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J Thorac Cardiovasc Surg 2005;129:1203
© 2005 The American Association for Thoracic Surgery

Letters to the Editor

Technique for microsphere injection

Yoshio Ootaki, MD, PhD, Kiyotaka Fukamachi, MD, PhD

Department of Biomedical Engineering, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, OH 44195

To the Editor:

We read with great interest the article by Hedayati and associates1 recently published in the Journal. The authors suggested that axillary artery cannulation for cardiopulmonary bypass is cerebroprotective from aortic atheroemboli by using canine models. We respectfully would like to note some procedural inconsistencies that might have lead to bias in the authors’ conclusions.

The authors assessed the distribution of microspheres simulating aortic atheroemboli shed by patients during cardiopulmonary bypass. However, the microsphere injection method was inconsistent (eg, the pump flow was not constant, and the rate of microsphere injection was unclear), and the reference blood withdrawal rate for calculating tissue blood flow was unclear. Because the distribution pattern of the microspheres can be influenced easily by the pump flow rate, microsphere injection rate, shape of the aorta, and location of the injection, more precise experimental protocols might affect this study’s results.

One more point of concern in this study is the size of the microspheres. Small microspheres (15 μm in diameter) have been used for measuring tissue blood flow,2 and large microspheres (>50 μm in diameter) have been used for creating microemboli3 by several investigators. Hedayati and associates1 used microspheres 15 μm in diameter; however, they did not use the microspheres to measure tissue blood flow but rather as microemboli in this study. Because atheroemboli are generally larger than 15 μm in diameter and because size affects the degree of cerebral ischemia and infarction,4 we believe that the larger microsphere should have been used to analyze the risk of atheroemboli in the aorta during cardiopulmonary bypass.

In light of these considerations, the authors’ conclusion that “axillary artery cannulation for cardiopulmonary bypass is cerebroprotective” cannot be fully supported on the basis of the data presented. More studies with larger microspheres or flow characterization with both particle image velocimetry and laser Doppler velocimetry could provide more meaningful results and insights on this subject to further understand this clinically important topic.

References

  1. Hedayati N, Sherwood JT, Schomisch SJ, Carino JL, Markowitz AH. Axillary artery cannulation for cardiopulmonary bypass reduces cerebral microemboli. J Thorac Cardiovasc Surg. 2004;128:386-390.[Abstract/Free Full Text]
  2. Reinhardt CP, Dahlberg S, Tries MA, Marcel R, Leppo JA. Stable labeled microspheres to measure perfusion. validation of a neutron activation assay technique. Am J Physiol Heart Circ Physiol. 2001;280:H108-H116.[Abstract/Free Full Text]
  3. Takagaki M, Rottenberg D, McCarthy PM, Smedira NG, Dessoffy R, Al-Ahmadi M, et al. A novel miniature ventricular assist device for hemodynamic support. ASAIO J. 2001;47:412-416.[Medline]
  4. Rapp JH, Pan XM, Yu B, Swanson RA, Higashida RT, Simpson P, et al. Cerebral ischemia and infarction from atheroemboli <100 microns in size. Stroke. 2003;34:1976-1980.[Abstract/Free Full Text]




This Article
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Right arrow Cerebral protection
Right arrow Extracorporeal circulation

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