On-Pump and Off-Pump Coronary Revascularization Surgery

Abstract

Coronary artery disease is a lead cause of global mortality. Off pump coronary-artery bypass grafting (OPCAB) was developed to avoid complications of cardiopulmonary bypass and on pump coronary-artery bypass grafting (CABG). This chapter discusses the development of OPCAB and CABG, the general features and surgical procedures of both procedures, and the current literature and recommendations regarding both techniques.

FormalPara Main Messages

• 1. Off-pump coronary-artery bypass grafting (OPCAB) surgery was established to avoid complications related to cardiopulmonary bypass and aortic manipulation that accompany ON-PUMP coronary-artery bypass grafting (CABG); nevertheless, only 20% of myocardial revascularization procedures worldwide are performed off‑pump.

• 2. Several large-scale RCTs did not demonstrate differences in major adverse cardiovascular and cerebrovascular outcomes and some studies showed more frequent incomplete revascularization, reduced long term graft patency and mortality in OPCAB surgery. However, these RCTs did consistently show lower ventilation times, ICU stay and transfusion rates with OPCAB, with significant variability in experience with OPCAB techniques.

• 3. Until multivariable analysis of patients from these large-scale RCTs identify subgroups of patients who will benefit from OPCAB or on-pump CABG, and until the current guidelines are updated, the single absolute indication for OPCAB is severely atherosclerotic aorta.

• 4. Retrospective data from specific high-risk subpopulations suggest significant benefit from an OPCAB approach in females, in patients 75 years of age or older, and in patients with elevated Society of Thoracic Surgeons (STS) predicted risk score (>3%).

• 5. Absolute contraindications for OPCAB include cardiogenic shock, ischemic arrhythmia, anatomic factors preventing rotation of the heart, and urgent/emergent cases of left main coronary artery disease.

• 6. Balanced general anesthesia with narcotic and inhalation agent with or without regional anesthesia block is commonly used in OPCAB surgery, and the goal of early extubation and fast track recovery.

• 7. OPCAB can be very challenging in patients with cardiomegaly and severe left ventricular dysfunction, deep intramyocardial coronary artery targets, and anticipated need for endarterectomy or plasty.

Coronary artery disease (CAD) is the leading cause of hospital admissions and mortality worldwide. Coronary-artery bypass grafting (CABG) reduces mortality among patients with extensive coronary artery disease [1]. The first milestones in CABG development were without cardiopulmonary bypass (CPB) support (Table 35.1).

Table 35.1 History of the development of coronary artery bypass surgery (CABG)

Soon after the introduction of off-pump CABG (OPCAB), the need for a clean, still, and bloodless field was very noticeable, resulting in the introduction of on-pump CABG in 1967. This resulted in more ideal and reproducible results, with considerably better operating conditions, and was performed by a broad group of surgeons. The enthusiasm for on-pump gradually gave way to concerns about its safety, especially regarding complications arising from CPB (not specifically CABG). These concerns included micro-embolic showering during manipulation of the aorta and neurocognitive dysfunction, and CPB triggered whole-body inflammatory response due to contact activation of the complement cascade, leading to multiple organ dysfunction affecting the kidneys, liver, lungs, brain and heart itself. With on-pump, perioperative mortality is about 2%, and myocardial infarction, stroke, or renal failure requiring dialysis develop in an additional 5–7% of patients. The proportion of patients recovering without any complication was found to be only 64.3%. These and other observations, with the development of mechanical and pharmacological organ stabilizers and intracoronary shunts, revived OPCAB in the early 1990s.

General Features

Full median sternotomy is performed in both on-pump and OPCAB surgery. The type of harvested conduits used, and the technique for the actual suture anastomosis of the vessels are the same for both procedures. Both on-pump and OPCAB surgery differ in terms of: method of perfusion and pump-related complications; stabilization of operative field; cannulation; type of cross-clamp; and heparinization. In addition, OPCAB surgery requires specialized anesthetic management that focuses on short-acting medications, preservation of normothermia, aggressive hemodynamic support, early extubation and postoperative analgesia. A comparison of on-pump and OPCAB surgery is provided in Table 35.2.

