Continuing Education Activity

The coronary artery bypass graft (CABG) procedure is used to improve blood flow to at-risk areas of myocardial tissues. When a patient requires subsequent CABG procedures, they may require additional perioperative management techniques and considerations. CABG is one of the most common cardiac procedures undertaken nowadays. With an aging population and high prevalence of coronary artery disease, a percentage of patients will require a second intervention which is mostly carried out in the form of percutaneous coronary intervention. Few will require a redo CABG for various reasons, which carries significant risk as a redo procedure and requires specific measures for work up to avoid complications. This activity reviews the management of patients undergoing a redo CABG procedure and explains the role of the interprofessional team in managing patients who undergo redo CABG.

Objectives:

• Identify the indications of repeat revascularisation.
• Review the challenges anticipated with redo sternotomy in general and redo CABG in particular.
• Describe the surgical approach and myocardial protection strategy in redo CABG as well as conduit selection.
• Summarize the importance of secondary prevention measures.

Introduction

Advances with percutaneous coronary interventions have led to a reduction in repeat coronary artery bypass grafting.[1] As the population ages, the risk profile of these patients increases, creating a challenging situation for the surgeon and the team involved. Redo sternotomy increases the risk of mortality due to the increased risk of graft injury and subsequent myocardial injury upon sternal re-entry.

Redo coronary revascularisation provides a peculiar challenge to cardiac surgeons and carries one of the highest mortality rates amongst redo cardiac surgeries, either isolated or in combination with other pathologies. This requires the establishment of a solid indication in the absence of any other alternative as well as specific work up to obtain the relationship between different anatomical structures, including previous patency and location of grafts.[2][3][4]

Another challenge that the surgeon faces in this situation is that of myocardial preservation in the presence of patent coronary artery grafts. During cardiopulmonary bypass, the most common way to preserve the myocardium is by applying a cross-clamp to the ascending aorta diverting the blood from the heart-lung machine away from the heart towards the rest of the body and infusing a cold, potassium-rich solution in the aortic root to perfuse the coronaries and arrest the heart in diastole; bringing down the metabolic activity.

The presence of patent grafts maintains a continuous flow of normal warm blood with low potassium content to the heart, which negates the protective effects of cardioplegia and restores electrical activity leading to a resumption of cardiac contractility. The isolation of any patent grafts is, therefore, crucial for a successful redo CABG to allow for a safe procedure.[5]

Anatomy and Physiology

Coronary artery disease requiring intervention is managed either by PCI or bypass grafting. Anatomically, the coronaries arise as two main arteries (left and right) from the sinuses of Valsalva, traveling along the surfaces of the heart. The left coronary commonly bifurcates into the left anterior descending and circumflex arteries, and the right continues along the right border of the heart to end as a posterior descending artery in 50% of the population. This configuration is important in redo surgery in the context of determining different areas of the myocardium, which are subject to ischemic insult.

Previous grafts normally travel within the pericardial cavity, mostly in the pericardial sinuses, to connect the proximal aorta to the coronary targets. This is of particular importance as these would normally cross the midline at different levels and will inadvertently lie in close proximity to the sternum, exposing them to the risk of injury during redo sternotomy. Commonly, the left internal mammary artery (LIMA) is used to revascularize the LAD, which supplies the interventricular septum and a considerable area of the anterior surface of the heart. The LIMA graft is considered the most important as patency rates are excellent compared to other types of grafts. The proximity of these structures to the sternum should be assessed with the help of a preoperative CT chest.

Patients presenting with ischemic heart disease symptoms and evidence of myocardial ischemia due to coronary artery disease after receiving an initial CABG procedure require coronary angiography to visualize the native coronary artery anatomy as well as the patency of previous grafts. This is coupled with echocardiography to assess myocardial contractility and valvular function. In some cases, myocardial viability studies (i.e., cardiac MRI) are needed to determine the ischemic burden and benefit of revascularization. ECG gated CT scans are of particular value to assess patent coronary grafts in cases where coronary angiography is not advisable. Cases with aortic valve infective endocarditis carry a high risk of thromboembolism during coronary angiography due to the physical manipulation of the catheter within the aorta, and a CT scan in these cases is a safer alternative. It also allows for a topographic map of the cardiac structures in relation to the posterior table of the sternum when planning re-entry.

