REOPERATIVE CARDIAC SURGERY: A MULTIDISCIPLINARY APPROACHMichelle Capdeville, M.D.

Associate Professor

Cleveland Clinic Lerner College of Medicine

Program Director, Cardiothoracic Anesthesia Fellowship

The Cleveland Clinic FoundationGOALS AND OBJECTIVES

1. To understand the factors that make cardiac reoperations distinctly different from primary operations.2. To appreciate how the risk of cardiac reoperations has changed over the past 25 years.3. To discuss the technical advances and improvements in myocardial preservation strategies that have reduced the risk of cardiac reoperations.4. To understand the pathophysiology of vein graft atherosclerosis and its relevance to patient outcomes and management.5. To illusrate novel techniques using a multidisciplinary approach to the management of patients presenting for cardiac reoperations.INTRODUCTION

Cardiac reoperations are complex procedures that are performed in a very unique patient population. These operations have become increasingly prevalent in cardiac surgical practice and are distinctly different from first-time operations. Unfortunately, little detail about cardiac reoperations is presented in textbooks geared towards the cardiac anesthesiologist, with the general teaching being limited to placement of large intravascular access and having checked blood in the operating room in anticipation of catastrophic hemorrhage.THE CHANGING FACE OF CARDIAC SURGERY

After the first coronary revascularization procedures were performed in the 1960s, it became clear by the 1970s that many of these patients would be presenting for a second operation. Indications for reoperation have changed over the past several decades, with early graft failure becoming a lesser problem. The use of arterial conduits such as the internal mammary and radial arteries has extended the time interval between operations.

Coronary artery bypass operations have declined in volume, due in large part to a high prevalence of percutaneous interventions. Regular use of antiplatelet agents and lipid lowering agents may also contribute to this decline. What was once referred to as a routine CABG is almost considered an aberrancy today, since typical CABG patients present with a history of multiple PCI with stents and decreased cardiac reserve. In fact, many of todays routine CABG patients would not have been considered surgical candidates 25 years ago. Coronary reoperations have increased in frequency (though this trend is changing), with approximately 8% of all CABG cases in the United States being repeat operations.

REOPERATIONS AND PERIOPERATIVE RISK

Despite increased surgical experience and improved perfusion strategies, cardiac reoperations are associated with an increased risk of death, perioperative myocardial infarction, low output syndrome, increased need for inotropic and intra-aortic balloon pump support, increased transfusion rate, increased postoperative organ dysfunction, increased incidence of arrhythmias, increased need for permanent pacemaker, prolonged mechanical ventilation, increased ICU and hospital length of stay, and increased overall cost of hospitalization.Outcomes have improved over the years, secondary to increased surgical experience and improved anesthetic, perfusion, and perioperative management. Patient-related factors still contribute to the added relative risk compared to first-time operations.

Between 1971 and 1974, in a study of 4000 patients undergoing CABG operations at the Cleveland Clinic, the cumulative risk of reoperation was 3% at 5 years, 10% at 10 years, and 25% at 20 years. Data collected between 1990 and 2003 showed a relative decline in the number of coronary reoperations, largely due to the use of IMA grafts.

Interestingly, hospital mortality following redo CABG, though higher than primary CABG, has declined steadily between 1990 and 2004, with the most noteworthy decline occurring after 1997. The increased mortality has been attributed to a higher patient risk profile rather than to technical complexity of the operation. In fact, once considered a significant risk factor for mortality, LV dysfunction is no longer considered a primary risk factor. Improved myocardial preservation during cardiopulmonary bypass accounts for this trend.RISK FACTORS FOR REOPERATION

Risk factors for reoperation can be separated into modifiable and non-modifiable factors. Modifiable risk factors include: diet; exercise; smoking cessation; compliance with medical management; serum lipid profile. Unmodifiable patient risk factors include: heredity; progression of native CAD; presence of diffuse disease; lack of suitable conduit; emergency operation. Surgical factors that have lessened operative risk include: alternative surgical approaches (e.g. thoracotomy); meticulous technique; approach to sternal re-entry; blood conservation strategies (antifibrinolytics, local hemostatic agents); temperature management on bypass; type of conduit (arterial versus venous); type of cardioplegia and mode of delivery; adequacy of revascularization; handling of diseased patent saphenous vein grafts; presence of cross-over arterial grafts; use of no-touch technique; earlier patient referral.

