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Surgery for aortic root abscess
Introduction
Infective endocarditis can be associated with several clinical and anatomic complications. Among these is aortic root abscess. Aortic root abscess is defined by the presence of necrotic tissue in the aortic root, annulus, or as aortoventricular discontinuity. In this chapter, the presentation, diagnosis, and surgical management of endocarditis complicated by aortic root abscess will be discussed.
Clinical presentation and diagnosis
The definitive diagnosis of endocarditis is based upon a combination of clinical, echocardiographic, and microbiology findings. The modified Duke criteria, introduced by Durack et al., are utilized by most clinicians for the diagnosis of endocarditis and they have been reported to have a sensitivity and specificity of over 80% [ ].
Major criteria include, but are not limited to, positive blood cultures and new echocardiographic findings of cardiac valve vegetation or regurgitation, oscillating intracardiac mass, partial dehiscence of a prosthetic valve, and abscess. Aortic root abscess with extension to surrounding structures may also lead to symptoms prompting presentation. These include involvement of the conduction system with arrhythmias or heart block, compression of the coronary arteries with acute coronary syndromes, or pseudoaneurysm formation with resultant chest pain and/or compression of adjacent structures. In extreme situations, the abscess can erode into adjacent cardiac chambers leading to fistulous connections within the heart. Frequently, patients require cardiac surgical attention after presenting with positive blood cultures and one of the aforementioned echocardiographic or radiologic findings.
It is estimated that intracardiac abscess will affect up to 14% of patients suffering from infective endocarditis [ , ]. Staphylococcus aureus is the most frequently isolated pathogen affecting approximately one-third of patients; however, many others have been implicated such as Haemophilus species, Enterococci, Beta-hemolytic streptococci, Bacteroides species, and others [ ].
Transthoracic echocardiogram (TTE) is frequently employed as the first diagnostic test in the setting of suspected endocarditis. However, the ability of TTE to detect new valvular vegetations is only 50%. Transesophageal echocardiogram (TEE), in contrast, has a sensitivity of 90%–100% in the detection of cardiac vegetations ( Fig. 18.1 ). When employed together TTE and TEE demonstrate vegetations in 90% of patients suffering from endocarditis. Further, TEE is the diagnostic test of choice for demonstrating aortic root abscess as well as fistulas and shunts [ , ].
It is our practice to undertake CT scanning of the brain, chest, abdomen, and pelvis to screen patients for possible septic emboli to the brain, lungs, and spleen as well as to evaluate for the presence and extent of a pseudoaneurysm when they present with infective endocarditis. CT scanning also allows for detailed delineation of the aortic root anatomy which is useful in operative planning, such as during dissection of an aortic root pseudoaneurysm ( Figs. 18.2 and 18.3 ).
A left heart catherization may also be useful in operative planning and may be undertaken safely if a large, mobile vegetation is not visualized on the aortic valve by echocardiography.
Initial management
The first step in successful management of infective endocarditis complicated by aortic root abscess is the assembly of a multidisciplinary team that includes clinicians who specialize in cardiology, cardiac surgery, intensive care, and infectious diseases. The cornerstones of treatment include infection eradication, as evident by negative blood cultures, and prevention of further cardiac damage and systemic complications.
Microbiological data suggest that staphylococci and streptococci are the causative agents in approximately 80% of aortic root abscess cases. Within these geniuses, it should be noted that the incidence of S. aureus –related infection is increasing while the incidence of streptococcus viridans is declining. When fungus is isolated as the causative organism it is most frequently Candida species followed by Aspergillus species [ ].
Prompt antibiotic therapy is required and should be employed as soon as infective endocarditis is clinically suspected. Initial treatment is with broad-spectrum agents, and this is then tailored based upon blood cultures and susceptibilities.
Indications for surgical intervention
When periannular extension, in the form of aortic root abscess or fistula, is present this alone is an indication for early surgical intervention. Additional indications include congestive heart failure, persistent bacteremia, septic emboli, or electrical rhythm disturbances. This is frequently associated with new-onset aortic and/or mitral valve regurgitation or prosthetic-valve dehiscence and/or obstruction [ ].
Systemic embolization also is an indication for surgical intervention. This also includes cerebrovascular complications including silent complications and transient ischemic attacks. Of note, surgery is relatively contraindicated for 1 month after an intracranial hemorrhage unless a neurosurgical procedure can be undertaken to reduce the risk of subsequent bleeding. However, in patients who are extremely ill from aortic root abscess the relative risks and benefits of waiting versus proceeding with surgery may favor early surgery [ , ].
Finally, persistent sepsis, as defined by persistent fevers and/or positive blood cultures after 5–7 days of appropriate antibiotic therapy, is an indication for surgical intervention [ ].
A small subset of patients may be managed without surgery. They include those with small abscesses measuring less than 1 cm not complicated by heart block, valvular dehiscence, or insufficiency and those that do not progress while the patient is undergoing antibiotic therapy. If a nonoperative approach is undertaken, we recommend serial exams with echocardiography at 2, 4, and 8 weeks after presentation [ ].
Principles of surgical management
Once the decision to pursue operative intervention is made, as will be the situation in the setting of an aortic root abscess in a patient fit for an operation, there are several principles that will facilitate a successful outcome. Even though there is not one “standard” operation for patients suffering from an aortic root abscess, all patients should be prepared in the same fashion. This includes a detailed and thorough TEE in the operating room. Further, given that patients have frequently undergone prior cardiac operations and that the disease process has a predilection for adhesion formation, the surgeon should prepare for difficult dissection. It is prudent to obtain femoral arterial access prior to dividing the sternum, should expeditious cardiopulmonary bypass be required. The bilateral lower extremities should be prepped into the sterile field in case conduit is needed for bypass grafting.
There are many different techniques for safely performing redo sternotomy. The surgeons should choose the technique they are most familiar with, but the importance of femoral access cannot be overstated. Once the median sternotomy has been completed, standard cannulation with an aortic cannula and dual-stage venous cannula is acceptable. However, it is our preference to utilize bicaval cannulation in these complex root operations. On occasion, severe adhesion formation to the right atrium, or fistulous connection to the right-sided cardiac structures requires opening the right atrium. This technique does greatly improve visualization of the aortic root in situations of dense adhesion formation. Given the association of aortic valve insufficiency with this disease process, we also routinely place a left ventricular vent via the right superior pulmonary vein.
Once cardiopulmonary bypass is initiated it is our preference to utilize retrograde cardioplegia followed by ostial cardioplegia once the aorta is opened. Given the long cardiopulmonary bypass and myocardial ischemia times in these complex root or multivalvular reconstructions, we perform systemic cooling, often to 30°C for additional metabolic protection.
After myocardial arrest has been achieved, the infected area should be exposed typically through transverse aortotomy, in order to identify the extent of involvement. This evaluation dictates the extent of root reconstruction required. An added principle to achieving a successful short- and long-term repair is to undertake a thorough and complete debridement of all infected and necrotic material. After the debridement is concluded we frequently place Rifampin-soaked cotton swabs into the aortic annulus and into the left ventricle in an attempt to sterilize the field.
Finally, at the conclusion of the case, it is our practice to utilize an irrigation catheter to infuse antibiotic solution into the mediastinum for 5–7 days after the operation. This is frequently a simple 16 French catheter with tip removed and positioned within the mediastinum. This catheter is tunneled through the chest wall in the second or third intercostal space to right of the sternum. Although the combination of Rifampin-soaked cotton swabs and mediastinal irrigation has not been definitively proven to improve outcomes we have found it useful in our practice, particularly for gram-positive organisms.
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