CHAPTER 88 Alternative Approaches to Coronary Artery Bypass Grafting

Limited Access Coronary Artery Bypass

Minimally Invasive Direct Coronary Artery Bypass

Robotic-assisted Coronary Artery Bypass Grafting

Hybrid Minimally Invasive Direct Coronary Artery Bypass Approach

Port-access Coronary Artery Bypass Grafting

Automated Distal Anastomotic Devices

In 1967, Sabiston and colleagues ¹ reported the first clinically successful coronary artery bypass graft (CABG) procedure. Other early pioneers included Favaloro,^2,³ who is credited with popularizing the use of autogenous saphenous vein, and Kolesov,⁴ who is generally recognized as having performed the first mammary artery to coronary artery anastomosis. During the several years that followed, centers around the world began performing the procedure in large numbers. Subsequent refinements in cardiopulmonary bypass (CPB), the introduction of cardioplegia, the growing acceptance of the left internal mammary graft, and the development of the intra-aortic balloon pump resulted in continued improvements in outcomes after CABG. By the early 1990s, more than 350,000 CABG procedures were being performed each year in the United States alone, with routine application in octogenarians, patients with severely impaired ventricular function, and patients with serious noncardiac morbidities.^5,⁶

As results continued to improve and mortality and major morbidity rates in the 2% range became commonplace, many surgeons turned their efforts toward decreasing the invasiveness of CABG. During the last several years, this effort has produced a number of new technologies, new techniques, and new variations of the traditional CABG procedure that are intended to avoid CPB, to minimize aortic manipulation, to improve graft patency, and to minimize the trauma associated with surgical access. These variations include multivessel CABG without CPB, single-vessel CABG without CPB by way of a left mini-thoracotomy, videoscopic single-vessel CABG by use of surgical robotics, and multivessel CABG by way of a left mini-thoracotomy with peripheral cannulation and CPB. Other new procedures include reoperative CABG through alternative incisions and grafting strategies and use of devices that minimize or eliminate aortic manipulation, facilitate construction of the distal anastomosis, and perhaps have an impact on long-term graft patency. This chapter describes these operations, discusses their relative merits, and summarizes current clinical results.

CARDIOPULMONARY BYPASS

The development of the heart-lung machine by Gibbon ⁷ and its early application by Kirklin⁸^–¹⁰ were among the most important advances in the ultimate growth of CABG surgery. CPB and, ultimately, the introduction of cardioplegia provided a motionless, blood-free surgical field that enabled the precision and reproducibility necessary for direct coronary anastomosis. Despite the obvious benefits of CPB, however, there has been an increasing awareness of its potential deleterious effects. As the formed elements of the blood come into contact with the surfaces of the various components of the heart-lung machine, they are activated, resulting in a number of hematologic and, ultimately, systemic changes. Typical sequelae include activation of complement, release of endotoxin, activation of leukocytes, increased expression of adhesion molecules, and release of inflammatory mediators (including cytokines, arachidonic acid metabolites, and free radicals).¹¹ These sequelae occasionally are manifested as coagulopathy, third-space fluid retention, and subtle end-organ dysfunction, including neurocognitive changes. The magnitude of this systemic inflammatory response is generally modest, but it can be quite severe, especially when the time on CPB is prolonged. Furthermore, it is well recognized that a small percentage of patients with preoperative end-organ dysfunction suffer significant morbidity when they are subjected to even a moderate degree of systemic inflammatory response.

Ongoing efforts have been directed at reducing the magnitude of the systemic inflammatory response associated with CPB. These efforts include decrease in the surface area and modification of the surface composition of the CPB circuit to minimize surface activation, minimization of hemodilution by decrease of the volume of crystalloid prime needed to institute CPB, avoidance of the use of a cardiotomy sucker, and pretreatment of patients with various anti-inflammatory medications, such as aprotinin (Trasylol).¹² Despite progress in these areas, performance of CABG without CPB remains attractive.

MULTIVESSEL OFF-PUMP CORONARY ARTERY BYPASS

Off-pump coronary artery bypass grafting (OP-CAB) is as old as coronary surgery itself. Large case series dating to the 1970s document its feasibility.¹³^–¹⁵ Nevertheless, OP-CAB only recently gained widespread acceptance and entered the mainstream of clinical practice, propelled by a greater awareness of the potential morbidity of CPB and aortic manipulation and facilitated by improvements in surgical tools and techniques. OP-CAB is part of the procedural armamentarium of a growing proportion of surgeons worldwide and can be performed in virtually any patient requiring coronary revascularization.