SAPHENOUS VEIN GRAFT ATHEROSCLEROSIS

Saphenous vein graft stenosis is a process that occurs in three distinctive phases. In the early phase, prior to hospital discharge, SVG occlusion has been noted in approximately 10% of grafts. This type of occlusion is typically due to thrombosis. This may be related to hemodynamic factors, small vessel size, and technical factors. In the intermediate phase, 5 to 10% of SVG become occluded 1 month to 1 year after surgery. These grafts develop fibrointimal proliferation, possibly as a result of exposure to arterial pressures. This is a concentric cellular process that extends the entire length of the graft and becomes a more fibrous lesion over time. This lesion is not friable. Fibrointimal proliferation affects the majority of SVG, but causes stenoses or occlusions of only a small number. The final phase of SVG disease is atherosclerosis. This can be seen as early as 3 to 4 years postoperatively, and is due to lipid infiltration of areas of fibrointimal proliferation. This is a concentric, diffuse lesion, that is superficial, extremely friable, and frequently associated with overlying thrombus. This is in contrast to native vessel atherosclerosis, which tends to be segmental, proximal, eccentric, encapsulated, and is not friable.An important point worth noting is that pathologic examination of what were believed to be disease-free saphenous vein grafts by angiography, has demonstrated more vessel disease than expected. Therefore, the extent of SVG disease is underestimated by angiography. This information is noteworthy, particularly when a surgeon must decide whether or not to replace old vein grafts at reoperation.

ADVANTAGES OF ARTERIAL CONDUITS

Use of the left internal mammary artery as an in situ conduit to the left anterior descending coronary artery has become the gold standard for coronary revascularization. This is due to the superior patency of this particular conduit, with patency rates exceeding 95% at 10 years. Once early patency of this vessel is established, late failure is exceedingly rare. This is in spite of the fact that the IMA delivers a smaller blood flow compared to a saphenous vein graft. IMA graft failure, when it occurs, is generally due to initial poor quality conduit, or inappropriate handling at the time of harvest. IMA stenosis typically occurs at the anastomotic site, and atherosclerosis is a rare finding with this conduit.Routine use of the IMA for grafting of the LAD territory has led to an increase in survival and freedom from reoperation when compared to saphenous vein grafts. In fact, use of bilateral IMA grafts has been shown to increase survival further when compared to single IMA grafting.

TECHNICAL CONCERNS

Various aspects of the technical approach to cardiac reoperation are important in reducing the hazards of this type of surgery. There is no substitute for careful planning and good communication with the OR team. The surgeon will want to obtain old operative notes if available.Several questions must be raised prior to the start of the operation, especially If the operation is to be performed through a repeat sternotomy. The following points must be addressed:

Are there structures adherent to the underside of the sternum (e.g. patent or diseased grafts, cross-over grafts, the right atrium or right ventricle, a dilated aortic root) that are vulnerable to injury?

Will cannulation sites be exposed or accessed prior to opening the sternum in case cardiopulmonary bypass needs to be instituted emergently? Will the surgeon institute CPB prior to attempting to open the sternum?

How will the patient be cannulated? This will determine the potential location of invasive lines to be placed.

Was the pericardium left open or was the heart covered at the first operation?

Will an alternative approach, such as right or left thoracotomy be used instead?

Will the procedure be attempted off-pump?

What type of conduit will be used? (This will affect the location of arterial line placement).

Is there adequate conduit available?

Does the patient have a left bundle branch block? This will be important to note during placement of a pulmonary artery catheter. The development of complete heart block in a patient with a prior sternotomy can prove fatal.

What was the timing of the previous operation. The risk increases dramatically if the time since the last operation is less than one year.

Will this be a complete revascularization attempt? Are the targets adequate?

How will old but patent saphenous vein grafts be dealt with?

From the anesthesiologists perspective, all of the above factors will impact patient management and help to anticipate potential problems post-bypass. It goes without saying that adequate large bore intravenous access must be secured, and that the patient must be fully monitored, including TEE.As the surgeons begin to prepare for sternotomy, the anesthesiologist should be aware of some of the potential hazards. For example, old sternal wires are excellent conductors of current, and inadvertent application of electrocautery to a sternal wire when the heart is adherent to the underside of the sternum, can lead to ventricular fibrillation. If cannulation sites have not been appropriately accessed prior to this step, the heart can become distended during the time needed to cannulate and institute cardiopulmonary bypass. The final outcome, needless to say, can be devastating.

Catastrophic hemorrhage can occur despite meticulous technique, and must be anticipated. Adequate blood must be available prior to the start of the operation and should be checked ahead of time and maintained in the operating room.

If an oscillating saw is used to open the sternum, the old sternal wires are generally clipped but left in place posteriorly to help protect the underlying structures as the posterior sternal table is divided. Once the sternum has been divided and spread apart, the next critical step is the dissection of adhesions. Depending on the time since the last operation, these adhesions can be quite dense and vascularized, with potential for significant blood loss.

