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The development of CABG

By Mr Alan Soo - 21st Jan 2024

CABG

Over the last number of years, a number of key developments have occurred in the field of coronary artery bypass grafting

Case study

A 51-year-old man with no previous significant comorbidities and only hypertension in his past history presented with inferior ST elevation myocardial infarction to his GP.

He was transferred to the emergency unit and subsequently transferred to the cardiac catheterisation lab immediately. During catheterisation, as expected, occlusion in his right coronary artery was found and this was deemed as the culprit artery. Angioplasty was performed and in normal circumstances, a stent would be deployed. However, in this patient’s particular case, his right coronary artery was chronically occluded and difficult to deploy a stent. Further imaging of his coronary artery revealed significant lesions in the left anterior descending and left circumflex system as well. The patient was stabilised and transferred to the coronary care unit.

This patient’s case was discussed in the heart team meeting and it was agreed that coronary artery bypass grafting (CABG) surgery would be the treatment of choice. The strategy of total arterial CABG was discussed whereby the surgeon would aim to harvest both internal mammary artery (IMA) and harvest the radial artery endoscopically. This should offer the patient the best long-term outcome. Intra-operatively, as planned, bilateral IMA and radial artery were harvested. It is the author’s preference to construct a Y-graft by anastomosing the right IMA to the body of the left IMA and using it to bypass the left-sided coronary system. The radial artery was then used to bypass the right coronary system.

The surgery was performed with cardiopulmonary bypass support, mild hypothermia, and full myocardial arrest using high potassium cardioplegia solution. The surgery took around three-to-four hours and upon completion, the patient was transferred to the ICU in a stable fashion, and transitioned to the ward 48 hours later. The patient made an uneventful recovery and was discharged on day six post-op. He was discharged on routine medication including aspirin, beta blocker, statin, and a calcium channel blocker (as anti-spasmodic medication for radial artery graft).

CABG is the most common and well-known cardiac surgery. It has been performed over a number of decades and is a successful treatment to revascularise stenosed coronary arteries. It has been demonstrated to confer symptomatic benefit to relieve angina and prognostic benefit to prolong life in patients suffering from coronary artery disease.

The development of coronary surgery can be traced back more than 100 years, when Alexis Carrel first described the concept of vascular anastomosis in 1910 and successfully performed intrathoracic aortic and cardiac anastomoses in dogs. In 1935, Claude Beck relieved his patients’ angina pectoris by placing muscle pedicles, omentum, and pericardial fat inside the pericardium in order to increase myocardial blood supply.

Arthur Vineberg further improved this concept in 1946 when he implanted the left internal mammary artery (LIMA) directly into the anterior portion of the left ventricle. However, the main obstacle for coronary artery bypass grafting (CABG) surgery was the inability to image the coronary arteries and identify the location of the stenosis, hence, the area that needed to be bypassed.

The solution to this problem appeared on 30 October 1958, when Mason Sones inadvertently injected dye contrast into the right coronary artery of a young man with rheumatic heart disease at the Cleveland Clinic. He subsequently followed this inadvertent technique with the first intentional selective coronary angiogram, which led to the birth of coronary angiography.

In the beginning of the development of CABG surgery, numerous surgeons attempted direct end-to-end coronary anastomosis either using the saphenous vein or the IMA as conduit without the aid of cardiopulmonary bypass in an off-pump fashion. This was met with variable results as it was a very technically challenging technique. With the introduction of the cardiopulmonary bypass machine in the 1960s, CABG surgery became safe and reproducible, leading to the evolution of the current state of CABG surgery. In the current era, CABG surgeries are the most frequently performed surgeries in most cardiac surgery departments. The most common configuration of the surgery comprises anastomosing the LIMA to the left anterior descending (LAD) coronary artery and saphenous veins to the remaining coronary arteries with cardiopulmonary bypass (CPB) support on an arrest heart. In some centres, the procedure is still being performed in an off-pump fashion without the aid of CPB support by a handful of surgeons. This technique has demonstrated to be challenging and offer marginal benefit by obviating the complication of cardiopulmonary bypass, and is not routinely used. However, performed by expert hands, it is a very useful technique for high-risk patients.

Indications in the era of PCI

Since the introduction of percutaneous coronary intervention (PCI), whereby stents are delivered percutaneously via catheter introduced into the radial artery or, less commonly, femoral artery to the coronary system, the indication of CABG has been rewritten. The current indications for CABG that confer benefit over PCI include:

  • Multivessel coronary artery disease with SYNTAX score >22;
  • Complex left main stem disease;
  • Patients with left ventricular dysfunction;
  • Diabetics;
  • Previous failed PCI;
  • Patients intolerable to dual antiplatelet therapy (DAPT).

