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Ann Thorac Surg 2001;72:981-982
© 2001 The Society of Thoracic Surgeons

Correspondence

Platelet aggregates and cardiopulmonary bypass

Yoshio Misawa, MDa, Hiroaki Konishi, MDa, Katsuo Fuse, MDa

a Department of Thoracic and Cardiovascular Surgery, Jichi Medical School, Yakushiji 3311-1, Minami-Kawachi, Tochigi 329-0498, Japan

e-mail: tcvmisa{at}jichi.ac.jp

To the Editor

It was with great interest that we read the article by Muriithi and associates [1]. The authors stated that plasma changes, which inhibited platelet macroaggregation, were induced by in vivo heparinization. Furthermore, it was noted that the inhibition was of an indirect, delayed nature which was transferable in vitro to normal platelets. Measurements of macroaggregation in whole blood were made by an impedance aggregometer (Chronolog 500-VS, Chronolog Corporation, Haverton, PA).

We have also evaluated platelet aggregation, however, utilizing the PA-200 aggregometer (Kowa Co Ltd, Tokyo, Japan) [2]. Platelet-rich plasma was obtained and platelet aggregates were shown as light-scattering intensity (LSI; in millivolts). Adenosine diphosphate (ADP) was used as the aggregating reagent (0.3 µmol/L). Three distint platelet aggregates were evaluated. Particles with an intensity of 25 to 400 mV were counted as small aggregates (9 to 25 µm); particles with an intensity of 401 to 1,000 mV were counted as medium aggregates (26 to 50 µm); and particles with an intensity of 1,001 to 2,048 mV were counted as large aggregates (51 to 70 µm). Data were recorded on a two-dimensional graph showing the changes. Time was expressed as a cumulative summation at 10-second intervals of LSI and the number of particles corresponding to that intensity in terms of particle size (volts x counts/10 seconds). Total intensity was recorded at 10-second intervals for 10 minutes. Small particle formation was observed mainly before heparinization (Fig 1A). Small-to-large particle formation took place approximately 5 minutes after systemic heparinization (Fig 1B). Small particles composed the main formation pattern 24 hours after operation (Fig 1C). Activated coagulation time of whole blood obtained before and after heparinization showed 109 seconds and 437 seconds, respectively.



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  		Fig 1. Platelet aggregation detected by the PA-200 aggregometer. (A) Platelet aggregation before operation. Small (S) particle formation was the main platelet aggregation. (B) Platelet aggregation after systemic heparinization. Not only small but also medium (M) and large (L) particle formations were recognized. (C) Platelet aggregation 24 hours after operation. Small particle formation was the main platelet aggregation. (LSI = light-scattering intensity.)

 
Muriithi and associates utilized whole blood, whereas we employed platelet-rich plasma. The aggregometer difference may have led to controversial results. As they suggested, macroaggregation in whole blood cannot be impaired directly by heparinization; however, the process may be influenced by the presence of transferable inhibitors produced by heparinization. We submit that the macroaggregation that was observed did not differ from the large platelet aggregates which we observed. How do the authors explain the difference between macroaggregation in whole blood and platelet aggregates in platelet-rich plasma? Comparing the study by Muriithi and associates using the Chronolog 500-VS aggregometer and our study using the PA-200 aggregometer, we hypothesize that platelet activity in platelet-rich plasma shows different patterns from those which occur in whole blood.

References

  1. Muriithi E.W., Belcher P.R., Day S.P., Menys V.C., Wheatley D.J. Heparin-induced platelet dysfunction and cardiopulmonary bypass. Ann Thorac Surg 2000;69:1827-1832.[Abstract/Free Full Text]
  2. Misawa Y., Konishi H., Kawahito K., Fuse K. Platelet activation and aggregation during normothermic cardiopulmonary bypass. J Jpn Assoc Thorac Surg 2001;49:21-28.

Related Article

Platelet aggregates and cardiopulmonary bypass: Reply
Elijah W. Muriithi and Philip R. Belcher
Ann. Thorac. Surg. 2001 72: 982. [Extract] [Full Text] [PDF]




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Katsuo Fuse
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