CORONARY REVASCULARIZATION

Angina pectoris is attributed to a circulatory mismatch of the heart muscles and results in contractile dysfunction affecting the blood circulation of the body eventually. The word 'angina' is derived from the Greek 'ankhone' and 'pectoris' is a Latin term for the chest. The use of Greek and Latin was conventional in Medical practice at early times and the term 'angina' remained indicative of pain originating from the heart.

In 1649 William Harvey in his paper  “Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus", and in front of the King proved that blood circulates in the body continuously to perfuse the organs and keeps them viable. Leonardo da Vinci, in 1511, diagrammatically showed the epicardial coronary arteries. He also conjectured causes and suggested the deposition of fatty material in the arteries of the heart as one of the major reasons for angina. First documented by a civilian Edward Hyde, while describing his observation in a family biography. His description was typical and William Heberden, in the late 18th century, gave the ‘physicians stamp’ to this condition. Heberden first used the term 'angina pectoris' in his paper and 100 years later Edward Jenner, of the smallpox vaccine fame, found atherosclerotic narrowing in John Hunter's coronary arteries during autopsy. Hunter had a massive clinically proven myocardial infarction and Jenner's findings scientifically corroborated the role and relationship of fatty material and the blood vessels.

Langer in, 1880, demonstrated a significant increase in the number of non-coronary blood flow and collateralization around a stenosed epicardial coronary artery signifying an effort to correct the circulatory demand. This was purely an autopsy finding where a dye was directly injected into the coronary ostia. The procedure was an autopsy finding. Typical ECG changes of ischemia were first introduced by Pardee in 1920. Thereafter a march of diagnostic tests evolved and percutaneous coronary catheterization followed by dye-injected selective angiography of the epicardial coronary arteries supplying the heart.  The pathogenesis and prognostic implications of coronary block and the pathophysiology of ischemic heart disease gradually unfolded over the years. First, it occurred to the physicians that symptomatic relief may reverse the pathogenesis. But, a frequent recurrence of symptoms, post-management dye angiography (actually a luminogram of the passage of blood flow) and other investigations, developed over the years, proved otherwise. Real-time imaging studies not only enabled life-like visualization but also helped in determining the calcium load of atherosclerotic deposits and the viability of the area of myocardium supplied. Now we can boast of investigations indicative of and the severity of the disease, investigations showing regional wall motion abnormalities, tests showing and demonstrating the contractile strength or the viability of the studied heart, and gated multi-acquisition imaging studies that helped identification in rhythm disturbances.

There has been a conflict of opinion in angina pathogenesis since Heberden's time. Deposition of ossific material, an attack of sudden spasms of the coronary arteries, irritation of nerves of the cardiac autonomic plexus, and so forth, all have been hypothesized as the cause of angina. But it was a practice to have spirits in the quiet warmth of the evening with the addition of a dose of opium late, also leading to a lower incidence of angina during the night. A few years later, in 1867, Thomas Lauder Brunton suggested angina relief with a concoction of nitroglycerin and alcohol. This was reported by William Murrel in Lancet, in 1879. The rampant use of nitroglycerin, especially the stable non-ignitable glyceryl trinitrate as the quick acting and the long-acting mononitrate, became the mainstay of anti-angina management.

Surgical relief from angina of cardiac origin was first proposed in 1899 when Francois Frank suggested thoracocervical sympathectomy as a method. The knowledge of the basic pathophysiology of the genesis of myocardial dysfunction leading to angina was lacking at that period and symptomatic relief was akin to curing. In about 1910, it was Alexis Carel, working with Thodore Tuffier at the Rockefeller Institute, who first attempted revascularization of the coronaries of a dog in the laboratory with the carotids. This was the first proposition of a direct approach to the coronary arteries. Gordon Murray, of Canada, and Demikov, behind the Iron Curtain, continued with the laboratory dog experiments having a firm belief in a positive outcome. A relatively long time elapsed thereafter before it was evident that there was a direct relation between angina and coronary flow distal to an obstructive lesion.

