Stroke prevention

Prediction and prevention of stroke after transient ischemic attack in the short and long term

Over the last 5 years, a number of studies have shown the early risk of stroke following transient ischemic attack (TIA) to be of the order of 5-10% at 1 week and 10-20% at 3 months, considerably higher than previously estimated. Because these studies have been carried out in a variety of different clinical settings, their findings are likely to be generalizable. Various independent prognostic factors for this early risk of stroke have been identified and models, based on clinical features at presentation, have been derived and validated to predict risk of stroke within 7 and 90 days after TIA. At the same time, diffusion-weighted magnetic resonance imaging and carotid imaging provide prognostic information and are likely to refine risk prediction further, although no unified model combining clinical and imaging data currently exists. Uncertainty continues surrounding the most effective secondary prevention in the hyperacute phase after TIA, especially in the choice of antiplatelet agents, although clinical trials to address this question are ongoing. However, the need for carotid endarterectomy in patients with symptomatic carotid stenosis is well established. The risk of vascular disease in the medium term (1-5 years) following TIA has been more widely studied, and predictive models for this are available. Recent data on the long-term (10 years and beyond) vascular risk after TIA demonstrate ongoing mortality from both cerebrovascular and cardiovascular causes, highlighting the need for continued secondary prevention.

Is there a role for combinations of antiplatelet agents in stroke prevention?

Antiplatelet medications are the agents of choice for secondary prevention of noncardioembolic ischemic strokes. Multiple clinical trials have proven their reliable albeit modest clinical benefits and relatively good safety profile. The most commonly recommended antiplatelet agents for secondary stroke prevention in North America and Europe are aspirin, clopidogrel, and the combination of aspirin and extended-release dipyridamole. Because of the multiple pharmacologic mechanisms available for platelet inhibition, combination antiplatelet agents have the potential for synergistic effects. However, combinations of antithrombotic agents do not necessarily improve clinical efficacy and are typically associated with increased toxicity. Clopidogrel and aspirin have been used in combination in patients with diverse arterial vascular diseases. Combination antiplatelet therapy with clopidogrel and aspirin has established clinical benefits, particularly in coronary disease and in patients who have undergone coronary stenting. Although it is tempting to extrapolate the benefits of clopidogrel and aspirin to the setting of secondary stroke prevention, recent clinical trials have failed to document significant clinical benefits in cerebrovascular patients. This failure has occurred because of a lack of significant efficacy for prevention of vascular events and a substantial increase in bleeding risk. Therefore, the clopidogrel and aspirin combination is not recommended for recurrent stroke prevention. In general, when clopidogrel is used for cerebrovascular patients, the addition of aspirin should be avoided unless there is a specific cardiac indication such as recent acute coronary syndrome or a coronary stent. The combination of aspirin and extended-release dipyridamole is supported by Class I data from two large studies demonstrating superiority over aspirin alone for recurrent stroke prevention. Although dual antiplatelet therapy with clopidogrel and aspirin has never been directly compared with the combination of aspirin and extended-release dipyridamole, clinical trial results favor the latter for secondary stroke prevention. Currently, there are no data for primary stroke prevention with dual antiplatelet agents regarding aspirin and extended-release dipyridamole. Limited data from the recent Clopidogrel for High Atherothrombotic Risk and Ischemic Stabilization Management and Avoidance (CHARISMA) trial indicate that the combination of clopidogrel and aspirin may be harmful, compared with aspirin alone.

Transcerebral platelet activation after aortic cross-clamp release is linked to neurocognitive decline

BACKGROUND

Neurocognitive decline after cardiac surgery requiring cardiopulmonary bypass (CPB) may be caused in part by highly prothrombotic atheroemboli to the brain; the source of these emboli is likely the ascending aorta and aortic arch. We examined transcerebral platelet activation gradients using simultaneous measurements in arterial and jugular venous blood and then compared gradients with post-CPB-associated neurocognitive injury.

METHODS

Eighty-one patients undergoing elective coronary artery bypass graft surgery requiring CPB were studied. Neurocognitive function was measured preoperatively and again at 6 weeks postoperatively. Paired arterial and jugular venous blood samples were drawn before surgery, immediately before and after aortic cross-clamp removal (an event previously linked to embolic showers), and at the end of the operation. Transcerebral platelet activation gradients (venous minus arterial values) were compared in patients with and without cognitive deficit.

RESULTS

Immediately after aortic cross-clamp removal, there was a significant increase in the transcerebral platelet activation gradient (increased % P-selectin-positive platelets during transcerebral passage) in the subset of patients who subsequently developed post-CPB cognitive deficit; this platelet activation gradient did not occur in patients without cognitive injury. In contrast, there was no transcerebral gradient of platelet activation in CPB patients as an entirety, nor was there a gradient at all other time points in the patient subset who went on to have cognitive deficit develop. This fleeting gradient of transcerebral platelet activation after cross-clamp removal was also significantly correlated with the overall change in cognitive injury score.

CONCLUSIONS

Transient intracerebral platelet activation after removal of the aortic cross-clamp is associated with post-CPB neurocognitive injury.