Objective To compare the prevalence and grade of right-to-left shunt (RLS) in children with arterial ischaemic stroke (AIS) and in controls.

Design Prospective study.

Setting Tertiary paediatric referral centre.

Patients 30 consecutive children with AIS.

Intervention Contrast transcranial Doppler (cTCD) with Valsalva manoeuvre was performed in children with AIS and in controls.

Main outcome measures Detection and quantification of RLS.

Results Logistic regression analysis showed that RLS was significantly associated with AIS and prothrombotic disorders or with AIS of undetermined aetiology (OR 6.10; 95% CI 1.41 to 26.3; p=0.015). The prevalence of RLS was significantly higher in a group of children with AIS and prothrombotic disorders or with AIS of undetermined aetiology compared to controls (p<0.05). Significantly more microembolic signals (MES) were detected in a group of children with AIS and prothrombotic disorders or with AIS of undetermined aetiology than in controls (p<0.005).

Conclusions Both the prevalence of RLS and number of detected MES were significantly higher in a group of children with AIS and prothrombotic disorders or with AIS of undetermined aetiology compared to controls. These findings suggest that paradoxical embolism may be an underestimated cause of AIS in children, particularly those with AIS and prothrombotic disorders or with AIS of undetermined aetiology.