The use of echo density to quantify pulmonary right-to-left shunt in transthoracic contrast echocardiography

Transthoracic contrast echocardiography (TTCE) is the recommended screening tool to detect pulmonary right-to-left shunt (RLS) caused by pulmonary arteriovenous malformations (PAVMs). We assessed a novel method to quantify the RLS using the change in echo density (ED) following contrast injection.

An analysis of 437 consecutive patients [58% female, 47 years, interquartile range (IQR) 33-60] who underwent TTCE for the detection of a pulmonary RLS. Using ImageJ (National Institutes of Health), the change in ED was measured for each patient. This method was strongly correlated (Spearman's ρ = 0.89; P < 0.0001) with our standard method based on a four-point grading scale (no, mild, moderate, and severe RLS). In patients without a history of embolotherapy (n = 334), a PAVM was detected with chest computed tomography (CT) in 66 and embolotherapy was judged possible in 35 of these patients. The median increase in ED was higher in the latter: +20.1% (IQR 12.3-34.0) compared to non-treatable PAVM +0.2% (IQR -0.2 to 1.1). The specificity to detect treatable PAVMs increased from 87% to 90% when using the novel method without affecting the sensitivity (of 100%). Using the optimal cut-off value of +4.5% increase in ED, 8/74 (11%) needed chest CT-scans-individuals with a moderate or severe RLS-were no longer required without missing any treatable PAVM.

The use of ED quantification for pulmonary RLS is promising; resulting in a substantial decrease in the number of chest CT scans needed. However, this method and the threshold should be validated in an independent study population.