Clopidogrel cessation triggers aspirin rebound in patients with coronary stent.

WHAT IS KNOWN AND OBJECTIVE: Premature discontinuation of clopidogrel in patients undergoing percutaneous coronary intervention is a significant risk factor for thrombotic adverse outcomes. However, recent studies indicate that even discontinuation of long-term use of clopidogrel may be associated with multiple adverse outcomes, that is, rebound phenomenon whose mechanism is not definitely clear. The aim of the study was to examine the effect of clopidogrel withdrawal in those on combined aspirin and clopidogrel therapy. METHODS: This prospective, multicenter study enrolled 200 patients who underwent coronary stent implantation and were on dual antiplatelet therapy (100 mg aspirin + 75 mg clopidogrel) 1 year after the stent placement. In all patients, we measured the platelet aggregation, by multiplate electrode aggregometry, using two agonists [adenosine diphosphate with PGE1 (ADPHS) and arachidonic acid (ASPI)] two times: on the day of cessation of clopidogrel and 90 days after clopidogrel was stopped. RESULTS AND DISCUSSION: Following clopidogrel discontinuation, we registered an increase in ASPI values (P < 0·001), linear correlation between changes in ASPI and ADPHS values (P = 0·009) and significant difference in the values of ASPI first quartile of ADPHS compared with the other three (P < 0·001, P = 0·016, P < 0·001, I vs. II, I vs. III and I vs. IV quartile of ADPHS, respectively). WHAT IS NEW AND CONCLUSION: Our findings show that cessation of clopidogrel causes loss of antiplatelet synergism with aspirin, leading to a weakening of the response to aspirin, which may be one explanation for the rebound after the clopidogrel cessation.

Performance of a Ge-microstrip imaging detector and polarimeter.

Using 98% linearly polarized radiation at the European Synchrotron Radiation Facility in Grenoble, the performance of a prototype two-dimensional microstrip Ge(i) detector for x-ray imaging and as a Compton polarimeter has been evaluated. Using the energy and position sensitivity of the detector, the ability to obtain a complete reconstruction of the Compton event has been demonstrated. The modulation coefficient of the polarimeter is in good agreement with the theoretical limit of a perfect detector.

First measurement of the linear polarization of radiative electron capture transitions.

For radiative electron capture into the K shell of bare uranium ions, a study of the polarization properties has been performed. For this purpose a position sensitive germanium detector has been used as an efficient Compton polarimeter. This enabled us to measure the degree of linear polarization by analyzing Compton scattering inside the detector and to determine the orientation of the polarization plane. Depending on the observation angle and the beam energy used, the radiation is found to be linearly polarized by up to 80%. In all cases studied, the plane of polarization coincides with the collision plane. The results will be discussed in the context of rigorous relativistic calculations, showing that relativistic effects tend to lead to a depolarization of the radiation emitted.