Preventing stroke after transient ischemic attack.

ischemic or hemorrhagic cause. It is now clear that transient ischemic attack and minor ischemic stroke are highly predictive of a subsequent disabling ischemic stroke within hours or days. The critical clinical problems for physicians and nurse practitioners who evaluate these patients are to identify that the patient has had a stroke or transient ischemic attack and to stratify risk to determine if the patient requires rapid intervention to prevent recurrent stroke. Diagnosing transient ischemic attack and minor ischemic stroke is not easy. Transient ischemic attacks are sudden. Although maximal symptoms occur at onset, it is a historical diagnosis since patients usually have no clinical signs by the time they are evaluated. Most transient ischemic attacks last 15 minutes or less. Persistent symptoms or signs, however minor, imply a diagnosis of minor stroke. However, this technical distinction is rarely made by clinicians in routine practice or in the current stroke literature. Common mimics of minor stroke or transient ischemic attack include migrainous aura, simple partial seizures and somatization. Stroke is the most common sudden neurologic event affecting adults; ischemia should be the default diagnosis when there is uncertainty. Symptoms are related to the area of the brain that is dysfunctional rather than to the cause of the dysfunction, making diagnostic inference difficult. Imaging is helpful, particularly diffusion-weighted magnetic resonance imaging, in which a positive result rules in the diagnosis of ischemia. A fast magnetic resonance protocol for stroke consisting of an axial diffusionweighted image, axial fluid-attenuated inversion recovery imaging and axial gradient-recalled echo imaging (to detect hemorrhage) takes less than 10 minutes of imaging time and could be made available in all large hospitals in Canada. A normal magnetic resonance image does not rule out a diagnosis of ischemia, but provides confidence that the immediate risk of stroke is low. Diagnosing transient ischemic attack identifies a patient who is at risk for subsequent stroke. The risk of stroke after transient ischemic attack is somewhere between 2% and 17% within the first 90 days. Among patients with transient ischemic attack, one in five will have a subsequent stroke (the most common outcome), a heart attack or die within one year. Recurrent stroke can occur in one of two ways: the initial stroke or transient ischemic attack progresses and worsens, with ischemia evolving in the initial vascular territory; or a subsequent ischemic event occurs (e.g., a new embolic event) in the same or new vascular territory. Each situation depends on the mechanism of the initial event and the residual vascular patency. A high proportion of strokes are due to embolic (arteroembolic or cardioembolic) occlusion of intracranial arteries. Early assessment of intracranial and extracranial vessels is critical to assessing risk. Patients with persistent intra cranial occlusions have a four-fold increase in risk of developing recurrent stroke. Stroke caused by arteroemboli from large atherosclerotic arteries (e.g., extracranial carotid or vertebral artery) can recur early after the initial event. These causes can be quickly identified with imaging of the intracranial and extracranial arteries. Lacunar syndromes are more challenging because the small penetrating arteries are too small to see using current imaging technology. Cardioembolic stroke events tend not to recur early, and there is no clear evidence that anticoagulation prevents recurrence within the first two weeks post-event; therefore, the cardiac work up can be done as an outpatient. Understanding the mechanism and vascular diagnosis involved in transient ischemic attack and stroke allows a rational approach to early intervention. This is not afforded by the ABCD2 score (age, blood pressure, clinical features, duration of symptoms and diabetes), which relies on clinical risk factors, and explains why the ABCD2 is largely an ineffective screening tool. Preventing stroke after transient ischemic attack