Overview of Coronary Artery Bypass Surgery

*Jorge Balaguer and Leshya Bokka*

### **Abstract**

This chapter provides an overview of coronary artery bypass surgery in clinical practice, beginning with a discussion about implications from a public health perspective, followed by indications for coronary artery bypass grafting (CABG), surgical options in heart failure patients, and minimally invasive approaches. Specific areas discussed include on- versus off-pump CABG, robotic procedures, coronary endarterectomy, the Dor procedure (Surgical Ventricular Restoration), Impella® and Intra-aortic balloon pump (IABP)-supported CABG, trans-myocardial laser revascularization (TMR), and hybrid and multiple arterial revascularization techniques. To conclude is a discussion on the growing importance of surgical simulation and different models of simulators in training residents and fellows. Faculty members similarly benefit from surgical simulation, particularly for complex or less frequent revascularization procedures.

**Keywords:** robotic procedures, simulation, public health, indications, heart failure patients, education, overview

### **1. Introduction**

The first planned coronary artery bypass graft (CABG) operation, intended to treat chronic coronary artery disease (CAD), was performed by Dr. René Favaloro at the Cleveland Clinic in 1967 [1]. This initial procedure involved anastomosing a saphenous vein graft (SVG) from the proximal right coronary artery (RCA) to the distal RCA. Soon after, the technique evolved into performing the proximal anastomosis to the ascending aorta and became known as aorto-coronary bypass. Since its introduction, several improvements have been very impactful and widely adopted. Of note is the comparison between CABG and the less-invasive revascularization option, percutaneous coronary intervention (PCI), as a means for myocardial revascularization due to coronary artery disease (CAD). As PCI techniques and technology developed significantly over the last decades, this option gained popularity due to increased accessibility and advances in drug-eluting stent technology (DES). CABG is still the preferred revascularization intervention for patients with advanced CAD and remains the gold standard treatment for coronary revascularization, particularly in some subsets of patients, showing superior outcomes compared to PCI/stenting and guideline-directed medical therapy (GDMT) in patients with advanced CAD. This chapter outlines the indications for CABG and its public health implications and considerations for special populations.

## **2. Epidemiology and public health**

CAD is the leading cause of mortality globally, accounting for 17.9 million deaths [2]. The leading symptom of CAD is angina, which could lead to different types of myocardial infarctions, ventricular arrhythmias, and heart failure. CAD significantly impacts quality of life as well as life expectancy and disability. Ischemic cardiomyopathy is responsible for about half of heart failure cases in the United States. Patients from low- and middle-income countries have a high disease burden from delayed presentation and treatment secondary to advanced disease, poor healthcare services access, and delayed treatments, resulting in excess mortality. In the United States, cardiovascular disease accounts for over \$300 billion annually, and ischemic heart disease spending was just under \$80 billion [3].

Despite the World Health Organization's targets to decrease morbidity and mortality from non-communicable diseases, CAD and stroke deaths are rising in the United States [4]. CABG is the most frequently performed cardiac operation, with about 400,000 CABG operations being performed each year in the United States [5, 6]. Overall, CAD contributes to significant morbidity and mortality globally, and coronary revascularization offers the chance for myocardial recovery. Coronary revascularization offers an incredibly effective treatment for myocardial function and protection that offers improved survival and event-free survival. CABG is a robust palliative intervention as the healthcare community and major public health organizations work towards enhancing primary prevention interventions targeting the incidence of CAD.

### **3. Indications for CABG**

In the last decade, the SYNergy between percutaneous coronary intervention with TAXus and cardiac surgery (SYNTAX) score became a widely used, accurate method to objectively assess the severity of CAD. Used for the first time in the SYNTAX Trial, the SYNTAX score is a valuable tool to aid clinicians in deciding the best strategy for revascularization [7]. A high SYNTAX score reflects a high burden of CAD; these patients greatly benefit from CABG if the surgical risk is low or moderate. Considering that some patients with advanced CAD are elderly, frail, or may have a significant degree of cardiac and non-cardiac comorbidities, the decision to proceed with CABG must account for the risk of morbidity and mortality associated with such an operation. Risk stratification models, including the Society for Thoracic Surgeons (STS), EuroScore, and many others, aid surgeons and heart teams in this decisionmaking process [8].

