Median sternotomy is the most frequently performed incision in cardiac surgery. It allows excellent exposure and access but also immediate control of all cardiac and vascular structures for most of the surgical procedures in adult and pediatric cardiac surgery. Due to the low perioperative mortality following primary surgery and the improved long-term survival of both pediatric patients following repair of congenital malformations and adult patients following coronary artery bypass grafting and valve and aortic surgery, the number of patients who require two or more cardiac operations is increasing. For this reason, redo-sternotomy has become a common procedure in cardiac surgery with an incidence between 1% and 15% per year; depending on the institutional experience with such procedures, the perioperative risks have significantly decreased. However, the increasing trend to proceed with transcatheter interventions (percutaneous coronary interventions and transcatheter valve repair and replacement) has been recently observed to minimize access and the overall trauma of a conventional cardiac operation and to accelerate recovery. These less-invasive options tend to reduce the necessity for conventional reoperative heart surgeries and are welcome, especially for older and high-risk patients.
General principles and indications for a redo cardiac surgery procedure
Strategies on how to plan a reoperative cardiac surgery have been established to minimize all technical risks due to redo-sternotomy (injuries to cardiac and vascular structures, life-threatening arrhythmias) and therefore to optimize outcomes. The increasing importance of multidisciplinary boards to discuss all potential therapeutic options and define the most suitable solution for each patient has been emphasized in recent guidelines. Depending on the situation, such boards may include cardiovascular radiologists, cardiologists, cardiac surgeons, cardiovascular anesthesiologists, hematologists with a special interest in transfusion medicine, intensive care specialists, and perfusionists. During the board discussion, the personalized approach must balance the risks and benefits of every procedure for each individual patient. Since the advent and dissemination of catheter-based procedures (percutaneous coronary intervention, transcatheter aortic valve implantation, transcatheter edge-to-edge repair of the mitral valve, and other less invasive technologies), every option should be analyzed, taking into account the overall risk profile of every patient (age, comorbidities, risk factors, frailty, life expectancy); the general intraoperative risks; the expected technical challenges; the incidence of perioperative complications; the benefit of a surgical versus transcatheter procedure; and the potential for the most expedient and complete rehabilitation. Finally, the wish of the patients has found broader recognition in the decision of the multidisciplinary teams in the most recent guidelines.
Considerations about prophylactic/protective techniques at initial surgery to facilitate a reoperative procedure
There are a few technical particularities that can be applied during the initial surgery that may considerably reduce the risks of a subsequent redo-sternotomy. Among them, closure of the pericardium whenever possible is the simplest, particularly in the presence of a somewhat prominent ascending aorta. , However, in some cases, closure of the pericardium over the cardiac cavities is not possible because this would compress the ventricles during the immediate postoperative phase and therefore significantly reduce cardiac performance.
In some situations (coronary artery bypass grafting, congenital surgery, left ventricular assist device [LVAD] implantation), it might be wise to use a thin synthetic pericardial membrane, especially when a redo-operation might be expected in the future. , The brachiocephalic vein should not be denudated from the surrounding fat (thymus) tissue; this probably helps minimize the risk of a subsequent injury in the case of a redo-sternotomy.
Another important detail in coronary artery bypass surgery is the positioning of the bypass grafts. Creation of a small lateral pericardial window to pass the left internal thoracic artery from the left pleural cavity to the pericardial space is useful as this creates a small groove between the left lung and the pericardium, and the internal thoracic artery falls down into this space and is not pushed into the middle of the mediastinum by the expanding left lung. A similar strategy is recommended for the positioning of the right internal thoracic artery when it is used to revascularize the left coronary system; to pass it through the transverse sinus posteriorly to the aorta and the main pulmonary artery may avoid injury at the time of a redo-surgery. Finally, whenever possible, radial artery and saphenous vein grafts should not cross the midline (over the right ventricle) nor lie directly behind the sternum. As a general strategy, a complete arterial revascularization will be followed by fewer redo-coronary artery bypass grafting procedures because of the better long-term patency of arterial grafts.
Value of imaging
Conventional chest x-ray with a lateral projection might help identify the close relationship between the anterior wall of the right ventricle and the aorta with the posterior surface of the sternum, but it is never as precise as a native or contrast computed tomography (CT). A CT scan of the chest with intravenous contrast application allows proper evaluation of the proximity of the brachiocephalic vein, the great vessels, and the right ventricle to the sternum, and in case of a prior coronary artery bypass grafting procedure, it will demonstrate the position of the bypass conduits in relation to the sternum and the great vessels. This information has major practical consequences as it will help in deciding in which cases preventive insertion of catheter wires for transcutaneous cannulation or even prior cannulation (with or without prophylactic institution of cardiopulmonary bypass) would be reasonable before sawing the sternum. Figs. 5.1 and 5.2 depict some potentially high-risk anatomic situations that may be encountered in reoperative cardiac surgery.
