The use of contrast in transesophageal echocardiography in patients with atrial fibrillation

Transesophageal echocardiography (TOE) is considered the gold standard imaging modality for detection of thrombi in the left atrium and left atrial appendage. Multiplane images taken of the left atrial appendage (LAA) are particularly important. This is particularly important in patients due for cardioversion (for treatment of atrial fibrillation), yet there are still a significant number of patients for whom a diagnosis is inconclusive (Jung et al., 2013) which can often lead to treatment being delayed or denied. In addition, around 1% of patients suffer an embolic event after cardioversion, which is likely to be due to a false negative TOE.

A thrombus in the left atrial appendage can be missed when the echogenicity of the thrombotic material is low, compounded by the fact that the overall image quality of the patient may also be suboptimal. The application of contrast opacifies the appendage and can result in a clear contrast-free area in the presence of a thrombus, allowing the operator to make a positive diagnosis.

In their 2013 study, Jung et al. looked at whether contrast enhancement aided the identification of thrombi in the LAA with TOE pre-cardioversion.

Of the patients in whom a thrombus was identified with the aid of contrast, 70% also had decreased LAA flow (=0.3m/s as assessed with pulse wave Doppler) and 80% had spontaneous echo contrast, again indicative of blood stasis. However, these parameters alone are clearly not sufficient to infer the presence of a thrombus, as they are not specific to the presence of thrombi and may be influenced by other factors such as the duration of atrial fibrillation and the size of the left atrium (Jung et al., 2013).

Equally important as the discovery of thrombi with contrast enhancement in 2 additional patients who would otherwise have been ‘missed,’ thrombi could also be more confidently excluded with contrast TOE (83.3% of patients versus 66.7%). Furthermore, no patients in the contrast enhanced group who went on to have cardioversion suffered thromboembolic complications, whereas 3 of the non-contrast enhanced group did.

Conclusions of this study

Although injecting a contrast bolus adds to the total examination time and cost, it greatly aids in achieving a definitive diagnosis in patients for whom there may be some doubt. There is now a very low threshold for delivering contrast in modern echo labs for endocardial definition on TTE; this study suggests that a similarly low threshold would be appropriate during the use of TOE for cardioversion.

References

Jung, P., Mueller, M., Schuhmann, C., et al. (2013). Contrast enhanced transesophageal echocardiography in patients with atrial fibrillation referred to electrical cardioversion improves atrial thrombus detection and may reduce associated thromboembolic events. Cardiovascular Ultrasound201311:1