Table 35.2 Comparison of features of on-pump and OPCAB coronary artery bypass surgery

Surgical Techniques of OPCAB Compared to On-Pump CABG

Preoperative Assessment

Preoperative assessment of patients undergoing OPCAB surgery requires the following:

• Careful history taking and thorough physical examination to investigate for the presence of risk factors associated with increased perioperative morbidity and mortality and to calculate the risk score to stratify and inform patients of their individual risk.

• Reviewing patient’s coronary anatomy and the extent of cardiac ischemia to choose the appropriate anesthetic approach.

• Discussion with the team regarding the surgical plan, the anesthesia management and sequencing of coronary revascularization in order to improve blood flow and myocardial oxygenation during subsequent anastomoses and cardiac displacement.

Premedication

Premedication includes:

• An intermediate-acting benzodiazepine (e.g. temazepam or lorazepam), administered orally 1 h before surgery, to reduce the patient’s anxiety.

• A β-blocker such as oral atenolol or metoprolol, at the time of premedication in order to prevent arrhythmia.

Operating Room Readiness

Operating room set-up procedures include:

• CPB machine ready for quick setup with a perfusionist in attendance.

• Temperature up to 24 °C, warming pad or mattress placed on the operating table, and use of air warming device.

• External pads connected to a defibrillator (internal pads and a pacemaker should also be available).

Monitoring

Monitoring include:

• A five-lead surface ECG (basic standard involves lead II and V5) with automated ST segment analysis.

• Oxygen saturation monitoring (pulse oximetry).

• Continuous urinary output (Foley catheter).

• End tidal carbon dioxide monitoring.

• Esophageal and rectal temperature.

• Arterial blood pressure by cannulating radial and/or femoral artery.

• Central venous pressure (CVP) catheter.

• Swan-Ganz catheters with continuous cardiac output and central venous oxygen saturation monitoring capability only used in very high-risk patients with poor ventricular function.

• Pacing pulmonary artery catheter can allow atrial or ventricular pacing if needed.

• Transesophageal echocardiography (TEE).

• Depth of unconsciousness in patients operated under general anesthesia (GA).

• Neuromuscular monitoring.

• Coagulation profile monitoring.

Pre-procedure Planning

Pre-procedural considerations include:

• Meticulous attention to details; this is critical to success, as the safety margin with OPCAB is reduced compared to traditional on-pump CABG.

• Every member the cardiac surgery team, including the surgeon, anesthesiologist, surgical assistant, nurse and perfusionist, should be educated in OPCAB protocols and the difference between conventional CABG and OPCAB. They should be prepared to go on cardiopulmonary bypass, if needed.

• Unlike on-pump where the anesthesiologist plays a passive role during the performance of bypass grafting, involvement of the anesthesia team is essential for successful OPCAB.

• The anesthesiologist should plan to inform the surgeon when administering vasopressors or inotropes, if there are ST segment or rhythm disturbances, and if the blood pressure is not responding to pharmacologic interventions.

• The surgeon should plan to communicate with the anesthesiologist prior to displacing the heart, occluding a coronary artery, inserting or removing a shunt, and especially when reperfusing the heart, since each of these procedures can be associated with significant hemodynamic disturbances during surgery.

Procedural Considerations

Anesthetic Considerations

In addition to providing safe induction and maintenance of anesthesia using a technique that minimizes myocardial ischemia, (the primary goal for any other coronary artery surgery), the anesthetic goals of management of OPCAB surgery should include: considering fast-track anesthesia; maintaining normothermia; and providing hemodynamic stability [2, 3].

Considering Fast-Track Anesthesia

Fast track anesthesia includes a balanced opioids and inhalational general anesthesia, rapid emergence and appropriate plan for postoperative care, which includes early extubation and ambulation along with excellent postoperative analgesia [4].

• It is currently the most commonly employed practice for OPCAB surgery.