CABG and PCI are the two direct revascularization options used today. Both interventions are very effective and have been part of clinical practice for decades. Multiple studies have evaluated the benefit of each procedure in specific patient populations. CABG is the best intervention in patients with left main disease, threevessel CAD, diabetes, and high SYNTAX scores [9, 10]. Mortality rates for emergency CABG and reoperations are high, likely due to severe illness and higher acuity at presentation. Alternatives to CABG are usually explored in these cases. In patients with three-vessel CAD or two-vessel CAD with proximal left anterior descending (LAD) artery involvement, CABG is a superior option, mainly based on the benefits of grafting the LAD with the left internal mammary artery (LIMA).

In contrast, PCI is the preferred intervention if the LAD is not involved [9, 10]. CABG outperformed GDMT in patients with advanced CAD, particularly if the

### *Overview of Coronary Artery Bypass Surgery DOI: http://dx.doi.org/10.5772/intechopen.114279*

### **Figure 1.**

*American Heart Association recommendations for the management of stable ischemic heart disease (SIHD) in patients with angina refractory to medical therapy [9].*

LAD is involved [11, 12]. While PCI is preferred over surgical intervention for AMI, cardiac surgery remains the primary mode of intervention for complications of AMI, including free wall ventricular rupture, ventricular septal rupture (VSR), and acute mitral insufficiency secondary to papillary muscle rupture. In these cases, the goal of care is two-fold: revascularizing myocardium and repairing post-infarct mechanical complications.

For patients with multi-vessel disease and ischemic cardiomyopathy with an ejection fraction (EF) < 35%, CABG is the preferred surgical approach, offering increased survival and symptom relief (**Figure 1**) [9, 11].

### **4. Interventions**

Although the fundamentals of surgical revascularization have changed very little since its introduction, multiple improvements have led to safer, less invasive operations with shorter recovery times. Surgical revascularization provides higher value if performed in higher-risk and more complex patient populations. Several approaches are now available for surgical coronary artery revascularization. This section outlines the traditional CABG operation, minimally invasive options, ventricular restoration considerations, coronary endarterectomies, and trans-myocardial laser revascularization.

### **4.1 General approach**

The basic principle behind the CABG operation involves constructing arterial and venous grafts to improve blood supply distal to the site of a coronary obstruction.

Revascularization in CABG requires delicate microvascular techniques in order to anastomose very small coronary arteries (1 to 2 mm in diameter) to grafts using very delicate monofilament sutures (Polypropylene 7-0 or 8-0), thinner than a human hair. The core surgical steps of the traditional CABG surgery include performing a median sternotomy, establishing access for cardiopulmonary bypass (CPB), and arresting the heart to obtain a motionless surgical field. Once these critical steps are achieved, arterial and venous vessel grafting can be performed (**Figures 2** and **3**).

Considerations for choosing "target vessels" for grafting to the coronary arteries include carefully analyzing multimodal anatomic factors of the coronary arteries to be bypassed. The coronary arteriogram is the gold standard, state-of-the-art imaging to evaluate the severity of lesions and site to perform distal anastomosis to the surgical target. The use of Intravascular Ultrasound (IVUS) and Functional Flow Reserve (FFR) assist in identifying significant lesions when images from the coronary arteriogram are not definitive. The graft choice is critical and should be individualized for each patient. These considerations make CABG a "tailor-made operation" designed specifically for each patient. Arterial grafts have demonstrated superior patency than venous grafts for multiple biologic factors; however, arterial grafts can be vulnerable to competitive flow and vasoconstriction, described in radial arterial grafts as the "string sign." The use of the LIMA is universally accepted and is utilized on most patients undergoing CABG where the LAD must be bypassed. The LIMA-to-LAD anastomosis has shown increased survival and decreased major adverse cardiovascular events. The additive value of using a second or a third arterial graft is less established when its risks are considered. Other factors such as diabetes, patient's age, life expectancy, and lesion severity must be assessed before proceeding with multiarterial revascularization.

