Surgical Treatment of Coronary Artery Disease

Abstract

Techniques and technology for treating coronary artery disease (CAD) have evolved significantly over the past 40 years. Although there are cases in which the best treatment approach (medical, surgical, or catheter-based) is clear, the best choice of intervention is not obvious for the majority of patients. Five, 7, and 10 years after initial treatment, mortality is lower for coronary artery bypass grafting (CABG) than for medical treatment alone. These survival benefits of CABG are particularly substantial for patients with three-vessel or left main artery disease, severe angina, or a positive pretreatment exercise stress test. Most trials comparing CABG with catheter-based interventions (CBIs) in patients with multivessel disease have shown similar short-term survival benefits for both treatments, but CBIs have been associated with less periprocedural morbidity and CABG with longer-lasting revascularization. Substantial evidence suggests that CABG is preferable to CBI in certain types of patients, including the one third of CAD patients who have chronic total occlusion of one or more vessels, and those with diabetes mellitus. Meta-analyses of large numbers of CABG studies report 30-day mortality rates in the 1% to 2% range. Numerous CABG techniques have evolved that seem to produce equally good results. Substantial evidence suggests that internal mammary artery grafts more effectively promote short- and longterm survival than do saphenous vein grafts, especially when used to graft the left anterior descending (LAD) coronary artery. In fact, the bulk of the evidence suggests that CABG with left internal mammary artery (LIMA)-to-LAD grafting provides better long-term results than does either CABG with other types of conduits or CBI. Technical innovations made in the attempt to reduce the negative impact of cardiopulmonary bypass (CPB) include coating the internal surface with heparin or other polymers to reduce contact between blood and the CPB mechanism, minimizing hemodilution by shrinking the bypass circuit to reduce the amount of crystalloid prime needed to start CPB, and using hemofiltration to protect the heart and end organs. Current United States estimates (based on industry reports) suggest that 18% to 25% of the 370,000 annual CABG procedures are performed without the use of CPB. There is not yet complete agreement about the relative safety and efficacy of off-pump coronary artery bypass (OPCAB) and conventional CABG with CPB. The difficulty in comparing the OPCAB and standard CABG stems in part from the low incidences of mortality and significant morbidity associated with both techniques. A meta-analysis of 37 randomized, controlled trials of OPCAB suggests that it is associated with significantly decreased transfusion and inotrope requirements, atrial fibrillation, respiratory infections, ventilation time, intensive care unit stay, hospital stay, and overall in-hospital and (1-year) postdischarge costs compared with standard CABG. Data from many large nonrandomized studies suggest that OPCAB is associated with a lower incidence of death, stroke, intraaortic balloon pump requirement, and postoperative transfusion, and a shorter average time on ventilator and length of hospital stay compared with conventional CABG. However, selection bias cannot be ruled out as a potential confounding variable in these data. Devices and techniques for lateral and inferior wall exposure have enabled surgeons performing OPCAB to attach grafts to all aspects of the heart. Recent series show no difference in the average number of grafts constructed in OPCAB and standard CABG, and several series have shown excellent graft patency. Off-pump bypass is ideal for patients with significant atheroma or calcification of the ascending aorta. A few studies have shown that OPCAB is associated with a reduced incidence of neurocognitive dysfunction compared with conventional CABG with CPB, but other studies have shown no significant differences. Results of small randomized trials suggest that, in patients with stenosis of the proximal LAD, minimally invasive direct coronary artery bypass (MIDCAB) is associated with a longer in-hospital recovery period and higher costs than is direct stenting, but that MIDCAB produces similar or better short- and long-term outcomes. Totally videoscopic LIMA-to-LAD procedures have been performed in which surgical robots were used to mobilize the LIMA and make the sutured anastomosis, but robots are not likely to be in widespread use for CABG in the near future because of their expense and the challenges involved in learning to use them. Although port-access CPB has been used successfully in multivessel CABG performed through small fifth intercostal space thoracotomies, this procedure has fallen out of favor, partly because of the difficulty of constructing grafts of appropriate length and lie.