Potentially high-risk situation for reoperative cardiac surgery: the ascending aorta lies in immediate continuity with the posterior surface of the sternum.
Potentially high-risk situation for reoperative cardiac surgery: the right atrium is adherent to the posterior surface of the sternum in a case of severe pectus excavatum.
Technique
Anesthesia induction and maintenance are similar to those performed for conventional primary surgery using a standard endotracheal tube. (A double-lumen tube is useful when the approach for reoperative surgery is performed via a right lateral thoracotomy.) The standard monitoring for open heart procedures (i.e., transesophageal echocardiography, electrocardiography, and near-infrared spectroscopy, including arterial and central venous lines) is used. Carbon dioxide (C o 2 ) with a flow of 2 liters per minute is continuously insufflated into the operating field throughout the procedure. No special surgical equipment that differs from that for conventional surgery is necessary, excepting a series of traumatic clamps ( Figs 5.3 and 5.4 ) to tightly close the skin in case of major bleeding. This is a very effective method to avoid exsanguination before cardiopulmonary bypass can be instituted and blood retransfused via the circuit.
Traumatic clamp to allow provisory tight (hemostatic) closure of the sternal incision in case of unexpected major bleeding requiring emergency peripheral cannulation.
View of a virtual sternotomy incision with several traumatic clamps in place.
Preliminary safety measures
Before disinfection and draping, disposable gel pads are placed in the midaxillary line on each side for external cardioversion if necessary. This is important to safely manage situations where the patient develops ventricular tachycardia or ventricular fibrillation before the heart is dissected and an internal defibrillator could be used. It is strongly recommended to have one groin region (usually the right one) disinfected and free for potential emergency cannulation. In addition, the perfusionist should be available in the operating theater, the cardiopulmonary bypass circuit should be filled before sternotomy, and the lines of the circuit should be available on the operating table.
The cannulation strategy (timing and location) for cardiopulmonary bypass is one of the most important points for a safe reoperative procedure. Central cannulation as usual is the preferred strategy if sternal re-entry is expected to be low risk on preoperative imaging. When central cannulation is planned, the aorta should not be calcified in the area of cannulation and clamping. The right atrium should be easily accessible without major manipulation. If central aortic cannulation is judged to be challenging, right subclavian artery cannulation through a separate subclavicular incision is performed. Cannulation of the artery can be done directly (using Seldinger’s technique or through a small surgical cut) or using an 8- or 10-mm vascular graft anastomosed end-to-side to the artery. Methods preserving the distal perfusion in the upper extremity are preferred. Subclavian artery cannulation has been established as a valuable alternative to femoral artery cannulation as the latter comprises the risk of embolization of atherosclerotic aortic particles or thrombi during retrograde perfusion.
Reopening the sternum
As for a primary sternotomy, the skin incision might extend from 2 to 3 cm below the suprasternal notch to a point situated at the distal end of the xyphoid process ( Fig. 5.5 ). Usually the skin is very mobile, and patients enjoy a limited skin scar, especially in the cranial part. The prior scar is excised when it is hypertrophic or when a keloid has developed, and the subcutaneous tissue is gently mobilized to avoid tension when the wound is closed at the end of the operation. Hemostasis of the subcutaneous tissue is performed meticulously, particularly when the patient is operated under antiplatelet drugs or oral anticoagulation. There might be a small transversal vein in the region of the suprasternal notch that should be coagulated with the electro-knife or ligated if possible. When bleeding is important, packing with a compress is useful, and definitive hemostasis will be performed once the sternum has been opened.
Following skin and subcutaneous incision, the sternal wires are removed either completely or only in their anterior location to give some posterior resistance against the saw. At the inferior part, the abdominal fascia is incised over the xyphoid in the midline.
