**5.5. Limitations of echocardiography**

Echocardiography, especially TTE, has a number of potential limitations due to patient and nonpatient factors. TTE image quality is influenced by body habitus, chest wall deformity, rib space size, and interposing lung tissue. Poor TTE image quality is the main factor accounting for the superior diagnostic accuracy of TEE [54].

Furthermore, the skills of the sonographer and echocardiologist also influence diagnostic accuracy as shown by interobserver variability. Clinical history is important to the reporting echocardiographer but may result in bias with a trade-off between sensitivity and specificity [102, 103].

The ultrasound equipment, machine settings, and transducer frequency all impact on diagnostic accuracy. The limits of image resolution allow detection of vegetations down to 1.5–2 and 3–4 mm, for TEE and TTE, respectively. Not surprisingly, it has been shown that smaller vegetation size reduces the sensitivity of TTE [54, 104].

Mimickers of vegetations are often responsible for false-positive findings. Examples include degenerative valvular tissue, calcification, flail chords, thrombus, tumor, artifact from calcium or prosthetic material, and even normal anatomical variants such as a prominent Eustachian valve. Small thin linear strands are common and are frequently seen on native valves along the leaflet coaptation zone and may be confused with vegetations. Also, small sterile strands are frequently (18–43%) seen on prosthetic valves and are of uncertain significance [105].

The limitations outlined underscore the need to repeat imaging in due course (usually within one week) if the initial TTE and TEE are both negative, but there remains ongoing clinical suspicion of IE.
