Coronary artery bypass grafting, or coronary artery bypass grafting, or CABG for short, is internationally recognized as the most effective treatment for coronary artery disease. Started in 1964, coronary artery bypass grafting is a procedure used to replace an obstructed coronary artery to improve myocardial blood supply, relieve angina pectoris, improve quality of life and reduce the risk of death from coronary heart disease.
It is performed by creating a vascular pathway between the root of the ascending aorta and the distal part of the obstructed coronary artery using a grafted vessel called a bridge (usually the saphenous vein and the tipped internal mammary artery, but also the radial artery, the tipped gastroretinal artery and other limb arteries), so that blood from the heart can flow from the aorta through the bridge, bypassing the coronary artery lesion, to the distal part of the coronary artery stenosis or obstruction and reaching the ischemic myocardium. This improves coronary perfusion and increases myocardial oxygen supply, without the need for the tipped artery to connect to the root of the ascending aorta.
The procedure can be performed under cardiac arrest with extracorporeal circulation, which is the traditional coronary artery bypass grafting (CABG), or on a beating heart, which is the “off-pump CABG” (OPCAB or OPCABG). Currently, the number of off-pump CABG cases in China exceeds the number of off-pump CABG cases in China.
Coronary Artery Anatomy
The coronary arteries are divided into: the left coronary artery (i.e., left trunk) and the right coronary artery, most of which open into the left and right coronary sinus of the aorta, respectively. The left coronary artery, the left trunk, divides into two thick branches, the anterior descending branch and the gyrus branch, respectively. Clinically, the left anterior descending branch, the circumflex branch and the right coronary artery are regarded as the “three vessels” supplying blood to the heart, and usually several lesions in coronary artery disease refer to the anterior descending branch, the circumflex branch and the right coronary artery.
Most of the coronary arteries travel within the myocardium, the right coronary artery and the gyral branch travel in the atrioventricular sulcus, and the anterior descending branch and the posterior descending branch travel in the interventricular sulcus. However, some of the coronary arteries travel on the surface of the heart, which is the site of the anastomosis during coronary artery bypass grafting.
The anterior descending branch, which travels in the interventricular sulcus, is, in most people, the most important artery. It supplies the anterior wall of the left ventricle, the anterior ventricular septum, the apex and part of the anterior wall of the right ventricle. The anterior descending branch has several diagonal and septal branches, of which the diagonal branch is also the coronary artery commonly used for bypass grafting.
The gyral branch may have one to several branches, namely the obtuse marginal branch, which supplies part of the anterior, lateral, and posterior walls of the left ventricle and the left atrium. The obtuse marginal branch is the coronary artery commonly used for bypass grafting.
The right coronary artery supplies the right ventricle, right atrium, and posterior ventricular septum, and its branches are the sinus node artery, the acute marginal branch, the posterior left ventricular branch, and the posterior descending branch that continues from the right coronary artery. A small number of posterior descending branches emanate from the gyrus branch (left dominant type). During bridging, the anastomosis may be located in the acute marginal branch, the posterior left ventricular branch, the posterior descending branch, and the right coronary artery trunk.
There may be collateral circulation between these coronary arteries and when one vessel is occluded, it is possible that another vessel may supply the coronary artery distal to the occlusion of the diseased vessel through collateral circulation.
Preoperative evaluation
Because patients with coronary artery disease are generally older and have some problems with the function of various body organs, the outcome of coronary artery bypass grafting is closely related to lung, brain, liver, kidney function and peripheral vascular conditions, in addition to the patient’s heart-related elements. The main heart-related conditions are left and right heart function, the quality of the bridge vessel and the condition of the target vessel (i.e., the diseased coronary artery or offender vessel). A small heart with left heart systolic function, such as left ventricular ejection fraction (LVEF) >40%, has a better prognosis for surgery. Bridge vessel material is best with internal mammary artery, and the most commonly used saphenous vein is too thick or too thin to match the coronary artery target vessel, or has poor results due to thickening of the vein wall from multiple infusions.
