Identification of echocardiographic "smoke" in a bench model with transcranial Doppler ultrasound

Background and Purpose-Spontaneous echo contrast in cardiac chamber has bee n indicated as a source of cerebral embolism. The nature of the echocardiog raphic smokelike signal is still not fully understood. This study was desig ned to regenerate spontaneous echo contrast and verify its thromboembolic c haracters in an in vitro model. Methods-Spontaneous echo contrast was reproduced in an expansion chamber un der low flow conditions in a close circulation system. The spontaneous echo contrast was monitored and recorded with a 2-dimensional cardiosonography system and a transcranial Doppler device. Meanwhile, clinically commonly en countered embolic materials such as whole-blood clots, platelet aggregate-r ich plasma, air bubbles, and 100-mL normal saline were injected into this m onitored circuit. The differentiation of spontaneous echo contrast from emb oli was performed by both visual observations of the echo images and offlin e Doppler signal intensity analysis. Average signal intensities produced by spontaneous contrast and injection of embolic materials and saline were co mpared. Furthermore, the effect of Doppler-detected flow velocity on genera tion of spontaneous contrast was also evaluated. Results-Spontaneous echo contrast was reproduced at low flow settings (90 t o 120 mL/min) in this model. There was no significant difference in average signal intensity between the flow with spontaneous echo contrast and that without the echo (P=0.71). However, injection of embolic materials or norma l saline did not generate smokelike image but caused much higher average si gnal intensity than the flow with spontaneous contrast (P<0.001). Injection of normal saline also increased average signal intensity. Conclusions-Our results suggest that smokelike echo is a special echo pheno menon occurring at low flow situations and does not itself produce material capable of embolizing into the systemic circulation.