• Research suggests that it is safe with no evidence of increased cardiopulmonary morbidity

• It is cost effective, and has many potential benefits including:

  • Improved postoperative hemodynamic performance

  • Earlier patient mobilization

  • Reduced risk of ventilator-associated pneumonia

  • Reduced ventilator-related costs

  • Shorter ICU time

  • Decreased hospital length of stay.

The three anesthetic approaches in OPCAB surgery [3] are:

• 1. General anesthesia (GA) with controlled ventilation, with balanced opioids and inhalation anesthesia or total intravenous anesthesia (TIVA).

• 2. Combined GA and regional analgesia with controlled ventilation using high thoracic epidural analgesia (TEA) or combined GA/intrathecal morphine (ITM). This approach can be beneficial, but further studies are required to verify the effectiveness of this technique and to determine the optimal dose of morphine, which provides adequate analgesia with minimal risk of respiratory depression (an impactful side effect during the postoperative period).

• 3. Awake regional anesthesia with spontaneous ventilation using TEA alone. The feasibility of this technique has been confirmed, but not the safety and effectiveness.

Anesthesia induction and maintenance commonly employs an induction dose of propofol with low dose of narcotic and balanced concentration of neuromuscular blocker and inhalational agent.

• Narcotics:

  • Remifentanil, sufentanil and fentanyl [5]. No benefit has been shown with the use of one agent over the other.

• Neuromuscular blockers:

  • Short acting neuromuscular blockers (cisatracurium, rocuronium or vecuronium) are recommended.

  • If a long-acting neuromuscular blocking agent such as pancuronium is used, care should be taken to avoid intermittent re-bolus, and neuromuscular blockade should be reversed before extubation.

• Inhalational agents:

  • Shorter acting agents, such as sevoflurane and desflurane, are beneficial with operating room extubation as a goal in applicable patients.

Management of postoperative analgesia options include:

• Most commonly titrating intravenous morphine with or without nonsteroidal anti-inflammatory drugs (NSAIDs) prior to the end of surgery.

• Prolonging the infusion of remifentanil (expensive) using higher doses to achieve an adequate level of analgesia.

• The use of dexmedetomidine (an ideal anesthetic adjuvant with no antiemetic effects) might lead to a better postoperative pain control by reducing intra-and postoperative consumption of opioids and better hemodynamic stability in some centers.

• Single shot spinal morphine prior to anesthesia induction or continuous epidural catheter have been used for postoperative analgesia.

Maintaining Normothermia

Maintaining normothermia (34–36 °C) is extremely important in optimizing patient outcomes and hemodynamic stability during OPCAB.

Postoperative hypothermia can increase the risk of:

• 1. Myocardial infarction

• 2. Wound infection

• 3. Blood loss

• 4. Extended anesthesia care

• 5. Prolonged recovery and hospitalization

Passive and active warming techniques to prevent unintentional hypothermia include:

• 1. Blankets and a hypothermia prevention cap.

• 2. Preheating the OR to 24 °C before set-up begins; the room temperature can then be cooled to a comfortable level for the surgical team.

• 3. Applying a Cath Lab blanket around the patient’s head and sides before starting the procedure.

• 4. Using warmed irrigation fluids intraoperatively.

• 5. Using warmed IV fluids.

• 6. Using a blood warmer.

• 7. Warming and humidifying ventilator gases by an airway heat/moisture exchanger.

Providing Hemodynamic Stability

It is vitally important that the anesthesiologist continually observes and treats the hemodynamic and rhythm responses throughout OPCAB surgery, but especially during cardiac manipulation and regional ischemia. Three critical events associated with hemodynamic instability—vertical displacement of heart; cardiac compression from myocardial stabilizer; myocardial ischemia during coronary artery occlusion for anastomosis. Prior to heart manipulation and positioning, the blood pressure should be elevated at least 20% above baseline using IV vasopressor bolus and Trendelenberg positioning.

