Analysis of Micro-embolic Signals and Their Clinical Significance.

Background: The embolic signal obtained by TCD varies in sound, pitch and duration according to the size of the embolus and the materials of which it is composed. We tried to differentiate the micro-embolic signal from various embolic sources by wave analysis and also to clarify its clinical significance.Methods and Results: We recorded micro-embolic signals using TCD in 10 patients with various embolic conditions; 3 patients on a left ventricular assistance system (LVAS), 3 patients after replacement of the mitral valve with a prosthesis (MV), 2 patients with non-valvular atrial fibrillation (NVAF), and 2 patients with high-grade carotid stenosis (CS) . Acoustic power (AP), frequency, duration and background blood velocity (Vbg) were measured by a microcomputer system. The average duration of the embolic signal was longer in patients with LVAS and MV than in those with NVAF and CS. All patients who showed a correlation between Vbg and all parameters (AP, frequency, duration) were asymptomatic.Conclusion: The duration of micro-embolic signals, which reflects the size and components of the embolus, differs largely according to the embolic source. The correlation of background velocity with three parameters of micro-embolic signals (AP, duration, frequency) which appear to reflect the homogeneity of micro-emboli, may be a parameter indicating stroke risk.