Coronary artery bypass surgery

PMID (identifier) Doi (identifier) PMC (identifier)
Coronary artery bypass surgery
Coronary artery bypass surgery Image 657C-PH.jpg
Early in a coronary artery bypass operation, during vein harvesting from the legs (left of image) and the establishment of cardiopulmonary bypass by placement of an aortic cannula (bottom of image). The perfusionist and heart-lung machine are on the upper right. The patient's head (not seen) is at the bottom.
Other namesCoronary artery bypass graft
ICD-10-PCS021209W
ICD-9-CM36.1
MeSHD001026
MedlinePlus002946

Coronary artery bypass surgery, also known as coronary artery bypass graft (CABG, pronounced "cabbage") surgery, and colloquially heart bypass or bypass surgery, is a surgical procedure to restore normal blood flow to an obstructed coronary artery. A normal coronary artery transports blood to the heart muscle itself, not through the main circulatory system.

There are two main approaches. In one, the left internal thoracic artery, LITA (also called left internal mammary artery, LIMA) is diverted to the left anterior descending branch of the left coronary artery. In this method, the artery is "pedicled" which means it is not detached from the origin. In the other, a great saphenous vein is removed from a leg; one end is attached to the aorta or one of its major branches, and the other end is attached to the obstructed artery immediately after the obstruction to restore blood flow.

CABG is performed to relieve angina unsatisfactorily controlled by maximum tolerated anti-ischemic medication, prevent or relieve left ventricular dysfunction, and/or reduce the risk of death. CABG does not prevent myocardial infarction (heart attack). This surgery is usually performed with the heart stopped, necessitating the usage of cardiopulmonary bypass. However, two alternative techniques are also available, allowing CABG to be performed on a beating heart either without using the cardiopulmonary bypass, a procedure referred to as "off-pump" surgery, or performing beating surgery using partial assistance of the cardiopulmonary bypass, a procedure referred to as "on-pump beating" surgery. The latter procedure offers the advantages of the on-pump stopped and off-pump while minimizing their respective side-effects.

CABG is often indicated when coronary arteries have a 50 to 99 percent obstruction. The obstruction being bypassed is typically due to arteriosclerosis, atherosclerosis, or both. Arteriosclerosis is characterized by thickening, loss of elasticity, and calcification of the arterial wall, most often resulting in a generalized narrowing in the affected coronary artery. Atherosclerosis is characterized by yellowish plaques of cholesterol, lipids, and cellular debris deposited into the inner layer of the wall of a large or medium-sized coronary artery, most often resulting in a partial obstruction in the affected artery. Either condition can limit blood flow if it causes a cross-sectional narrowing of at least 50%.

Terminology

René Gerónimo Favaloro was an Argentine cardiac surgeon and educator best known for his pioneering work on coronary artery bypass surgery using the great saphenous vein.
Three coronary artery bypass grafts, a LIMA to LAD and two saphenous vein grafts – one to the right coronary artery system and one to the obtuse marginal system.

There are many variations in terminology, in which one or more of "artery", "bypass" or "graft" is left out. The most frequently used acronym for this type of surgery is CABG (pronounced 'cabbage'),[1] pluralized as CABGs (pronounced 'cabbages'). Initially the term aortocoronary bypass (ACB) was more popularly used to describe this procedure.[2] CAGS (coronary artery graft surgery, pronounced phonetically) should not be confused with coronary angiography (CAG).

Number of arteries bypassed

Illustration depicting single, double, triple, and quadruple bypass

The terms single bypass, double bypass, triple bypass, quadruple bypass and quintuple bypass refer to the number of coronary arteries bypassed in the procedure. In other words, a double bypass means two coronary arteries are bypassed (e.g., the left anterior descending (LAD) coronary artery and right coronary artery (RCA)); a triple bypass means three vessels are bypassed (e.g., LAD, RCA and left circumflex artery (LCX)); a quadruple bypass means four vessels are bypassed (e.g., LAD, RCA, LCX and first diagonal artery of the LAD) while quintuple means five. Left main coronary artery obstruction requires two bypasses, one to the LAD and one to the LCX.

A coronary artery may be unsuitable for bypass grafting if it is small (< 1 mm or < 1.5 mm), heavily calcified, or located within the heart muscle rather than on the surface. A single obstruction of the left main coronary artery is associated with a higher risk for a cardiac death and usually receives a double bypass.[citation needed]

The surgeon reviews the coronary angiogram prior to surgery and identifies the number of obstructions, the percent obstruction of each, and the suitability of the arteries beyond the obstruction(s) as targets. The presumed number of bypass grafts needed as well as the location for graft attachment is determined in a preliminary fashion prior to surgery, but the final decision as to number and location is made during surgery by direct examination of the heart.

