An aortic root abscess is a severe localized infection within the aortic root, the part of the aorta closest to the heart. This life-threatening condition is a complication of infective endocarditis, an infection of the heart’s inner lining or valves. It requires prompt and aggressive intervention to prevent further damage.
What is an Aortic Root Abscess?
The aortic root is a complex structure at the base of the aorta, the body’s largest artery, where it connects to the heart’s left ventricle. This region includes the aortic valve, which regulates blood flow from the heart to the rest of the body, and the sinuses of Valsalva, small pouches behind the valve leaflets from which the coronary arteries originate. These structures work together to ensure efficient and unidirectional blood flow.
An aortic root abscess develops when bacteria or other microorganisms spread from an infected heart valve or prosthetic material into the surrounding heart tissue. This infection leads to the formation of a pus-filled cavity within the aortic root, which can expand and destroy nearby structures. Abscesses in this area are commonly associated with infective endocarditis, occurring in 10-37% of cases, particularly when the aortic valve is involved.
Abscess formation can occur in patients with native heart valves or, more frequently, in those who have undergone aortic valve replacement, especially within the first two years after surgery. In mechanical prosthetic valves, the infection often begins at the sewing line and spreads around the valve, while in bioprosthetic valves, the infection affects the valve cusps. Early abscesses, within two months of surgery, are often caused by contamination, with Staphylococcus epidermidis and Staphylococcus aureus being common culprits. Later abscesses, occurring more than two months post-surgery, resemble native valve endocarditis and are frequently caused by Streptococci species.
Symptoms and Diagnosis
Symptoms of an aortic root abscess can be subtle, often mimicking other conditions and delaying diagnosis. Patients commonly experience fever. Other symptoms include a new or changing heart murmur, indicating valve issues, and general signs of infection like weight loss and poor appetite. Heart failure symptoms, such as shortness of breath, or signs of systemic embolization may also occur.
Diagnosis involves clinical suspicion, laboratory tests, and advanced imaging. Blood tests may reveal elevated inflammatory markers, such as leukocytosis, and blood cultures identify the specific microorganism.
Echocardiography, particularly transesophageal echocardiography (TEE), is the primary diagnostic tool due to its high sensitivity for detecting perivalvular abscesses. TEE can visualize an echolucent (dark) area around the valve, which may appear as thickening of the aortic root in early stages. Computed tomography (CT) scans, sometimes with angiography, provide detailed anatomical information, showing fluid collections around the aortic valve with peripheral enhancement. CT can also reveal the spread of the abscess into surrounding structures like the interatrial septum or left ventricular myocardium, and identify complications such as fistula formation. Magnetic resonance imaging (MRI) and hybrid imaging techniques like Gallium-67 SPECT or [18F]fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) can offer additional insights in challenging cases.
Treatment and Management
Treatment for an aortic root abscess involves a combined medical and surgical approach. Medical management begins with long-term intravenous antibiotics aimed at eradicating the infection. The specific antibiotic regimen is tailored based on the identified causative pathogen and its sensitivities. However, antibiotics alone are often insufficient to control the infection, especially if the abscess is extensive or complicated.
Surgical intervention is often recommended early, as it significantly improves outcomes and can be curative. The procedure’s complexity depends on the infection’s extent and tissue damage. The primary goal of surgery is to aggressively debride, or remove, all infected and necrotic tissue. This debridement can leave significant defects in the aortic annulus and the left ventricular outflow tract.
Following debridement, reconstruction of the aortic root is performed. This can range from simple patch repair using autologous pericardium (tissue from the patient’s own pericardium) to complete replacement. For full replacement, a prosthetic valve or a homograft (a human donor valve) may be used. Homografts are often preferred in infected fields due to their resistance to infection and lack of prosthetic material. Complex procedures, like the Bentall procedure, involve replacing the aortic valve, aortic root, and ascending aorta with a composite graft.
A multidisciplinary team, including cardiologists, cardiac surgeons, infectious disease specialists, and intensive care clinicians, manages these patients. Early surgical intervention is generally favored over delayed surgery, leading to better outcomes even if blood cultures are still positive. While a short course of antibiotics (around 24 hours) may be given pre-operatively, prolonged courses should not delay necessary surgical repair.
Complications and Prognosis
If left untreated or delayed, an aortic root abscess can lead to severe complications due to its destructive nature and proximity to vital cardiac structures. The infection can damage the aortic valve, potentially causing severe dysfunction or complete destruction. Spread of the abscess can result in fistulas, abnormal connections between cardiac chambers or major vessels.
The abscess can also extend into the heart’s conduction system, causing electrical rhythm disturbances like heart block, which may necessitate a pacemaker. Other serious complications include pseudoaneurysm formation, a contained rupture of the aortic wall, and systemic embolization, where fragments of infected tissue travel through the bloodstream, potentially causing strokes or infarcts in other organs. Myocardial infarction can also occur if the infection obstructs coronary blood flow.
Despite aggressive medical and surgical treatment, the prognosis for patients with an aortic root abscess remains serious, with high morbidity and mortality. In-hospital mortality rates range from 12.2% to 30%. Survival rates at one and five years post-surgery are approximately 77.2% and 64.0%, respectively. Patients with prosthetic valve endocarditis and those infected with Staphylococcus aureus face a higher risk of mortality. Recurrence of infection after surgery is also a concern, with rates varying depending on the surgical technique. Recovery can be prolonged, often requiring extended antibiotic therapy and close monitoring for recurrent infection or cardiac complications.