Small vessel diseases, syndrome-x, angina precipitated by stress, etc., were later discoveries. Cardiac surgery only was successful in 1896  and cardiopulmonary bypass was predictably safe and protocolized by the fifth decade of the 20th century. By this time physicians rudely realized that the nature of the coronary artery arterial obstructive lesions was an irreversible, rather progressive, and total cessation of flow a distinct possibility shortly. Everyone was aware that direct coronary revascularization was the ultimate answer, but the effect was not known. Indirect methods like ---

1.  Surgical thoracocervical sympathectomy.

2.  Subtotal thyroidectomy.

3.  Indirect attempt by creating adhesions between the heart and the pericardium - pericardial poudrage -

a) using 2% novocaine or talc spray,

b) wrapping the heart with omentum, muscle, or a pedicled section of jejunum.

4.  Beck's efforts with the coronary sinus with an attempt to augment myocardial blood flow.

5.  Ligation of the mammary arteries above the 2nd intercostal space with belief in increased myocardial blood flow.

The introduction of cardiopulmonary bypass and the safety of cardioplegic arrest of the heart allowed physicians the liberty to think differently. Thoracocervical sympathectomy interrupts autonomic flow and is believed to prevent angina due to coronary spasms. It is said that Thomas Jonnesco and Charles Mayo were regular performers of this procedure. This was in the 2nd decade of the 20th century. The various effects of thyroid hormones on the heart were evident and this led Eliot Cuttler to believe that by surgical subtotal thyroidectomy, a clinical state of tolerable hypothermia could be created with consequent relief from angina and tachyarrhythmia. Claude Beck had a different idea - he opted for stenosing the coronary venous flow with a ligature over a probe in the sinus thus increasing the dwell time of blood. In 1935, he tried to introduce the famous Beck's procedure where a side-to-side anastomosis between the stenosed coronary sinus and the corresponding portion of the descending thoracic aorta.

However, contrary to the expectations, this procedure did not become popular because of the complexity involved. Results were not also predictable though the observations in survivors suggested myocardial improvement.  A popular belief at that time was blood flow to the heart would increase by default if mammary collateral supply was interrupted -  this led to ligation of the internal mammaries above the 2nd intercostal space. Results of two randomized controlled trials, in 1959-60, however, suggested that internal mammary ligation was of no help in angina and the procedure was abandoned.  1956 witnessed 7 successful endarterectomies by Charles Bailey and this followed an attempt at increasing the affected coronary lumen with a pericardial patch. The famous Swedish surgeon Ake Senning opted for a more direct approach - pericardial patch enlargement of the left main coronary artery.

In this era, clinicians realized the importance of revascularization of the LAD territory. Arthur Vineburg, a Canadian surgeon, promoted a unique proposition. He implanted the pedicle of a bleeding internal mammary artery in the substance of the left ventricular myocardium. A subsequent angiogram at the Cleveland Clinic showed the development of anastomoses and enhanced collateral circulation in the affected area.

This influenced a section of cardiac surgeons immensely and a combination of direct suture with a vein graft to the right coronary artery and Vineburg procedure for the left system remained a strategy for a long time, the late '90s.

 In 1960 Robert Goetz engineered the first direct coronary revascularization attempt. He used a thin Payr's ring to interconnect the right internal mammary artery with the right coronary artery beyond the obstructive lesion. A ligature instead of a suture hastened the process. Angiographic anastomotic patency was demonstrated 14 days later and there was immediate relief from angina. The physicians of that time were not convinced. The greatest difficulty was the inability in visualize the lumen and the course of the epicardial coronary arteries and their branches. Mason Sone's serendipitous discovery of selective coronary angiography changed the scenario. Sabiston, in '62, claimed the honour of first suture anastomosis of a vein conduit to a blocked coronary artery. Technically this procedure was performed off-pump using an end-to-end distal anastomosis. However, the death of the patient from a different issue disheartened Sabiston.

Kolesov, behind the iron-curtain, was later discovered to have revascularized ischemic myocardium by anastomosing a LIMA to the LAD.  At that time and like others, his feat was on beating heart. He also developed an automatic reusable stapler, but the intricacies of set-up and the cumbersome nature of the device never made it popular. Kolesov did not have the advantage of any sophisticated and updated appliances. His patients had such severe debilitating angina that they consented to an unproven procedure.  Visual assessment and surface ECG were the only tools at his hand.  This is why his feat is considered remarkable.

Safety of cardiopulmonary bypass and unhurried distal anastomosis was emphasized and coronary revascularization with vein graft was popularized by  Rene Favaloro of Cleveland Clinic in the '60s. The march of surgical revascularization proceeded henceforth with modifications on the way mainly directed at patient comfort. The goal of complete revascularization was never compromised.

