Coronary Artery Bypass Grafting-(On Pump Arrested)
Jennifer S. Lawton, M.D.
Professor of Surgery, Division of Cardiothoracic Surgery, Washington University School of Medicine
This chapter will detail the technical aspects of coronary artery bypass grafting (CABG) with cardiopulmonary bypass (CPB) with the heart arrested. The conduct of the procedure as performed by the author is detailed below.
Indications/Contra-indications for CABG with CPB
Indications for CABG are well described [1,2]. The decision to use cardiopulmonary bypass with or without cardioplegia is made by the surgeon and is typically determined during preoperative planning. Indications for the use of CPB with the heart arrested may include: planned grafting of more than 4 coronary vessels, small or heavily calcified vessels, the need for sequential anastomoses for multiple vessels, significant left ventricular dilatation making manipulation of the heart for off pump CABG difficult, or intramyocardial vessels.
There are cases in which the decision to utilize cardiopulmonary bypass is made intraoperatively and these may include hemodynamic insufficiency during manipulation of the heart during off pump CABG, technical difficulty with small coronary targets, or the inability to locate coronary targets.
Cardiopulmonary bypass with cardioplegic arrest should be avoided in cases of a porcelain aorta. Challenges (but not contraindications) for CABG with CPB include: heparin-induced thrombocytopenia, cold agglutinins, and pregnancy.
Preoperative – Special diagnostic or imaging tests
Cardiac catheterization is utilized to delineate coronary anatomy for bypass planning and is reviewed immediately prior to each procedure. Echocardiography is utilized preoperatively if valvular disease is suspected or if left ventricular function was not evaluated at the time of cardiac catheterization. Viability assessment is performed when left ventricular function is reduced. Carotid Doppler examination is performed in patients with a history of transient ischemic attack, cerebrovascular accident, or carotid endarterectomy. Additional tests are performed to determine operative risk depending upon significant co-morbidities (pulmonary function tests).
Comorbidities (age, end stage renal disease, diabetes mellitus, and obesity) are considered during conduit planning. Venous mapping will aid in finding adequate greater saphenous vein when patients have had previous lower extremity revascularization surgery or vein stripping. Allen testing is imperative for planned radial artery use, and body mass index and diabetes mellitus dictate appropriate use of bilateral internal mammary arteries.
Specific Intraoperative Details
- General anesthesia with endotracheal tube
- Monitoring lines include: arterial line, central line (Cordis), and foley with temperature probe
- Transesophageal echocardiography or Swan Ganz catheter utilized only if poor left ventricular function
- Antibiotics are administered 30 min prior to incision and include: Vancomycin (1gm IV) and Ancef or Aztreonam (if penicillin allergy) (2gm IV)
- ChloraPrep sticks from chin to ankles and circumferential prep of arm when radial artery conduit planned
- Supine position with both arms tucked unless radial artery utilized as conduit
- Full sternotomy (Stryker sternal saw)
- Open radial artery harvest, endoscopic saphenous vein harvest, IMA harvest with pedicle
- Topical papaverine or milrinone for arterial conduits after harvest and before use
- Morse retractor for sternum and Rultract for IMA harvest (Figures 1,2)
- Morse with deep blades if large amount of subcutaneous tissue between skin and sternum
Intra-op –special imaging
- Flow probe to assess graft flow
- Ultrasound imaging of ascending aorta prior to aortic cannulation if significant atherosclerotic disease
Heparin and adjuncts
- Heparin intravenous bolus 5,000 units at the initiation of conduit harvest
- Heparin bolus for CPB based on ACT level
- Heparin drip during case at discretion of anesthesiologist
- Tranxecemic acid
- Protamine dose based on heparin level/ACT at conclusion of procedure
- Two 2-0 Ethibond sutures (only the first is pledgetted) for aortic cannula
- One 2-0 Ethibond nonpledgetted for venous cannula
- Specific cannulas listed in (Table 1) (Perfusion equipment)
- (Figure 2) demonstrates completion of cannula placement
- Antegrade cardioplegia via DLP catheter, single pledgetted 5-0 prolene mattress suture
- Retrograde cardioplegia via coronary sinus catheter, single pledgetted 5-0 prolene mattress suture
- A combination of antegrade and retrograde utilized for all
- Induction dose 10cc/kg (1/2 antegrade, ½ retrograde) cold (4 °C) blood cardioplegia (4:1) with Plegisol
- Maintenance dose 300 ml retrograde and 60 ml induction concentration cardioplegia down each completed graft
