Coronary Artery Surgery

Anatomy and Physiology

The anatomy and physiology of the coronary arteries left main (LM), left anterior descending (LAD), circumflex artery (Cx), and right coronary artery (RCA) are covered elsewhere.[9][10][11][12]

Indications

The original 1970s data supporting the use of CABG was accrued before the maturation of minimally invasive catheter-based interventions. The American College of Cardiology (ACC) and the American Heart Association (AHA) published updated consensus guidelines in 2011 for which patients benefit most from CABG surgery versus PCI.[13] These guidelines are widely used as the standard indications for CABG, divided into class I recommendations and class II recommendations, as summarized below.

Class I indications for CABG

• Stenosis of the left main >50% without a patent bypass graft (unprotected left main disease)
• Stenosis of three vessels >70%
• Stenosis of two vessels >70% if one of the two vessels is the proximal LAD.
• Either CABG or PCI may be used to treat single vessel stenosis > 70% if the patient has unacceptable angina despite the best medical therapy.
• Either CABG or PCI might be used for survivors of sudden cardiac death if ventricular tachycardia was caused by a vessel with >70% stenosis.
• If the patient requires concomitant non-coronary cardiac surgery, and the left main is >50% stenosed, or any other vessel is 70% stenosed.
• Emergency CABG for a post-infarction complication such as ventricular septal rupture, acute mitral insufficiency from papillary muscle rupture, or free wall rupture
• Emergency CABG for failed PCI if substantial myocardium or hemodynamic stability is at risk
• Emergency CABG in cardiogenic shock with CABG amenable lesions, irrespective of the time of onset
• Heart Team approach (multidisciplinary review) is the recommendation for unprotected left main disease and complex coronary artery disease.

Class II indications for CABG

• CABG is preferred to PCI for complex three-vessel CAD with a medium risk Syntax score >22 (scoring system based on the angiographic appearance of coronary vessels).
• Multivessel stenosis >70% and ejection fraction (EF) 35 to 50%
• Two vessel disease, neither of which is proximal LAD, but ischemia is extensive or severe (>20% perfusion defect)
• Single vessel stenosis >70% in the proximal LAD with extensive ischemia.
• CABG is preferrable to PCI for multivessel disease if the patient has diabetes, and the surgeon uses a left internal mammary (LIMA) graft.

Contraindications

The ACC/AHA 2011 consensus guidelines also identify situations where the use of CABG has been associated with harm and is contraindicated as summarized below.[13]

• Emergency CABG in a hemodynamically stable patient who has persistent angina but only a small area of viable myocardium
• Emergency CABG after PCI reperfuses the epicardium but not the microvascular circulation (no reflow).
• Emergency CABG after failed PCI but no active ischemia or imminent occlusion  
• Patients with ventricular tachycardia and myocardial scar but no sign of active ischemia
• Stable ischemic heart disease with either <70% stenosis of non-LM vessel, the disease only implicating the RCA or Cx, or maintained fractional flow reserve >0.80.
• RCA should not be grafted with an arterial graft unless stenosis is >90%.
• Patients with end-stage kidney disease with limited life expectancy due to non-cardiac conditions

Furthermore, CABG performed in a three-day interval after a transmural myocardial infarction or within a six-hour interval of a non-transmural myocardial infarction are both associated with in-hospital mortality, so clinicians should avoid CABG should during those time frames.[14] It is reasonable to wait at least four weeks from the onset of an acute stroke before performing CABG. Other major life-limiting comorbid conditions such as liver failure, end-stage pulmonary disease, profound psychiatric impairment, and advanced malignancy should be approached on a case by case basis.

