NEWER AND EMERGING APPROACHES TO CARDIAC SURGERY

A number of newer approaches to revascularization have emerged in recent years, including OPCAB grafting, minimally invasive direct coronary artery bypass (MIDCAB), use of robotics, use of port-access adjuncts, and trans-myocardial revascularization. Although results with conventional approaches to revascularization are satisfactory, these methods have limitations that include complications related to CPB, aortic cannulation, and aortic

1994

Off-Pump Coronary Artery Bypass Grafting

OPCAB grafting has become increasingly popular. The purported benefits of this approach include decreased cerebral microemboli and stroke rates as a result of reduced aortic manipulation, decreased bleeding and blood product use as a result of the avoidance of CPB, decreased time to extubation, decreased length of stay, and decreased overall cost. Although the procedure has been shown to be comparable to CAB with CPB,^[327] it has not yet been proved to be superior. In fact, the most recent data^{[328] [329]} indicate that OPCAB does not confer any advantages over conventional CAB in the low-risk patient population studied. No reliable data are available on high-risk patients, and leaders in the field emphasize the need for larger studies and ongoing scrutiny and are still unable to determine whether OPCAB is a step forward, backward, or sideways.^{[330] [331]} OPCAB procedures are a challenge to the anesthesiologist, who must manage profound hemodynamic fluctuations, ischemia, and changes in myocardial function that result from manipulation of the heart.

Decreases in preload resulting in decreased cardiac output are frequent problems during OPCAB. Placement of pericardial sling sutures in the posterior portion of the pericardium can cause constriction of the inferior vena cava and/or pulmonary veins, or both, thus limiting venous return to the right and/or left sides of the heart. This decrease is exacerbated when the heart is lifted out of the pericardium so that conduit anastomoses can be performed on the posterior surface. To overcome these effects, the patient is usually placed in a steep Trendelenburg position, and crystalloid or colloid is administered to augment preload. Monitoring pulmonary vascular and central venous pressures helps optimize loading conditions of the heart. Experience and judgment are required to interpret vascular pressure measurements in this setting because of the aberrant heart position. Ischemia and atrioventricular valvular regurgitation may alter pressure

TABLE 50-23 -- Minimally invasive coronary artery bypass surgery without cardiopulmonary bypass

Advantages	Disadvantages	Unknowns
Avoidance of cardiopulmonary bypass	Technically more demanding	Operative risk
Less risk of stroke or neuropsychiatric deficits	Multivessel disease contraindicated	Appropriate patient selection
Shorter hospitalization, intensive care unit length of stay	May not be a reproducible technique	Short- and long-term graft patency rates
Cost saving	Hemodynamic instability and arrhythmias	Adequacy of overall revascularization
Decreased transfusion requirements	Unsafe in unstable patients	Cost considerations
From Cheng D, Vegas A: Anesthesia for the surgical management of ischemic heart disease. In Thys DM (ed): Textbook of Cardiothoracic Anesthesiology. New York, McGraw-Hill, 2001, pp 530–588. Copyright © by McGraw-Hill, Inc. Used by permission of McGraw-Hill Book Company.

readings and confound interpretation of the data. TEE allows direct visualization of the heart to determine the adequacy of preload. It can also detect new-onset valvular regurgitation or diastolic dysfunction. However, the placement of pericardial sutures, lifting of the heart out of the pericardium, and sponges placed behind the heart all obscure images of the heart on TEE. Generally, all available data should be used to determine the adequacy of preload during OPCAB.

Ischemic changes and new regional wall motion abnormalities (RWMAs), as well as global cardiac dysfunction, are not uncommon during OPCAB procedures. Ischemia can result from the temporary occlusion of a coronary artery for the purpose of completing a distal anastomosis. New-onset ischemia may be seen on the ECG lead distribution of the occluded coronary artery. Transient and minor ST segment and axis changes are usually seen after the heart is positioned or the coronary artery is occluded. These changes may be minor and not progressive, but if associated with RWMAs, they are indicative of significant ischemia. TEE manifestations of ischemia include the development of new RWMAs and new-onset valvular regurgitation secondary to papillary muscle ischemia and diastolic dysfunction. Ischemia may also be manifested as an increase in pulmonary artery pressure (dysfunction, mitral valve regurgitation). Ischemia should be managed in the standard way by optimizing the determinants of myocardial oxygen supply and demand. Blood flow to an ischemic region can be increased by using shunts, opening the occluded coronary artery, or placing a new graft. Ischemia can also result in heart block, necessitating pacing. If the myocardium becomes profoundly ischemic, it can result in failure to pace. (Note that failure to pace may be physiologically based and not a mechanical problem.)