Platelet Inhibition and Transcranial Doppler (TCD)-Detected Microemboli During and After Carotid Artery Stenting (CAS) in Asymptomatic Patients Prior to Cardiac Surgery

As with coronary artery stenting, activation and embolisation of platelets occurs with carotid artery stenting (CAS). Based on promising data on the use of clopidogrel plus aspirin in coronary stenting this dual antiplatelet regimen has been introduced as adjunctive treatment during CAS. There is as yet, however, no randomized controlled trial which compared different loading doses of clopidogrel during CAS. Taking into account that a wide interindividual variability in the response to a loading of clopidogrel exists, this study is intended to establish the optimal loading dose of clopidogrel. Therefore platelet function testing and a 1-hour of postprocedural TCD (transcranial doppler) monitoring will be performed.

Objective: Firstly, to investigate whether the absolute magnitude of Platelet Inhibition inversely correlates with the number of TCD-detected microemboli during and after CAS in patients who are being pre-treated with either a 300 mg or a 600 mg loading dose of clopidogrel. Secondly, if there is any impact on early neurological outcome determined by the loading dose of clopidogrel.

Carotid angioplasty with stent placement (CAS) has become a well-accepted treatment option for carotid artery stenosis. In combination with experience in CAS procedures and the introduction of protection devices and low-profile systems, the periprocedural risk of thromboembolic complications are comparable to that of standard surgical carotid endarterectomy (CEA) In our centre, all patients with severe asymptomatic carotid artery disease ( luminal diameter reduction of more than 80%, according to NASCET criteria) scheduled for cardiac surgery are eligible for CAS.

As with coronary artery stenting , activation and embolisation of platelets occurs with CAS. Based on promising data on the use of clopidogrel plus aspirin in coronary stenting, this dual antiplatelet regimen has been introduced in CAS. Specifically, an antiplatelet regimen with aspirin(300mg) and a 300 mg loading dose of clopidogrel at least 24 hours before carotid angioplasty has currently been the treatment of choice in carotid angioplasty with stent placement.

However, several studies have reported a wide interindividual variability in the response to a 300 mg loading of clopidogrel with a subsequent substantial proportion of patients not receiving the optimal benefit from it. Therefore, it has been suggested that a 600 mg loading dose will result in a faster onset, a higher responsiveness and a higher magnitude of platelet inhibition without any increase in bleeding complications. For these reasons, the interventional cardiology has already adopted the 600 mg loading dose regimen as standard of care during percutaneous coronary interventions. There is as yet, however, no randomized controlled trial which compared different loading doses of clopidogrel during CAS.

Using transcranial Doppler (TCD) monitoring of the middle cerebral artery during CAS, it is possible to register the number of TCD-detected microembolic signals during and after CAS. This monitoring enables the operator to diminish the risk of stroke during CAS. However, a significant number of patients develop an ischemic stroke in the hours following CAS after a symptom-free interval As published by van der Schaaf et al., in TCD monitoring after CEA, one hour of monitoring appeared to be effective to select those patients in whom the number of microemboli did not spontaneously decrease. More important, postoperative TCD monitoring was able to detect those patients who were at risk for new adverse cerebral events after the operation. Other studies demonstrate the potential application of ultrasonic emboli detection to examine the efficacy of new platelet agents in relatively small number of patients.

It remains to be established whether a higher magnitude of platelet inhibition before CAS has an additional protective effect by decreasing the microembolic load measured on TCD after the procedure. Moreover, such a TCD-monitoring post-CAS has not been performed systematically in the past and thus could reveal valuable information helpful to the understanding of post procedural cerebral complications and risk stratification.

Eligibility Criteria:
Inclusion Criteria:

* patient \> 18 years of age
* patient accepted for CAS
* temporal window for TCD available

Exclusion Criteria:

* severe renal impairment (creatinine\> 1.5mg/dl), abnormal liver function, malignancy, febrile disorder, acute or chronic inflammatory disease and other diseases influencing platelet reactivity
* extreme tortuositas or calcification of the lesion
* inadequate arterial access
* contraindication for angiography
* patient already receiving clopidogrel
* contra-indication to study drugs
* patients with active bleeding or at high-risk of bleeding
* uncontrolled hypertension ( \> 180/110 mmHg) despite optimal medication
* pregnancy and women with inadequate anticonception