In reoperative cases only, it might be wise to extend the incision at the inferior level below the xyphoid to allow visualization and/or dissection of the underlying heart and pericardium from the posterior aspect of the sternum. The subxiphoid plane is developed widely to include the diaphragmatic surface and rectus muscle. Subcostal adhesions to the pericardium can be divided, and a space is freed in this plane up to the costal margin on both sides ( Fig. 5.6 ). Thereafter, sharp retractors help lift the costal margin and indirectly the sternum. At this time, a small visible area of the anterior wall of the right ventricle is visible when the inferior pericardium has been left open and can be dissected from the posterior table of the sternum.
Advantage of the incision slightly below the level of the xyphoid. This allows visualization and preparation of subcostal adhesions to the pericardium after some soft tissue is dissected from the abdominal fascia. Lifting the costal margin anteriorly helps to dissect the most inferior part of the right ventricle free from the posterior surface of the sternum.
In my practice, I always excise the wires; it is important to analyze the preoperative conventional chest x-ray before surgery to be informed about the number and types (simple or double loop) of wires. However, some recommend removing the anterior portion of the wires only to create some posterior resistance when sawing is performed as this may protect against excess downward penetration and myocardial injury by the saw. Once the wires have been removed, the midline should be identified either by palpation of the costosternal articulations or, once the subcutaneous tissue has been opened, the midline is located usually between the medial insertions of the pectoral muscle. Before sawing, the proper site for splitting the sternum can be marked with electrocautery. Especially in reoperative surgery, unequal division of the sternum may render closure at the end of surgery difficult since the wires may tear through an unequal width of the sternum or injure the articulations between the ribs and the sternal body.
A standard oscillating saw is used (alternatively a micro-sagittal saw that can be used with one hand only) that allows good tactile feedback when the posterior cortical bone of the sternum is split. This type of saw is heavier, somewhat slightly more cumbersome to handle, and requires some practice for the surgeon to sense when the blade is penetrating the posterior corticalis of the sternum. During sawing, small retractors are inserted into the bone marrow on both sides of the sternum incision and gently lifted anteriorly by the assistant ( Fig. 5.7 ). Using a thin sucker very close to the saw avoids blood squirting out of the wound, and it improves visualization of the operative field. This facilitates further preparation of the adhesions between the sternum and epicardium of the right ventricle. Sometimes, scissors can be introduced within the narrow space between both sternal halves and gently spread to completely open the posterior table of the sternum. During these maneuvers, excessive traction of the retractors should be avoided as this may lead to tears in the underlying right ventricle. The adhesions can be prepared with scissors or better with electrocautery; the plane of dissection must remain close to the posterior sternum surface ( Fig. 5.8 ).
Once the costal margins can be lifted anteriorly, the oscillating saw is used to divide the sternum. The anterior cortical layer of the bone is split first on the full length and during continuous anterior tension, the posterior table is divided in a second step. Particular care is needed to avoid excessive tension that may tear the anterior wall of the right ventricle.
Once the sternum has been opened on its full length, dissection of adhesions between the sternum and the pericardium (if the latter had been closed at initial surgery) or between the sternum and the right ventricle (in case the pericardium had been left open) is performed. Electrocautery is used to achieve immediate perfect hemostasis, and the plane of dissection is kept very close to the sternum. This step is performed on both sides under slight anterior traction with sharp retractors.
Once the sternum has been divided along its full length, a small sternal retractor can be inserted that will provide visualization of the anterior mediastinum. Care is taken to open it very gently as already minimal overstretching of the right ventricle and brachiocephalic vein may cause a catastrophic injury of these structures. In most cases, it is helpful to open both pleural spaces and lower the inspired tidal volumes to allow the mediastinum to fall away from the sternum. Opening the pleural cavities also facilitates the introduction of a sternum spreader and may help to avoid injury to the cardiac structures. Usually, the preparation starts at the inferior aspect along the diaphragmatic surface of the right ventricle, because at this level it is easy to find the correct plane and the adhesions can be easily split. The dissection can then be performed cranially, along the right atrium and then along the ascending aorta, which is usually easy to identify by palpation ( Fig. 5.9 ). The pericardial edge is stay-sutured and pulled up to facilitate the separation of the right atrium. Dissection is better performed sharply with scissors and/or electrocautery than blunt with fingers as blunt digital dissection may easily result in tears of the right ventricle, particularly in older female patients with a very thin anterior wall of the ventricle. Care who has to be taken not to enter the epicardial fat tissue of the ventricle; this can easily be perceived because venous oozing or bleeding from the epicardial veins may occur. In this case, the full thickness of epicardial fat tissue should be left on the heart surface. Another danger is denudating the aorta when the proper plane of dissection is not correct. In this situation, the adventitial layer (which is sometimes confounded and perceived as pericardial layer) is dissected away from the aorta, leaving a friable residual wall that may be further weakened by preparation, purse-string sutures, or later cross- or tangential clamping. These types of lesions are challenging because any efforts to repair the tear, even through very fine sutures of 5.0 or 6.0 polypropylene, may cause additional damage and end up in a major defect of the aortic wall. If the proper plane for aortic preparation is difficult to identify, dissection can be started at the level of the proximal arch where the aorta has not been touched at initial surgery. At this location, it is easier to find the proper plane and gently prepare more proximally to identify the suture material used for previous cannulation. At this place, the preparation of the brachiocephalic vein from the ascending aorta may be easier.
