Infective endocarditis

Infective endocarditis (IE) is defined as infection of the endocardium. It commonly affects the valve leaflets and chordae tendinae, as well as prosthetic valves and implanted devices.

Epidemiology

IE has an estimated general prevalence of 3 to 9 cases per 100,000 persons. It is prevalent among intravenous drug abusers (approximately 2,000 cases per 100,000 intravenous drug abusers). It is more common in men than women (>2:1). In the general population, it affects more individuals older than 65 years ¹.

Pathology

The following conditions appear to play critical roles in the creation of an endocarditic lesion ¹:

• endocardial abnormality
  • endocardial inflammation
  • endothelial injury from central lines and other forms of cardiovascular instrumentation
  • valvular disease including prosthetic valves
• bacteremia
  • microorganism access to the bloodstream from oral, genitourinary, or gastrointestinal sources
  • trauma
  • intravenous and subcutaneous injections
• microbial properties and associated components
  • microbial virulence properties such as adhesion proteins and tissue-destructive factors
  • microbial quantity
  • particulate and diluent materials
  • repetition of microbial entry into the bloodstream

Once the endocarditic lesion is initiated, the clotting pathway catalyses vegetation formation. The microbes become buried in the vegetation and may form a biofilm around them, thereby becoming inaccessible to immune cells or antibiotic drugs for clearance and eradication. Endocarditic vegetation is the pathologic hallmark of IE and commonly appears as an irregular, mobile or fixed mass and is usually attached to the endocardium on the low-pressure side of a valve, chordae tendinae or ascending aorta. Vegetation fragments can break off and undergo embolisation, causing more conspicuous clinical signs and symptoms of infection like pneumonia and stroke.

Radiographic features

Plain radiograph

Chest radiographic findings are nonspecific and may show opacities suggestive of underlying pneumonia and septic pulmonary emboli. Patients with valve leaflet destruction may manifest with signs of congestive heart failure. The cardiac silhouette may be enlarged due to pericardial effusion. Some patients may also show pleural effusion.  

Echocardiography

Echocardiography is the primary imaging modality of cardiac infections.  It has been integrated into the modified Duke criteria for diagnosis of IE.

Endocarditic vegetation is usually echogenic or isoechoic to muscle on echocardiography. 

Other possible echocardiographic findings:

• abscess
• dehiscence of prosthetic valve
• valvular regurgitation

CT

Cardiac CT angiography may demonstrate endocarditic vegetations as hypoattenuating filling defects surrounded by intravenous contrast material. Cardiac gated CT angiography can also demonstrate valve tissue destruction, and perivalvular extension with pseudoaneurysm or fistula formation

MRI

Cardiac MRI can detect valvular vegetation features of IE. The appearance of vegetations depends on the imaging sequence used and ranges from low to intermediate signal intensity and isointense to muscle with balanced steady-state free precession (SSFP) and inversion-recovery sequences. Post-gadolinium images may show enhancement of the vegetations and abscess. In the absence of vegetations, MR can demonstrate delayed enhancement representing endothelial inflammation of the cardiovascular structures, which can contribute to the diagnosis and treatment planning of IE ². Cardiac MR imaging also allows quantification of regurgitation fraction.

Treatment and prognosis

IE is a disease with high morbidity and a mortality even with appropriate diagnosis and therapy ³. With treatment, which includes antibiotics and surgery, the mean in-hospital mortality of IE is 15-20% with a 1-year mortality approaching 40% ¹. If untreated, IE is invariably fatal.

Complications

Septic emboli occur in 12-40% of IE cases ³. It can affect any organ or tissue in the body with an arterial supply:

• central nervous system (most common)
• lungs (especially in right-sided IE)
• spleen
• kidneys
• liver
• musculoskeletal system

Other complications:

• paravalvular, annular or aortic abscess
• mycotic aneurysms
• heart block
• valve dehiscence or severe dysfunction
• intracardiac fistula

Differential diagnosis

Differential diagnosis of vegetations include

• myxomas
• thrombi
• lipomas
• papillary fibroelastomas