**Figure 2.** *Median sternotomy incision.*

*Overview of Coronary Artery Bypass Surgery DOI: http://dx.doi.org/10.5772/intechopen.114279*

**Figure 3.** *Cannulation for cardiopulmonary bypass and flow of blood through cardiopulmonary bypass pump.*

Strictly from the vascular behaviors of individual grafts, arterial grafts have demonstrated higher patency when compared to SVG. While LIMA grafts have a patency of over 90% beyond the 10-year mark [13, 14], SVG grafts have failure rates between 15% and up to 25% within the first 18 months [15]. Approximately 50% of all vein grafts become diseased, and many become occluded 10 years after CABG due to vein graft CAD, which results from a combination of early endothelial damage during surgery, inflammation, and gradual lipid deposition [16]. The more extensive use of arterial grafts is appealing, as they are protected from the biological failure seen on vein grafts; however, care should be taken when using the RIMA and the radial artery. The use of multiple arterial grafts may pose additional risks and may not significantly benefit the patient. Sternal complications are of concern when using the LIMA and the right internal mammary artery (RIMA) in the same patient [17]. Harvesting the internal mammary artery compromises sternal blood flow [17, 18]. Using the LIMA and RIMA simultaneously significantly decreases sternal blood flow, compromising sternal wound healing and increasing the risk of sternal complications, including infection [17]. The effect of poor sternal wound healing is more pronounced in patients with diabetes. Skeletonizing the LIMA and RIMA involves harvesting only the arteries without their associated veins or fascia, which mitigates this risk (**Figure 4**) [19].

Vasospasm and string sign due to competitive flow in radial artery grafts is infrequent if the target vessel being bypassed has more than 70% stenosis, and even lower if the stenosis is above 90%. Biological factors that influence venous graft patency are endothelial damage and low levels of arterial endothelial cell factors, including nitric oxide, that help decrease inflammation and thrombosis. The coronary system where the anastomosis is performed also affects patency. The LIMA-to-LAD anastomosis is favorable due to the position of both vessels (LIMA and LAD) and the extensive runoff of the LAD system. Coronary artery diameter also influences patency. The larger the coronary artery, the better the patency, independent of the graft used.

Patient comorbidities also guide graft selection. For example, patients with chronic kidney disease (CKD) may not be suitable candidates for radial artery grafting to preserve the radial artery in case of fistula placement. In addition, the radial

**Figure 4.** *Multi-arterial grafting.*

artery is unsuitable in patients with insufficient ulnar artery flow, as grafting the radial artery will compromise hand perfusion, although this is an infrequent event. Patients with advanced vascular disease may have poor radial artery quality as well. If the patient had a recent cardiac catheterization via the radial artery, this vessel should not be used for grafting. Preoperative ultrasound of the radial artery, ulnar artery, and patency of palmar arches are evaluated prior to using the radial artery as a graft.

### **4.2 Minimally invasive CABG**

Less invasive approaches to traditional CABG operations via median sternotomy and extracorporeal circulation were introduced to clinical practice in the 1990s. The first iteration of a minimally invasive direct CABG (MIDCAB) involved minimizing the surgical trauma associated with a traditional CABG. MIDCAB (minimally invasive direct coronary artery bypass) is sought after for several reasons. While a traditional CABG allows for complete visualization of the heart in an immobile and blood-free operative field, it requires several invasive steps, including a median sternotomy that divides the sternum, cannulation CPB via the ascending aorta (most common), and cardioplegic arrest. The alternatives described are intended to avoid these complex and potentially risky steps to minimize surgical trauma, decrease surgical morbidity, and enhance recovery. This section outlines the advantages and disadvantages of these alternative approaches.

