Opcab

The MIDCAB technique does not address circumflex disease which is not easily accessible with a limited thoracotomy, and is, therefore, applicable to only a minority of CABG patients requiring complete surgical revascularization. "Offpump coronary artery bypass" (OPCAB) refers to complete surgical coronary revascularization without the heart-lung machine. It is generally done via median sternotomy in order to approach the anterior surface of the heart as well as the less readily accessible areas through which the circumflex and right coronary vessels course. Exposure of all vessels is feasible with sternotomy, but even for single vessel LAD disease, a sternotomy approach may be preferred to MIDCAB. Compared to mini-thoracotomy, a sternal approach simplifies LIMA harvesting, identification of the LAD is done with greater confidence, and access for cannulation is readily available if emergency CPB is needed. Minithoracotomy does not necessarily result in less pain than a sternotomy, rather the converse is often true. However, one advantage of MIDCAB to OPCAB may be in reoperations where adhesion takedown through a sternotomy is obviated.

Patient Selection

Although most CABG patients tolerate CPB well, certain subgroups have a higher incidence of adverse outcomes from CPB, including the elderly and patients with prior stroke or severe pulmonary, renal, or ventricular dysfunction. It is these patients who may benefit the most with OPCAB compared to standard CPB. Ejection fraction should not necessarily be used as a basis to reject a patient from OPCAB. The "worst" operative candidate physiologically may paradoxically be the "ideal" patient for OPCAB.

OPCAB appears to have decreased morbidity compared to on-pump CABG, presumably because of elimination of CPB. Several studies trend toward a decrease in the incidence of stroke, renal failure, prolonged ventricular dependence, and operative mortality. The effect appears to be even more pronounced in high risk patients.

Some groups of patients may anatomically be suboptimal OPCAB candidates. These include patients whose angiograms reveal small, intramyocardial, or heavily calcified vessels which may require endarterectomy. Cardiomegaly is a relative contraindication to OPCAB because these hearts are particularly difficult to position for OPAB, particularly in the circumflex distribution. Hemodynamically unstable patients are not candidates for OPCAB.

Technique

After sternotomy and IMA harvesting, systemic heparinization is established using one-third to one-half of the CPB loading dose and the activated clotting time kept at 200-300 seconds. Reversal with protamine is done for most patients at the end of the procedure. Deep pericardial sutures are placed in strategic locations in the left posterior pericardium to facilitate pericardial retraction for cardiac elevation and exposure. Care is taken to avoid the phrenic nerve or pulmonary veins. Different amounts of traction on these sutures elevates the heart in different ways, by either lifting the apex up and out of the sternotomy or rolling the lateral heart toward the surgeon (Fig 9.4). The Trendelenburg position further elevates the apex out of the chest. Since the deep pericardial suture adj acent to the left superior pulmonary vein could conceivably lacerate the left atrial appendage if pulled too taut, a rubber snare is used on these sutures to proved a softer buttress.

Deep Pericardial Sutures Cabg
Fig. 9.4. Deep intrapericardial sutures which, when elevated, achieve exposure of the anterolateral aspect of the heart. Steep Trendelenburg achieves further exposure.

One of the several commercially available stabilizing systems is used to immobilize the area of the target vessel. Vascular control, shunts, and occluders are used in a manner similar to that described for MIDCAB. As a general rule, the first vessel grafted is the LAD because of its ease and importance (Fig 9.5). The subsequent order of vessel grafting depends on the size, importance, and ease in maintaining tissue perfusion while achieving exposure. Generally, vessels with the least difficult exposure and technical grafting complexity are done first. The greatest danger to injury to the LIMA to LAD anastomosis comes from torquing the heart inferiorly and to the right, such as when exposing the ramus intermedius or high obtuse marginals. Hence, firmly anchoring the LIMA pedicle to the epicardium is essential. All distal anastomoses may be completed first, followed by proximal grafting to the aorta using a partial occlusion clamp. Alternatively, proximal grafting may be accomplished in turn after each distal.

Cardiac manipulation to achieve exposure may be poorly tolerated hemody-namically. This is especially true for exposure of the obtuse marginal vessels. Active, vigilant participation by the anesthesiologist using anticipatory, as well as reactive, strategies is a requirement for safe and successful OPCAB. Short-acting

Fig. 9.5. Retractor and stabilizer positioned via median sternotomy for OPCAB procedures. The LAD vessel is being exposed.

beta blockers such as esmolol help control the heart rate and reduce cardiac oxygen consumption. Phenylephrine, dopamine, and epinephrine support vascular resistance and perfusion pressure, and volume loading with infusions and Trendelenburg position optimize cardiac output during cardiac manipulations.

An important risk of hemodynamic instability arises when achieving vascular control of the right coronary artery. Intraoperative cardiac arrest may arise in this instance from ventricular tachycardia, fibrillation, or bradydysrhythmias. If possible, OPCAB grafting of the branches of the right coronary artery, rather than the right coronary itself, may be preferable to help minimize this risk. If grafting on the right coronary directly is necessary, a shunt occluder which maintains perfusion may be of the most benefit. Although extubation in the operating room is possible, it is not necessary and OPCAB patients can usually undergo early extubation within several hours postoperatively.

Probably the most popular and easy to use device is the Medtronic Octopus suction-stabilizing device ot immobilize the target area this is often used in conjunction with a suction cup over the ventricular apex to left and position the heart, primarily to achieve exposure of the inferior and lateral aspects of the heart. This generally results in less hemodynamic compromise than if sponges or other retraction techniques are used. The apical suction cup obviates the need for deep pericardial retraction sutures.

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