If the target vessel has obvious calcification and thickened wall, the results are not good. If the internal diameter is <1mm, it is not recommended to make anastomosis in this vessel. Other influencing factors, such as: patients with poor pulmonary function, difficulties in getting off the ventilator after surgery, high chance of pulmonary infection; brain and central nervous system with preoperative lesions, liver and kidney insufficiency, all may be further aggravated after surgery, and serious complications may occur; carotid artery with severe stenosis or complete occlusion, the incidence of postoperative cerebral infarction is extremely high, carotid endothelial stripping can be done at the same time, and it is recommended to do it under non-extracorporeal circulation Coronary artery bypass grafting surgery.
There are many factors that affect the efficacy of surgery, and foreign clinics use the Multi-Organ Failure Scoring System (MODS), APACHE Scoring System, and Sequential Failure Scoring System (SOFA) scores to assess the outcome of coronary artery bypass graft surgery. both the MODS and SOFA systems observe six systems: respiratory, circulatory, renal, hepatic, coagulation, and neurological, each with a score of 0-4 and a total score of 24. In addition, age, gender, and weight are also influential factors.
Indications for surgery
Treatment of coronary artery disease is divided into medication, medical intervention (coronary balloon dilation i.e. PTCA and intracoronary stenting PCI) and surgical treatment. Surgical procedures, i.e. coronary artery bypass grafting (coronary artery bypass grafting), are the last resort in the treatment of coronary artery disease, and their indications are not invariable, but may change as medical and surgical techniques evolve.
The American College of Cardiology (ACC)/American Heart Association (AHA) publishes guidelines for the treatment of coronary artery disease, which are frequently updated and specifically address indications for the surgical treatment of coronary artery disease from the principles of evidence-based medicine. In general, patients with coronary artery disease for whom drug therapy and medical interventions are ineffective, inappropriate for treatment, significantly ineffective for treatment, or extremely risky for treatment, may be suitable for surgical treatment.
1, stable angina: angina affects daily life and work, conservative medical treatment is ineffective, and coronary angiography reveals that the proximal stenosis of the main trunk or anterior descending branch/gyrus of the coronary artery is >70%, and three branches of the coronary artery are diseased, especially those with low left ventricular ejection fraction of cardiac function.
2, unstable angina: typical angina affects daily life and work, conservative medical treatment is ineffective, and the proximal stenosis of the main trunk or anterior descending branch/gyrus of the coronary artery is found to be >70% by coronary angiography.
3.Post-myocardial infarction: those who failed medical intervention, patients with persistent symptoms, hemodynamic instability, and combined ventricular wall tumor, mitral valve insufficiency and ventricular septal defect.
4.Severe coronary artery stenosis: Those with severe stenosis (stenosis more than 75%) in the three main branches of the coronary artery (anterior descending branch, ileal branch, and right coronary artery) can be considered for surgery regardless of the severity of symptoms.
5.Fatal ventricular arrhythmia caused by coronary artery disease, such as those caused by lesions of the left main stem or three branches of the coronary artery.
6.Failed cases of medical intervention.
7, Previously received coronary artery bypass grafting, symptomatic, non-surgical treatment failure cases.
The 2005 ACC (American College of Cardiology)/AHA (American Heart Association) guidelines state coronary artery bypass grafting as the treatment of choice in the following cases: left main stem coronary artery lesions; all three coronary artery lesions (left anterior descending branch, right coronary artery and left circumflex branch); diffuse disease that is not amenable to interventional treatment.
The 2011 ACCF (American College of Cardiology Foundation)/AHA (American Heart Association) CABG guidelines further state that coronary artery bypass grafting is the treatment of choice in patients with a combination of other high-risk conditions such as severe cardiac insufficiency (e.g., low ejection fraction) or diabetes mellitus[4] .
