Pulmonary shunt fraction measurement compared to contrast echocardiography in hereditary haemorrhagic telangiectasia patients: time to abandon the 100% oxygen method?

Background: The presence of pulmonary right-to-left shunting (RLS) is associated with severe neurological complications from paradoxical embolisation in patients with hereditary haemorrhagic telangiectasia (HHT) and screening is warranted. Pulmonary shunt fraction measurement with the 100% oxygen method can be used for the detection and quantification of functional pulmonary RLS, although transthoracic contrast echocardiography (TTCE) has emerged as the gold standard over the last few years.

Objective: The aim of this study was to determine the true diagnostic accuracy of the established 100% oxygen method in detecting pulmonary RLS, as compared to TTCE.

Methods: We analysed 628 persons screened for HHT between 2004 and 2010, all of whom underwent TTCE. A quantitative 3-point grading scale was used to differentiate between minimal, moderate or extensive pulmonary RLS on TTCE (grade 1-3, respectively). Additional shunt fraction measurement with the 100% oxygen method was pursued in cases of pO2 <13 or <12 kPa in patients younger or older than 30 years, respectively. A shunt fraction >5% was considered pathological.

Results: Both TTCE and the 100% oxygen method were performed in 210 subjects. Although the presence of a pathological shunt fraction correlated with an increased pulmonary shunt grade on TTCE, the 100% oxygen method confirmed a >5% shunt fraction in only 51% of patients with pulmonary RLS on TTCE (14, 20 and 72% for grade 1, 2 and 3, respectively).

Conclusion: Pulmonary shunt fraction measurement with the 100% oxygen method is not a useful screening technique for the detection of pulmonary RLS in HHT as its sensitivity is too low and large pulmonary shunts on TTCE may remain undetected using this method.