Indications

In patients with a history of prior CABG, revascularization with either redo CABG or PCI may be indicated to either improve the symptoms or mortality, and indications are generally similar to that in patients with coronary artery disease.

Indications differ by the stage at which the patient presents with symptoms, and this can be split into early and late presentation following the initial procedure.

Early graft failure is one of the known complications of coronary artery bypass grafting. It has been reported to be up to 12% in some series.[6]

Although early postoperative graft problems are overlooked due to non-specific changes in ECG and echocardiographic findings, patients who clinically exhibit signs and symptoms of ischemia receive PCI with an effort to limit the extension of infarction. Stenting may be considered for native coronaries as well as LIMA grafts; however, redo CABG should be considered in case of anastomotic site stenosis or vein graft thrombosis.[7]

Per the American College of Cardiology and American Heart Association, the indications for primary CABG include the following: greater than 50% stenosis of the left main coronary artery, greater than 70% stenosis of the left anterior descending or the proximal circumflex arteries, patients that are asymptomatic or have mild, stable angina with the three-vessel disease, patients that have proximal left anterior descending stenosis with poor left ventricular function and three-vessel disease, a high-risk patient with stable angina that has one or two-vessel disease in an area of viable myocardium, a patient with a left ventricular ejection fraction of less than 50% and inducible ischemia seen on non-invasive testing with greater than 70% stenosis in the left anterior descending artery.[8] 

Redo CABG may be considered appropriate for similar indications as primary CABG in late presentation; however, due to increased surgical complexity and surgical mortality risk of redo CABG (generally three to four-fold higher than primary CABG) and with the improvement of percutaneous interventions, redo CABG procedures are becoming less frequent.[9]

In CABG patients presenting with stable angina, elective PCI is generally preferred over redo CABG in patients who have preserved LIMA graft to the LAD, have relatively limited or small areas of myocardial ischemia with suitable PCI targets and in those who have poor CABG targets. In patients who have extensive medical comorbidities with overall limited life expectancy, redo CABG is generally discouraged due to a relatively higher risk/benefit ratio and generally non-significant mortality benefit.

Redo CABG should be generally considered for patients who cannot undergo PCI due to technical reasons and in those patients who may potentially have a survival benefit with the placement of arterial conduit to LAD, such as in patients with new significant LAD stenosis. If redo surgical revascularization is felt to be high risk, PCI would be considered reasonable.

In general, the preferable approach is a heart team, an interprofessional approach comprising of general cardiology, cardiac surgery, and interventional cardiology team members. This discussion helps in reviewing various treatment options with regards to accounting medical comorbidities and ischemic areas involved and thus allows to best determine the feasibility and correctness of the revascularization procedure.

Contraindications

Contraindications are generally based on a risk-benefit assessment, with surgery avoided in the presence of suitable targets for PCI, low life expectancy, or when surgery carries prohibitive risk where the patient's clinical condition carries a significant risk of mortality with a redo surgical procedure.[1]

Redo CABG is usually contraindicated in cases where severe established myocardial infarction has taken place with extensive areas affected and no evidence of myocardial viability present. Patients with multiple comorbidities and low life expectancy normally will not benefit from the long term effect on survival, and discussion among the team and with the patients usually takes place to decide the best medical management.

Equipment

Personnel includes the surgeon, surgical assistants, anesthesiologist, operating room nurses and techs, and a perfusionist. Besides the presence of a primed cardiopulmonary bypass machine as with any redo sternotomy procedure, general and specific equipment is needed.

1. Defibrillation pads on induction as adhesions within the pericardium will prevent the application of internal defib pads to cardiovert arrhythmias during entry.
2. Blood should be ready for transfusion if needed.
3. Different arterial and venous cannulae should be available to allow peripheral access to establish CBP.
4. Redo sternotomy using an oscillating saw.

Preparation

Patients are prepped in the supine position exposing the whole body, neck to ankle. The decision about conduits is usually taken prior to induction, and a vein mapping might be required to allocate potential conduits as normally, saphenous vein grafts would have been used in the previous procedure. The arm can be prepped as well, in case a radial artery graft is needed.

Defib pads are applied in all redo sternotomy cases. Exposure of the groin is also required to allow for femoral access in an emergency situation.

