Off Pump Coronary Artery Bypass (OPCAB)

Patient Selection

Beginner Beating Heart Surgeon (< 50 beating heart cases)

The beginner should consider avoiding patients with unfavorable characteristics, such as:

• Cardiomegaly (cardiothoracic ratio > 0.7) as this makes exposure of lateral and inferior walls of LV difficult.
• Small (<1.5 mm diameter), intramyocardial or diffusely diseased target vessels.
• Hemodynamically unstable patients.
• Patients with critical left main disease.
• Patients suffering or having recently suffered an acute myocardial infarction
• Patients with severe left ventricular dysfunction (LVEF < 35%)

Expert Beating Heart Surgeon (> 50 beating heart cases)

With experience OPCAB can be performed safely in the vast majority of cases (>90%). However it is not advisable to perform OPCAB if MULTIPLE unfavorable characteristics are present (e.g. cardiomegaly in a patient with LVEF 25% and small targets)

Operative Steps

Operating Room Setup and Preparation

Preserve normothermia by keeping the operating room warm, avoiding radiant heat loss and monitoring core body temperature. Ensure that the heart-lung machine and perfusionist are available. It is not necessary to prime the heart-lung machine. Review the chest roentgenogram to assess cardiomegaly before committing to OPCAB. Confirm availability of stabilizer instrument set of choice, a CO2 blower and appropriately sized intracoronary shunts. Assure that the anesthesiologist is comfortable with beating heart surgery as collaboration crucial for success.

Anesthesia

Unlike traditional CABG where the anesthesiologist plays a passive role during the performance of bypass grafting, involvement of the anesthesia team is essential for successful OPCAB. A continuous cardiac output swan ganz catheter and continuous mixed venous saturation monitor are helpful. Maintenance of systolic pressure is important for the heart to tolerate hemodynamically unfavorable positioning. Alpha agents and inotropic agents are important to maintain cardiac output during manipulations. If necessary, an intraaortic balloon can be inserted for temporary support.

Procedure

A traditional sternotomy is performed. All conduits are harvested as for traditional CABG. The left internal mammary should be made as long as possible. This will help avoid excessive tension when the heart is elevated after the graft to the LAD is performed. Hemi-skeletonization of LIMA (the "Suma technique") preferable as maximal length achieved in shortest time. Total arterial revascularization is feasible with OPCAB. Use of composite conduits (Y or T graft) with the left and right IMA and the radial artery is preferred.

The heparin dose (1-1.5 mg/Kg) is 1/3 of the standard dose for cardiopulmonary bypass. The target ACT is greater than 300 seconds. The ACT should be checked every 30 minutes with heparin supplemented as needed.

Sequence of anastomoses

The coronary arteries should be grafted in order of increasing cardiac displacement, i.e. anterior wall vessels followed by inferior wall vessels and finally lateral wall vessels. The guiding principle that more cardiac displacement is tolerated with increasingly complete revascularization. The LIMA to LAD graft is usually first, the inferior wall grafts (PDA, RCA) are usually next and the lateral wall grafts (OM) are usually last.

The proximal anastomoses can be performed before or after the distal anastomoses. The advantage of completing the proximal anastomosis first is immediate perfusion through the graft after the completion of the distal anastomosis. The author's preference is to perform the proximal anastomoses first.

Positioning the heart with mechanical stabilization for target vessel presentation

Proper positioning and stabilization are critical for the success of OPCAB! The use of a dedicated instrument for target vessel stabilization strongly encouraged, especially for the beginner beating heart surgeon (see preference cards)

For Anterior LV wall (Figure 1) presentation (Anterior Descending, Diagonal, Ramus), a deep pericardial retraction suture, (DPRS, #1 Silk or Ethibond) is placed 1-2 centimeters above the left superior pulmonary vein ( Figure 2), pulled taut and secured to the drape on the left side of the patient. If necessary, especially for the Ramus, an additional deep pericardial retraction suture (second in Figure 2) is placed anterior to the phrenic nerve and caudal to the first deep pericardial retraction suture. Additional deep pericardial retraction sutures are positioned until the target vessel is midline in the sternal incision. Placement of these deep pericardial retraction sutures must be done deliberately and quickly. The retraction required to expose the posterior pericardium causes severe hemodynamic compromise. The blood pressure will recover faster if the patient is head down with preparatory volume loading.

For Lateral LV wall presentation (Obtuse Marginals, Posterolateral branches of right coronary artery) the OR table is placed in steep Trendelenburg position (Figure 3) and the table is raised and rotated toward the right (Figure 4). This will allow gravity to displace heart to the right and apex anteriorly. Suspensory sutures on the right side of the pericardium are removed. The right pleural space is opened and the right pericardial incision is extended towards the inferior vena cava. These maneuvers allow the heart to move toward the right pleural space. Additional deep pericardial retraction sutures are placed on the posterior pericardial surface on a line drawn from the left inferior pulmonary vein to the inferior vena cava, halfway between the cava and pulmonary vein (third in Figure 2).

