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(Stroke. 2006;37:1065.)
© 2006 American Heart Association, Inc.

Original Contributions

The Use of Embolic Signal Detection in Multicenter Trials to Evaluate Antiplatelet Efficacy

Signal Analysis and Quality Control Mechanisms in the CARESS (Clopidogrel and Aspirin for Reduction of Emboli in Symptomatic carotid Stenosis) Trial

Ralf Dittrich, MD; Martin A. Ritter, MD; Manfred Kaps, MD; Mario Siebler, MD; Kennedy Lees, FRCP; Vincent Larrue, MD; Darius G. Nabavi, MD; E. Bernd Ringelstein, MD; Hugh S. Markus, FRCP Dirk W. Droste, MD

From the Department of Neurology (R.D., M.A.R., D.G.N., E.B.R., D.W.D.), University Hospital of Münster, Germany; Department of Neurology (M.K.), University Hospital of Giessen, Germany; Department of Neurology (M.S.), University Hospital of Düsseldorf, Germany; Division of Cardiovascular and Medical Sciences (K.L.), University of Glasgow, United Kingdom; Department of Neurology (V.L.), University of Toulouse, France; Centre for Clinical Neuroscience (H.S.M.), St. George’s University of London, United Kingdom; and Department of Neurology (D.W.D.), Centre Hospitalier de Luxembourg.

Correspondence to Martin A. Ritter, MD, Department of Neurology, University of Münster, Albert-Schweitzer-Straße 33, 48129 Münster, Germany. E-mail ritterm{at}uni-muenster.de

Background and Purpose— The CARESS (Clopidogrel and Aspirin for Reduction of Emboli in Symptomatic carotid Stenosis) trial proved the effectiveness of the combination of clopidogrel and aspirin compared with aspirin alone in reducing presence and number of microembolic signals (MES) in patients with recently symptomatic carotid stenosis. The present study aimed at installing primary and secondary quality control measures in CARESS because MES evaluation relies on subjective judgment by human experts.

Methods— As primary quality control, centers participating in CARESS evaluated a reference digital audio tape (DAT) before the study containing both MES and artifacts. Interobserver agreement of classifying signals as MES was expressed as proportions of specific agreement of positive ratings (ps±values). For all DATs included in CARESS (n=300), online number of MES and off-line number of MES read by the central reader were compared using correlation coefficients. As secondary control, a sample of 16 of 300 DATs was cross-validated by another independent reader (post-trial validator).

Results— For the reference tape, the cumulative ps±value was 0.894 based on 12 of 14 observers. Two observers with very different results improved after a training procedure. Agreement between post-trial validator and central reader was ps+=0.805, indicating very good agreement. Correlation between online evaluation and off-line evaluation of DATs was very good overall (cumulative =0.84; P<0.001).

Conclusion— Multicenter studies using MES as outcome parameter are feasible. However, primary and secondary quality control procedures are important.

Key Words: antiplatelet agents • carotid stenosis • stroke • ultrasonography, Doppler, transcranial

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