Sources of morbidity associated with traditional CABG operation come from three main steps: (1) median sternotomy, (2) CPB, and (3) cardioplegic arrest. The median sternotomy of a traditional CABG is performed as an incision dividing the sternum longitudinally. One or both halves of the sternum get de-vascularized in the process. Approximately 30–40% of patients subjected to CABG operations are diabetics. In addition to diabetes, comorbidities such as COPD and obesity increase the risk of sternal complications, including osteomyelitis, acute mediastinitis, and poor wound healing. While these complications are uncommon (1%), they are serious, morbid conditions.

Performing a CABG through a small 8 cm incision on the left side of the chest became the first step to reducing the mechanical trauma to the chest wall. In MIDCAB, the risk of sternal complications is of low concern due to the sternum being left intact. Similarly, mini-thoracotomy and limited anterior thoracotomy are both

### *Overview of Coronary Artery Bypass Surgery DOI: http://dx.doi.org/10.5772/intechopen.114279*

approaches to decrease the stress from sternal devascularization and rib spreading. Fewer and smaller incisions also aid in post-operative wound healing and decrease the risk of wound infections. Micro-fixation systems, including titanium plates and screws, help reduce wound healing complications, especially in those with high-risk comorbidities, and enhances bone healing [20, 21].

The physiologic impact of CPB has been extensively documented; it involves artificial, non-pulsatile perfusion, resulting in the potential for whole-body inflammatory response, endothelial damage, and end-organ damage, particularly in patients with pre-existing or underlying cerebrovascular disease, visceral disease, and renal dysfunction. The mechanical stress cells undergo while contacting the extracorporeal circulation surface is another source of the inflammatory process, which has been well confirmed with an increase of other serum pro-inflammatory markers [22–24]. Total body inflammatory response leads to vasoplegia, coagulopathy, third spacing, platelet activation, and subsequent platelet dysfunction [22–24]. In addition, CPB cannulation induces the risk of disrupting atherosclerotic plaques in the ascending aorta (common in older patients), which is directly associated with intraoperative embolic stroke with devastating consequences [25, 26].

An alternative approach is to perform CABG without CPB, which mitigates the physiologic disarray that takes place when the patient's blood encounters the inner surface of the extracorporeal circulation tubing. This method is known as off-pump CABG (OPCAB). Depending on the situation, MIDCAB could also be performed with extracorporeal circulation via cannulation of the femoral vessels while still limiting chest wall trauma.

Lastly, in traditional CABG, cardioplegic arrest is necessary to operate on an arrested heart. This step is essentially a controlled ischemic event to which the myocardium is subjected. Patients with depressed ventricular function are more vulnerable to complications of cardioplegic arrest, including intra- and post-operative systolic and diastolic dysfunction. Despite using state-of-the-art myocardial protection solutions, consequences could include worsened ventricular dysfunction and cardiogenic shock (**Table 1**).

### *4.2.1 On- vs. off-pump*

In patients with pre-existing aortic atherosclerosis, chronic kidney disease, cerebrovascular disease, visceral vascular disease, liver cirrhosis, bone marrow suppression, and diabetes, CPB may pose a higher risk of end-organ dysfunction and stroke. OPCAB, or beating heart CABG, is an attractive surgical option in such patients. OPCAB still requires a traditional median sternotomy, and because CPB and cardioplegia are not used during this approach, OPCAB confers the advantage of reduced inflammatory response, lower risk of end-organ dysfunction, and lower risk and stroke. However, as expected, anastomoses are technically more challenging in an OPCAB, particularly in visualizing the lateral wall. Regional ischemia while the anastomosis is being performed and dysfunction can occur. In expert hands, OPCAB produces comparable revascularization to traditional on-pump CABG, lower perioperative morbidity, particularly regarding stroke, and excellent long-term results.

