Coronary artery bypass surgery


The most common surgical procedure in the world.

Coronary artery bypass graft surgery is the second most common method of coronary artery revascularization after percutaneous coronary intervention (PCI.

More than 400,000 CABG procedures are performed each year in the US.

The incidence of death at one year reported to be 2-3%.

For most procedures the procedure entails implantation of a single internal mammary artery graft and 2 venous bypass grafts to the three major coronary artery blood vessels.

CABG surgery using a combination of venous and arterial conduits is often the preferred revascularization approach for patients with complex coronary artery disease who are good surgical candidates.

Coronary artery bypass surgery, also known as coronary artery bypass graft (CABG, cabbage) surgery, and heart bypass or bypass surgery, is a surgical procedure to restore normal blood flow to an obstructed coronary artery.

Coronary artery bypass graft surgery with the use of left internal thoracic artery graft plus vein grafts is an effective way to treat patients with symptomatic advanced coronary artery disease and is superior to percutaneous coronary intervention in patients with severe coronary artery disease and in those with diabetes.

There are two main surgical 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.

The left internal mammary artery is pedicled and not detached from the origin.

In the other process, 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.

The use of the internal thoracic artery as a bypass conduit followed  a single center  study that showed a significant reduction in ten-year mortality when an internal thoracic artery graft was used to bypass the left anterior descending coronary artery.

Preferred treatment for disease of the left main coronary artery, disease involvement of all three coronary vessels, diffuse disease not amenable to treatment with a PCI, in other high-risk patients such as those with severe ventricular dysfunction, or diabetes mellitus.

Long-term patency of graft conduits is limited: saphenous vein grafts have a higher rate of failure than do arterial grafts.

3 to 12% of vein grafts fail before hospital discharge, 8 to 25% failing at one year, and 40 to 50% failing at 10 years.

Only the use of postoperative aspirin and statins have been shown in randomized trials to reduce saphenous vein graft failures.

Risk factors for early saphenous vein graft occlusion is related to procedural techniques: trauma to the  venous conduit during harvesting or a size mismatch between the conduit and the target vessel: these mechanical issues serve as a nidus for thrombus formation that can lead to saphenous vein occlusion.

CABG is performed to relieve angina,  prevent or relieve left ventricular dysfunction, and/or reduce the risk of death.

CABG does not prevent myocardial infarction.

The terms single bypass, double bypass, triple bypass, quadruple bypass and quintuple bypass refer to the number of coronary arteries bypassed in the procedure. 

Left main coronary artery obstruction requires two bypasses, one to the LAD and one to the LCX.

The left main coronary artery is associated with a higher risk for a cardiac death and usually receives a double bypass.

The presumed number of bypass grafts needed as well as the location for graft attachment is determined prior to surgery, but the final decision as to number and location is made during surgery by direct examination of the heart.

A coronary artery may be unsuitable for bypass grafting:  small (< 1 mm or < 1.5 mm), heavily calcified, or located within the heart muscle rather than on the surface. 

This surgery is usually performed with the heart stopped, necessitating the usage of cardiopulmonary bypass.

Two alternative techniques are also available, allowing CABG to be performed on a beating heart either without using the cardiopulmonary bypass, off-pump surgery, or performing beating surgery using partial assistance of the cardiopulmonary bypass, on-pump beating surgery.

CABG is often indicated when coronary arteries have a 50 to 99 percent obstruction.

The obstruction being bypassed is typically due to arteriosclerosis, which 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.

In an observational study among patients 65 years of age or older with 2 or 3 vessel CAD disease there was a long-term survival avantage for CABG compared with PCI. (Weintraub WS et al).

Current clinical guidelines recommend coronary artery bypass graft as the preferred revascularization strategy, particularly in patients with complex coronary lesions and without excessive operative risk.

CABG guidelines:

Preferred treatment for:

Disease of the left main coronary artery (LMCA).

Disease of all three coronary arteries (LAD, LCX and RCA).

Diffuse disease not amenable to treatment with a percutaneous coronary intervention (PCI).

It is the preferred treatment with other high-risk patients such as those with severe ventricular dysfunction, low ejection fraction or diabetes mellitus.

When it can provide relief of angina when the location of partial obstructions precludes improving blood flow with stents.

Rates of most adverse clinical outcomes among patients with multivessel coronary artery disease are lower after coronary artery bypass grafting than after percutaneous coronary intervention.

In the above ASCERT study there was no significant difference in mortality at 1 year, but mortality at 4 years was lower in the CABG group than in the PCI group.