Some surgeons will elect to expose the femoral vessels or even cannulate them prior to chest opening for two reasons. The first is to allow fast cannulation and control of the circulation by the heart-lung machine. The second is to allow patient cooling for cerebral and myocardial protection if bleeding is encountered or injury is inflicted on the previous grafts during re-sternotomy.

Technique or Treatment

Both on-pump and off-pump techniques have been employed with success.[10] The decision to go for on or off-pump depends on the surgical access required.[11] Although the duration of surgery is often much longer in redo CABG (vs. primary CABG), a significant portion of this is for the initial exposure and setting up the bypass circuit itself.

Most surgeons undergo the same general approach for initial exposure, to include median sternotomy. Often, surgeons will attempt to retrace a patient’s previous incisional scar. They will also need to remove sternal wires, sometimes with difficulty due to adhesions and scarring. In contrast to a primary sternotomy, most surgeons will not request for deflation of the lungs, as they anticipate a significantly longer period of time for dissection and exposure.

Minimally-invasive direct coronary artery bypass (MIDCAB) techniques are now being utilized more often. These include axillary artery to left anterior descending coronary artery graft via a small, intercostal thoracotomy, a left internal mammary artery to the left anterior descending coronary artery graft via a left, lateral thoracotomy, and a gastroepiploic artery to posterior descending artery graft via an inferior, subxiphoid approach.[12]

Surgical access depends on the vessels requiring revascularization. Various techniques are described in the literature, including on and off-pump approach. The incision is usually in the form of a redo midline sternotomy, excluding the previous scar. Some surgeons opt to cut the stainless steel wires and leave them in place to prevent the oscillating saw from traveling deeper. The anesthetist will usually hyperinflate the lungs in an effort to get them to lie between the sternum and the heart during the sternal opening.

Once the sternum is opened, retraction is not attempted until careful dissection of the heart (right ventricle) of the sternum is achieved to release the tension, with extra care taken on the left side to identify the left internal mammary graft if it has been used previously. The dissection is extended upwards until the innominate vein is freed since it might be avulsed during the application of the retractor.

The sternal retractor is applied. Slow retraction with gradual dissection of the heart from the adhesions is performed. The ascending aorta is identified to allow for safe cannulation if an emergency arises. Dissection usually commences from the diaphragmatic surface of the pericardium extending around to free the right atrium to allow cannulation for venous access then finally the apex identifying any grafts in the process.

Once the heart is free of adhesions and cannulation is feasible, heparin is given prior to inserting the arterial and venous cannulae.

Enough space for the aortic cross-clamp should always be thought of to allow safe cardioplegia. A retrograde cardioplegia cannula may be inserted via the right atrium into the coronary sinus to compliment the antegrade root plegia.

Patients are usually cooled down on bypass, and any patent grafts should be isolated and clamped to avoid perfusing the heart with warmer blood, which will wash out and counteract the effect of cardioplegia.

Targets are identified, and coronary artery bypass grafting is performed in routine fashion. In case no space is available in the ascending aorta for more grafts to be anastomosed, sequential and Y-grafts could be used.

Top ends could be done on cross-clamp or on side occluding clamp to avoid extra dosages of cardioplegia if feasible.

Once rewarming commences, and cross-clamp is removed, the clamps on old patent grafts, especially the LIMA, should be removed to avoid ischemic injury to the heart.

Atrial and ventricular pacing wires are usually applied, and weaning off bypass is commenced. As hemostasis is achieved, protamine is administered, and the venous cannula is removed, followed by the arterial one after the establishment of stable hemodynamics.

Complications

The biggest complication risk with a redo CABG is typically associated with the repeat sternotomy. Because of the scaring and adhesions that form after an initial sternotomy, a surgeon loses the definitive planes and anatomical clarity they may have experienced during the primary surgery. Complications of repeat sternotomy and dissection can include damage to the heart itself, the coronary vasculature (to include the still patent bypass grafts), the great vessels, the lungs, and any surrounding nerves (i.e., phrenic).[13] 

In addition, repeat CABG is often associated with higher bypass times, likely because of more extensive dissections and ischemic myocardium. Therefore, increased bypass time leads to increased inflammatory response, increased risk of infection, and increased coagulopathy. Finally, because of the higher chances of needed blood products during surgery, they are at an increased risk of transfusion reactions.[14][15]

Another risk associated with redo sternotomies where previous grafts present is intraoperative myocardial infarction due to thrombus dislodgment during manipulation of venous grafts, which carry a higher risk of thrombosis compared to arterial grafts.[16]

Clinical Significance

Redo CABG is a major encounter for both the patient and the team involved. More patients will need redo revascularization. The complexity of coronary artery disease is on the rise as the population ages.

