Is There an Effect of Contrast Media on Multifrequency Transcranial Doppler Classification of Cerebral Microemboli During Coronary Angiogram?

Dear Editor:

We have read with great interest the study by Jurga et al about guidewire withdrawal in ascending aorta increasing cerebral microembolism during coronary angiography.¹ In this study, saline/contrast flushing of the catheter in the ascending aorta (after discarding >10 mL of blood) clearly generated more particulate cerebral microemboli (solid + gaseous) compared to the descending aorta. Lack of contrast injection during the second part of the study resulted in less microemboli detection. Similarly, during carotid stenting of 11 patients, at the time of contrast injections without the protection device, a total of 1013 emboli were detected (28% of these being solid). After the procedure, even with the protection device, there was still no statistical difference in the amount of emboli (total 1241; 31% solid) during contrast injections.²

Both of these studies used multifrequency transcranial Doppler (TCD) system (Embo-Dop; DWL Elektronische Systeme GmbH) to detect particulate cerebral microemboli in middle cerebral arteries. In this system, differentiation between solid and gaseous microemboli is based on the principle that solid microemboli reflect more ultrasound at the higher versus the lower frequency, whereas the opposite is the case for gaseous microemboli.³ During in vitro validation of this technique (in an irodinium or pig blood closed system), plastic spheres with a diameter of 80 µm and 50 µm, and gas bubbles with a diameter from 8-25 µm were used with 95.1% correct classification.³The contrast media has not been used during validation of cut-off for gas bubble detection in this study³ and the effect of contrast on acoustic reflection from bubbles is not very clear. We think bubbles in contrast might have a different embolus-blood ratio (EBR) than the bubbles in whole blood and they might have been falsely classified as solid rather than gaseous and might have resulted in the finding of increased solid embolization during contrast injections in these studies. As also mentioned by Russell et al, embolus detection and differentiation can also be limited when there are bursts of gaseous or solid emboli or when several emboli may enter the sample volume at the same time,⁴ and this might have also effected the differentiation of microemboli.

It was reassuring to see in this well done study that the advancement of coronary catheters beyond the aortic arch without using wire does not increase microemboli.¹ We were wondering if the authors have a different explanation for increased microemboli during contrast injections. 

References

1. Jurga J, Tornvall P, van der Linden J, Sarkar N.Guidewire withdrawal in ascending aorta increases cerebral microembolism during coronary angiography — a randomized comparison of two guidewire techniques. J Invasive Cardiol. 2014;26(1):1-6.
2. Chen CI, Iguchi Y, Garami Z, et al. Analysis of emboli during carotid stenting with distal protection device. Cerebrovasc Dis. 2006;21(4):223-228. Epub 2006 Jan 27.
3. Russell D, Brucher R. Online automatic discrimination between solid and gaseous cerebral microemboli with the first multifrequency transcranial Doppler. Stroke. 2002;33(8):1975-1980.
4. Russell D, Brucher R. Embolus detection and differentiation using multifrequency transcranial Doppler. Stroke. 2005;36(4):706.

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From the Louisiana State University Health Sciences Center, Shreveport, Louisiana.

Address for correspondence: Assistant Prof Nuri I. Akkus, MD, LSU Health Sciences Center, Shreveport Cardiology, 1501 Kings Highway, Shreveport, LA 71111. Email: iakkus@hotmail.com

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Authors’ Reply:

We would like to thank Drs Akkus and Edevettal for their comment on our study. It is an interesting thought that contrast medium alters the relation between particulate and gaseous emboli. However, this criticism remains hypothetical since the authors fail to present any data in support of their view that the use of contrast could decrease the validity of discrimination between particulate and gaseous emboli. Second, and clinically more important, the results of part two, where no contrast was given, were similar to the overall results including contrast injections. Furthermore, we have previously shown that particulate emboli are mainly detected during advancement, retraction and exchange of catheters when no contrast is injected.¹

Sincerely,

Juliane Jurga, MD; Per Tornvall, MD, PhD; Jan van der Linden, MD, PhD, Professor; Nondita Sarkar, MD, PhD; Karolinska Institutet, Stockholm, Sweden

Reference

1. Jurga J, Nyman J, Tornvall P, et al. Cerebral microembolism during coronary angiography: a randomized comparison between femoral and radial arterial access. Stroke. 2011;42(5):1475-1477.