In a meta-analysis of six randomized trials enrolling 6055 patients with multi vessel coronary disease comparing PCI and coronary artery bypass graft surgery:showed an unequivocal reduction in long-term mortality and myocardial infarctions and reductions in repeat revascularizations, regardless of whether the patients are diabetic or not (Sipahi l et al).

The risk of death in the first month after coronary artery bypass graft surgery averages 3-6%, and is higher in patients with poor left ventricular function.

Up to 50% of deaths within the first 30 days after coronary artery bypass graft surgery are attributed to cardiac causes.

The terms single bypass, double bypass, triple bypass, quadruple bypass and quintuple bypass refer to the number of coronary arteries bypassed.

Deep hypothermic circulatory arrest is the standard technique used to reduce metabolic activity and risk of ischemic cerebral damage during bypass.

Bypass of more than four coronary arteries is uncommon.

A coronary artery may be unsuitable for bypass grafting if it is less than 1 mm or < 1.5 mm, heavily calcified or the blood vessel is intramyocardial.

In 2008 163,048 patients had CABG in the US.

Between 2001 and 2008 a 15% decrease in CABG utilization rates (Epsein AJ et al).

Medicare costs $6.7 billion 2006.

CABG surgery has a risk of death in the first month after coronary artery bypass graft averaging 3-6% and can be higher in patients with poor left ventricular function.

With coronary artery bypass graft by on pump technique the perioperative mortality is about 2%, and myocardial infarction, stroke, renal failure requiring dialysis develop in an additional 5-7% of patients.

Up to 50% of deaths in the first month after coronary artery bypass graft surgery has been attributed to cardiac disease: this suggests cases of ischemia/repercussion injury to the myocardium during cross clamping has not been fully addressed by current technics of myocardial protection.

3% of patients have stroke and 3% have encephalopathy as complications.

Stroke after CABG 1-6%, so ith recent studies reporting in overall rate of stroke of 1.6%.

Stroke in relation to coronary artery bypass graft (CABG) may occur intraoperatively or postoperatively.

Among patients undergoing elective, isolated CABG, and intraoperative anesthetic regimen that included volatile anesthetics does not result in significantly fewer deaths at 30 days orbone year than a regimen of total intravenous anesthesia.

Stroke occurrence with coronary artery bypass graft is reduced when CABG is performed without cardiopulmonary bypass.

Among the 45,432 patients undergoing coronary artery bypass graft (CABG) surgery 705 experienced a stroke, with 279 strokes occurring intraoperatively, and 58% postoperatively (Tarakji KG et al).

Stroke rates vary following CABG depending upon the underlying risks of the patient population and the definition of stroke.

Estimated frequency of stroke is increased by a factor of 10 when radiographic infarct is included in the definition of stroke, and the use of MRI rather than CT scans are used to identify infarcts.

Surgical death rate for coronary artery bypass approximately 2.7%.

With on-pump CABG perioperative mortality about 2%, with 5-7% having complications including myocardial infarction, stroke, renal failure requiring dialysis.

In the past decade hospital mortality has declined from 2.8 to 1.6%, a 43% reduction in the relative risk, despite being performed on older and more ill patients.

Age at the time of CABG is related to prognosis: younger patients with no complicating diseases do better, while older patients can usually be expected to suffer further blockage of the coronary arteries.

Studies do not demonstrate benefit for bypass surgery vs. medical therapy in stable angina patients.

30% of patients undergoing CABG surgery are women.

Coma for more then 24 hours is 0.43%.

Inverse relationship between annual surgeon volume of coronary artery bypass graft procedures.

More than 1,000,000 coronary artery bypass grafts (CABG) done annually in the U.S.

Standard of care for patients with disease involving at least three coronary artery vessels or the left main coronary artery.

In the EXCEL Trial patients with left main coronary artery disease of low or intermediate anatomical complexity treated with PCI or CABG there was no significant difference with respect to the rate of death, stroke, or myocardial infarction at five years.

Revascularization can improve the perfusion of viable myocardium but does not restore function in areas of prior infarction.

Surgical death rate for coronary artery bypass approximately 2.2%.

More than 20% of procedures use off-pump technology.

Off pump procedures have acute patency rates exceeding 90%.

Lower incidence of bleeding complications with off-pump bypass surgery.

Off-pump CABG vs on-pump CABG: no difference with respect of 30 day rate of death, myocardial infarction, stroke or renal failure requiring dialysis, but off-pump reduced transfusions, reoperation for perioperative bleeding, respiratory complications, acute kidney injury, but had an increased risk of early revascularization. (Lamy A et al).

