Echocardiographic diagnosis of paradoxical embolism and the potential for right to left shunting.

Echocardiographic techniques are useful in establishing the presumptive clinical diagnosis of paradoxical embolism. Once a clinical diagnosis of systemic embolism has been established and a potential systemic venous source for embolic material has been diagnosed, echocardiographic (and particularly transesophageal echocardiographic techniques) can readily establish the presence or absence of an intracardiac communication and can help define the potential for right to left shunting across that communication (using saline contrast techniques). Except for the rare circumstance where echocardiography has been used to actually image paradoxical embolization in progress (such as may occur during intraoperative monitoring), the technique can only show the potential for such a mechanism for systemic embolization. Because patency of the foramen ovale is a common anatomic variant (occurring in approximately 25% of subjects) and transesophageal contrast echocardiography will show at least transient right to left shunting in most patients with patent foramen ovale, a mechanistic relationship between such findings and the occurrence of a systemic embolic event cannot be immediately inferred. Clinical assessment of alternative mechanisms for systemic embolization is required to judge the likelihood that the potential for paradoxical embolization is, in fact, the cause for systemic embolism in a given patient.