In all cardiac surgery units, patients requiring coronary revascularisation are discussed in the heart team meeting, which comprises non-interventional cardiologists, interventional cardiologists and cardiac surgeons. In these meetings, the indication for revascularisation and strategy of revascularisation are discussed and decided for each individual patient.

Over the last number of years, a number of developments have occurred in the field of CABG, the most significant including the following:

Endoscopic harvesting of conduits

The most common conduit used for the last few decades remains the great saphenous vein. It is easy to harvest, there is an abundance of length, and it is available on both legs. It is also versatile and easy to use to construct a coronary bypass. All these qualities have enabled the great saphenous vein to be the favourite conduit. The only contraindications of using the saphenous vein are the lack of it due to previous varicose vein surgery, previous trauma, etc, or existing severe varicose veins that render the veins unusable for constructing the bypass grafts.

The main complication of harvesting saphenous vein grafts remains leg wound infection. While it does not increase mortality, it is debilitating. Leg wound infection often occurs in patients with peripheral vascular disease and it can lead to reduced mobility, sometimes requiring multiple hospital admissions, and treatment with intravenous antibiotics and wound debridement and dressing. The leg wound infection can often progress to the whole wound from ankle to thigh, depending on the size of the wound.

Therefore, over the years, numerous techniques have been developed to reduce this complication. These include the ‘bridging skin technique’, ‘meticulous closure’, usage of drainage bottles, etc. However, none proved to reduce leg wound complications significantly until the introduction of the endoscopic vein harvest technique.

In this technique, an endoscope is introduced via a small incision made on top of the intended saphenous vein harvest site. The saphenous vein is mapped out using an ultrasonic device prior to this. CO2 insufflation is then used to create a tunnel for visualisation and dissection of the saphenous venous branches. Under video assistance, the surgeon can then dissect out the venous tributaries, and harvest and retrieve the saphenous vein. At the end of the procedure, the ‘freed’ saphenous vein is retrieved via another stab incision, leaving two small incisions in total. Using this technique, the leg wound incision is significantly reduced, as is the incidence of leg wound infections. In the early era of this technique, concerns are raised regarding the quality of the vein harvested. However, evidence has shown that these concerns are unfounded with experience. In the author’s unit, endoscopic harvesting of veins for CABG has been in routine use since 2017. This technique is also a routine in most major cardiac surgery centres.

Since 2022, the author’s unit also extended this technique to harvest the radial artery. This is a more challenging technique and is not well recognised worldwide.

Multiple arterial grafting

The Cleveland Clinic group established that anastomosing the LIMA to the LAD coronary artery (LIMA to LAD graft) confers long-term survival benefit in patients undergoing CABG. This is principally owing to the superior patency of the LIMA compared to saphenous vein grafts. With this in mind, over the last number of years, surgeons are increasingly encouraged to perform more arterial grafts. Emerging evidence suggests that arterial grafts have superior long-term patency compared to venous grafts and patients who receive multiple arterial grafts have improved long-term survival following CABG. Gaudino et al, in a propensity matched study, went a step further to suggest that total arterial grafting using three arterial grafts instead of two arterial grafts is not associated with increased operative risk and is associated with superior long-term survival, irrespective of sex and diabetes mellitus status.

In the author’s practice, younger patients (<65 years old) are offered total arterial grafting unless there is a contraindication that will increase the risk of wound infection (ie, high BMI, COPD). In this cohort of patients, both IMA are harvested together with the radial artery, which is harvested endoscopically. The two IMA grafts are then anastomosed into a Y configuration and used to bypass the left-sided coronary system. The radial artery is then used to bypass the right-sided coronary circulation. As for older patients, a single IMA is harvested together with radial artery and saphenous veins harvested endoscopically. The arterial grafts are used to bypass the left-sided coronary circulation and the saphenous vein graft is used to bypass the right coronary system, as evidence suggests that patency rates of arterial grafts on the left-sided coronary system are superior to the right.

Type of conduits10 year patency of conduits
Left IMA>95 per cent
Right IMA>95 per cent
Radial artery>70 per cent
Saphenous veins~50 per cent

References on request

Mr Alan Soo, Consultant Cardiothoracic Surgeon, Saolta University Health Care Group

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