Surgical methods
1. Traditional extracorporeal circulation bypass surgery
Temporary replacement of cardiopulmonary function by an extracorporeal circulation machine. The heart is stopped during the operation, and the bloodless operative field facilitates the surgical operation. This surgery requires relatively low technical requirements, but the use of extracorporeal circulation may cause damage to the body and more postoperative complications.
2.Bypass surgery under non-stop non-extracorporeal circulation
The procedure is performed with the heart beating, and part of the heart is fixed by a special heart table fixator. Since the operation is performed without the aid of extracorporeal circulation, bypass surgery is done on a beating heart, which requires a higher level of surgical skill, but except for the complications caused by extracorporeal circulation, and the postoperative recovery is relatively fast.
3.Minimally invasive bypass surgery/robotic bypass surgery
A further improvement of non-external circulation coronary artery bypass surgery is minimally invasive coronary artery bypass surgery, which is performed through a 5 to 10 cm incision between the ribs, or through several small holes in the chest wall to place special surgical instruments in the pericardial cavity without splitting the sternum, reducing the chance of injury and postoperative infection. The procedure is performed with special surgical instruments under direct vision or with the aid of a large real-time image from the thoracoscope.
This minimally invasive bypass surgery is currently only applicable to a specific part of the lesion with fewer branches, and for patients with a large number of vascular lesions, it is not easy to achieve complete revascularization, which is a future direction of development as technology improves.
Robotic bypass surgery is the use of 3D simulation technology, using special machines and medical devices, the camera probe is placed into the patient’s pericardial cavity on the surface of the heart in real time out of the large screen, the tiny simulated human hand robotic hand is placed through the chest wall into the heart table, the operator is far away from the operating table, under the table, fingers on the manipulation device remote control robotic hand, through the display screen image, remote control robotic hand in the patient’s body to do coronary artery bypass surgery.
This procedure must be done with the assistance of special equipment, which is expensive (equipment worth tens of millions of RMB) and technically demanding, plus it is not easy to achieve complete blood flow reconstruction of ischemic myocardium, so currently China is still in the exploration and development stage.
Hybrid surgery
In other words, coronary artery bypass grafting is complemented by medical intervention in the operating room.
Bridge vessel material.
Arteries: left internal mammary artery, right internal mammary artery, left/right radial artery, gastroretinal artery, superior abdominal wall artery, splenic artery, etc.
The left/right internal mammary artery has the best results, the radial artery is prone to spasm after surgery (usually treated with heparin and calcium channel blockers), and the gastroretinal artery is highly traumatic.
Veins: saphenous vein, noble vein of the upper limb, etc. Saphenous vein is the most commonly used bridge vessel material
Artificial materials: homogeneous veins, tissue-engineered artificial vessels, the former with low patency rate, the latter not yet used clinically.
Brief procedure of coronary artery bypass surgery operation
Anesthesia: Intravenous complex anesthesia is used. The anesthesiologist places various intravenous catheters into the patient and injects anesthetic and analgesic agents. After tracheal intubation, ventilator-assisted breathing is performed, and the anesthesiologist monitors vital signs. Anesthetics are administered slowly and continuously intravenously throughout the procedure, supplemented by intermittent inhalation of anesthetic gases to maintain general anesthesia.
Surgery: The vessels used for interception of the bypass – usually the left internal mammary artery and the saphenous vein – are selected. The patient is also given systemic heparin to prevent blood clotting. The coronary artery is explored, the diseased coronary artery and its lesion (obstruction or stenosis) are identified, the anterior wall of the artery is opened with a coronary knife at the appropriate part of the distant coronary artery, the incision is enlarged with special scissors to about 5 mm, depending on the internal diameter of the coronary artery and the internal diameter of the bridge vessel, and then the corresponding size incision is made at the corresponding part of the bridge vessel measured in advance to make the anastomosis between the bridge vessel and the diseased coronary artery. The anastomosis of the bridge vessel and the diseased coronary artery is made with 7-0 or 8-0 fine polypropylene sutures, and rarely with 9-0 sutures, mostly by continuous sutures.