- Patient temperature is allowed to drift to 32° C
- Rewarming begins immediately following last distal anastomosis, external warming blankets utilized
- Two right atrial and 2 right ventricular pacing wires (Medtronic temporary pacing lead 6500) placed on epicardial surface and exteriorized laterally beneath costal margin
- Pacing wires are color coded and location coded (atrial always on the patient’s right side and ventricular always on the patient’s left side) for convention and safety
- 32F Silastic chest tubes (angled in any open pleural space and straight in anterior mediastinum)
- Silastic tubes preferred if bilateral internal mammary artery harvest
- Alternatively Blake drains utilized
- Surgicel is useful for anastomotic sites
- FloSeal may be useful for minor venous bleeding at anastomotic sites
- Sternum closed with #7 wires (3 in manubrium and one in each rib space)
- Skin and subcutaneous tissues closed using absorbable suture in layers
Conduct of the Operation
Sternotomy is performed following informed consent, induction of adequate general anesthesia, skin prep, team time out, and antibiotic administration. A Swan Ganz catheter is utilized only in cases of poor ventricular function. Following median sternotomy, Vancomycin powder mixed with saline is utilized on the sternal bone. Internal mammary arteries (IMA) are harvested while surgical assistants (RN surgical assistant) harvest radial artery (open) and saphenous vein (endoscopic) conduits. Arterial grafts are topically treated with papaverine solution (2ml papaverine with 30 ml heparinized blood) or milrinone solution (10ml with 10 ml heparinized blood). Rapid IMA harvest or IMA harvest after commencement of CPB may be accomplished in cases of ongoing myocardial ischemia.
A pericardial well is then created. The ascending aorta is evaluated for the presence of atherosclerotic disease and for the placement of cannulae. Cannulation is performed after adequate systemic heparinization confirmed by ACT and relative systemic hypotension is induced (systolic blood pressure 90-100 mmHg). Two pursestrings are placed in the aorta and the aorta is cannulated. Confirmation of pulsatile flow in the cannula as well as confirmation of blood pressure identical to that in the arterial line is confirmed prior to using the aortic cannula. The right atrium is then cannulated and secured. The cardioplegia manifold is then set up and flushed from the anesthesia pressure line. The ascending aorta antegrade cardioplegia cannula is then placed. Placement of the retrograde cardioplegia cannula is then performed if the perfusionist checklist is complete, the conduit harvest has been completed, and the patient tolerates manipulation of the heart to place the cannula. Cardiopulmonary bypass (CPB) is not commenced until all conduit is prepared, adequate, and ready for use to decrease CPB time.
Following commencement of CPB, the distal targets are evaluated and plans made for each conduit and the order of grafting. The patient temperature is allowed to drift to 32 degrees C while on CPB. The cardioplegia manifold is flushed with blood from the CPB machine. The two ends (ties) of the heart support (Janke Barron) are placed beneath the IVC and in the transverse sinus to facilitate heart manipulation. The ties are then knotted together on the right side of the sternal retractor. The IMA grafts are sized in length and brought through openings in the lateral pericardium with care to not injure the phrenic nerves. All preparations that can be performed are completed prior to placement of the aortic cross clamp. White towels are utilized to drape around the sternal wound to facilitate visualization of blue prolene suture.
Following placement of the aortic cross clamp (with CPB flow significantly reduced), cold blood antegrade cardioplegia is administered via the ascending aorta (typically ½ of the full dose of 10cc/kg) if there is no aortic insufficiency. Warm induction is utilized in cases of ongoing ischemia with hemodynamic compromise. Pressure is measured by the perfusionist and the surgeon (palpation of the aorta) to ensure adequate distension of the ascending aorta. In addition, care is taken to ensure that left ventricular dilatation does not occur. Retrograde cardioplegia is then administered (1/2 the full dose) with suction on the aortic root vent. Pressure is measured to ensure appropriate and safe administration. Hypothermia for the heart is augmented with cold saline topical pour and occasionally iced slush applied only to the diaphragmatic surface of the heart to prevent phrenic nerve injury. Maintenance cardioplegia doses are administrated every 20 min or if any myocardial activity is noted prior to 20 min.