In a randomized study of 4752 patients assigned to undergo off pump or on pump coronary artery bypass graft: No significant difference appeared between off pump and on pump CABG with respect to primary outcome, the is rate of repeat coronary revascularization, quality off life, or neurocognitive function at 1 year (Lamy A et al, CORONARY Investigators).

GOPCABE Study Group randomized 2539 patients 75 years of age or older to CABG off or on pump: There was no significant efforts between the patient groups with regard to the composite outcome of death, stroke, myocardial infarction, repeat revascularization, or new renal replacement therapy within 30 days and within 12 months after surgery (Diegeler A et al).

Loss of mental function is a common complication, and one study using MRI imaging just after coronary bypass surgery found significant brain damage in 51% of patients (Knipp SC et al.)

Cognitive decline after coronary artery bypass surgery related to heart-lung blood pump system and the surgery itself releasing debris, including bits of blood cells, tubing, and plaques.

On-pump surgery associated with a greater decrease in platelet count and activation of fibrinolysis than with off-pump surgery.

Contact between cellular and hormonal components of circulating blood in contact with the extracorporeal surfaces cause activation of platelets, white blood cells and endothelial cells to increase thrombotic events.

Increases myocardial susceptibility to ischemia with aortic cross clamping, hemodynamic instability, coronary artery embolization and technical problems such associated spasm or kinking of the arterial grafts.

Up to 80% of all such patients have cognitive deficits with most deficits resolving within 6 weeks to 6 months. In 35% the deficit persists at least 12 months.

Cognitive deficits are related to low middle cerebral artery blood flow during bypass and to the number of emboli entering the middle cerebral artery.

The morbidity and mortality from coronary artery bypass grafting increase with even mild-moderate elevation of the preoperative serum creatinine level.

Perioperative myocardial infarction after CABG occur in as few as 1.3% and as many as 25% of patients which reflects lack of gold standard in diagnosing perioperative myocardial infarction.

Patients with uncomplicated perioperative myocardial infarction have no decrease in long-term survival.

Internal thoracic artery grafts are less prone to late graft closure than vein grafts and are the conduit of choice in myocardial revascularization.

Studies have shown lower long-term mortality with both left and right internal thoracic artery grafts are used for CABG than when a single internal thoracic artery graft is used.

Long term angiographic patency of the right internal thoracic artery graft is similar to that of the left.

In a study of patients treated with CABG with either bilateral a single internal thoracic artery grafting, there was no significant difference in the rate of death from any cause at 10 years (Taggart D).

The majority of patients receive left internal mammary artery grafts to the left anterior descending coronary artery and saphenous vein grafts of the remaining vessels.

Internal thoracic artery graft for the left anterior descending artery is widely accepted.

Using bilateral internal thoracic artery grafts decreases risk of death by 20% at 5 years.

The most common use of internal thoracic artery graft is as a left internal thoracic artery in situ graft to the left anterior descending artery, with patency rate of 90% at 1 year after surgery with a similar number at 20 years indicating little late graft attrition.

The internal mammary artery is almost immune to atheromatous disease and degeneration with patency rates exceeding 90% at 10 years, while 50% of vein grafts a decade after surgery are occluded, and of those veins still ptent around half are diseased.

Radial artery bypass grafts have a higher rate of patency at one year than saphenous vein graft.

In 2008 10,319 patients received radial artery grafts, suggesting about 6% of patients undergoing CABG have such grafts.

In a meta-analysis with a medium follow up of 10 years among patients undergoing CABG, the use of radial artery compared with saphenous vein was associated with a lower risk of a composite of cardiovascular outcomes (Gaudino M).

In a multi-center randomized controlled trial among 757 participants, 99% men, study comparing one year angiographic patency of radial artery grafts versus saphenous vein grafts in patients undergoing elective CABG Colin at one year there was no significant difference in graft patency-radial artery aging 9%, saphenous vein-89%.

One-year occlusion rates for saphenous vein grafts 10-15%.

Failure of saphenous vein grafting typically occurs between five and 10 years after coronary artery bypass graft.

With saphenous vein graft there is progressive graft failure so that by 10 years after surgery 60-70% of grafts remain patent and half of those have angiographic changes of atherosclerosis.

20 years after placement of saphenous graft only 20-25% of grafts are patent.

Saphenous vein grafts are still commonly performed, despite their lower patency rate, because they are long, bilateral and easy to utilize.

Prevalence of postoperative atrial fibrillation about 32%.

The left internal thoracic artery is the artery of choice for an arterial graft.

Annualized mortality from 1% per year in patients with no risk factors to 3.3% for patients with obesity, diabetes, hypertension and hypertriglyceridemia.

Women have higher perioperative mortality after coronary artery bypass surgery compared to men.