Though the angina was relieved after the operation, physicians were concerned about graft. Studies suggested a variety of reasons and as a reversed segment of the saphenous vein was the commonest conduit, most of the studies were on this vein only.

Around 1968 George Green forwarded the concept of revascularization of the left anterior descending artery (LAD) with a pedicled left internal mammary artery (LIMA). Around this time it was found that the internal mammary arteries were particularly resistant to atherosclerotic deposition. As the LAD system was involved in the vascular supply of a major portion of the active myocardium, logic dictated an arterial graft for LAD and venous conduits for the rest. Arterial grafts take some time to mature and the initial velocity of flow is higher for the vein conduits that originate from the ascending aorta. LIMA to LAD and individual reversed SVGs to other stenosed coronary branches became the "Gold standard" for myocardial revascularization. In acute salvage situations, a venous graft is more helpful as the size is larger, faster anastomosis is possible, and the higher initial flow beyond the lesion (40 ml/s vs 20 ml/s) perfused the affected myocardium quickly ensuring a better recovery. Sequential graft anastomosis with a single proximal aortic anastomosis was done by Flemma and his team in 1971. SVGs were used first and after some studies and deliberations, the fact that was established was:--

1. Overall graft flow was increased for the proximal anastomoses, though there was a reduction in the distal anastomoses.

2. The diamond configuration of sequential graft anastomosis was best for immediate and long-term patency.

3. The number of conduits and proximal aortic anastomoses are at a bare minimum.

Other conduits for aorto-coronary bypass grafting were gradually being added. Carpentier introduced the free radial artery, needing a re-introduction by Acar after an angiographic demonstration of high long-term patency. Free inferior epigastric artery is another option. The pedicled gastroepiploic artery was shown to be a good alternative for the inferior vessels.

Several conduits were suggested during the development of coronary bypass surgery. SVG harvested from the leg and thigh remained the commonest graft for aorto-coronary bypass. Studies, however, revealed superior results with the arterial grafts. There was an acceptable attrition rate, but when mammary arteries were used, the 10-year patency rate was consistently 85% for IMA grafts and 61% (p < 0.001). If an SVG or IMA graft was patent at 1 week, that graft had a 68% and 88% chance, respectively, of being patent at 10 years. The 10-year patency of radial artery grafts was 83%, which was lower than the patency of left internal thoracic arteries (95%, P < .001) and similar to the patency of right internal thoracic arteries (87%, P = .66) and veins (81%, P = .50) the.

Immediate graft failure is a technical issue and can be corrected by re-anastomosis. Graft dysfunction, stenosis, and luminal obstructive cut-off are all features of progression of the native arteriosclerosis and the slow but relentless natural progressive character of such vascular lesions should be kept in mind. Another simple logic is arterial conduits fare better in arterial blocks. The vein conduits at autopsy have after a few days acted like inert passages for blood and failed to show any integration with native tissue. Arterial grafts, on the other hand, grow with the heart. There was a time when the internal mammary harvest was implicated in poor sternal healing, especially in diabetic subjects where BIMA harvest was done. Later studies showed that such apprehensions were unfounded.

The technique of anastomosis as established by Carel in 1912 has remained the same even today. A continuous whip stitch is preferred but some are happy with closely packed interrupted stitches. Both have advantages and disadvantages. Minor modifications with time have been inevitable and full advantage of the principle of triangulation is taken when joining cylindrical blood vessels. To ensure adequate run-off to distal epicardial coronaries during an end-to-side anastomosis, snake-head spatulation or a flaring of the anastomotic end of the graft/conduit was deliberately made. A diamond-shaped side-to-side anastomosis was found better for the delivery of blood and also a lie of a conduit while wrapping the heart with a sequential anastomosis. However, the last anastomosis is always an end-to-side one and most prone to anastomotic failure.

However, how anastomosis is done depends on the surgeon and the suture used is non-absorbable synthetic. Polypropylene is preferred as the material invites the least tissue reaction. The nitinol alloy U-clip for interrupted anastomotic suture is a recent addition, but the cost is prohibitive.