Following completion of cardioplegia, attention is turned first to the inferior wall (if indicated). This territory is chosen first as cardioplegia may then be given down this completed graft for the remainder of the procedure to provide additional protection to the right heart. Positioning of the heart is maximized by the use of the heart support (Figures 3,4). Coronaries are dissected using round beaver blade and then opened with 15 degree beaver blade followed by forward and then backward coronary scissors. Distal anastomoses are accomplished by running end-to-side anastomosis or sequential side-to-side anastomosis (7-0 prolene BV-1) and then immediately flushed with cold blood cardioplegia to assess for bleeding and to deair the conduit. A Medtronic blower/mister and DLP coronary artery retractor clip (parsonett) are utilized to visualize the construction of the anastomosis. The graft to the right heart is then connected to the cardioplegia manifold and cardioplegia is given prior to retrograde cardioplegia following each subsequent anastomosis. The heart is returned to the normal anatomic position for the administration of retrograde cardioplegia.
Distal anastomoses are then accomplished in the following order: distal lateral wall, proximal lateral wall, diagonal, and left anterior descending coronary artery. The patient is systemically rewarmed when the IMA pedicle is parachuted down to the myocardium. The mammary pedicle is tacked to the epicardium to prevent twisting using 6-0 prolene suture.
Proximal anastomoses are then accomplished with running end-to-side anastomoses to the ascending aorta following circular punch removal of the aortic wall (using 5 mm for vein grafts and 4 mm punch for arterial grafts). A single cross clamp method is utilized. Each proximal anastomosis is marked with a radiopaque marker. De-airing maneuvers (Trendelenburg position, several inflations of the lungs, and a warm retrograde cardioplegia dose) are performed. The bull-dog clamps on the IMAs are removed. Bull-dog clamps are placed on each of the aorto-coronary grafts and the aortic cross clamp is removed. The aorto-coronary grafts are de-aired with a 27 gauge needle on a TB syringe and the bull-dog clamps are removed.
With flow restored to the heart, the coronary sinus catheter is then removed. The distal anastomoses are checked for bleeding. Two right atrial and 2 right ventricular temporary pacing wires are placed and brought out via separate stab incisions below the costal arch on each side. Color coated wires are utilized to prevent inappropriate pacing (atrial wires are always on the patient’s right side and are always blue, and ventricular wires are always placed on the patient’s left side and are always white). Any arrhythmias are treated, and the patient is paced (preferably atrially paced) if necessary. The lungs are ventilated once again and the patient is then weaned from cardiopulmonary bypass with return of volume and appropriate inotropes and pressor agents as needed. Protamine is administered and the cannulas are removed. Hemostasis is obtained, chest tubes are placed and the sternum is closed using #7 single wires. Skin and subcutaneous tissues closed with absorbable suture in layers.
Early extubation is preferred (in the operating room) if bleeding is minor and the patient is hemodynamically stable. Patients are transported immediately to the Cardiothoracic Intensive Care Unit. Care is dictated by hemodynamic stability and under the direction of Cardiothoracic Anesthesia intensivists. Aspirin is prescribed immediately and beta blockers, statins, and ACE inhibitors are initiated as soon as possible. Modification of risk factors is stressed including early mobilization and instruction by physical therapy, dietician consultation, and counseling for smoking cessation.
1. Patel MR, Dehmer GJ, Hirshfeld JW, et al. ACCF/SCAI/STS/AATS/AHA/ASNC/HFSA/SCCT 2012 appropriate use criteria for coronary revascularization focused update: a report of the American College of Cardiology Foundation Appropriate Use Criteria Task Force, Society for Cardiovascular Angiography and Interventions, Society of Thoracic Surgeons, American Association for Thoracic Surgery, American Heart Association, American Society of Nuclear Cardiology, and the Society of Cardiovascular Computed Tomography. J Am Coll Cardiol 2012;59:857-81.
2. Hillis LD, Smith PK, Anderson JL, et al. 2011 ACCF/AHA guideline for coronary artery bypass graft surgery: executive summary: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. J Thorac Cardiovasc Surg 2012;143:4-34.