For Inferior LV Wall presentation (distal Right Coronary Artery and Posterior Descending Artery), with the table in steep trendelenberg position, the tension applied to the deep pericardial retraction sutures is modulated to expose the target vessel in the center of the operative field (Figure 5, 6). The posterior descending artery is the preferred site for grafting the right coronary distribution. The necessary temporary occlusion of the artery, if proximal to the bifurcation, can cause ischemia of the AV node with resultant bradycardia. For grafting the right coronary artery the table made flat and retraction sutures are relaxed with the heart failing to the left side.

Stabilization of target site is accomplished using one of the many excellent stabilizers available on the market. These devices work by compression with or attachment (suction or direct) to the stabilizing arm (Figures 7,8). It is important that these devices be used as stabilizers, not retractors. The techniques described above are used to expose the vessel, the stabilizers create an immobile field. If used as retractors the heart will slip and compression will cause hemodynamic compromise.

Anastomosis

Proximal occlusion of target vessel is accomplished with an encircling suture or silastic tape passed widely around the vessel proximal to the site chosen for anastomosis. No distal occlusion is necessary (Figure 9). The use of intracoronary shunts is recommended whenever possible, especially for LAD and RCA. These are very useful when hemodynamically significant ischemia develops (Figure 10). The anastomosis is performed in a routine manner according to the surgeon's preference.

Preference Card

Genzyme OPCAB retractor system. This system uses silastic tapes to surround the vessel, attaching it to a template that immobilizes the vessel.

Guidant (formerly CardioThoracic Systems) Ultima II retractor and stabilizer. This system uses compression to immobilize the vessel.

Guidant Flocoil intracoronary shunt (sizes from 1.5 mm to 2.5 mm in 0.25 mm increments).

Medtronic Octopus 2 Stabilizer. This system attaches to the existing reusable retractor. Suction is used to secure the heart to the retractor and immobilize the vessel.

Tips & Pitfalls

• Meticulous attention to detail is critical to success, as safety margin with OPCAB is reduced compared to traditional CABG.
• Intracoronary shunts are extremely useful in minimizing the amount of ischemia and improving the safety of the operation. In cases of a training institution use of shunts allows residents to be safely trained in OPCAB.
• Allow extra time to obtain the best presentation and stabilization for obtuse marginal vessels. Do not compromise your exposure. If adequate exposure cannot be obtained the anastomosis should not be compromised and the traditional approach should be used.
• A CO₂ blower is crucial for beating heart surgery but has to be used VERY sparingly at a flow rate not > 5 L /min, to prevent damage to the coronary endothelium. Avoid directing the gas jet directly into the vessel lumen to prevent gas embolization.
• Heparin reversal is not mandatory. The author's preference is to administer one-half the calculated protamine dose.
• Anastomosis of the obtuse marginal vessels is easier from the left side of the table.
• Place temporary pacing wires before occluding the right coronary artery proximal to the bifurcation to manage possible A-V block.

References

1. Calafiore A, Teodori G, Di Giammarco G, et al. Multiple Arterial Conduits without Cardiopulmonary Bypass: Early Angiographic Results. Ann Thorac Surg 1999;67:450-6.
2. Mohr R, Moshkovitch Y, Shapira I, et al. Coronary artery bypass without cardiopulmonary bypass for patients with acute myocardial infarction. J Thorac cardiovasc Surg 1999;118:50-6.
3. Wan S, Izzat MB, Lee TW, et al. Avoiding cardiopulmonary bypass in multivessel CABG reduces cytokine response and myocardial injury. Ann Thorac Surg 1999;68:52-7.
4. Pym J. Off pump arterial grafting: 125 cases using the Medtronic-Utrecht Octopus. Eur J Cardiothorac Surg 1999;16:S88-94.
5. Jansen EW, Borst C, Lahpor JR, et al. Coronary artery bypass grafting without cardiopulmonary bypass using the octopus method: results in the first one hundred patients. J Thorac Cardiovasc Surg 1998;116:60-67.
6. Murkin JM, Boyd WD, Ganapathy S. Beating heart surgery: Why expect less central nervous system morbidity? Ann Thorac Surg 1999;68:1498-501.
7. Koh TW, Carr-White GS, DeSouza AC, et al. Effect of coronary occlusion on left ventricular function with and without collateral supply during beating heart coronary artery surgery. Heart 1999;81:285-291.
8. Grundeman PF, Borst C, van Herwaarden JA, et al. Vertical displacement of the beating heart by the octopus tissue stabilizer: influence on coronary flow. Ann Thorac Surg 1998;65:1348-52.
9. Baumgartner FJ, Gheissari A, Capouya ER, et al. Technical aspects of total revascularization in off pump coronary bypass via sternotomy approach. Ann Thorac Surg 1999;67:1653-8.
10. Cartier R. Systematic off-pump coronary artery revascularization: Experience of 275 cases. Ann Thorac Surg 1999;68:1494-7.
11. Boyd WD, Desai N, Del Rizzo D, et al. Off-Pump surgery decreases postoperative complications and resource utilization in the elderly. Ann Thorac Surg 1999;68:1490-3.
12. Spooner TH, Hart J, Pym J. A two-year, three institution experience with the Medtronic Octopus: systematic off-pump surgery.