Off-Pump Coronary Artery Bypass Grafting




Keywords

OPCAG, coronary artery bypass surgery, off-pump surgery, surgical technique

 





  • The ability to perform coronary artery bypass grafting (CABG) competently without the use of cardiopulmonary bypass is an important skill for all cardiac surgeons. There are cases in which a safe coronary revascularization procedure can only be performed as an off-pump procedure. Although off-pump coronary artery bypass (OPCAB) has a steeper learning curve than on-pump revascularization, there are clear benefits to it.



  • After an initial surge in popularity following its widespread adoption, the frequency of OPCAB has declined. In 2012, only 17% of all coronary artery bypass surgery was performed as an off-pump procedure. Much of this decline could be attributed to the results of several cohort studies and clinical trials, which showed no survival benefit for off-pump surgery. Despite this, OPCAB has consistently been shown to decrease blood transfusions and lower the risks of postoperative bleeding and renal and respiratory failure. OPCAB performed with the aorta no–touch technique also seems to lower the risk of postoperative stroke.



  • The results of the initial large trials have also highlighted potential pitfalls of OPCAB. Results suggested a higher proportion of incomplete revascularization with off-pump cases and a lower graft patency rate. This reinforces the notion that this procedure has a significant learning curve, and surgeons must ensure that the choice to use an off-pump approach does not affect the overall quality of the surgical revascularization.



  • Understanding when an off-pump approach is not in the patient’s best interest is also critical; severe ventricular dysfunction, left main disease, ongoing ischemia, and pulmonary hypertension are associated with poorer outcomes and the need to convert to on-pump procedures.



  • To perform OPCAB, a keen understanding of cardiac physiology is essential, because it allows more careful positioning of the heart to visualize the targets without affecting hemodynamics.



  • In this chapter, we describe a systematic, step by step approach to performing complete myocardial revascularization using an OPCAB technique. We discuss and illustrate key maneuvers, major pitfalls, and important strategic considerations for off-pump coronary revascularization. We also highlight the importance of total arterial revascularization and strategies to decrease aortic manipulation.






Preoperative Assessment and Planning





  • The benefits of complete revascularization are well established, and surgeons should bypass all vessels 1.5 mm or larger with stenosis of 70% or more. The off-pump approach should never jeopardize the ability to perform complete revascularization. Careful OPCAB planning should have a composite goal of a safe, complete revascularization without the use of cardiopulmonary bypass.



  • Planning an OPCAB begins at the time of the preoperative assessment. Patients presenting for isolated CABG should be carefully and thoroughly examined and undergo a complete diagnostic imaging workup. Particular attention should be paid to congenital anomalies of the chest, such as pectus excavatum, which may affect the feasibility of the operation.



  • A comprehensive preoperative assessment and diagnostic imaging workup should be carried out, as with any cardiac operation.



  • A noncontrast computed tomography (CT) of the chest to rule out aortic calcification is recommended for patients with advanced age (> 75 years), chronic renal disease, severe vasculopathy, and a history of heavy smoking. Ascending aorta calcification might make cross-clamping the aorta inadvisable or, in the case of a porcelain aorta, impossible.



  • Aortic manipulation likely increases the risk of stroke, and an off-pump approach allows myocardial revascularization without aortic manipulation. The aortic no–touch technique should be strongly considered for patients at increased risk for stroke.



  • Aortic calcification is one of the more common reasons to choose OPCAB, but there are other indications. Patients who decline blood transfusions (e.g., Jehovah’s Witnesses), and have borderline kidney and respiratory dysfunction likely benefit from OPCAB.



  • Just as some preoperative findings might make OPCAB the preferred choice, other findings, such as severe left ventricular dysfunction, ongoing ischemia, pulmonary hypertension, and valvular heart diseases will strongly suggest an on-pump approach to surgical revascularization. On-pump CABG is the safest approach in these scenarios.






Conduit Assessment





  • With any surgical coronary revascularization, the choice of conduits should be tailored to the patient. In the case of OPCAB, careful consideration of the patient’s coronary anatomy, targets to be grafted, and availability of conduits is required.



  • The use of the left internal thoracic artery (LITA) to graft the left anterior descending (LAD) territory has long been the standard of care for surgical revascularization. For patients with multivessel coronary artery disease, the remaining targets may be grafted with either arterial or venous grafts.



  • For patients younger than 75 years, the literature has demonstrated a survival benefit for multiarterial revascularization. In general, high-grade stenosis (> 80%) will be the preferred target for either radial or gastroepiploic arteries due to their susceptibility to competitive flow.



  • The internal thoracic arteries are less prone to competitive flow and can be considered for stenosis of 60% to 80%.