Equipment

A multitude of equipment is needed to perform a CABG procedure:

• Surgical operating room
• Sterile drapes, gowns, gloves
• Cardioplegia
• Cardiopulmonary bypass machine
• Endoscopic vein harvest scope
• Echocardiography ultrasound
• Swan-Ganz catheter
• Sternotomy saw
• Operative instruments and all supplies (sutures, pledgets)

Personnel

Pre-operative

• Internal medicine physician
• Cardiologist
• Interventional cardiologist
• Cardiothoracic surgeons
• Echo tech
• Nursing 

Intra-operative

• Cardiac anesthesia team
• Perfusionist team
• First assistant 
• OR nursing staff and scrub techs
• Cardiac intensivist 
• Echo tech

Post-operative

• Cardiac ICU nurse
• Physical therapist
• Cardiac rehab specialist

Preparation

Candidates for CABG, identified for the procedure under the indications above, will likely have already been worked up with an angiogram, electrocardiogram, echocardiogram, and studies of myocardial viability.

A thorough history and physical should identify conditions that will affect the operative plan, conduit choice, and long term success of CABG, including heart failure, valvular disease requiring repair, pulmonary hypertension, arrhythmias indicating prior ventricular scarring such as ventricular tachycardias, diabetes, obesity, chronic obstructive pulmonary disease requiring steroids, smoking history, renal insufficiency, history of chest surgery, prior chest radiation, the presence of tracheostomy, subclavian stenosis, peripheral vascular disease, Raynaud’s disease, carpal tunnel syndrome, venous insufficiency, previous abdominal surgery, mesenteric ischemia, carotid stenosis, stroke history, and residual neurologic deficits.

Medical therapy requires optimization in the perioperative period according to ACC/AHA consensus guidelines, summarized here. Provided the patient has an ejection fraction (EF) >30%, beta-blockers should be dosed for at least 24 hours before CABG to prevent mortality and atrial fibrillation. This benefit extends into the post-hospitalization period for some patients. If there are contraindications to beta-blockers, amiodarone may be a substitute as prophylaxis for atrial fibrillation. Digoxin may be useful as rate control for postoperative atrial fibrillation, but not as prophylaxis.

Statin dosing should focus on reducing LDL to <100mg/dL or 30% reduction from prior levels and continued indefinitely to reduce mortality, major adverse cardiac events, and stroke. An insulin drip should be used to lower blood sugar to <180mg/dL before surgery and for at least three days postoperatively to prevent cardiac death and sternal wound infections. Postmenopausal estrogen/progesterone therapy should be discontinued to avoid thromboembolic complications.

Data on preoperative ACE inhibitors and angiotensin receptor blockers (ARBs) are mixed, but these medications should be resumed or initiated as soon as possible postoperatively, especially if the patient has diabetes, kidney disease, hypertension, or an EF <40%. Clopidogrel and ticagrelor should be held for five days prior to CABG; prasugrel should be held for seven days before CABG to prevent bleeding complications. Shorter acting agents may be used in the interim, but eptifibatide and tirofiban must be held two to four hours prior to surgery, and abciximab must be held for twelve hours. Hypothyroid patients should receive their thyroid hormone supplementation to reduce atrial fibrillation, heart failure, and gastrointestinal complications. Aggressive smoking cessation, depression care, and cardiac rehabilitation should be offered to all patients.[13]

Technique or Treatment

A dedicated discussion of the technical details of the CABG operation appears elsewhere.[3] A discussion of general principles follows.

In essence, CABG involves connecting upstream blood flow from the ascending aorta or the subclavian artery through a conduit to a target downstream of coronary occlusion, thereby “bypassing” the occlusion. Revascularization of a vessel should always be complete, with post occlusion targets chosen based on their anatomy identified on the angiogram. The anastomosis should be constructed in such a way that if the bypass occludes, the bypass will not occlude the native coronary artery, and the patient will retain some perfusion to that segment. Cardiopulmonary bypass pump technology allows for a motionless, near bloodless field for the construction of technically excellent anastomoses, with metabolic protection for myocardiocytes during the anastomosis time. Technically excellent anastomotic geometry and no-touch technique (meaning atraumatic to the target intima and the conduit) will yield the longest possible patency for the graft.

