Coronary Artery Bypass Grafting Technique

Updated: Apr 04, 2014
  • Author: R H Bilal, MBBS, MRCS; Chief Editor: Richard A Lange, MD, MBA  more...
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Technique

Approach Considerations

The goal of coronary artery bypass grafting (CABG) is complete revascularization of the area of the myocardium that is perfused by coronary arteries with luminal stenosis of more than 50%. Several methods may be used for this purpose. A durable conduit is vital for successful CABG. There are a number of sites from which the conduit can be harvested, including the following:

  • Saphenous vein
  • Radial artery
  • Left internal thoracic (mammary) artery (LITA)
  • Right internal thoracic (mammary) artery (RITA)
  • Right gastroepiploic artery
  • Inferior epigastric artery
  • Splenic artery
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Harvesting of Conduit

Saphenous vein

The great (long) saphenous vein (GSV) is located 2 cm anterior to the medial malleolus, traverses the tibia, and ascends posteriorly up the tibial border before emptying into the femoral vein. It receives numerous tributaries, notably at the knee, and contains 10-20 valves. Key associated structures are the saphenous nerve, femoral cutaneous nerve, and saphenous branch of the genicular artery. The small (short) saphenous vein (SSV) is located 1 cm posterior to the lateral malleolus, runs centrally up the posterior calf, and drains into the popliteal vein.

As CABG conduits, the saphenous veins have an 80-90% early patency rate, which decreases to 50% at 10 years. The saphenous vein is generally acceptable as a conduit in the absence of other vascular pathologies in the leg (varicosities in the vein, venous insufficiency, previous deep vein thrombosis [DVT], or small lumen diameter) or overlying infection.

The GSV can be procured either via an open harvest technique (see the image below), starting from either the ankle or groin and using a vein stripper, or via an endoscopic technique. Likewise, the SSV vein can be harvested either with an open procedure or endoscopically.

Open saphenous vein harvest technique. Open saphenous vein harvest technique.

The legs and groin should be shaved, prepared, and draped in the operating room. Care should be taken to avoid getting skin preparation solution on the diathermy plate; this can result in diathermy burns. Once the anesthetist is ready for surgery to start and the surgeon has confirmed the number of lengths (25 cm) of vein required, the vein harvest can begin.

Internal thoracic artery

The LITA and the RITA arise from their respective subclavian arteries. The internal thoracic artery can be harvested either by itself or as a pedicle (see the figure below).

Internal thoracic (mammary) artery harvest as pedi Internal thoracic (mammary) artery harvest as pedicle.

Whereas the LITA is most commonly harvested as a pedicle, the RITA is generally skeletonized because an RITA pedicle may interfere with sternal wound healing. The LITA is useful in left anterior descending (LAD) artery anastomosis and has a good patency rate in this setting (98% at 1 year and 90% at 10 years). The RITA has a good patency rate when anastomosed to the LAD (96% at 1 year and 90% at 5 years) but a reduced rate when grafted to the circumflex or the right coronary artery (75% at 1 year).

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Coronary Artery Bypass

The usual incision for CABG is a midline sternotomy (see the image below), although an anterior thoracotomy for bypass of the LAD or lateral thoracotomy for marginal vessels may be used when an off-pump procedure is being performed.

Median sternotomy Median sternotomy

CABG with cardiopulmonary bypass and cardioplegic arrest is demonstrated in the video below.

Coronary artery bypass grafting with cardiopulmonary bypass and cardioplegic arrest. Video courtesy of Dale K Mueller, MD.

Cardiopulmonary bypass

The first step in cardiopulmonary bypass is to cannulate the aorta and right atrium. The aortic area selected for cannulation must be soft and nonatherosclerotic. To insert the aortic cannula, unfractionated heparin is given, and the systolic blood pressure is lowered to less than 100 mm Hg. At this point, 2 purse-string sutures are placed into the aorta, and the aortic adventitia within the diameter of the purse-string sutures is divided. An aortotomy is performed with a scalpel, the cannula is placed, and the purse-string sutures are tightened around it.

The aortic cannula is then secured to a rubber tourniquet with a heavy silk tie. Once in place, the cannula is deaired and connected to the arterial pump tubing, where its position in the aorta can be confirmed by watching the pattern of tube filling. The venous cannula is inserted into the right atrial appendage in a similar fashion, with the end of the cannula positioned in the inferior vena cava. Adequate anticoagulation is confirmed by assessing the activated clotting time; once this is done, cardiopulmonary bypass can be commenced.

The aorta is cross-clamped distal to the cannula, and cold cardioplegia solution is infused via the aortic cannula (some centers also cool the patient). Retrograde cardioplegia may also be administered via the coronary sinus, especially in the patient who is undergoing repeat CABGs and has few or no patent grafts for adequate perfusion with antegrade cardioplegia. Compared with crystalloid cardioplegia, blood cardioplegia is associated with a lower incidence of intraoperative mortality, postoperative myocardial infarction, shock, and conduction defects.