Hemodynamic goals can be achieved through:

• 1. Fluid management

• 2. The use of table positioning. Using Trendelenburg positioning will fill the heart maximally and increase blood pressure. Rolling the table to the right allows gravity to pull the heart over and provides access to the back wall when the surgeon works on the diagonal and circumflex vessels.

• 3. The use of small boluses of nor-epinephrine or levophed to support blood pressure and cardiac output, but all efforts should be made to avoid significant inotropic or vasopressor support.

A simplified approach to the diagnosis and management of different causes of hemodynamic instability during OPCAB [6] is shown in Fig. 35.1.

Fig. 35.1

Diagnosis and management of hemodynamic instability during OPCAB surgery. (Reprinted with permission from Couture et al. Mechanisms of hemodynamic changes during off-pump coronary artery bypass surgery. Can J Anesth. 2002:49:835–859). CABG coronary artery bypass grafting, CVP central venous pressure, CO cardiac output, HR heart rate, IV intravenous, IVC inferior vena cava, MR mitral regurgitation, MV mitral valve, NTG nitroglycerin, AP pulmonary artery pressure, RWMA regional wall motion abnormality, SVR systemic vascular resistance, TEE transesophageal echocardiography

Surgical Considerations

Initial Stage Considerations

• A traditional sternotomy is performed.

• The left IMA should be made as long as possible in order to avoid excessive tension when the heart is elevated after the graft until the LAD is performed. Skeletonization of LIMA is preferable as maximal length is achieved in shortest time.

• Total arterial revascularization is feasible with OPCAB and the 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 s. The ACT should be checked every 30 min with heparin supplemented as needed.

Exposure of the coronary arteries:

• During OPCAB, the surgeon needs good coronary artery exposure in order to be able to position the heart without affecting its natural ability to pump; therefore, extra time should be allowed to obtain the best presentation and stabilization.

• If adequate exposure cannot be obtained, the anastomosis should not be compromised and the traditional approach should be used.

• Anatomic structures in the chest cavity, including the sternum, pleura and pericardial edge should be assessed first prior to positioning the heart, as they can compress the heart and lead to decreased cardiac output and hemodynamic instability during OPCAB.

Positioning the Heart

Positioning the heart for OPCAB surgery is a balance between achieving good exposure and maintaining hemodynamic stability. Communication between surgeon and anesthesiologist is a critical component of successful surgery.

Proper positioning and stabilization are critical for the success of OPCAB and can be achieved by many available dedicated instruments:

• 1. Suction devices: These devices have a flexible arm that can be adjusted and tightened to make rigid, as well as clips by that can be attached to the sternal retractor. There are two types of suction devices:

  • (a) A cup-shaped device that is placed on the apex of the heart to position and stabilize.

  • (b) A two-pronged foot, where the prongs are placed on either side of the segment of artery being grafted to stabilize that region of the heart.

• 2. Tape and snare: A broad tape (or a small pack) is fixed to the posterior pericardium between the right and left superior pulmonary, which is then snared. Traction on the tape and the snare serves to lift the apex of the heart.

• 3. Direct pressure stabilizers: These are simple rigid systems that use metal plates to stabilize the area being grafted by pressing down on it. They do not stabilize as effectively as the suction devices, and tend to cause more hemodynamic compromise. These devices are used more in mini-thoracotomy coronary surgery, because they are less bulky than suction stabilizers and are reusable.

Drawbacks of using stabilizers:

• 1. Myocardial bruising can be caused when suction is too high.

• 2. The phrenic nerve can be injured when widely opening the pleura.

• 3. The descending aorta and esophagus can be damaged if stay sutures are placed too deep in the pericardium.

• 4. Cardiac output can be reduced by compressing and distorting the heart.