The conduit with the best long-term patency (>90% at ten years) is the internal mammary artery, which in >96% of people is uniquely spared of atherosclerosis.[13] The left internal mammary artery (LIMA) is the most common option, but some groups advocate simultaneous use of both right and left as providing both morbidity and mortality benefits with some acceptable levels of infectious complications at 2 to 6.5%.[15][16] The LIMA may be left connected to its upstream origin from the subclavian, or it may serve as a free graft. The LIMA may be skeletonized to preserve sternal perfusion at the risk of conduit injury, or it may be harvested in pedicled fashion to favor conduit patency at the risk of sternal infections.

The radial artery has the advantageous long-term conduit patency characteristics of an artery, but it has the disadvantage of vasospasm and the steal characteristic of a muscular peripheral artery, so it should not be used to bypass a lesion with less than 70% stenosis. Some operative protocols require pharmacologic vasodilator applications to reduce spasm during or after harvest. Radial conduits should not be harvested from patients whose professions require an abundant blood supply to the hand.[17]

The greater saphenous vein is still a commonly used conduit despite its significantly reduced short-term and long-term patency characteristics; 10 to 25% occlude at one year after CABG, and only 50 to 60% are patent at ten years. This decreased patency does not appear to be necessarily related to atherosclerosis per se; instead, trauma from the harvesting process and elevated arterial pressure exposure on the venous endothelium may initiate platelet binding and cascade that culminates in intimal hyperplasia.[13] Greater saphenous vein harvests may be performed in an open fashion with continuous or skip incisions, or they may be harvested endoscopically, introduced in the 1990s. Endoscopic vein harvests had shown significantly reduced patency and nearly doubled mortality compared with open harvest in a 2009 randomized clinical trial, but the more recent REGROUP trial in 2019 found no difference between open and endoscopic harvest.[18][19]

The gastroepiploic artery has also seen use as a conduit with mixed results, with ten-year patency rates reported at 62%. Lesser saphenous vein and inferior epigastric artery have also been used as conduits, with fewer data available.[13]

CABG may be performed with or without the use of cardiopulmonary bypass. Off-pump CABG (OPCAB) techniques were originally pioneered in the Soviet bloc. They gained enthusiasm in the western world for the avoidance of the inflammatory side effects of cardiopulmonary bypass, renal failure, neurocognitive depression, bleeding, and the stroke risk of aortic cannulation. However, although there may be up to a 30% stroke reduction in off-pump (1.4%) compared to on-pump CABG (2.1%),[20] overall outcomes and quality of life outcomes do not currently seem to show any difference.[21][22] The ACC/AHA endorses consideration of off-pump CABG to reduce perioperative bleeding and blood transfusions.[13] At select centers, CABG may also be performed in off-pump minimally invasive direct coronary artery bypass fashion (MIDCAB)[23] or on-pump robotic-assisted total endoscopic coronary artery bypass (TECAB) fashion.[24]

As mentioned above, coronary endarterectomy (CE) predated CABG as an approach to coronary surgery, but quickly fell out of favor for inferior outcomes. Some groups are now exploring augmentation of CABG procedures with CE for complex lesions.[25] Regarding the technique, an incision is made proximal to the stenosed segment. A pair of fine forceps extracts all the calcified coronary intima from the lumen, with counter tension applied to the adventitia. If all plaque is extracted from the directly visualized incised portion, it is an open endarterectomy; if some plaque is extracted from a segment of vessel untouched by the incision, it is called a closed endarterectomy. The lumen is irrigated free of residual atherosclerotic debris, and CABG proceeds in standard fashion using the endarterectomized segment as the target. Although it appears to be safe at some centers, more favorable data will need to accrue for the approach to become more widespread.[25][26]