### *4.2.2 Minimally invasive direct CABG (MIDCAB)*

Minimally invasive direct coronary artery bypass (MIDCAB) involves a small thoracic incision in the left fourth or fifth intercostal space to harvest the LIMA and perform


*graft; and +/− indicates can be performed either with or without.*

#### **Table 1.**

*Comparison of minimally invasive CABG techniques.*

### *Overview of Coronary Artery Bypass Surgery DOI: http://dx.doi.org/10.5772/intechopen.114279*

an off-pump LIMA-to-LAD anastomosis. The LIMA is harvested through the small incision as far superiorly as possible, usually with specialized instruments and equipment. Stabilization devices may allow for more precise anastomosis of the LIMA to the LAD. In some cases, and in expert hands, more extensive revascularization may be performed by accessing the ascending aorta to perform proximal anastomoses as required.

MIDCAB offers the double benefit of reduced thoracic trauma and avoiding extracorporeal circulation and its inflammatory response, leading to faster recovery times and shorter hospital lengths of stay. However, this approach is technically demanding.

Multivessel small thoracotomy (MVST) and minimally invasive coronary surgery (MICS) share the same principles of MIDCAB and can be considered a subcategory of MIDCAB. However, as the name suggests, MVST CABG allows multiple anastomoses to be performed on various coronary vessels. Commonly used grafts include the LIMA and radial artery. MIDCAB, MVST CABG, and MICS are technically demanding operations with steep learning curves. These procedures are considered expert operations and should be performed at centers with highly experienced and skilled teams.

### *4.2.3 Robotic procedures*

It has been decades since the Da Vinci Robot was introduced to the field of cardiac surgery. Robotic cases have been mainly directed towards mitral valve and coronary operations. Outstanding advancements in tools have enhanced the possibilities of coronary surgery. For example, the endo-wrist allows improved maneuvering that exceeds a surgeon's inherent hand mobility. Features such as enhanced visualization and three-dimensional optics offer 10X image magnification, thus, providing superior conditions for surgical performance. Despite these capabilities, acquiring expertise in robotic procedures is associated with a steep learning curve. As a result, robotic procedures have been adopted relatively slowly, particularly in coronary surgery.

In expert hands, the outcomes of Totally Endoscopic Coronary Artery Bypass (TECAB) are impressive, providing complete, all arterial revascularization using LIMA and RIMA using only port sites and mostly performed off-pump [27]. Anastomoses are performed on a closed chest using anastomotic connectors [28–32] or are sewn using robotic arms. Patients may be safely discharged 24–48 hours postoperatively because this operation is associated with minimal surgical trauma (chest wall and physiologic trauma). A common alternative to the TECAB is the Robotic Assisted MIDCAB [27, 33, 34]. With the assistance of the Da Vinci Robot, the LIMA is harvested with minimal rib spreading. Then, a small incision (4 cm is performed in the 4th or 5th LICS to identify the LAD. Under direct vision, the LIMA-LAD anastomosis is then performed off-pump.

Robotic approaches are ideal for patients with CAD limited to the LAD or proximal LAD, although more extensive revascularization can be performed in expert hands [27]. Hybrid revascularization considerations are becoming more popular for patients with two- or three-vessel CAD interested in a minimally invasive approach for the LIMA-to-LAD anastomosis while utilizing third-generation DES for the remainder of the affected non-LAD coronary vessels. This option allows for the longterm benefits of bypass surgery while minimizing the trauma of a median sternotomy.