Once enough posterior surface of the sternum has been prepared (this is especially the case when both pleural cavities have been opened at an early stage), a small Cooley retractor is placed and gently opened. Further preparation within the pericardium starts at the diaphragmatic aspect of the heart because here it is rather easy to find the most optimal dissection plane. The preparation is carried toward the right along the right atrium and then in the direction of the ascending aorta, which is easily located by palpation.
Potential injuries and their management
A simple grading of cardiac injury during re-entry sternotomy was proposed by O’Brien and colleages several years ago that may be useful to unify the classification when reporting on such injuries ( Table 5.1 ).
TABLE 5.1
Grading of Cardiac Injury on Re-sternotomy
From O’Brien MF, Harrocks S, Clarke A, Garlick B, Barnett AG. How to do safe sternal reentry and the risk factors of redo-cardiac surgery: a 21-year review with zero major cardiac injury. J Card Surg . 2002;17:4-131.
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Injury to the brachiocephalic vein
Injury of the brachiocephalic vein must be suspected when major venous bleeding occurs during sawing at the upper end of the sternotomy. In case of massive bleeding that can’t be controlled because the sternum cannot yet be spread, packing and rapid peripheral institution of cardiopulmonary bypass may be necessary to retrieve blood into the circuit. If bleeding appears after sternum spreading, small injuries can be treated with simple sutures, keeping in mind that the wall of the vein is very thin. Therefore, 5.0 or better 6.0 polypropylene suture is the ideal monofilament material to be used. To allow a tension-free stitch, the sternum spreader should be somehow turned back. Care should be taken not to fix a central venous catheter introduced through the left internal jugular vein. Before reopening the retractor, the vein should be dissected free from the posterior surface of the manubrium on both sides.
In case bleeding can’t be controlled by soft pressure with gauze or a small clamp, blockage using one or two Fogarty balloon catheters may be the less traumatic method to control the situation. In such cases, the vein must again be dissected from the posterior sternal surface and repaired once there is no residual tension on it. Major injuries should either be handled by division of the vein and repaired later by direct reconstruction (end-to-end anastomosis) when the tension on the vein can be reduced by closing the sternal retractor or using a short polytetrafluoroethylene (PTFE) interposition graft in case of a substantial tissue defect.
Injury to the right ventricle
The risk of a significant injury of the right ventricle may be particularly high when the pericardium has been left open on its whole length at primary surgery and/or in case of right ventricular hypertrophy/dilatation. As for the brachiocephalic vein, the injury may happen either during sternum sawing or after insertion of the sternal retractor. Opening both pleural cavities may facilitate spreading the sternum retractor and reducing the tension of adhesions between the sternum and anterior part of the ventricle.
Otherwise, opening of the retractor should be done very gently since a too-strong stretching of the anterior surface of the right ventricle may lead to tears that may be difficult to repair. When a tear in the right ventricle has occurred and can’t be immediately repaired because of the lack of space between both sternal sides, digital control or packing with large compresses may be attempted. If this is not possible or not efficient enough, temporary closure of the sternotomy with several traumatic clamps may control the hemorrhage (see earlier) and give enough time to institute cardiopulmonary bypass via peripheral cannulation. Once cardiopulmonary bypass has been instituted, the heart can be unloaded, and repair of tears in the right ventricle is much easier. U-stitches with autologous pericardial reinforcement or with Teflon-pledgeted sutures are the most common technique to close right ventricular injuries. Fortunately, there are no major coronary arteries crossing the anterior wall of the right ventricle, but any branch and/or bypass graft should be avoided, of course.