Complications

CABG outcomes are well studied; the Society of Thoracic Surgeons (STS) database and other organizations have been logging and reporting procedural outcomes for over thirty years, and it remains a class 1 recommendation that all CABG programs should participate in a larger registry to receive reports regarding their outcomes and generate improvement.[13] Summary of CABG complications is also covered elsewhere.[3]

Although CABG brings an overall long-term mortality benefit to patients fitting indications for CABG, there is an upfront operative mortality risk after CABG. The rates reported in the FREEDOM and SYNTAX trials are consistent with standard mortalities, reported to be 1.7% and 3.5%, respectively.[27][28][27] The one-year mortality rate is close to 6 to 8%; the rate at three years is between 11 and 23%.[29][30][29] Emergent operation, need for reoperation, and shock increase this upfront mortality risk, but by two years post-surgery, such patients do as well as other CABG patients.[30]

Cardiac complications occur with CABG. Myocardial infarction may occur, as well as initial low cardiac output states requiring inotropes and/or intra-aortic balloon pump support to maintain systolic pressures >90mmHg. Post-operative atrial fibrillation, which occurs in 20 to 50% of patients postoperatively is not benign, increasing mortality three-fold and disabling stroke four-fold, hence the recommendations for pharmacologic prophylaxis.[13]

Stroke remains a particular Achilles heel of CABG surgery, with an incidence of 1.4% to 3.8%, in addition to adding a ten-fold increase in mortality. Etiologies include embolization from aortic cannulation, microemboli from cardiopulmonary bypass, and the potential for low flow hypoperfusion of borderline ischemic brains. Prevention strategies include optimal medical therapy, carotid endarterectomy for patients meeting indications, and operative adjuncts such as epiaortic ultrasound and transesophageal echocardiography (TEE) to guide aortic cannulation.[13]

Acute kidney injury reportedly occurs in 2 to 3% of CABG patients, with 1% requiring dialysis; this is hypothesized to result from hypoperfusion, cardiopulmonary bypass inflammatory states, and possibly low hematocrit levels.[13] Bleeding during and after CABG remains a common problem, often stemming from required anticoagulation for cardiopulmonary bypass. However, transfusions can cause myocardial depression and represent an increased mortality risk.[13]

The sternal wound is a dreaded complication in CABG patients. Superficial wound incidence is reported 2 to 6%, with a deeper wound incidence of 0.5 to 5%, adding a mortality risk of 10 to 47%. Such wounds are not surprising given the internal mammary artery side branches provide 90% of the blood flow to the region. When harvesting the mammary artery, much of this perfusion is lost.[13] People with diabetes are especially prone to wound healing issues, hence the emphasis on optimal perioperative glycemic control.

Clinical Significance

It has been posited that CABG might be the most well studied, most proven beneficial, life-saving surgery on record.[2] A summary of the landmark CABG trials can help illustrate this.

Three randomized controlled trials from the 1970s before mature PCI compared CABG to medical therapy in patients with coronary artery disease (CAD). Although these trials found no difference in overall survival, they found subgroups of patients with more severe CAD who experienced large survival benefits, thereby providing the foundational data for CABG indications.[1] The Veterans Administration (VA) Coronary Artery Bypass Surgery Cooperative Study Group randomized patients with stable angina and reported increased survival after CABG for subgroups with left main (LM) and triple vessel disease. This increased survival disappeared after eleven years when the predominantly saphenous vein grafts were mostly occluded.[31] The European Coronary Surgery Study (ECAS) studied angina patients with at least >50% dual vessel stenosis and confirmed increased survival after CABG for LM and triple vessel disease. The Coronary Artery Surgery Study (CASS) randomized anginal patients with a history of myocardial infarction, and it reported survival benefit after CABG for a subgroup of patients with reduced ejection fraction from 35 to 50% and triple vessel disease after seven years follow up.[1]

