficult to be reached with a high presence of calcium (type II) are those who offer the worst results and have a higher incidence of complications. It is our opinion that coronary angioplasty and surgery are complementary in therapy of coronarosclerosis. In waiting for data obtained from randomized prospective studies, we think that to angioplasty should be addressed only those patients who have one or two vessels diseased and stenotic lesions of type A or B (intermediate between A and C). These same patients, in a more or less far future, wìth the progression of the arteriosclerotic disease, coutd undergo surgery, which remains indicated in patients with three-vessel disease, or with two diseased vessels and lesions of type C. Moreover, surgery is indicated in patients with stenosìs of the common trunk over 50%. Coronary surgery in the elderly Patients of age older than 65 years have a Rreater perioperative risk. In rhe CASS Study, the surgical death-rate was: I) l.9% in patients younger than 65 years; 2) 4.6% for patienrs of age between 65 and 69 years; 3) 6.6% for parients of age between 70 and 74 years; 4/ 9.5% for patients of age between 75 years and over (16). In the same study, the period of hospital stay was longer (11.6 days for patients younger than 65 years versus 16.5 days for patients older than 65 years) and the following complications occurred wirh a higher rate 1) supraventricular arrhythmias 2) perioperative low output syndrome; 3) sepsis. In the CASS Srudy (I7), the 5-year survival was 83% in patients older than 65 years. The statistically significant factors in causing the 5-year surviva were the following: l) left ventricle function; 2) presence of other associated pathologies. In patients with normal ventricular function, the 5-year survival was 87%, whereas it decreased to 65% if, at the time of surgery, alterations of the ventricular function were present. Myocardial revascularization surgery preserves its effcacy in causing the regression of anginal symptomatology in thìs category of patients. In 80% of patients the symptoms are absent and in the remaining 20% a remarkable clinical improvement is obtained (17). Therefore, when it is advisable to refer to surgery the elderly patient? We think the criteria adopted for younger subjects may be applied also to patients of age between 65 and 75 years. Surgery may be offered to these patients, with an acceptable surgical death-rate (3 to 5%) and an excellent far outcome (70% asymptomatic at 5 years). This applies especially to those patients who are in good general conditions without combined pathologies and with a preserved left ventricle function. Far patients older than 75 years, a more conservative approach is preferable. In this patients' population, myocardial revascularization wirh percutaneous angioplasty is an excellent alternate, with a low perisurgery risk (death-rate l to 3.5% and 1.3% for myocardial infarction) (18, 19). Of course, also in elderly subjects, the criteria of indicatìon for surgery and coronary angioplasty remain valid.

Hibernated myocardium

In the last ten-year period, a new clinical reality appeared, hihernated myocardium. Rahìmtoola defined as "hihernated myocardium" the persistent alteration of the function of vital myocardial tissue due to a remarkable reduction of coronary blood flow (20). In this pathophysiological situation, the restoration of a sufficient coronary blood flow causes the recovery of the function of hibernated area. Theierm "hibernated" was adopted to mean the self-reduction of metabolísm of the muscle cell to survíve in the presence of a reduced nutritional supply. Identification of hibernated areas ín patients with previous episodes of infarction acquires a special importance, since a correct revascularization induces a functíonal recovery of the hibernated area (21). The diagnosis of hibernated myocardium is based on the performance of such tests as: 1) Positron Emission Tomography (PET); 2) exercise heart scintiscan with double passage; 3) bidimensional echocardiography associated with infusion of increasing doses of dobutamine. The areas identified as "hibernated" can be subjected to therapeutic interventions (percutaneous angioplasty, aortocoronary by-pass) which enable their revascularization and functional recovery.

Arterial myocardial revascularization

The introduction of the use of internal mammary artery (or internal thoracic artery) as a conduit for the revascularization was performed in the sixties by Spencer and Kolassov. The first clinical series of patients undergoing myocardial revascularization with internal mammary artery alone or in combination with venous conduit was presented by Green (22). However, the use of this arterial conduit makes surgery more complex. Therefore, the majority of surgeons preferred the

