Disadvantages

The main disadvantage associated with the use of MIDCAB and OPCAB, compared with conventional CABG, is lack of optimal exposure of coronary vessels. MIDCAB allows the most limited exposure; therefore, fewer vessels can be grafted—often only the internal thoracic artery to the left anterior descending artery. Other vessels must be treated with angioplasty. OPCAB, however, allows grafting of multiple vessels. MIDCAB is also associated with more trauma to costal cartilages (with or without removal of rib segments) and more postoperative pain. Both procedures are associated with more hemodynamic instability (especially during displacement of the heart with OPCAB), which may pressure the surgeon to perform the procedure more quickly and, along with limited exposure, result in questionable anastomotic quality and completeness of revascularization. Patients will benefit from on-pump CABG if they have multiple lesions and their anatomy is complex. Patients who are not at increased risk for developing the complications associated with CPB have more effective revascularization if an on-pump CABG is performed. Overall, graft patency rate is higher and mortality is likely lower after on-pump CABG, compared with OPCAB.

Induction and maintenance

To avoid prolonged intubation, a “fast-track” anesthetic approach is used, limiting opioids to 2 μg/kg of sufentanil, 10 μg/kg of fentanyl, or an infusion of remifentanil. Any anesthetic technique that facilitates early extubation and provides hemodynamic stability is acceptable.

Some surgeons prefer one-lung ventilation during the procedure for improved exposure. For MIDCAB, one-lung ventilation is particularly useful if the internal thoracic artery pedicle is harvested thoracoscopically. The use of one-lung ventilation is not necessary with OPCAB.

The use of antifibrolytic agents is not indicated for these procedures because of the concern that their use might contribute to graft thrombosis.

Induced bradycardia facilitates surgical success, especially with MIDCAB. Besides optimizing the surgical field, bradycardia reduces myocardial O₂ demand until revascularization is complete. Bradycardia may be facilitated by the choice of anesthetic agent (Box 145-1). Induced bradycardia is less critical with OPCAB since the advent of newer stabilization devices, such as the CTS retractor, the Octopus, and the Cohn stabilizer (see Figure 145-1). These devices hold a segment of the diseased coronary artery immobile while the heart is beating so that the anastomoses can be performed.

Surgery on the beating heart readily precipitates arrhythmia—from ischemia, manipulation, and reperfusion—that must be treated aggressively. Lidocaine and magnesium are used routinely; other antiarrhythmic agents must be readily available, and antiarrhythmic strategies may be used (Box 145-2).

Surgical considerations

After anesthesia induction, saphenous vein, radial artery, or both saphenous vein and radial artery harvesting is accomplished. A median sternotomy (OPCAB) or anterior thoracotomy (MIDCAB) is used. One half to two thirds of a full heparinizing dose for CPB (150-200 units/kg) is given. The internal thoracic artery is dissected. The activated clotting time is checked every 30 min, and additional heparin doses of 3000 to 5000 units are given as necessary to maintain an activated clotting time of 300-350 sec. Antiarrhythmic agents are given before vessel occlusion is done. Baseline cardiac output pulmonary artery pressures, and ST-segment analyses are assessed before and after vessel occlusion to guide interventions.

To facilitate surgical exposure, the heart must be lifted and rotated. When the heart is repositioned, venous return is compromised, causing insufficient preload and a possibly precipitous drop in cardiac output. Fluid resuscitation, inotropic medications, and peripheral vasoconstricting agents (e.g., phenylephrine) are used. Mean arterial pressures must be maintained at or above preoperative pressures to ensure adequate coronary perfusion.

Once the internal thoracic artery is anastomosed to the left anterior descending artery, hemodynamics improve. If necessary, vein grafts or radial artery grafts are then grafted to other coronary arteries. For OPCAB proximal anastomoses, a side-biting C-clamp is placed on the aorta while the blood pressure is temporarily reduced. Nitroglycerin causes vasodilation of the coronary arteries, prevents vasospasm of the radial artery, and reduces wall stress during ischemic periods. Sodium nitroprusside can also be used for rapid titratable control of blood pressure.

If the patient’s heart cannot tolerate the ischemia from vessel occlusion, options include stenting of the artery via an arteriotomy or emergent institution of CPB. Although the stented vessel provides blood flow to distal ischemic myocardium, there is a risk of intimal dissection.

Postoperative considerations

The incision is closed after all anastomoses are completed. Heparin is not routinely reversed, or only partially reversed. The patient may be extubated in the operating room. Infiltration of a local anesthetic agent into the anterior thoracotomy wound reduces postoperative pain.