Currently it is believed that right-to-left shunt is closely associated with cryptogenic stroke.Right-to-left shunt is classified into intracardiac shunt and extracardiac shunt.As for intracardiac shunt,patent foramen ovale(PFO)has been widely recognized by neurologists,but as for extracardiac shunt,pulmonary arteriovenous malformation(PAVM)is often neglected due to its low incidence rate,but with significantly higher probabilities of stroke and recurrence than PFO.At present,the foaming test has been widely used in the screening for right-to-left shunt.The patients with positive emboli in early shunt and three cardiac cycles are often classified as PFO,and it is believed that the emboli caused by in-trapulmonary right-to-left shunt tend to appear earlier than those caused by intracardiac shunt.In fact,there is no absolute limit for the time of shunt,and it is impossible to distinguish intracardiac shunt from extracardiac shunt based on such time alone.This article mainly analyzes the characteristics of right-to-left shunt caused by PAVM using contrast-enhanced tran-scranial Doppler(c-TCD).
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