In a comparative trial of 428 patients undergoing CABG, reducing the hemoglobin trigger for blood transfusions to 8 g/dL does not adversely affect patient outcomes (Bracey AW et al).

Higher frequency of cardiac and neurologic complications account to a large extent for higher operative mortality for women.

Readmission rates range from 13-16%.

Higher chances of readmission rates found in female sex, older age, African-American race, congestive heart failure, chronic obstructive pulmonary disease, diabetes, hepatic failure and renal failure.

Superiority of arterial revascularization over venous grafting.

Increases the levels of prostacyclin and thromboxane A2.

Low-dose aspirin inhibits the formation of thromboxane by platelets and is associated with a reduced risk of death and vascular ischemic complications.

Resistance to aspirin occurs after coronary artery surgery.

COX-2 inhibitors should be avoided associated they are associated with increased cardiovascular events in this setting.

Increases in creatinine kinase-MB or troponin levels following CABG is common and is associated with cell death resulting from insufficient myocardial protection during cardiopulmonary bypass, orl with off pump techniques, air embolism, and regional and global ischemia during the procedure (Califf RM et al).

Elevation of cardiac enzymes in the first 24 hours following bypass procedure is usually associated with worse prognosis.

Coronary artery grafts may occlude in the months to years after bypass surgery is performed, and is considered patent if there is flow through the graft without any significant stenosis in the graft.

Graft patency depend on the type of graft used, the size or the coronary artery that the graft is anastomosed with, and the skill of the surgeon performing the procedure.

Arterial grafts are more sensitive to handling than the saphenous veins and may go into spasm.

Highest patency rates are achieved by using the left internal thoracic artery connected to the subclavian artery with the distal end being anastomosed with the coronary artery, and lower patency rates with radial artery grafts and internal thoracic artery grafts excised from the subclavian artery.

Left internal thoracic artery grafts graphs are longer-lasting than vein grafts because it is stronger than veins and it is already connected to the arterial tree and therefore needs grafting the only at its distal end.

The left internal thoracic artery is usually grafted to the left anterior descending coronary artery.

The least successful patency rates are from saphenous vein grafts, but these vessels can supply multiple grafts for use.

Saphenous veins have their valves removed or are turned around to prevent occlusion of graft blood flow.

Complications include: Post perfusion neurocognitive impairment, nonunion of the sternum, myocardial infarction, graft stenosis, stroke, acute renal failure, pneumothorax, hydrothorax, pericardial effusion, pericardial tamponade, pleural effusion and vasoplegic syndrome.

Grafts last 8 – 15 years.

Elevations of cardiac enzymes within the first 24 hours after CABG is independently associated with increased intermediate and long-term risk of mortality, with a doubling of mortality with CK-MBE ratio of 4.4, and similar elevations of the troponin level (Domanski MJ et al).

In the above study the mortality rate more than doubles at a CK-MB ratio of 4.4, and similar results were seen for troponin elevations (Domanski MJ et al).

Mortality and left ventricular dysfunction was almost 10 times more likely for CK-MB levels of 100 ng per milliliter or higher compared with patients whose levels with 25 nanograms per milliliter following CABG (Ramsay J et al).

Left ventricular dysfunction in patients with coronary artery disease may be reversible related to previous myocardial infarction, since left ventricular function improves substantially and may even normalize following coronary artery bypass graft.

Assessing myocardial viability with single photon emission computed tomography (SPECT) or low dose dobutamine echocardiography is commonly performed to predict improvement in left ventricular function after CABG, and identification of such viable myocardium predicts improved survival.

In a randomized trial of patients with ejection fractions of 35% less and coronary artery disease amenable to CABG were randomized to medical therapy alone or medical therapy plus CABG with the primary outcome the rate of death from any cause: there was no significant difference between medical therapy alone and medical therapy plus CABG with respect to the death from any cause, but patients assigned to CABG had lower rates of death from cardiovascular causes and death from any cause or hospitalization for cardiovascular causes (Velasquez EJ et al).

In the Guard During Ischemia Against Necrosis trial of high risk patients noted a significant association of CK-MB elevation and six month survival with a mortality rate of 3.4% for CK-M.D. ratios less than 1, 5.8% for ratios higher than57.8% for ratio is higher than 10, and 20.2% for ratios higher than 20 (Klatte K et al).

Intraoperative hyperglycemia increases complications including death following surgery.

Preoperative inspiratory muscle training reduces the incidence of postoperative pulmonary infections by 50%, and hospitalization stay in patients at high risk of developing such complications.


Leave a Reply

Your email address will not be published. Required fields are marked *