Sequence of Anastomoses

The coronary arteries should be grafted in order of increasing cardiac displacement: the anterior wall vessels followed by inferior wall vessels, and finally, lateral wall vessels. Therefore, the LIMA to LAD graft is usually first, followed by the inferior wall grafts (PDA, RCA), and the lateral wall grafts (OM) are usually last. The guiding principle is that more cardiac displacement is tolerated with increasingly complete revascularization. Although the proximal anastomoses can be performed before or after the distal anastomoses, completing the proximal anastomosis first has the advantage of immediate perfusion through the graft after the completion of the distal anastomosis. Proximal occlusion of the 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). Anastomosis of the obtuse marginal vessels is easier from the left side of the table. Temporary pacing wires should be placed before occluding the right coronary artery proximal to the bifurcation to manage possible A-V block. A CO₂ blower is crucial for beating heart surgery but must be used very carefully at a flow rate not >5 L/min, to prevent damage to the coronary endothelium. Directing the gas jet directly into the vessel lumen must be avoided to prevent gas embolization or intimal dissection.

Managing Myocardial Ischemia

Reducing myocardial ischemia during OPCAB can be achieved by:

• 1. Increasing oxygen delivery by:

  • (a) Maintaining an adequate mean arterial pressure (MAP): This is the most important maneuver to decrease myocardial ischemia.

  • (b) Using intra-coronary shunts: Inserting a small shunt into the coronary artery is extremely useful in minimizing the amount of ischemia and improving the safety of the operation as it can provide:

    • (i) Distal perfusion,

    • (ii) A bloodless field

    • (iii) A guide for the placement of anastomotic sutures.

  • (c) Nitrates: Nitroglycerin (NTG) has been used to treat active ischemia; however, it decreases preload and can be detrimental when higher filling pressures are needed to ensure optimal ventricular filling.

• 2. Reducing the oxygen consumption through a decrease in HR and contractility as well as decreasing the occurrence of arrhythmias. The following pharmacological prophylaxis can be used:

  • (a) Perioperative use of β-blocking agents such as esmolol or metoprolol.

  • (b) Calcium antagonists such as diltiazem.

• 3. Increasing tolerance to ischemia (preconditioning), which could be:

  • (a) Mechanical: Though on the decline, ischemic preconditioning, by coronary occlusion followed by a period of reperfusion, can also increase the tolerance to ischemia and can be used as a technique of myocardial protection.

  • (b) Pharmacological: Using isoflurane and sevoflurane can activate a preconditioning mechanism when administered at minimum alveolar concentration at least 30 min before ischemic insult.

Total Arterial Grafting Without Aortic Manipulation (No-Touch Strategy)

• An extension of OPCAB designed to optimize graft patency of arterial grafts and minimize stroke risk.

• This technique is associated with the lowest stroke rate.

• It is accomplished by using single or double IMA with sequential grafting.

• Depending on the coronary anatomy and available conduits, there are several potential graft–target arrangements:

  • Bilateral IMAs with radial arterial/saphenous vein T/Y-graft(s)

  • Bilateral IMAs with radial artery/saphenous vein extension(s)

  • K-grafts IMAs with arterial graft(s)

Heparin Reversal

• Although heparin reversal is not mandatory, one-half of the calculated protamine dose can be administered.

On-Pump Versus OPCAB in the Literature

OPCAB surgery was established to avoid complications related to CPB and aortic manipulation that accompany OPCAB. Nevertheless, despite the initial enthusiasm on this technique, only 20% of myocardial revascularization procedures worldwide are performed off-pump. In large retrospective studies of surgical revascularization, OPCAB has outperformed on-pump for major outcomes including risk-adjusted operative mortality [7, 8]; however, these studies were challenged by selection bias that led to several large-scale randomized controlled trials (RCTs) [9,10,11,12,13,14,15,16,17]. Several large-scale RCTs did not demonstrate differences in major adverse cardiovascular and cerebrovascular outcomes and some showed increased death, more frequent incomplete revascularization and reduced long term graft patency for OPCAB [18]. However, these RCTs did consistently show lower ventilation times, ICU stay and transfusion rates with OPCAB and importantly, there was significant variability in experience with OPCAB techniques. Retrospective data from specific high-risk subpopulations suggest significant benefit from an OPCAB approach in females, patients 75 years of age or older and patients with elevated STS predicted risk score (>3%). The details of these RCTs and their follow-up data are summarized in Table 35.3.