Self-retaining Coronary Stabilizers

The introduction of self-retaining coronary stabilizers and the development of techniques for their use are key factors that have led to resurgent interest in OP-CAB. When they are properly used, coronary stabilizers provide a relatively motionless and blood-free field, similar to that provided by CPB. The subsequent introduction of self-retaining cardiac positioning devices and the evolution of surgical techniques for rotation of the heart enable precise anastomoses to be constructed on the inferior, posterior, and lateral walls of the beating heart while maintaining adequate hemodynamics without CPB. A number of coronary artery stabilizers are available for clinical use. Current stabilizers can be categorized as compression, suction, and capture devices, depending on their design. Each type provides excellent immobility when it is used properly.

Compression-type stabilizers are generally two-pronged forks that are placed lightly on the epicardial surface of the heart, such that the prongs are parallel to and flanking the coronary artery at the intended anastomotic site. The undersurface of the prongs is designed to provide traction to avoid slippage. The fork is attached to the retractor by way of an articulating arm and can be locked tightly once the desired position has been achieved. In general, the best stability occurs when only slight downward force is used on the surface of the heart. Paradoxically, an increase in motion occurs when excessive downward force is applied. Therefore, the exposure techniques described later in this chapter should be used to present the target artery before the stabilizer is positioned, rather than relying on the stabilizer to retract the heart. Compression-type stabilizers are advantageous in that they set up quickly and simply and have an extremely low profile, allowing unrestricted access to the coronary artery. For some aspects of the heart, however, slightly more downward pressure may be required with compression stabilizers to avoid slippage (Fig. 88–1).

Figure 88–1 Compressive-type stabilizers are generally low profile and have a textured bottom surface to improve their ability to grip the epicardium.

Suction-type stabilizers also are generally two-pronged forks attached to the retractor by means of an articulating arm. These stabilizers, however, are constructed with a series of ports on the undersurface of the prongs that are connected by sterile tubing to wall suction (−100 to −300 mm Hg). The epicardium and epicardial fat flanking the vessel are sucked into these ports, allowing the stabilizer to grip the surface of the heart. As such, less downward force is required at the anastomotic site. Suction stabilizers also set up quickly, but they require a regulated vacuum line. They have the added advantage of providing traction and countertraction of the fat surrounding the coronary artery, making them well suited for coronaries deep within the fat. Suction stabilizers tend to be slightly higher profile than compression-type stabilizers, but in general, access to the coronary artery is not a problem (Fig. 88–2).

Figure 88–2 Vacuum-assisted stabilizers use a series of suction cups to grip the epicardium. Although slightly higher profile, they often require less downward force than compressive footplates.

Capture-type stabilizers are usually fenestrated platforms that frame the intended anastomotic site. Silicone elastic tapes are passed deep to the coronary artery and locked to the platform under tension, pulling the epicardium up against the platform’s undersurface (Fig. 88–3A). Like suction, this effect reduces the demand for downward force to prevent slippage. Capture stabilizers, by virtue of their circumferential stabilization, provide superior anastomotic stability.¹⁶ In addition, the silicone elastic tapes compress the coronary against the platform’s posterior aspect, providing integrated biplanar coronary occlusion (Fig. 88–3B). Capture stabilizers arguably are more complex to position, however, and require proper spacing and alignment of the silicone elastic tapes to ensure adequate hemostasis. Furthermore, because of their larger size, they may not be well suited if tightly spaced sequential anastomoses are being constructed.

Figure 88–3 Capture-type stabilizers use silicone elastic tapes to ensure tight apposition of the textured surface of the footplate and the epicardial surface. This arrangement results in integrated coronary compression.

Maintaining Hemodynamic Stability during Multivessel OP-CAB

One of the greatest challenges in performing the early OP-CABs was maintaining hemodynamic stability while grafting coronaries on the lateral and posterolateral aspects of the heart. This challenge was greatest in patients with poor ventricular function and marginally compensated ischemia. Advances in surgical techniques, including placement of deep pericardial retraction sutures, right vertical pericardiotomy and pleurotomy, and right hemisternal elevation, as well as the introduction of cardiac positioning devices and advances in anesthetic management, have largely eliminated this problem. To understand how these tools and techniques minimize the adverse effects of cardiac manipulation, it is important to understand the etiology of potential hemodynamic compromise during an OP-CAB procedure.