Fig. 4: Dati di sopravvivenza nei pazienti con una sola AMI, 2 AMI, o condotti venosi  Raw survival data over time after coronary bypass for patients who received vein grafts only, one IMA, or double IMAS

revascularization with great saphenous vein. Data analysis on patency of venous conduits showed that only 70% of venous grafts was functioning 10 years after surgery and already after 5 years obvious signs of arteriosclerosis were present (23). Loap et al. analysed the 10-year survival and the cardiovascular events occurring during this period in 5,931 patients subjected to myocardial revascularization (24). In 60% of patients surgery was performed using only venous conduits, while in the remaining 40% also internal mammary artery was used as a conduit (IMA). The two patients' populations presented with significant differences. The subjects with internal mammary artery had generally a better ventricular function and were younger. Moreover, the use of IMA was increased in the last years of the study. The 10-year patency of IMA was of 98%. The modifíed statistical analysis using the Cox proportional model af hazard by functions demonstrated a better survival in patients with IMA in the various anatomieal subgroups (Fígs 1 and 2). The rate of reinterventions and of non-fatal cardiac events was reduced in patients wíth IMA (Fig. 3). The presence of more than one internal mammary artery induced a further improvement of the results obtained (Fig. 4). Other studies had evidenced the positive effect exerted by the employ of internal mammary artery on the survival and reduction of non-fatal cardiac episodes. Therefore, the need of extending the use of this arterial conduit is obvious, until reaching ideally the purpose of performing the whole technical problems. However, the employ of this conduit may be associated with some important problematic techniques. The use of an internal mammary artery with inadequate blood flow could cause the occurrence of a peri-operative myocardial infarction. Moreover the surgical technique requires a careful attention. The build-up of an anastomosis with IMA in patients with reduced ventricular function and high left ventricle end-diastolic pressure could cause a state of reduced or absent blood flow in the revascularized coronary artery. The use of both mammary arteries was correlated in some studies with increased complications. In our opinion, IMA should be used in all ihe patients to revascularize the heart arterial wall and, in young subjects, to obtain the most complete possible arterial revascularization. The following are considered as the absolute contra-indications to the emplo of IMA: 1 ) presence of cardiogenic shock in progress; 2) presence of impending infarction; 3) acute complicatios of coronary percutaneous angioplast. The presence of a severe pulmonary emphysema shoutd be considered as a relative contra-indication. The excellent results obtained with internal mammary arlery aroused a true interest for arterial conduits. Gastric and epigastric arteríes are also used often to obtain a complete arterial revascularization. However, long-term studies on the results obtained with these conduits, are nat yet available.

Reinterventions

Degenerative processes occurring in the venous grafts and the progression of native arteriosclerosis caused a steady increase in the number of patients subjected to a second surgery of myocardial revascularization. The statistically significant factors in inducing the risk of reintervention are the following: 1) use of only venous conduits; 2) incomplete revascularization; 3) young age. The

Fig. 5: Sopravvivenza a 10 anni dopo reintervento e sopravvivenza senza eventi cardiaci a 10 anni (da Haytle BW et al.: Fifteen hundred coronary reoperations: Results and Determinations of early and late survival. J. Thorac Cardiovasc Surg 93:851, 1987  Ten years actuarial survival after coronary artery reoperation. The 10-year actuarial survival is 75% (top curve), and the 10 years eventfree survival is 48%

angiographic indications for reinterventions are rather more complex than the first surgery. However, they may be related to the previously described criteria. Coronary percutaneous angioplasty plays an important role in therapy of this category of patients. The global death-rate for reintervention ranges from 3% to 5% (25). The incidence of peri-operative infarction often due to embolization of venous conduit is particularly important (6 to 8%). After reintervention, the regression of symptomatology occurs in a less efficient way than the first surgery. The most important factor for a good surgical outcome after reintervetion is the presence of a normal left ventricularfunction. These findings denote that the results after reintervention are good and not comparable to those obtained with the first surgery.

Conclusions

The advent of myocardial revascularization induced a modification of the natural history of arteriosclerotic disease of coronary arteries. Data analysis shows the need of identifying the patients before a remarkable impairment in the left vetricle function. The knowledge of new entities, such as hibernated myocardium, offered therapeutic prospects to patients considered in the past as inoperable. The advent of complete arterial revascularization offers the concrete hope of a further improvement of the results obtained. For those patients who have a severe and irreversible impairment of heart function, when other contraindications are absent, heart transplantation is a valuable therapeutic solution.

New developments in operative technique such as minimally invasive surgery are promising but need to be the compared carefully with the results of conventional surgery which are very favourable.

E.Caradonna- G.Fransen Dept-of Thoracic Surgery St.Jan Hospital - Gent - Belgium

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