Efficacy

Age per se is not a factor in determining risk vs benefit of CABG.[5]

Prognosis following CABG depends on a variety of factors, and successful grafts typically last 8–15 years.[citation needed] In general, CABG improves the chances of survival of patients who are at high risk (generally triple or higher bypass), though statistically after about five years the difference in survival rate between those who have had surgery and those treated by drug therapy diminishes. Age at the time of CABG is critical to the prognosis, younger patients with no complicating diseases doing better, while older patients can usually be expected to suffer further blockage of the coronary arteries.[6]

Veins that are used either have their valves removed or are turned around so that the valves in them do not occlude blood flow in the graft. External support may be placed on the vein prior to grafting into the coronary circulation of the patient. LITA grafts are longer-lasting than vein grafts, both because the artery is more robust than a vein and because, being already connected to the arterial tree, the LITA need only be grafted at one end. The LITA is usually grafted to the left anterior descending coronary artery (LAD) because of its superior long-term patency when compared to saphenous vein grafts.[7][8]

Results compared to stent placement

CABG or stent placement is indicated when medical management - anti-angina medications, statins, antihypertensives, smoking cessation, and/or tight blood sugar control in diabetics - do not satisfactorily relieve ischemic symptoms.

A 2018 meta-analysis with over 4000 patient cases found hybrid coronary revascularization (LIMA-to-LAD anastomosis combined with percutaneous stents at other atherosclerotic sites) to have significant advantages compared with conventional CABG. Reduced incidence of blood transfusion, reduced hospital stay duration and reduced intubation duration were all reported. In contrast, HCR was found to be significantly more expensive compared to CABG.[15]

Complications

CABG associated

Open heart surgery associated

General surgery associated

Procedure

Illustration of a typical coronary artery bypass surgery. A vein from the leg is removed and grafted to the coronary artery to bypass a blockage.
Coronary artery bypass surgery during mobilization (freeing) of the right coronary artery from its surrounding tissue, adipose tissue (yellow). The tube visible at the bottom is the aortic cannula (returns blood from the HLM). The tube above it (obscured by the surgeon on the right) is the venous cannula (receives blood from the body). The patient's heart is stopped and the aorta is cross-clamped. The patient's head (not seen) is at the bottom.
  1. The patient is brought to the operating room and moved onto the operating table.
  2. An anaesthetist or anesthesiologist places intravenous and arterial lines and injects an analgesic, usually fentanyl, intravenously, followed within minutes by an induction agent (usually propofol or etomidate) to render the patient unconscious.
  3. An endotracheal tube is inserted and secured by the anaesthetist and mechanical ventilation is started. General anaesthesia is maintained with an inhaled volatile anesthetic agent such as isoflurane.
  4. The chest is opened via a median sternotomy and the heart is examined by the surgeon.
  5. The bypass grafts are harvested – frequent vessels are the internal thoracic arteries, radial arteries and saphenous veins. When harvesting is done, the patient is given heparin to inhibit blood clotting.
  6. In the case of "off-pump" surgery, the surgeon places devices to stabilize the heart.
  7. In the case of "on-pump" surgery, the surgeon sutures cannulae into the heart and instructs the perfusionist to start cardiopulmonary bypass (CPB) normally instructing the perfusionist to "Go on pump". Once CPB is established, there are two technical approaches: either the surgeon places the aortic cross-clamp across the aorta and instructs the perfusionist to deliver cardioplegia with a cooled potassium mixture to stop the heart and slow its metabolism or performing bypasses on beating state (on-pump beating).
  8. One end of each vein graft is sewn on to the coronary arteries beyond the obstruction and the other end is attached to the aorta or one of its branches. For the internal thoracic artery, the artery is severed and the proximal intact artery is sewn to the LAD beyond the obstruction. Aside the latter classical approach, there are emerging techniques for construction of composite grafts as to avoiding connecting grafts on the ascending aorta (Un-Aortic) in view of decreasing neurologic complications.
  9. The heart is restarted by removing the aortic cross clamp; or in "off-pump" surgery, the stabilizing devices are removed. In cases where the aorta is partially occluded by a C-shaped clamp, the heart is restarted and suturing of the grafts to the aorta is done in this partially occluded section of the aorta while the heart is beating.
  10. Once the grafts are completed distally and proximally, the patient is rewarmed to a normal temperature and the heart and other pressures are normal to support coming off the bypass machine, weaning off the bypass machine begins.
  11. The perfusionist makes sure they have enough volume to come off bypass, confirms that anesthesia is ventilating the patient, confirms that vacuum assist is off (if used), and vocalizes each step in the weaning process to the surgeon and anesthesia. Volume can be given to the patient through the arterial line of the bypass machine while the aortic cannula is still in.
  12. Protamine is given to reverse the effects of heparin.
  13. Chest tubes are placed in the mediastinal and pleural space to drain blood from around the heart and lungs.
  14. The sternum is wired together and the incisions are sutured closed.
  15. The patient is moved to an intensive care unit (ICU) or cardiac universal bed (CUB) to recover. Nurses in the ICU monitor blood pressure, urine output, respiratory status, and chest tubes for excessive or no drainage.
  16. After awakening and stabilizing in the ICU for 18 to 24 hours, the person is transferred to the cardiac surgery ward. If the patient is in a CUB, equipment and nursing is "stepped down" appropriate to the patient's progress without having to move the patient. Vital sign monitoring, remote rhythm monitoring, early ambulation with assistance, breathing exercises, pain control, blood sugar monitoring with intravenous insulin administration by protocol, and anti-platelet agents are all standards of care.
  17. The patient without complications is discharged in four or five days.