The use of bilateral internal mammary was first in 1973 by Suzuki et al. But till date only a handful of surgeons, particularly those who do not believe in having "all eggs in one basket", even though long-term large cohort studies show a better event-free survival benefit. Extra time and procedural difficulties are factors.

The '70s also saw the ill effects of cardiopulmonary bypass and the magnitude of this in patients with other comorbidities. Coronary arteries were sporadically anastomosed with conduits without the employment of cardiopulmonary bypass.  It was Benetti of Argentina and Buffolo of Brazil who, individually in their own countries, carried on doing off-pump epicardial coronary revascularization with a better operative outcome in a cohort of poor patients and presented their report. This influenced the cardiac surgeons radically and off-pump-coronary-artery became the standard procedure. Anesthetic participation and adjustment of fluids, inotropes and other vasoactive agents gained profound importance and it was their job to maintain –

1.  A mean arterial pressure (MAP) > 60 mm of Hg.

2.  A supple heart with low PA pressure.

3. For surgical comfort, the brain circulation was maintained even with extreme malposition (MAP /maintained >60 mm of hg).

The use of composite grafts, regular employment of arterial grafts (especially if the age is < 65 years), and an emphasis towards sequential side-to-side anastomoses all influenced the changes in the evolution of coronary artery bypass grafting. Though studies show that BIMA grafts on ischemic heart disease make them live longer, the concept did not pick up the way it should have. Strategies of total arterial grafting became increasingly acceptable to coronary surgeons and Tector-type pedicled LIMA with a free RIMA anastomosed to it. The manner of anastomosis could either be T, Y, or I and this depended on the appearance of the heart on visual inspection, size and position of the heart in the thorax, appearance of the epicardial coronary arteries, and a mental plan of sequential anastomoses with significant obstructive lesions. An acceptable relaxed lie of the anastomosed vessels with avoidance of kink is the objective. Surgeons who want more than one pedicle, use the radial artery. The pedicled Gastroepiploic is another good option for the inferior surface vessels and a group of surgeons preferred this option. The cumulative patency rate of the GEA graft was 98.5% at 1 month, 93.7% at 1 year, 86.2% at 5 years, and 70.2% at 10 years. The following images are examples of various strategies currently employed and grafts used:-

Modification of the access, rather than minimization, and sternal sparing were the new focus of interest. Once long-term survival of arterial graft and better quality of life were established, especially in the relatively younger patients (<75 years) who expected to live around 10 years more, coronary revascularization surgeons devoted a part of the energy to reducing the morbidity of access. Initial efforts were all with the heart arrested and the main focus was centered on the precision of the anastomoses and ensuring uninterrupted coronary flow distal to the lesion. Lower partial sternotomy, in various forms, was initially fancied by several continental surgeons for coronary revascularization and internal mammary harvest. However, this did not solve the problem of pain of the sternotomy even though the upper manubrio-costo-vertebral girdle was maintained and the skin incision was limited. A modified left anterior thoracotomy and a specially made rib spreader provide adequate access to the diseased epicardial coronary and also visualization and harvest of the left internal mammary artery. Thus minimally invasive direct coronary artery bypass (MIDCAB) was developed and Subramanian, Calafiore, and other people contributed. Like MIDCAB McGinn further revolutionized minimal invasion in coronary revascularization surgery by further limiting the intercostal space incision, using soft tissue protectors, modified suction stabilizers for the epicardial coronaries, and retractors for visualization, and long-handled endoscopic instruments for LIMA harvest. The procedures were essentially done without cardiopulmonary bypass thus avoiding the complications and morbidity associated. McGinn’s minimally invasive coronary bypass has now become a cornerstone and with time endoscopic harvest of RIMA has been added to the armamentarium.

Development of small and long-handled instruments and stabilizers were designed to help the hazardous surgery without the need for conversion. Camera improvement in magnification and introduction through endoscopic trocars made viewing easier and dissection safe.

With the present state of development and sophistication of the long-handled endoscopic instruments total endoscopic coronary artery bypass grafting (TECAB) has become a reality, and cost permitting, robotic assistance in CABG is a new avenue.

Nitinol needle-suture composite is used to facilitate interrupted coronary anastomosis.

Specially designed robotic arms need to be introduced by trained operating room assistants, and the main surgeon is elsewhere with the console. The robotic arms carry instruments and appliances for the surgery. The main advantages are less pain and faster recovery.