Definition and Evaluation of Transient Ischemic Attack

This scientific statement is intended for use by physicians and allied health personnel caring for patients with transient ischemic attacks. Formal evidence review included a structured literature search of Medline from 1990 to June 2007 and data synthesis employing evidence tables, meta-analyses, and pooled analysis of individual patient-level data.

The review supported endorsement of the following, tissue-based definition of transient ischemic attack (TIA): a transient episode of neurological dysfunction caused by focal brain, spinal cord, or retinal ischemia, without acute infarction. Patients with TIAs are at high risk of early stroke, and their risk may be stratified by clinical scale, vessel imaging, and diffusion magnetic resonance imaging.

Diagnostic recommendations include: TIA patients should undergo neuroimaging evaluation within 24 hours of symptom onset, preferably with magnetic resonance imaging, including diffusion sequences; noninvasive imaging of the cervical vessels should be performed and noninvasive imaging of intracranial vessels is reasonable; electrocardiography should occur as soon as possible after TIA and prolonged cardiac monitoring and echocardiography are reasonable in patients in whom the vascular etiology is not yet identified; routine blood tests are reasonable; and it is reasonable to hospitalize patients with TIA if they present within 72 hours and have an ABCD2 score >3, indicating high risk of early recurrence, or the evaluation cannot be rapidly completed on an outpatient basis.

Recent scientific studies have revised our understanding of 3 key aspects of transient ischemic attack (TIA): how it is best defined, what the early risk of stroke and other vascular outcomes is, and how it is best evaluated. This statement reviews and synthesizes recent scientific advances regarding the definition, urgency, and evaluation of TIA and is designed to aid the clinician in the short- and long-term management of patients with TIA.

Definition
TIAs are brief episodes of neurological dysfunction resulting from focal cerebral ischemia not associated with permanent cerebral infarction. In the past, TIAs were operationally defined as any focal cerebral ischemic event with symptoms lasting < 24 hours. Recently, however, studies from many groups worldwide have demonstrated that this arbitrary time threshold was too broad because 30% to 50% of classically defined TIAs show brain injury on diffusion-weighted magnetic resonance (MR) imaging (MRI).

Several groups have advanced newer, neuroimaging-informed, operational definitions of TIA such as “a brief episode of neurological dysfunction caused by focal brain or retinal ischemia, with clinical symptoms typically lasting less than one hour, and without evidence of acute infarction” (p 1715). However, with rare exceptions, the newer definitions have not yet been formally considered for endorsement or rejection by authoritative organizations. This statement reviews the data supporting revision of the definition of TIA. For those aspects found to be strong or conclusive, this statement endorses a specific revised definition, moving the field forward.

Urgency

Large cohort and population-based studies reported in the last 5 years have demonstrated a higher risk of early stroke after TIA than generally suspected. Ten percent to 15% of patients have a stroke within 3 months, with half occurring within 48 hours. Acute treatments for TIA also have evolved, with new data supporting early rather than delayed carotid endarterectomy for TIA patients with carotid stenosis.

Methods for Patient Evaluation
Over the last decade, substantial new diagnostic advances have occurred, including the widespread availability of MR angiography (MRA) and computed tomographic (CT) angiography (CTA), the recognition that diffusion MR frequently shows abnormalities in classic TIA patients, and the development and validation of risk stratification algorithms that identify TIA patients at higher and lower risk of early stroke.

Accordingly, clinicians are in need of updated guidance regarding the definition, urgency, and evaluation of patients with TIA. Formal levels of evidence and classes of recommendations are used. Because there are few definitive clinical trials in this area, this document is a scientific statement rather than a guideline. The treatment of TIA was not addressed by this writing panel because it is already covered in the Stroke Council’s guideline statements on treatment of acute cerebral ischemia and secondary prevention after ischemic stroke and TIA.

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