### *4.2.4 Hybrid revascularization procedures*

Considering that the LIMA-to-LAD is the most critical graft in a CABG operation. This graft is primarily responsible for increased survival and low rates of MACCE;

therefore, it would be reasonable to propose that a minimally invasive LIMA-to-LAD (MIDCAB, robot-assisted MIDCAB or TECAB) combined with stenting of the circumflex and RCA systems with third-generation DES would lead to the "best of both worlds" [35]. Complete revascularization with the combination of LIMA and DES would be achieved with minimal trauma [35]. Intraoperative angiography would also be performed to confirm the quality of the LIMA-to-LAD anastomosis while the patient is still in the operating room, provided that the operation takes place in a hybrid operating room [35]. Using such approaches allows the surgeon to confirm complete revascularization [35]. Patients undergoing this hybrid procedure have enhanced recovery, spend only 2 or 3 days in the hospital, are able to drive in 10–14 days, and return to unrestricted activity in three to 4 weeks. Several studies have validated the benefits of this approach [36]. Third- and fourth-generation stents are demonstrating comparable results with respect to graft patency compared to vein grafts [37]. By contrast, no current stent has been shown to be superior to the LIMAto-LAD anastomosis, supporting the use of a hybrid approach. These indisputable results support the use of a hybrid approach for revascularization.

### *4.2.5 IABP and Impella® supported CABG*

Intra-aortic balloon pump (IABP) and Impella ®-supported CABG are practical approaches utilized to assist the left ventricle function and overall hemodynamics in patients with ischemic cardiomyopathy (ejection fraction (EF) < 30%) who require surgical revascularization. Patients with advanced CAD and heart failure frequently have a depressed EF. The etiology of low EF varies from infarcted to hibernating myocardium (chronically ischemic but alive). Infarcted myocardium will not recover its function after revascularization while hibernating myocardium will. Patients with depressed EF are a high-risk surgical population that would greatly benefit from coronary surgery [9, 10, 38]. These benefits were more recently confirmed by a 10-year follow-up study of the original Surgical Treatment for Ischemic Heart Failure (STICH) trial, in which the advantages of surgery over medical management, particularly in terms of survival, is demonstrated with statistical significance [39].

One of the challenges with these patients is the perioperative management and the risk of postoperative cardiogenic shock. For many years, patients in this group underwent IABP-supported CABG, which involved placing an IABP 24–48 hours before surgery. The IABP remains in place postoperatively for the necessary length of time until signs of hemodynamic and ventricular function improvement and stunned myocardium resolution, generally a few days. Although helpful, the disadvantages of this approach are reflected by the need for prolonged bedrest, leading to physical deconditioning and lower extremity muscle weakness. In addition, peripheral vascular complications involving the lower extremities are complications of IABP via the femoral arteries, particularly left in situ for several days. It is essential to mention that the IABP does provide a moderate increase in cardiac output and blood pressure while decreasing afterload. However, one of its limitations is that it does not decompress the left ventricle meaningfully, especially when compared to the Impella® device.

More recently, since the introduction of Impella® [40], many patients with low EF and heart failure have undergone bypass surgery supported by Impella® instead of an IABP. The Impella® device, available in varying sizes and power, is placed into the left ventricular cavity and ascending aorta across the aortic valve via femoral,

axillary/subclavian, or ascending aorta [41]. The Impella® device has an inlet pump that draws in blood from the LV. This blood then moves through the device and, via a sophisticated intra-corporeal pump, is pumped out distal to the aortic valve on the ascending aorta.

In addition to the ventricular support during CABG, decompression of the left ventricle with the Impella® is highly beneficial and decreases the left ventricular diameter, reducing oxygen consumption by reducing myocardial oxygen demand [41]. The 5.5 model of the Impella® pump has the ability to pump up to 5 L per minute, providing superior hemodynamic support and increasing coronary artery and end-organ perfusion [40]. As a result, these patients can be out of bed by postoperative day one and ambulate while the Impella® remains in place. In other words, as the device is being weaned, the patient is already eating, ambulating, and undergoing physical rehabilitation. The Impella® device is removed at the bedside under local anesthesia as the myocardium stunning recovers between days four and seven.