In the years that followed, over 25 studies have compared each successive generation of PCI (angioplasty, bare-metal stent, or drug-eluting stent) to CABG, with the overall data supporting the ACC/AHA consensus indications listed above. Discussion of the BARI, CABRI, ARTS, LE MANS, multiple MASS, multiple ERACI, multiple GABI, AWESOME, PRECOMBAT, SOS, and CARDia trials are beyond the scope of this article, but two trials FREEOM and SYNTAX may be worth summarizing. The FREEDOM trial randomized 1900 diabetic patients with multi-vessel CAD across 140 centers to treatment with either drug-eluting stent or CABG and observed a primary composite outcome of death heart attack and stroke. At five years follow up, the patients receiving PCI had higher composite death, heart attack, and stroke than patients treated with CABG (27% vs. 19% p=0.005), although CABG was associated with a higher risk of stroke.[27] The FREEDOM trial has led to the recommendation that diabetic patients who require revascularization to merit strong consideration for CABG. The SYNTAX trial randomized 1800 patients with triple vessel or left main CAD across 85 centers to treatment with either drug-eluting stent or CABG to observe a primary endpoint of death, heart attack, stroke, or need for repeat revascularization. At twelve months, largely because of a higher need for repeat revascularization in PCI, fewer CABG patients reached the primary endpoint (12% vs. 18% p = 0.002). The SYNTAX trial solidified CABG as the gold-standard treatment for left main and triple vessel disease.[28]

More recent studies have begun to reexamine revascularization compared to medical therapy, given medical advances since the 1970s. The BARI 2D trial examined CABG, PCI, and medical therapy and found at five years for diabetic CAD patients with middle to high-risk SYNTAX score >22 (scoring system based on the angiographic appearance of coronary vessels), CABG reduced major adverse cardiac events compared to medical therapy. There were no differences between PCI and medical treatment.[32]

A common critique of clinical trial data is that potential bias introduced by such a heavy selection of patients before the trial may miss a more representative patient population who may benefit from therapies. For example, the SYNTAX trial included fewer than 50% of patients screened.[1] Registry data may be seen as more clinically representative. Data from the New York State CABG and PCI registries with more than 60,000 patients[33] and the Canadian APPROACH registry with more than 16,000 patients[34] also support the indications and data trends discussed above.

Enhancing Healthcare Team Outcomes

An endeavor as complex as coronary artery surgery demands attention to non-technical aspects such as teamwork, communication, human factors, culture of safety, and optimizing the operative environment. There are increasing data and consensus that focus on these issues is needed to achieve and maintain high-quality interventions.[35]

Nursing, Allied Health, and Interprofessional Team Interventions

A large team of professionals is required to not only manage the patient but to be in constant communication with each other to provide the best overall outcome. Coronary artery surgery requires a cardiothoracic surgeon, a first assistant, a pharmacist, a team of nurses, a perfusionist, an anesthesiologist or nurse anesthetist, and scrub techs in the perioperative period. As mentioned above, each of these team members plays a specific part in monitoring the patient. Though these members are crucial during the actual operation, so many more members are also vital in the pre-operative and post-operative stages of the patient.

Monitoring the patient is just as important as it is in the intra-operative stage as it is in the pre- and post-operative stages. Those involved outside of the intra-operative stage include a cardiologist, ICU, and floor nursing staff, echo techs, physical therapists, and cardiac rehabilitation specialists. Nurses are critical in the care of post-op CABG patients. They are responsible for managing all drains, lines, and educating the patient and their family regarding post-operative care. Excellent perioperative care is crucial to the success and outcomes of the patient. Interprofessional team management and interventions made collectively as a team provide the best outcomes for CABG patients. 

Nursing, Allied Health, and Interprofessional Team Monitoring

It is the responsibility of every member involved in a CABG to monitor the patient for possible complications that can occur. Team members should monitor the sternotomy incision site and vein harvest site for signs of a hematoma or excessive bleeding, the quality and quantity of the chest tube output, and any other complications that may occur.