Redo sternotomies carry significant mortality and morbidity and require meticulous preoperative assessment, thorough investigation, and experience of the surgeon and the team.

The importance of preoperative CT chest is emphasized, and this is usually coupled with a CT aorta to review the peripheral vessels for cardiopulmonary bypass access.

The surgical strategy should be communicated by the surgeon with the team, including the anesthetist and the perfusionist. This includes a plan to deal with issues during anesthetic induction, early exposure of femoral vessels to allow emergency cannulation if required, appropriate instrument availability and number and type of grafts to be used for particular targets.

Although this is normally the routine practice with any cardiac procedure, proper planning with such complex cases provides the team with the confidence to deal with any complications should they arise.

Enhancing Healthcare Team Outcomes

There is no doubt that the complexity of heart disease is on the rise. An aging population means an increased chance of second intervention with the increased use of percutaneous approaches. This is associated with a higher rate of comorbidities at the time of presentation. The introduction of heart teams is a recent approach in cardiac surgery; however, it has proven crucial in patients' outcomes, especially in complex cases.[17]

Although not extensively studied, the utilization of heart teams for patient selection for randomization in some RCTs showed the benefit of this approach.[18] The involvement of a heart team was suggested to provide better long term outcomes compared to blind randomization, as shown in the results of the EAST registry.[19]

The level of evidence when it comes to heart team involvement remains expert opinion (Level 5) due to the lack of large RCTs to compare results with and without the involvement of heart teams; however, the recommendation is Class 1 in consecutive guidelines since 2010.[20]

The benefit of a heart team is more pronounced in redo CABG, which is a major encounter for both the patient and the team involved. Decisions about the best timing and method of intervention are usually discussed in an MDT meeting to involve cardiologists, cardiac surgeons, anesthetists, perfusionists as well as nursing staff. The presence of a cardiothoracic radiologist is very important due to the complexity of the anatomical relationships in redo cases.

Preoperative assessment is crucial, which is usually done either in outpatient or inpatient settings by dedicated staff. This extends beyond the medical review to the patient's social circumstances and needs. Early involvement of physiotherapy and family liaison services ensure a plan is in place for when patients are out of the hospital. The decision of surgery is usually communicated to the patient by the surgical team after the MDT results. The consenting process requires great interpersonal skills, and the involvement of the patient's family is of great help.

Discussion between the surgeon, anesthesiologist, and perfusionist usually takes place prior to the procedure to determine the best cardiac protective strategies for the patient and bail out options in case of complications.

Postoperative care requires plans to be put in anticipation by the treating team, which involves surgeons, anesthesiologists, pharmacists, physiotherapists, and microbiologists.

Involving other specialties is needed in some cases, such as nephrology, neurology, and hematology, with various complications arising postoperatively.

Teamwork in cardiac surgery is fundamental to achieve the desired outcome for each surgical procedure.

Nursing, Allied Health, and Interprofessional Team Interventions

Nursing staff plays a fundamental role in the care after redo cardiac surgery:

Some units recruit specialized nursing staff for preoperative clinical and social assessment.

Postoperative care requires a high degree of experience and diligence by the nursing staff to be able to foresee possible complications early during the course of treatment.

Advanced practitioners such as advanced nurse practitioners and surgical care practitioners are involved deeper in patients' care than before, and the subspecialization in cardiac surgery provides continuity of care to the patients.

Allied healthcare professionals such as physiotherapists and social care provide the patient with means of fast recovery and advice clinicians on the safety of patients to be discharged.

Nursing, Allied Health, and Interprofessional Team Monitoring

Different pathways have been developed to facilitate interprofessional communication and monitoring. These pathways provide standardized protocols of care to eliminate human errors as much as possible. The use of clinical audit cycles by clinicians or nursing staff gives insights on different aspects of practice within the units, and all members of the heart team are encouraged to participate in these activities.