Since most of the coronary arteries are anastomosed with the anterior wall, the anastomosis is called “lateral”, and end-lateral anastomosis refers to the anastomosis of one end of the bridge vessel with the coronary artery; lateral-lateral anastomosis refers to the anastomosis of one side of the bridge vessel with the coronary artery. Except for the internal mammary artery (or other tipped artery), which does not need to be treated after anastomosis with the diseased coronary artery, the other bridge vessels should be anastomosed with the aortic root after anastomosis with the coronary artery, so that the aortic blood can be directed far away from the coronary artery lesion through the bridge vessel.
If the coronary artery lesion is severe, the thickened wall of the vessel is calcified, the inner diameter of the lesion becomes small, and the vessel is very important, such as the anterior descending branch lesion, then endothelial debridement is feasible, that is, the thickened and calcified coronary artery endothelium is stripped out completely with the help of the instrument, and then the bridge is bypassed at the lesioned coronary artery.
If the patient is young or has very poor venous condition, then whole artery bypass can be used. The options are: left internal mammary artery/right internal mammary artery (one end of the right internal mammary artery or right internal mammary artery is connected to the left internal mammary artery/ascending aorta and the other end is anastomosed to the diseased coronary artery); internal mammary artery/radial artery (one end of the radial artery is connected to the ascending aorta and the other end is anastomosed to the diseased coronary artery); gastroretinal artery. less frequently used clinically.
In the case of bypass grafting with extracorporeal circulation (ONCABG), the surgeon first establishes extracorporeal circulation by cannulating the aortic root, right atrium, and left atrium (if necessary). The ascending aorta is blocked, myocardial protection fluid is instilled in the aortic root, and ice chips are placed on the heart surface.
In the case of non-extracorporeal circulation bypass surgery (OPCAB), the surgeon uses a special table fixator to relatively immobilize the area of the heart where the anastomosis is to be made so that this particular area of the heart is relatively stationary, blocking the proximal and/or distal coronary arteries where the anastomosis is to be made, and then dissecting the coronary arteries and cleaning the coronary openings with water or carbon dioxide so that the coronary arteries can be opened in a relatively bloodless state using the the method described above for coronary artery bypass grafting.
Similarly, minimally invasive surgery and robotic surgical approaches are much the same as OPCAB, with the difference being the size of the incision and whether special instruments are used.
If the patient has a combined left ventricular ventricular wall tumor, the procedure should be performed at the same time. The principle of surgical treatment of ventricular wall tumors is to eliminate the paradoxical motion of the ventricular wall and, if necessary, to reshape the left ventricle as much as possible. The main method is the “sandwich” method: it is suitable for cases with small ventricular wall anomalies, using two sticky spacers to sandwich the ventricular wall anomalies inside them and tightening them with polypropylene sutures, with or without extracorporeal circulation; 2. 2, “Dor” and modified “Dor” method: under extracorporeal circulation, the junction of normal and necrotic in the left ventricle is circumferentially reduced or patched, and then the ventricular incision is closed with the “sandwich” method.
If mitral valve insufficiency is combined with moderate or above, depending on the condition, valvuloplasty (with or without an annulus) can be performed, and mitral valve replacement is also feasible if necessary.
If combined with a ventricular septal defect, septal repair can be performed under extracorporeal circulation.
If the patient has severe intraoperative cardiac insufficiency, is hemodynamically unstable, or cannot be removed from the extracorporeal circulation machine, a cardiac assist device such as intra-aortic balloon counterpulsation (IABP), left heart assist, or extracorporeal membrane lung therapy (ECMO) may be used.
Number of bypasses
The surgeon will evaluate the coronary angiography results to determine the location of the coronary lesion and will estimate the number of bypasses before surgery, but the final number of bypasses will be determined after intraoperative examination of the coronary arteries.