Minimally invasive technique

Alternate methods of minimally invasive coronary artery bypass surgery have been developed. Off-pump coronary artery bypass (OPCAB) is a technique of performing bypass surgery without the use of cardiopulmonary bypass (the heart-lung machine).[28] Avoidance of aortic manipulation may be achieved through the "anaortic" or no-touch OPCAB technique, which has been shown to reduce stroke and mortality compared to on-pump CABG.[29] Further refinements to OPCAB have resulted in minimally invasive direct coronary artery bypass surgery (MIDCAB), a technique of performing bypass surgery through a 5 to 10 cm incision.[30]

Hybrid Coronary Revascualrisation, where the LIMA-to-LAD anastomosis is combined with percutaneous stents in other atherosclerotic sites, has been shown to have significant advantages compared to conventional CABG, including a decrease in the incidence of blood transfusion, and a reduced intubation time. A 2018 meta-analysis has however demonstrated a greater financial cost when compared to conventional CABG.[31]

Choice of source of grafts

Heart bypass patient showing almost invisible residual scarring. Left: days after operation. Middle: chest scar, two years later. Right: leg scar from harvested vein, two years later.

The choice of vessel(s) is highly dependent upon the particular surgeon and institution. Typically, the left internal thoracic artery (LITA) (previously referred to as left internal mammary artery or LIMA) is grafted to the left anterior descending artery and a combination of other arteries and veins is used for other coronary arteries.[32] The great saphenous vein from the leg is used approximately in 80% of all grafts for CABG.[33] The right internal thoracic (mammary) artery (RITA or RIMA) and the radial artery from the forearm are frequently used as well; in the U.S., these vessels are usually harvested either endoscopically, using a technique known as endoscopic vessel harvesting (EVH), or with the open-bridging technique, employing two or three small incisions. The right gastroepiploic artery from the stomach is infrequently used given the difficult mobilization from the abdomen.

Follow up

Number performed

CABG is one of the most common procedures performed during U.S. hospital stays; it accounted for 1.4% of all operating room procedures performed in 2011.[36] Between 2001 and 2011, however, its volume decreased by 46%, from 395,000 operating procedures performed in 2001 to 213,700 procedures in 2011.[37]

Between 2000 and 2012, the number of CABG procedures carried out decreased across the majority of OECD countries. However, there remained substantial variation in the rate of procedures, with the U.S. carrying out four times as many CABG operations per 100,000 people as Spain.[38] These differences do not appear to be closely related to the incidence of heart disease, but may be due to variation in financial resources, capacity, treatment protocols and reporting methods.[39]

History

Cost

According to the CDC, the average cost of hospitalization (only) associated with a coronary bypass operation in the United States in 2013 was $38,707, for an aggregate hospitalization cost of $6.4 billion.[54] The International Federation of Healthcare Plans[55] has estimated the average cost of hospitalization and physician fees for a coronary bypass operation in various countries as shown in the Table below.[56]

Country Cost
United States $75,345
Australia $42,130
New Zealand $40,368
Switzerland $36,509
Argentina $16,492
Spain $16,247
Netherlands $15,742
India $1,583[57]

See also

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