Table 35.3 Major randomized controlled trials comparing on-pump with OPCAB revascularization

Current Recommendations

Recommendations for On-Pump CABG in the Practice Guidelines

Clinical guidelines on on-pump CABG have been issued by the American College of Cardiology (ACC)/American Heart Association (AHA), the European Society of Cardiology (ESC)/European Association for Cardio-Thoracic Surgery (EACTS) and the Society of Thoracic Surgeons (STS) [19,20,21,22,23]. A summary of the recommendations provided by these guidelines is shown in Table 35.4.

Table 35.4 Indications for on-pump CABG in the guidelines

Recommendations for the preoperative and postoperative management of antiplatelet therapy in patients undergoing CABG have been provided by the same organizations [24, 25] and are summarized in Table 35.5.

Table 35.5 Antiplatelet therapy in patients undergoing CABG

Recommendations for OPCAB in the Practice Guidelines

The issue of off- versus on-pump approaches to CABG surgery was only addressed by the 2011 ACC/AHA Guidelines for CABG Surgery and the 2014 ESC/EACTS Guidelines on Myocardial Revascularization.

In the ACCF/AHA Guidelines, no formal recommendation was given, but the concluding remarks focused on the avoidance of aortic manipulation, regardless of an on- versus off-pump approach in patients with evidence of aortic atherosclerotic disease, acknowledging that this may be more readily achieved with an off-pump approach.

The European Task Force in 2014 had the benefit of more robust data to make the following recommendations:

• 1. OPCAB and/or no-touch on-pump techniques on the ascending aorta are recommended in patients with significant atherosclerotic disease of the ascending aorta in order to prevent perioperative stroke as a Class I.

• 2. OPCAB surgery can be ‘considered’ for subgroups of high risk patients in high-volume off-pump centers as a Class IIa.

Subsequent controlled trials and a large volume of retrospective database evidence suggest that complexity of the debate between off- versus on-pump approaches may revolve around surgical expertise and patient, with major points of argument are generally summed up as follows:

Pro-OPCAB Arguments:

• 1. Reduction of neurocognitive dysfunction by avoiding cannulation and aortic cross-clamping.

• 2. Avoidance of the systemic inflammatory response and its postoperative sequelae.

• 3. Decreased blood product use with better postoperative pulmonary and renal function.

Pro ON-PUMP Arguments:

• 1. Incomplete revascularization with OPCAB, which translates into poorer long-term graft patency.

• 2. Emergency conversion of OPCAB into on-pump resulting in higher mortality.

• 3. Higher degree of technical difficulty of OPCAB, with no proven advantage for clinically-important outcomes.

Multivariable analysis involving thousands of patients in the reported large RCTs will likely identify subgroups of patients who will benefit from on-pump or OPCAB CABG. When this occurs, the procedure that is best for the patient can be selected. Until this occurs, and until the current guidelines are updated, the following recommendations can be made:

• 1. The single absolute indication for OPCAB, which can be used to accomplish a completely no-touch aorta technique, is severely atherosclerotic aorta.

• 2. OPCAB surgery might be associated with more favorable outcomes in patients presenting with the following risk factors:

  • (a) Elevated STS predicted risk score (>3%).

  • (b) Patients 75 years of age or older.

  • (c) Female.

  • (d) Acute/subacute STEMI.

  • (e) Repeat revascularization.

  • (f) Renal failure.

  • (g) Previous stroke/cerebrovascular disease.

• 3. Absolute contraindications for OPCAB include:

  • (a) Cardiogenic shock.

  • (b) Ischemic arrhythmia.

  • (c) Anatomic factors preventing rotation of the heart.

    • (i) Previous left pneumonectomy.

    • (ii) Severe pectus excavatum.

  • (d) Urgent/emergent classes left main coronary artery disease.

• 4. Factors that can make OPCAB very challenging:

  • (a) Cardiomegaly Severe left ventricular dysfunction.

  • (b) Deep intramyocardial coronary artery targets.

  • (c) Anticipated need for endarterectomy or plasty.