The number of bypasses is generally defined as the number of anastomoses between the bridge vessel and the diseased coronary artery. To conserve bridge vessels, except for important coronary arteries, such as the anterior descending branch, which are anastomosed with a single vessel, the same bridge vessel is used for all other diseased vessels, with a maximum of two bridge vessels, and different vessels are anastomosed in different parts of the bridge vessel. If the internal mammary artery and saphenous vein are bridged with 4 vessels, there can be 4 anastomoses: internal mammary artery – anterior descending branch, aorta – saphenous vein – diagonal branch – obtuse marginal branch – posterior descending branch; some operators use the scheme: internal mammary artery – anterior descending branch, aorta – saphenous vein – diagonal branch – obtuse marginal branch, aorta – saphenous vein – posterior descending branch.
A higher number of bypasses does not equate to a more critical patient, and similarly, a lower number of bypasses does not equate to a healthier patient. A patient with a large number of coronary lesions may receive a relatively small number of bypasses due to the lack of a suitable “target vessel”.
A coronary artery that is too thin (<1 mm I.D. < span="">) and severely calcified (meaning that there are no segments of the coronary artery free from coronary disease or no suitable site for an anastomosis) may not be a good candidate for bypass grafting. A patient with left main stem stenosis will need a bypass bridge over the left anterior descending branch and its diagonal branch (if appropriate) and the obtuse marginal branch (1 or several) of the left circumflex branch. Left main stem lesions are the greatest risk of death from heart disease.
Post-operative management
The same routine management as after cardiac surgery, such as volume replacement, water-electrolyte stabilization, anti-inflammatory, and sedation. In the field of coronary surgery, postoperative anticoagulation is very important, either intravenous heparin or subcutaneous small molecule heparin, lifelong oral enteric antiplatelet agents, and two antiplatelet agents can be used for a short period of time, with nitrates, calcium channel blockers acting on the coronary arteries, beta blockers to regulate the heart rate, and if necessary, blood pressure control, lipid and glucose agents to keep them at low levels.
Complications of surgery
Patients undergoing transcoronary artery bypass grafting will have the same postoperative complications as other surgeries, plus some more common or specific risks in coronary artery bypass grafting.
1. General complications.
Bleeding, incisional infection or sepsis, deep vein thrombosis, anesthesia complications, malignant hyperthermia, scarring, acute/chronic pain in the incision, psychiatric symptoms, pneumothorax, hemothorax.
2.Related to cardiac surgery
(1) Central nervous system complications, incidence between 5-6% in cases operated with extracorporeal circulation, and a substantial decrease in neurological complications in cases operated without extracorporeal circulation.
(2) Mediastinal infection and non-union of the sternum: incidence between 1-4%. Obesity is an important risk factor, and others such as combined diabetes, previous coronary artery bypass grafting, use of unilateral/bilateral internal mammary arteries, etc.
(3) Perioperative infarction: myocardial infarction due to embolism, hypoperfusion or bridge incompetence.
(4) Acute renal insufficiency.
Surgical prognosis
The use of preoperative assessment methods provides a general idea of the surgical risk. Early complications are associated with advanced age, female gender, whether the procedure was performed urgently, decreased cardiac function, left main stem lesions, diffuse coronary artery disease and previous coronary artery bypass grafting.
Coronary artery bypass grafting has a 30-day operative mortality rate of less than 1% in experienced cardiac centers. The long-term prognosis of coronary artery bypass grafting depends on various factors, such as the bridge vessel, the quality of the target vessel, the surgeon’s microsurgical anastomosis technique, and the patient’s satisfaction with the control of blood glucose, blood pressure, and lipids. Obstruction of the bridge vessel after coronary artery bypass grafting is a relatively serious complication, and successful procedures usually maintain patency rates of 10 years (more than 60%) for venous bridges and 15 years (more than 90%) for internal mammary artery bridges.
Patency rates of bridging vessels
In the months to years following coronary artery bypass grafting, bridges become diseased and may become blocked. The patency of a bridge depends on a number of factors, including the type of bridge, whether the intima was damaged during interception of the bridge, the degree of coronary artery disease such as the severity of calcification of the thickened arterial wall, the internal diameter of the coronary artery distal to the lesion, and the surgeon’s vascular suturing skills.