If old vein grafts are present, their handling must be avoided in order to prevent the distal embolization of friable atheromatous material that can lead to infarction. Close attention should be paid to the electrocardiogram throughout the dissection period. A no-touch approach is advocated to prevent distal embolization of atheromatous debris, and in many instances the heart may only be partially dissected out before going on pump to dissect the remainder of the adhesions. Careful attention must be paid to patent arterial grafts, as injury can lead to fibrillation and infarction. Presently, the incidence of left IMA damage at reoperation has been reduced from approximately 8% to 3.7% in experienced hands.MYOCARDIAL PROTECTION

Myocardial preservation during cardiopulmonary bypass is achieved with the administration of cardioplegia immediately after aortic cross-clamping. Cardioplegia can be delivered antegrade (into the aortic root; down constructed vein grafts; directly into the coronary ostia) or retrograde (into the coronary sinus). Diastolic arrest from the cardioplegic solution leads to a profound reduction in metabolic demand. The administration, composition, timing of delivery, and temperature of cardioplegia solutions is highly variable.The improved outcomes of reoperative cardiac surgery are due in large part to improvements in myocardial preservation strategies, most notably the routine use of retrograde cardioplegia. Antegrade delivery of cardioplegia can be impeded by coronary occlusions, and its distribution may be unpredictable in redo CABG operations, where myocardial blood flow follows complex patterns (i.e. native circulation, vein grafts, and in situ mammary artery grafts). Delivery of retrograde cardioplegia, on the other hand, is across an unobstructed transmural venous network, that is independent of flow-limiting lesions (unlike antegrade delivery).

It is believed that subendocardial cooling is superior with retrograde cardioplegia versus antegrade. However, not all cardioplegia entering the coronary sinus reaches the venous capillaries because of losses across Thebesian veins draining into the cardiac chambers. Additionally, delivery of retrograde cardioplegia takes longer compared to antegrade delivery because of lower flow rates and pressures employed to prevent the development of myocardial edema and coronary sinus injury (antegrade cardioplegia is delivered at systemic pressures). Because of this, many surgeons advocate initiating cardiac arrest with a single dose of antegrade cardioplegia, followed by interval dosing of retrograde cardioplegia.Whenever possible, patent in situ mammary artery grafts should be temporarily occluded, because persistent flow within the graft may impede myocardial protection from retrograde delivery of cardioplegia, because cardioplegia washout can occur. Antegrade cardioplegia, on the other hand, is essentially ineffective in protecting the territory of an in situ graft, especially if there is a complete occlusion proximal to the graft.

With hypertrophic hearts, retrograde cardioplegia alone may be inadequate to protect the myocardium, and combining antegrade cardioplegia or instituting hypothermia may be a more appropriate approach.

In the presence of patent saphenous vein grafts, antegrade cardioplegia can cause distal embolization of friable atherosclerotic material. Retrograde cardioplegia can flush this embolized material out of native coronaries via an open arteriotomy.

PERFUSION STRATEGIES

Many surgeons advocate securing cannulation access sites prior to attempting re-sternotomy. This can be done by isolating and exposing the femoral vessels, assuming that the femoral artery is disease free. An alternative arterial inflow site is the right axillary artery. Use of this site is associated with low morbidity, especially if a side graft is sewn to the vessel. Advantages of this vessel are its resistance to atherosclerosis, and the ability to institute antegrade cerebral perfusion if circulatory arrest becomes necessary.

Venous cannulation is generally secured remotely via a long cannula inserted into the femoral vein and advanced to the junction of the inferior vena cava and right atrium. With axillary (or femoral) artery cannulation and femoral venous cannulation, partial cardiopulmonary bypass can be instituted rapidly if it becomes necessary. In most instances, the superior vena cava is cannulated after the chest has been opened. An alternative is to secure the SVC site percutaneously via the right internal jugular vein. This approach is particularly useful if the femoral vein cannot be cannulated, secondary to occlusion or the presence of an inferior vena cava filter.

PREOPERATIVE IMAGING STUDIES

Previously, surgeons relied on preoperative imaging with standard chest X-rays and coronary angiograms to assess the proximity of mediastinal structures to the undersurface of the sternum. This method was highly imprecise and has been replaced with computed tomography, most notably 3-D imaging. This form of imaging can identify native coronary vessels and grafts, and gives precise information about underlying structures at risk during repeat sternotomy. These studies are particularly useful in assisting the surgeon with the decision of whether or not to institute cardiopulmonary bypass prior to re-sternotomy.CONCLUSIONS

Cardiac reoperations are distinct procedures from first time operations and must be approached very differently. With an organized approach that involves refinements in surgical technique, perfusion strategies, anesthetic and perioperative management, and preoperative imaging, these operations have been made safer over the last 25 years, despite a much higher patient risk profile.

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