Many surgical groups, including ours, favor using the Impella® device in this capacity for patients with severely decreased ventricular function, more advanced cardiomyopathy, and heart failure.

### **4.3 Coronary endarterectomy**

Coronary endarterectomy (CE) was the mainstay for coronary artery revascularization prior to CABG. CE refers to stripping atherosclerotic plaque of extended length from a diseased coronary artery and therefore recreating the lumen of the vessel. Due to the complexity of CE, it is more demanding than CABG, and it is often only performed alongside CABG. Age, advanced CAD, and comorbidities such as diabetes or hyperlipidemia may increase the rate of more diffuse CAD and the need for CE. The presence of diabetes is especially notable for associations with diffuse CAD. In the current era, CE is rarely performed but it might constitute the only option to achieve myocardial revascularization.

Considerations for maintaining the patency of the coronary vessels after CE include maintaining some degree of anticoagulation in the postoperative period. As soon as surgical bleeding is not an issue, postoperative dual antiplatelet therapy with aspirin + clopidogrel or aspirin + ticagrelor will assist in mitigating the risk of early thrombosis. Some surgeons may decide to only partially reverse heparinization in the OR to maintain some early anticoagulation and prevent thrombosis.

The procedure itself involves creating a small proximal arteriotomy in the diseased coronary vessel. Then, a plane between the tunica media and atherosclerotic plaque is established via blunt and sharp dissection to begin the process of releasing plaque from the vessel. The endarterectomized coronary artery is grafted appropriately with a patch or directly with a graft. In addition, intraoperative angiography can be used in conjunction with hybrid operating rooms to verify the completion of CE and graft patency.

CE has higher postoperative morbidity compared to CABG alone [42, 43], but both short- and long-term patency have been demonstrated in CE in combination with CABG [44, 45]. MI rates are up to 10% [46, 47]. Despite the higher risk of perioperative complications associated with CE, it is essential to consider that these patients present with more advanced, diffuse CAD and calcified vessels, posing a higher perioperative risk regardless of whether CE is performed (**Figure 5**).

**Figure 5.** *Coronary endarterectomy.*

### *4.3.1 Other revascularization techniques*

Trans-myocardial laser revascularization (TMR) employs the energy of a laser to create channels from the epicardium to the endocardium, where areas of ischemic myocardium are identified by nuclear test and by coronary artery disease substrate. Lasers employ carbon dioxide or holmium yttrium-aluminum-garnett to induce angiogenesis in the treated areas to mitigate the decreased blood supply in treated myocardial regions. TMR involves performing a left anterolateral thoracotomy through which the ischemic myocardium is treated via laser pulses of energy delivered during ventricular diastole. This operation is performed off-pump. No heparinization is required.

Studies have shown a significant decrease in angina symptoms [48–52] but no survival benefits after TMR [51, 53]. While there was an improvement in angina symptoms, it is difficult to document directly improved perfusion in treated areas. These findings suggest that the mechanism by which TMR produces a therapeutic effect of angina relief has yet to be precisely identified. As with traditional CE, TMR may be used concomitantly with CABG to improve the revascularization of distally diseased vessels.

Indications for TMR as a sole therapy include patients with Canadian class III/IV angina symptoms for whom direct revascularization via PCI or CABG is not feasible [48, 54, 55]. Nuclear imaging studies should be obtained to evaluate for ischemic myocardium. Patients without angina, with an EF <30%, unstable angina, and without ischemia on thallium stress tests are not candidates for TMR. When combined with CABG, TMR has shown clear benefits in short-term survival [56]. Coronary targets amenable to CABG should be grafted. Territories with poor-quality arteries not amenable to grafting or stenting should be considered for laser revascularization in combination with CABG (**Figure 6**).

*Overview of Coronary Artery Bypass Surgery DOI: http://dx.doi.org/10.5772/intechopen.114279*

**Figure 6.** *Angiogenesis surrounding channels created by CO2 laser in TMR.*