Placement of graft

After the initiation of cardiopulmonary bypass, the distal coronary bypass targets are identified. As a rule, anastomoses to the right coronary artery and the marginal branches of the circumflex are completed first.

The circumflex is accessed by retracting the heart laterally, whereas the posterior descending artery and posterolateral circulation are accessed by retracting the heart cephalically. The LITA is then usually anastomosed to the LAD if possible. In rare circumstances (eg, CABG performed for acute anterior myocardial infarction), a saphenous vein graft may be placed to the LAD artery for expediency.

To accomplish the bypass, an incision is made in the distal coronary artery, and the conduit ostium is sutured around the full circumference of the anastomosis (see the image below). The conduit is then infused with cold cardioplegia solution, and the end is tied with a polypropylene suture.

Distal anastomotic technique. Distal anastomotic technique.

When all the distal anastomoses are completed, rewarming of the heart is initiated, the aortic cross-clamp is removed, and a partially occluding clamp is placed on the ascending aorta where the grafts are to be anastomosed. Holes are punched in the ascending aorta, secured by the partially occluded clamp, and the proximal ends of the anastomoses are sutured into place in the aorta (see the image below). Before the cross-clamp is finally removed, air is evacuated from the grafts and ascending aorta. The patient is then weaned off bypass.

Proximal anastomotic technique. Proximal anastomotic technique.

When normal rhythm is resumed, the patient is once again mechanically ventilated and electrolyte abnormalities (commonly hypomagnesemia and hypokalemia) are corrected. If the patient is bradycardic or experiences temporary heart block, temporary pacing is performed using wires placed to the right atrium and right ventricle. When cardiopulmonary bypass has been successfully stopped, protamine is given to reverse the heparin. [21]

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Alternative Approaches to Coronary Artery Bypass Grafting

Off-pump CABG

The key to off-pump CABG is the maintenance of blood pressure, heart rate, and normothermia (with the use of warming blankets). Preload must be optimized during manipulation of the heart to minimize hemodynamic instability. A number of techniques can be used to prevent hypotension, including prophylactic intravenous fluid infusion, use of the Trendelenburg and reverse Trendelenburg positions, and low-dose alpha-agonist infusion. [22]

A systematic review did not demonstrate any significant benefit of off-pump compared with on-pump CABG regarding mortality, stroke, or myocardial infarction. [23]

Totally endoscopic CABG

Endoscopic surgical techniques with robotic assistance were developed to enable the performance of surgery in difficult spaces and are now widely used across most surgical disciplines. The specific application of these techniques to the treatment of coronary artery disease (CAD) is known as totally endoscopic CABG. This procedure, which aims to decrease postoperative morbidity, duration of hospital stay, and overall cost, allows surgeons to perform endoscopic surgery on both the beating and arrested heart. [24]

The first step in totally endoscopic CABG is to deflate the lung. Next, 3 small incisions are made at the intercostal spaces, through which 1 robotic arm with an attached endoscope and 2 arms carrying surgical accessories are passed. These arms are controlled by the operator from a unit located away from the operating table. Grafts are then harvested from suitable sites, and anastomosis is completed across the affected coronary artery. [25]

Hybrid technique

Advances in surgical techniques and introduction of drug-eluting stents have provided a platform for a hybrid combined strategy that involves grafting the LAD with the LITA, then stenting the other coronary territories with drug-eluting stents instead of bypassing them with saphenous vein grafts.

Although preliminary data indicate that such a hybrid strategy may be a reasonable alternative for some patients with multivessel CAD, the real clinical utility of this approach will not be known until results of randomized clinical trials are available.

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Complications

A number of complications are associated with CABG, both in the short term and in the long term; they are associated with anesthesia, cardiopulmonary bypass, sternotomy, and the operation itself. These complications may include the following:

In the initial postoperative period, there is a decline in myocardial function secondary to myocardial edema and ischemia-reperfusion injury. Additional factors (eg, incomplete revascularization and postoperative graft failure) may exacerbate the dysfunction. Patients may exhibit a low-output syndrome, with 4-9% requiring the use of inotropes or intra-aortic balloon pulsation. Additionally, segmental transmural myocardial infarction occurs in 1-5% of patients, and postoperative arrhythmias occur in approximately 30% of patients after CABG. [26]

Adverse neurologic outcomes are a major concern in cardiac surgery, with 3.1% for major (type I) events (eg, major neurologic deficits and coma) occurring in 3.1% of cases and less debilitating (type II) events (deterioration of intellectual function or memory) in 3%. Both types of event result in a significant increase in mortality: 21% for type I events and 10% for type II. [27] Despite the increased mortality associated with type II events, the majority of survivors return to normal activity in the following 3-12 months. [28]

Postoperative renal failure is a significant cause of mortality after CABG. There is a 4% incidence of renal failure; 20% of these patients require dialysis, and the mortality is 50%.

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