  • Venous grafts will tolerate almost any degree of stenosis, although their suboptimal durability and patency remain a major drawback, particularly in younger patients.



  • A composite graft of a LITA with a radial artery grafting seems to confer the same benefits as for a bilateral internal thoracic artery (BITA) and may be preferable in diabetic patients, who may be at greater risk for sternal wound complications.






Operative Steps



General Strategies, Tools, and Tactics





  • OPCAB is a team effort. The anesthesia team should be engaged prior to surgery for better support of the patient’s hemodynamics during induction and conduit harvesting and at the time of grafting.



  • The operating room should be kept warm during these operations, similar to the practice in pediatric operating rooms. If this is not done, the patient’s temperature can drop to a dangerous level, where spontaneous, malignant ventricular arrhythmias, such as ventricular fibrillation and ventricular tachycardia, could occur.



  • The availability of pacing wires, atrial and ventricular, can help maintain normal hemodynamics in patients with heart block or extreme bradycardia.



  • Both the surgical and anesthesia teams should carefully monitor hemodynamic changes during heart positioning. If inadequate hemodynamics are observed, the best course of action is to return the heart into the pericardium for optimal functioning. The surgeon should then consult with the anesthesia team while the heart is allowed to recover. Once hemodynamics stabilizes, an attempt may be made to carefully reattempt the required positioning.



  • Off-pump CABG has been made possible by the development of many specialized tools. Two of the most important tools are vacuum-based devices that are used to position the heart or stabilize the segment of coronary artery to be anastomosed. For the purposes of this text, the former will be referred to as positioning devices, and the latter will be referred to as stabilization devices. In addition to adequately placed pericardial sutures, these allow for optimal exposure of the target vessels.



  • Enhanced visualization devices, such as the Blower/Mister (Clear View Misted Blower; Medtronic, Minneapolis), have also been adopted, and they allow a safe construction of the anastomosis. We routinely use a Blower/Mister to optimize visualization. It delivers a jet of CO 2 under pressure in the middle of a jet of a pH-balanced saline solution, resulting in atomization of the liquid. The resulting stream of mist and CO 2 , when directed over the arteriotomy, clears the blood from the anastomosis without resulting in air embolism because the CO 2 is rapidly resorbed. The device does not prevent blood loss but improves visualization during the anastomosis.



  • Table tilt maneuvers can aid with visualization and allow adequate filling of the heart. If table tilting is not sufficient to correct preload, fluid infusion should be initiated by anesthesia. The Trendelenburg position and rotating the operating table toward the surgeon may also optimize lateral wall visualization. Changes to the operating table should be performed slowly and incrementally to allow the heart to adapt to different loading conditions.




Incision, Conduit Harvesting, and Pericardium Preparation





  • Most OPCAB procedures are performed through the standard median sternotomy.



  • An extensive inverted-T pericardial incision is usually required. The opening should reach the cardiac apex on the left side and reach the pericardial reflection on the right side ( Fig. 4.1 ). This allows heart positioning without any compressions or deformity.




    Figure 4.1


    Inverted-T pericardial incision.



  • When harvesting the internal thoracic arteries, we strongly recommend complete skeletonization. This approach decreases the rate of pleural effusions postoperatively and decreases the incidence of ischemic injury to the chest wall and subsequent mediastinitis. This is particularly important during BITA harvesting.



  • The lie of the conducts is critical to avoid kinking and compression by the lungs. An incision is made on the pericardium to accommodate the internal thoracic artery (ITA). This pericardial incision starts at the edge and is located at the level of the base of the left appendage for the LITA and at the level of the transverse sinus for the right internal thoracic artery (RITA). It is posteriorly directed toward the phrenic nerve. At 1 cm anterior to the phrenic nerve, the incision extends 2 cm superiorly and inferiorly, creating a T-inverted incision. This trench accommodates the in situ ITAs where they enter the pericardium.



  • The radial artery can be harvested endoscopically or using an open approach, and either pedicled or skeletonized, depending on the surgeon’s preferences. The gastroepiploic artery should be harvested in a skeletonized manner for better patency. Veins can be harvested endoscopically or using an open approach. Veins harvested through an endoscopic approach have shown lower patency rates than those harvested in an open manner.



  • There are several possibilities for graft configuration, and the approach should be tailored to the number and location of targets to be grafted:




    • In situ grafts do not require aortic anastomosis, but they offer fewer distal anastomoses, and their length is constrained.



    • Free grafts are less constrained by length but require aortic manipulation for the inflow creation.