Mechanisms of Adverse Hemodynamic Effects

Left Ventricle

When a coronary stabilizer is positioned with excessive downward force, the stabilized aspect of the heart is constrained, leading to diastolic dysfunction and decreased left ventricular end-diastolic volume, stroke volume, and cardiac output.¹⁷ Whereas volume loading and Trendelenburg positioning attenuate these effects by elevating left ventricular filling pressures, their recourse carries a risk of exacerbating intraoperative third-space fluid sequestration and associated morbidity. Similarly, the use of short-acting α-adrenergic agents can effectively maintain perfusion pressure in this setting, but these agents may be associated with an increased risk of perioperative mesenteric ischemia.¹⁸ β-Adrenergic agents should similarly be avoided in the setting of yet-to-be-grafted coronary disease. There are also anecdotal reports of severe mitral regurgitation during exposure of the lateral wall, possibly related to deformation of subvalvular structures in combination with coronary insufficiency. Exposure techniques that minimize or eliminate left ventricular deformation are therefore desirable.

Right Ventricle

Exposure of the lateral wall of the left ventricle displaces the heart toward the right, resulting in the right ventricle’s being compressed against the pericardium and the right side of the sternum. The relatively low pressure in the right ventricle makes it particularly vulnerable to deformation and reduction in right ventricular end-diastolic volume.^19,²⁰ The decreased right ventricular stroke volume leads to poor left ventricular filling and a drop in cardiac output. Volume loading and Trendelenburg positioning can compensate for this effect, as noted before, but not without potential risk. Right ventricular compromise is thought by many to be the dominant cause in many cases of hemodynamic instability that occur during exposure of the lateral wall. Various groups have proposed the use of right ventricular assist as palliation for right ventricular compromise during multivessel OP-CAB.^21,²² Clearly, however, exposure techniques that minimize right ventricular deformation are desirable.

Myocardial Ischemia

Intraoperative myocardial ischemia, secondary to decompensated coronary disease, transient coronary snaring during grafting, or poor perfusion pressure during heart manipulation, constitutes another mechanism that leads to hemodynamic instability. Communicating closely with the anesthesiologist, planning a revascularization strategy that minimizes myocardial ischemia, and using exposure techniques that maintain hemodynamic stability best prevent it. Although each case should be managed on an individual basis, useful axioms exist. Patients with significant left main stenosis and marginally compensated ischemia may benefit from completion of the left internal mammary artery (LIMA) to left anterior descending (LAD) graft before the heart is manipulated. Similarly, initial revascularization of occluded, collateralized coronary arteries should be carried out before transiently occluding those vessels that supply collaterals to them. The selective use of intracoronary shunts, aorta-coronary shunts, or assisted coronary perfusion devices ²³ can be essential in grafting a moderately stenosed right coronary artery proximal to the origin of the posterior descending branch or in grafting the proximal portion of a moderately stenosed LAD (Fig. 88–4). The judicious use of an intra-aortic balloon pump can occasionally prove invaluable.²⁴

Figure 88–4 A shunt connected to a 5 French cannula in the ascending aorta inserted into the coronary artery distal to the arteriotomy may be used to maintain brisk coronary flow while the graft is being constructed.

Exposure Techniques

Depending on the size and shape of the patient’s heart and the dimensions of the chest cavity, visualization of the proximal obtuse marginal and posterolateral branches of the circumflex system may be obstructed by the left hemisternum. Although intuitive attempts at improving exposure may involve the application of additional rightward force with the stabilizer to that aspect of the heart, this maneuver frequently leads to hemodynamic compromise as well as paradoxically poor stabilization. Maximized access and stability at the anastomotic site with minimal compromise of cardiac performance is most readily achieved when the stabilizer is applied with little or no pressure; thus, coronary stabilizers should be used only to stabilize the anastomotic field rather than to assist in retracting the heart. In many patients with relatively normal hearts and readily accessible coronaries, little attention to exposure techniques is required. In contrast, in performing multivessel OP-CAB on patients with large, poorly contracting hearts, attention to these techniques is essential. In these patients, exposure of the lateral wall of the heart is best obtained with maneuvers such as the use of deep pericardial sutures, right pleurotomy and pericardiotomy, right hemisternal elevation, and apical suction devices, each of which is described.

Deep Pericardial Sutures

One of the most important advances in exposure techniques for OP-CAB has been the use of deep pericardial sutures. First described by Lima,²⁵ these sutures, when placed under tension, create a ridge of pericardium that supports the base of the lateral left ventricle adjacent to the atrioventricular groove and allows the heart to be rotated rightward to assume an “apex up” position (Fig. 88–5). In this subluxed position, the apex of the heart points toward the ceiling and protrudes through the sternotomy incision, often above the plane of the sternal retractor. This generally allows adequate exposure of the lateral and inferior aspects of the left ventricle before the coronary stabilizer is applied.