Paradoxical embolism as a cause of ischemic stroke of uncertain etiology. A transcranial Doppler sonographic study.

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Abstract
This study was designed to test the hypothesis that paradoxical embolization would be a cause of embolic strokes and transient ischemic attacks in patients with stroke of uncertain etiology in all age groups. Thirty patients who had stroke of uncertain etiology were studied. They were divided into the following three groups: 13 patients with sudden onset (group A), 11 patients with subacute onset (group B), and 6 asymptomatic stroke patients (group C). Eleven patients with stroke of obvious etiology (group D) and 11 normal healthy volunteers (group E) were also studied as controls. In all patients transcranial Doppler sonography and contrast echocardiography were recorded simultaneously after intravenous injection of the contrast medium. Findings of positive patient foramen ovale in contrast echocardiography or "chirp" sounds in transcranial Doppler sonography were defined as positive for paradoxical contrast embolization. Radioisotope phlebography of the lower extremities and pulmonary scintigraphy, using technetium-99 macroaggregated albumin, were performed in all 17 patients who had positive findings of paradoxical contrast embolization and in 12 patients whose findings were negative. Positive findings of paradoxical contrast embolization were found in 17 subjects by transcranial Doppler sonography but in only 8 on contrast echocardiography. These positive findings were detected more frequently in group A (77%) than in groups B, D, and E (9%, 18%, and 9%, respectively) (P < .05). In group C, 4 of 6 patients (67%) had positive findings. There were positive findings on both phlebography and pulmonary scintigraphy only in 6 group A patients, with positive findings of paradoxical contrast embolization. Transcranial Doppler sonography is a sensitive detector of right-to-left shunts. Paradoxical cerebral embolization might be frequent in patients with stroke of unknown etiology, especially when the stroke is of sudden onset.