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(Stroke. 1995;26:2281-2284.)
© 1995 American Heart Association, Inc.

Articles

Interpretation of Embolic Phenomena During Carotid Endarterectomy

Julia L. Smith, BSc; David H. Evans, PhD; Lingke Fan, PhD; Michael E. Gaunt, FRCS; Nick J.M. London, MD; Peter R.F. Bell, MD A. Ross Naylor, MD

From the Departments of Surgery (J.L.S., M.E.G., N.J.M.L., P.R.F.B., A.R.N.) and Medical Physics (D.H.E., L.F.), Faculty of Medicine, Leicester University (England).

Correspondence to Miss Julia Smith, Department of Surgery, Clinical Sciences Building, Leicester Royal Infirmary, Leicester, England LE2 7LX.

Background and Purpose Air and particulate emboli are a major source of morbidity during carotid endarterectomy (CEA); however, amplitude overload and poor time resolution have restricted the ability of transcranial Doppler ultrasound to differentiate between the two.

Methods We have now overcome these two limitations by (1) rerouting embolic signals away from the audio frequency amplifier to avoid amplitude overload and (2) substituting the Wigner distribution function for the fast Fourier transform to improve time and frequency resolution. Thus, we can now accurately determine embolic duration and embolic velocity, the product of which is the sample volume length (SVL). This measurement represents the physical distance over which an embolic signal can be detected. The underlying hypothesis was that air reflected more ultrasound and would therefore be detected over a greater SVL.

Results The median SVL (interquartile range) for 75 in vitro air emboli was 1.97 cm (range, 1.70 to 2.35) compared with 0.27 cm (range, 0.16 to 0.43) for 185 particulate emboli detected during the dissection phase of CEA. Off-line analysis on an additional 560 embolic signals detected during different phases of CEA suggested that 46 of 143 (32%) of emboli immediately after shunt insertion were particulate, as were 19 of 33 (58%) occurring during shunting, 28 of 78 (36%) after restoration of flow in the external carotid artery, 23 of 251 (9%) after restoration of flow in the internal carotid artery, and 55 of 55 (100%) of those emboli detected during the early recovery phase.

Conclusions This development provides objective physical criteria upon which embolus characterization (particulate/air) can be based. This could have major implications for future patient monitoring with respect to modification of surgical technique and pharmacological intervention.

Key Words: carotid endarterectomy • embolism • ultrasonics

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