Arterial bridges are much more sensitive to rough handling than the saphenous vein. A gentle maneuver to remove the bridge vessel with good endothelial protection will inevitably improve the long-term patency rate. Using the saphenous vein cases, the anastomosis of the saphenous vein to the ascending aorta will have stenosis within one year in 20% of cases, but only 25% of these cases will be obstructed within 5 years. Long-term patency of the left internal mammary artery is much higher than that of the saphenous vein, with a patency rate of 90-95% over 10-20 years, so it is usually anastomosed to the left anterior descending branch of the coronary artery (the most important coronary artery).
Postoperative precautions
1.Postoperative activities
As soon as physical strength allows, you can do a moderate amount of small range of activities, from bedside activities to bedside activities to activities on the ground, all should be done with the help of family members. Proper activities are beneficial to recovery and reduce the chance of infection.
2.Cautions for the sternum
Most of the heart surgeries are performed through the open-chest route, and the sternum is fixed with wires after the surgery. Therefore, patients need to avoid doing some exercises for both upper limbs for 8 to 12 weeks after receiving coronary artery bypass graft to facilitate the early healing of the sternum and reduce the occurrence of complications. First, patients need to avoid excessive use of their arms, such as pushing themselves out of the seat or dragging the seat before sitting down. Secondly, patients should avoid lifting any heavy objects. Finally, patients should avoid raising their hands above their heads to do things. after 12 weeks (3 months), they can basically return to normal life.
3.Cautions for the surgical incision
After surgery, there will be slight redness, pain, swelling, local numbness and other phenomena at the incision, which are common. With the gradual strengthening of body recovery and nutrition, the discomfort will be reduced until it disappears. Experienced hospitals use pain pumps (a slow-release compound analgesic device) in the early post-operative period to enable patients to pass through the early post-operative period smoothly. Due to interception of the saphenous vein, pain in the lower extremity and swelling of the lower extremity due to poor reflux can occur. Solutions include elevating the affected extremity and using elastic stockings or elastic straps.
Postoperative diet
Some patients have symptoms such as stomach distension, nausea and vomiting after surgery. Initially, the diet structure is based on light and easily digestible food, supplemented by appropriate activity stimulation, and the digestive system will gradually recover. Family members can use hot towels or hot water bags to warm up the small abdomen to promote voluntary urination; use open cork to help defecation.
Postoperatively, limiting fat in food, especially saturated fatty acids from animal foods, is the primary principle. Attention should also be paid to adequate protein supplementation. Foods containing high protein and in line with low fat principles include nonfat dairy products, soy products, some birds of prey and fish. Semi-liquid foods made of grains and cereals (porridge, soup, lotus root powder, etc.) are suitable as the main source of energy. Prevention of drug-induced nutritional deficiencies.
Some diuretics have a great impact on the electrolyte balance of potassium, sodium, magnesium and calcium in the body, and anticoagulant drugs can cause damage to the mucous membrane of the gastrointestinal tract, making the absorption of iron, calcium and vitamins decrease and the loss increase, so proper supplementation of vitamin C, vitamin K, vitamin E, folic acid and iron is necessary after coronary artery surgery. If you have pre-existing diabetes and are using insulin, you may also need to supplement with B vitamins and potassium, which can promote energy metabolism. Soluble dietary fiber is also suitable for patients after coronary artery surgery to prevent and treat gastrointestinal disorders caused by surgical stress and to prevent constipation. The reasonable application of health food can regulate blood lipids, lower blood pressure, control blood sugar and guarantee the long-term effect of surgery.
Postoperative follow-up
Be sure to obtain the contact information of the surgeon before discharge so that you can contact the surgeon when necessary after surgery. When discharged from the hospital, be sure to ask the surgeon about the postoperative medication precautions, and return to the hospital for review 6 months after surgery. The main review is blood biochemistry, electrocardiogram, echocardiogram, chest X-ray, coronary CTA if necessary, and adjustment of postoperative medication.