    • Composite grafts pair an in situ graft, usually a LITA, with another conduit branching in a Y or T fashion. Composite grafts offer greater length and flexibility for grafting. In all cases, the graft configuration should be planned to take into consideration the availability of conduits and degree of stenosis in the target vessel.




  • For a full arterial revascularization in a patient with multivessel coronary artery disease, the plan should almost always include composite grafts due to the limited length of arterial conduits.




Inflow Preparation





  • Once the surgical plan has been made, conduits harvested, and the pericardium prepared, graft inflows should be considered.



  • Lateral pericardial sutures should be placed on each edge of the pericardium. These should be attached to the drapes using hemostats to keep the lungs away from the operative field and to expose the aorta for proximal anastomosis.



  • Side-biting clamping is safe for aortas with a wall thickness less than 3 mm throughout the clamp length and the anastomotic site. Plaques that are more than 3 mm in thickness increase the risk of adverse neurologic events during aortic manipulaton ( Table 4.1 ). We recommend the use of epiaortic scanning to assess the quality of the ascending aorta.



    Table 4.1

    Katz classification (grading) of aortic atheroma




























    GRADE DESCRIPTION INCIDENCE OF STROKE (%)
    1 Normal aorta 0
    2 Extensive intimal thickening < 3 mm 0
    3 Protrudes < 5 mm into aortic lumen 5
    4 Protrudes > 5 mm into aortic lumen 10.5
    5 Mobile atheroma 46.5

    Patil TA, Nierich A. Transesophageal echocardiography evaluation of the thoracic aorta. Ann Card Anaesth . 2016;19(Suppl 1):S44-S55.



  • When manipulation of the ascending aorta is not advisable, the use of proximal anastomosis sealing devices, such as the Heartstring Proximal Seal System (Maquet Cardiovascular, Wayne, NJ), is recommended. They allow for minimal manipulation of a severely diseased aorta.



  • In patients for whom this is not an option, and an aortic no–touch technique is the only possible course of action, composite grafting allows for multiple anastomoses.



  • When the aorta can be manipulated without concern, the standard sequence of events is as follows: (1) blood pressure is brought below 90 mm Hg; (2) an atraumatic side-biting clamp is applied; (3) small aortotomies are made with an aortic punch, followed by direct anastomosis of each of the free grafts to the ascending aorta; and (4) the partial clamp to fill the graft is released, avoiding a purse-string effect of the proximal anastomosis as one ties the suture.



  • If the surgeon plans to use a composite graft approach, the ideal site of the Y- or T-graft anastomosis is 1 cm distal the point of entry of the LITA into the pericardial sac, at the level of the left atrial appendage. This can be constructed in a Y or a T configuration, depending on which sequential anastomosis will be constructed first. For high proximal branches, such as a high diagonal (diagonal-LAD angle ≥ 90 degrees), ramus intermedius, or high marginal, a T approach is ideal because it allows an optimal lie of conduct once it is anastomosed in a diamond shape on those vessels ( Fig. 4.2A ). For more distal branches of the circumflex and right coronary artery, either a Y or a T graft will suffice, depending on the length of the available conduit (see Fig. 4.2B ).






    Figure 4.2


    T and Y configurations of the composite graft.




Heart Positioning





  • Skillful heart positioning is vital to maintaining stable hemodynamics while still allowing visualization of target arteries. The heart should move freely inside the pericardial sac and should not be squeezed or compressed against taut pleurae and the sternal borders. This can be achieved by releasing some of the pericardial sutures that hold the pericardial cradle up, specifically the right-sided sutures.



  • The heart can be elevated using three methods: (1) pericardial stitches (Lima stitch); (2) the deep stitch–sling technique; and (3) the use of suction-driven positioning devices.



  • Posterior pericardial stitches (Lima stitches) can be used to enucleate the heart; the number of stitches and location is a matter of surgeon preference. We place three sutures to the posterior pericardium. The first suture is placed anterior to the left superior pulmonary vein (LSPV) and below the phrenic nerve, the second is anterior to the left inferior pulmonary vein (LIPV) and inferior to the phrenic nerve, and the third suture is placed on the medial aspect of the inferior vena cava (IVC; Fig. 4.3 ). A Rummel tourniquet is then passed through each of these sutures to avoid injury to the epicardium. If each tourniquet is sequentially put under tension, the heart will lift incrementally and rotate medially. This will cause a broad posterior pericardial ridge, which helps herniate the heart from the pericardial sac, with its apex pointing to the ceiling. In most cases, these sutures allow for complete elevation of the heart without hemodynamic consequences.


Jan 26, 2019 | Posted by in CARDIAC SURGERY | Comments Off on Off-Pump Coronary Artery Bypass Grafting

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