Injury to the ascending aorta and of the main pulmonary artery
Injury of the ascending aorta is another catastrophic event that may occur, particularly in case of aortic aneurysm or pseudoaneurysm following previous aortic surgery. Injury of the main pulmonary artery is the less-frequent fatal injury that may occur during reoperative surgery; prior repair of the right ventricular outflow tract using a prosthetic or a xenograft conduit or a homograft in a heterotopic position with the pericardium left open is a typical high-risk situation for such an injury. Both conditions will be discussed later in this chapter.
Injury to the lung
Injury to the lung parenchyma is relatively uncommon, but this problem may happen in patients with chronic obstructive lung disease and emphysema and in those in whom both pleural cavities have been opened at initial surgery and the pleura have been sutured together to help cover the great vessels and eventually bypass grafts. Generally speaking, ventilation can be completely stopped during sawing, but when this step takes more time, reducing the tidal volume is more appropriate.
Depending on the size of the injury, suturing the lung parenchyma with monofilament sutures may be necessary in case of major air leaks, although use of fibrin glue may be sufficient for small injuries. Control of such injuries should be done at the end of the procedure before sternal closure, using water to look for residual air leaks.
Specific situations
Redo for coronary artery bypass surgery
Reoperation because of coronary artery disease following prior surgical myocardial revascularization has become less frequent in more recent years. There are multiple reasons for this observation: the increased use of multiple arterial grafts up to complete arterial revascularization at initial surgery, the better secondary prevention of cardiovascular risk factors with aggressive medicament treatment of hypercholesterolemia and arterial hypertension, and increased awareness and better compliance of patients to life-long antiplatelet treatment. , Finally, the broader use of percutaneous coronary interventions in the long term following coronary artery bypass grafting to treat progression of the disease in the native coronary arteries and in the bypass conduits, together with better stent materials and combined antiplatelets treatment, have also contributed to a decrease in the necessity for reoperative coronary surgery. ,
Nevertheless, redo-coronary bypass grafting might still be indicated in younger patients because of progression of coronary artery disease in the native vessels (especially in the left main stem), incomplete revascularization at the initial surgery, stenosed vein grafts, in situations where the diseased vessels are not easily amenable to percutaneous intervention, and in those patients who may potentially have a survival benefit with the placement of an arterial conduit to the left anterior descending branch.
There are many challenges that might occur during redo-coronary artery bypass grafting. , As for any reoperative cardiac surgery, opening of the sternum represents the first challenge, followed by safe establishment of cardiopulmonary bypass without injury to patient nor embolization from patent but stenosed grafts, and finally the proper identification of the target coronary arteries and the availability of bypass graft material (the second internal thoracic or radial artery, or residual vein graft material). Therefore, preoperative assessment is exactly the same as for primary coronary surgery. Preoperative coronary angiography is mandatory since it will demonstrate the patency of previous grafts, and CT scan may show precisely the trajectory of these grafts, especially when they are close to the posterior surface of the sternum and/or when they cross the midline (for instance, a right internal thoracic artery to the left descending branch or to a marginal branch) ( Figs. 5.10 and 5.11 ).
Potentially high-risk situation for redo-sternotomy in a patient with acute aortic dissection in whom a bypass graft implanted at the time of a prior coronary and valve procedure is in close relationship with the sternum.
Potentially high-risk situation for redo-sternotomy in a patient with multiple previous aortic operations and with a single venous graft for the revascularization of the right and left coronary system, crossing the midline just at the inferior part of the right anterior ventricular wall.
A similar strategy may be applied for the right internal thoracic artery when it is used to revascularize the left coronary system at initial surgery; the artery is preferentially passed through the transverse sinus behind the aorta and the main pulmonary artery to be anastomosed with any branch of the circumflex artery. In case the risk of injury of life-threatening structures is judged to be high, preliminary percutaneous introduction of wires into the external iliac artery and vein or even percutaneous cannulation should be performed.
Besides the risk of classical injuries (to the brachiocephalic vein and the right ventricle), reoperative surgery following prior coronary artery bypass grafting may include an additional risk of bypass graft injury with the potential for ischemic consequences when the affected bypass is still patent. In such a case, there are several options:
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Repair of the bypass with 6.0 or 7.0 polypropylene suture avoiding too narrow or occluding the graft
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Immediate cannulation and institution of cardiopulmonary bypass to unload the heart and mitigate the consequences of myocardial ischemia
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If possible with regard to the size of the bypass graft (mainly for venous grafts), introduction of a smooth and small silicon shunt as used for carotid endarterectomy or a larger intracoronary shunt used for off-pump surgery. This allows for further preparation while coronary perfusion is maintained ( Fig. 5.12 ).
