Infective Endocarditis and Vegetations

Vegetation Appearance and Location

Infective endocarditis (IE) begins with vegetations — irregular, shaggy, echogenic masses with independent, chaotic motion distinct from normal leaflet excursion. Vegetations attach to the upstream (low-pressure) surface of the affected valve relative to blood flow: the atrial surface of the mitral and tricuspid valves, and the ventricular (arterial-facing) surface of the aortic and pulmonic valves. This orientation reflects turbulent flow and endothelial injury on the low-pressure side of a regurgitant or high-velocity jet. Echodensity evolves with age: acute/active vegetations are soft and similar to or slightly lower in density than myocardium, while healed or chronic vegetations become denser and may calcify.

Left-sided IE (mitral and aortic valves) predominates in the general population and in patients with pre-existing valve disease or prosthetic valves. Right-sided (tricuspid) IE is the classic pattern in intravenous drug use and in patients with indwelling catheters, pacemaker/ICD leads, or other intracardiac hardware — organisms are introduced directly into the venous circulation and strike the first valve encountered.

Modified Duke Criteria

Diagnosis integrates clinical, microbiologic, and echocardiographic findings using the modified Duke criteria:

Diagnostic categories:

1. Definite IE: 2 major criteria, OR 1 major plus 3 minor criteria, OR 5 minor criteria
2. Possible IE: 1 major plus 1 minor criterion, OR 3 minor criteria
3. Rejected: a firm alternate diagnosis, resolution with 4 or fewer days of antibiotics, or failure to meet possible-IE criteria

Echocardiography supplies one of the two possible major criteria (endocardial involvement), which makes the sonographer's image quality and search pattern directly determinative of a patient's diagnostic classification.

Complications

Untreated or advanced IE extends beyond the valve leaflet itself:

• Perivalvular (annular) abscess — the most common serious complication, most frequently involving the aortic root/annulus in aortic valve IE; appears as a thickened, echolucent, or heterogeneous perivalvular area that fails to demonstrate flow.
• Pseudoaneurysm and fistula — abscess cavities that communicate with a cardiac chamber or the pericardial space, seen as pulsatile echolucent spaces with flow on color Doppler.
• Leaflet perforation — a color-flow jet passing through the body of a leaflet rather than through the coaptation line.
• Chordal rupture / flail leaflet — sudden, severe regurgitation with a leaflet tip that whips into the receiving chamber.
• Prosthetic valve dehiscence — a rocking, unstable prosthesis with a new paravalvular regurgitant jet outside the sewing ring.
• Septic embolization — systemic (stroke, splenic/renal infarct) from left-sided vegetations; pulmonary (septic emboli, cavitary lesions) from right-sided (tricuspid) vegetations.

TEE vs. TTE

TTE is the appropriate first-line study, but TEE is indicated whenever TTE is technically limited or non-diagnostic, when a prosthetic valve or intracardiac device (pacemaker/ICD lead) is present, when clinical suspicion remains high despite a negative TTE, when Staphylococcus aureus bacteremia is present, or when a complication (abscess, fistula, perforation) is suspected. TEE's proximity to the posterior cardiac structures and higher-frequency transducer make it far more sensitive for small vegetations, prosthetic valve involvement, and perivalvular extension than TTE.

Causative Organisms and Risk Stratification

While microbiology is primarily a clinical/laboratory finding rather than an imaging one, sonographers benefit from recognizing the epidemiologic pattern behind the images they are asked to obtain. Staphylococcus aureus is now the leading cause of IE overall in most contemporary series, producing a typically aggressive, rapidly destructive course with large, friable vegetations. Viridans group streptococci remain the classic cause of subacute native-valve IE arising from dental or oral mucosal sources, generally producing a more indolent course. Staphylococcus epidermidis and other coagulase-negative staphylococci dominate early prosthetic valve IE (within roughly the first year after surgery), reflecting perioperative or hospital-acquired inoculation. The HACEK organisms (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella) are classic, though now uncommon, causes of culture-negative or slow-growing endocarditis.

Vegetation characteristics on echo carry direct prognostic weight and should always be reported: size (length in the largest dimension), mobility, and location. Vegetations larger than 10 mm, and especially those that are highly mobile, carry a substantially increased risk of systemic or pulmonary embolization and often prompt earlier surgical referral, particularly when involving the mitral valve or when embolic events have already occurred. Prosthetic valve IE deserves special emphasis: it is more likely than native-valve IE to involve the paravalvular tissue (abscess, dehiscence, fistula) rather than remaining confined to the leaflet, which is precisely why TEE is considered mandatory — not optional — whenever prosthetic valve endocarditis is suspected, and why early prosthetic valve IE in particular carries a disproportionately high rate of surgical referral.