Association between the amount of right-to-left shunt and infarct patterns in patients with cryptogenic embolic stroke: A transcranial Doppler study

Background: Paradoxical embolism has been documented as a mechanism of cryptogenic embolic stroke. We investigated the frequency of right-to-left shunt in patients with cryptogenic embolic stroke and evaluated the factors associated with diffusion-weighted imaging (DWI) lesion pattern. Methods: We analyzed data on 157 consecutive patients with acute ischemic stroke because of presumed cryptogenic embolism. Agitated saline transcranial Doppler study was conducted in all patients to detect right-to-left shunt. We evaluated the association of the amount (microemboli <20 vs. ≥20) and activity (spontaneous vs. after Valsalva maneuver only) of right-to-left shunt with diffusion-weighted imaging lesion patterns. Results: Right-to-left shunt was observed in 96 (61·1%) patients. The multiplicity and distribution of diffusion-weighted imaging lesions did not differ depending on the amount and activity of right-to-left shunt. However, the size of diffusion-weighted imaging lesions differed depending on the amount of right-to-left shunt (P=0·019). Right-to-left shunt was more frequently observed in patients with small (<1cm) infarcts than in those with a large infarct (66·7% vs. 45·9%), and most patients with a larger amount of right-to-left shunt were found to have small infarcts on diffusion-weighted imaging (80%). The clinical characteristics, including Framingham stroke risk strategy, did not differ between the groups. Conclusions: Our results indicate that the amount of right-to-left shunt determines the Diffusion-weighted imaging lesion patterns and suggest that mechanisms of stroke other than paradoxical mechanism may play an important role in patients with large cryptogenic embolic stroke.