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(Stroke. 2006;37:342.)
© 2006 American Heart Association, Inc.

Letters to the Editor

EmboDop: Insufficient Automatic Microemboli Identification

Markus Schoenburg, MD; Jeanette Baer, BS; Niko Schwarz, PhD; Erwin Stolz, MD; Manfred Kaps, MD; Georg Bachmann, MD Tibo Gerriets, MD

Justus-Liebig University, Department of Neurology, Experimental Neurology Research Group, Giessen, Germany

To the Editor:

We read with great interest the recent article by Drs Markus and Punter¹ on the assessment of the EmboDop ultrasound system. Independent evaluation of this device was overdue.

Differentiation between gaseous and solid microemboli in vivo is of utmost importance and would provide exciting new insights to the pathophysiology of stroke. Although the principle of the dual-frequency technique appears striking, the reliability of discrimination reported in the recent article is disappointing. Our own experience with the EmboDop system unfortunately supports these observations.

We performed transcranial Doppler monitoring of the left middle cerebral artery in 22 patients during coronary artery bypass grafting (CABG) using the EmboDop device. Standard machine parameters were used during data recording and offline evaluation. Digital Doppler data were then reevaluated offline by an experienced investigator according to the consensus criteria published in 1998.² The observer was blinded to the results of the automatic micro embolic signal (MES) detection. A subset of Doppler data was additionally evaluated by a second observer to determine interobserver reliability.

Interobserver agreement was acceptable; 92 of 96 MES (95.8%) were identified concordantly by both observers.

During cardiac surgery the experienced observer (gold standard) detected overall 1256 MES in 22 patients. Only 748 MES (59.6%) were correctly identified and classified as solid or gaseous; 508 MES (40.4%) were overlooked by the EmboDop equipment (false-negative). Furthermore, 718 (solid or gaseous) MES were identified by the machine that could not be verified by the human investigator (false-positive; Table).

View this table: [in this window] [in a new window]   Summary of the No. of Correctly Identified MES and the No. of False-Negative and False-Positive Findings as Provided by the EmboDop System

The percentage of false-negative MES varied between 19.4% and 73.1% (mean 40.4%; SD=16.2%) among the 22 patients, indicating that this poor recall ratio is not related to individual patients. The Figure indicates that misdiagnoses did not only occur if MES appear in clusters, which might complicate correct identification.

View larger version (37K): [in this window] [in a new window]   The figure shows representative Doppler frequency spectra of 2 patients during extracorporal circulation. Left: The micro embolic signal (arrow) was clearly identified by the human observer but wrongly classified as an artifact by the EmboDop system (arrowhead). Right: The EmboDop system identified a (gaseous) embolus (arrow) that could not be found by the human observer.

Unambiguous identification of microembolic signals and sufficient artifact rejection are basic requirements before a differentiation between solid and gaseous particles can be performed. In the present study, the EmboDop system as it stands now did not fulfill these requisites. This fact might in part explain and confirm the disappointing findings reported by Drs Markus and Punter.

References

1. Markus HS, Punter M. Can transcranial Doppler discriminate between solid and gaseous microemboli? Assessment of a dual-frequency transducer system. Stroke. 2005; 36: 1731–1734.[Abstract/Free Full Text]

2. Ringelstein EB, Droste DW, Babikian VL, Evans DH, Grosset DG, Kaps M, Markus HS, Russell D, Siebler M; for the International Consensus Group on Microembolus Detection. Consensus on microembolus detection by TCD. Stroke. 1998; 29: 725–729.[Abstract/Free Full Text]

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This Article Extract Full Text (PDF) All Versions of this Article: 37/2/342    most recent 01.STR.0000199640.74844.a5v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Schoenburg, M. Articles by Gerriets, T. Search for Related Content PubMed PubMed Citation Articles by Schoenburg, M. Articles by Gerriets, T.