Introduction
The most common conduits used during coronary artery bypass surgery (CABG) include saphenous venous grafts (SVGs), internal mammary artery (IMA), radial artery (RA), and gastroepiploic artery (GEA) . Regardless of the conduit of choice, each bypass requires an inflow to supply arterial blood to the myocardial territory distal to the bypassed lesion. These inflows may be the conduit’s own native blood supply (i.e., with in situ IMA or GEA), or in the case of SVGs and RA grafts, the bypass will require the construction of a proximal anastomosis.
Historically, when a proximal anastomosis is required, the graft’s inflow is the ascending aorta . Recently, studies have demonstrated that minimizing aortic manipulation during CABG is associated with improved postoperative neurologic outcomes . In our institution, we still routinely perform aortocoronary anastomosis under cardioplegic arrest. Nonetheless, in cases of porcelain ascending aorta, off-pump anaortic CABG is preferred.
Whenever a proximal aortocoronary anastomosis is planned, preoperative steps ensure safe aortic manipulation. Routine chest computerized tomography scan is ordered, to investigate the presence of ascending aorta calcifications. Intraoperatively, prior to aortic cannulation and cross-clamp, the aorta is interrogated with epiaortic ultra-sound to avoid manipulation of a diseased segment of the aorta . Transesophageal echocardiography (TEE) is usually performed. Although most of the ascending aorta is not visualized by TEE, other sections of the thoracic aorta can be screened for atherosclerotic disease, which may be a marker for disease in the ascending aorta. By employing all the mentioned steps the risk of any aortic complication during CABG (rupture, dissection, hematoma, or plaque disruption) may be reduced.
Aortic anastomosis
Aortocoronary anastomosis may be performed during cardioplegic arrest, while the single aortic clamp is in place, or using a partial side-biding clamp. We typically prefer the first option, anastomosing first aortocoronary grafts (SVG and/or RA) followed by in situ arterial grafts (IMA).
During construction of the anastomoses the cardioplegia tack located in the ascending aorta is used as a vent, with gentle suction applied, to provide a bloodless field. Furthermore, a gentle atraumatic bulldog clamp is applied to the conduit, to prevent air from entering the graft. The aorta is deaired after each proximal anastomosis by leaving blood in the heart.
Proper positioning of the graft is key to ensure a normal trajectory from the proximal to distal anastomosis, avoiding kinks or malrotation. On a clockface, with 12 o’clock being directed toward the patient’s head and 6 o’clock the patient’s feet ( Fig. 12.1 ), the grafts bypassing the left-sided coronary vessels are directed to 1 or 2 o’clock, toward the patient’s left shoulder. The proximal anastomoses of these grafts are positioned on the left anterolateral surface of the aorta, or anteriorly. In the case of multiple left-sided bypasses, careful orientation is mandatory to prevent grafts crossing along their courses. We avoid left-sided grafts crossing by placing the diagonal as the most proximal graft on the aorta, followed by an intermediate or first obtuse marginal graft, and finally a more distal obtuse marginal graft is placed more distally in the ascending aorta ( Fig. 12.2 ). The more proximal the anastomosis is placed on the aorta (typically the diagonal graft), the more cephalad angulated it should be (1 o’clock), whereas more distally placed anastomosis in the aorta (i.e., distal obtuse marginal) may be placed at 2 o’clock, with less cephalad angulation. Grafts bypassing the diagonal or intermediate coronary arteries are usually directed anterior to the left atrial appendage, while grafts to the obtuse marginal are usually directed posterior to the appendage. For grafts bypassing any of the right-sided coronary vessels, the proximal anastomosis is typically directed toward 6 o’clock, toward the patient’s feet, along the course of the native right coronary artery.
In some cases, because of the length or quality of the graft, the size of the heart or its cardiac structures, the quality of the aorta, or the number of proximals, some alternative techniques are used. Grafts to the left-sided coronary arteries may be anastomosed on the right anterolateral surface of the aorta, directed at approximately 9 o’clock, after coursing through the transverse sinus, usually anterior to the left atrial appendage. Likewise, grafts bypassing the posterior descending or posterolateral coronary arteries may be anastomosed to the aorta at the 9 o’clock position, on the right anterolateral surface of the aorta, after coursing along the interatrial groove and the over the superior vena cava ( Fig. 12.3 ). Grafts to the posterolateral vessels may be grafted at the 7–8 o’clock position on the right anterolateral surface of the aorta after coursing behind the inferior vena cava through the oblique sinus ( Fig. 12.4 ).
