Article under review: Easton JD, Saver JL, Albers GW, et al. Definition and evaluation of transient ischemic attack: a scientific statement for healthcare professionals from the American Heart Association/American Stroke Association Stroke Council; Council on Cardiovascular Surgery and Anesthesia; Council on Cardiovascular Radiology and Intervention; Council on Cardiovascular Nursing; and the Interdisciplinary Council on Peripheral Vascular Disease. Stroke 2009;40(6):2276-93.
Background: Beginning in the 1960s, transient ischemic attack (TIA) was operationally defined as a focal cerebral ischemic event with symptoms lasting less than 24 hours; a reversible ischemic neurologic event (RIND) was defined as a focal cerebral ischemic event with symptoms lasting 24 hours to 7 days; and only symptoms lasting more than 7 days were thought to reliably indicate a stroke. However, during the 1970s it became evident that most events with symptoms lasting 24 hours to 7 days were associated with cerebral infarction and, hence, were strokes. More recently, studies in the 1980s utilizing high-resolution CT and later studies utilizing diffusion-weighted MRI have demonstrated that about one third of individuals with traditionally defined transient ischemic attacks (ie, with symptoms lasting less than 24 hours) have evidence of new cerebral infarction (Shah et al 2007). As a result, in 2002 a new tissue-based definition of transient ischemic attack was proposed: "a brief episode of neurological dysfunction caused by focal brain or retinal ischemia, with clinical symptoms typically lasting less than 1 hour, and without evidence of acute infarction" (Albers et al 2002).
Purpose: To promulgate a new American Heart Association/American Stroke Association Stroke Council practice guideline concerning the definition and evaluation of transient ischemic attacks.
Methods: The authors developed practice guidelines based on evidence-based literature review and consensus of subject-matter experts.
Definition of transient ischemic attack:
Because the previous 24-hour criterion for transient ischemic attack does not adequately distinguish between patients with and without infarction and because defining transient ischemic attack with a maximum 24-hour duration has the potential of delaying the initiation of effective therapies, the authors propose a revised definition of transient ischemic attack based on the earlier one proposed by Albers and colleagues in 2002 (Albers et al 2002). Notably, the phrase "typically less than 1 hour" in the definition proposed by Albers and colleagues was not helpful, because a 1-hour time point also did not accurately distinguish between patients with and without cerebral infarction.
The revised definition of transient ischemic attack endorsed by the American Heart Association is "a transient episode of neurological dysfunction caused by focal brain, spinal cord, or retinal ischemia, without cerebral infarction" (Easton et al 2009).
Evaluation of patients with transient ischemic attack:
Conclusions and commentary: The revised definition of transient ischemic attack does not use an arbitrary time-based criterion, recognizing that the typical duration of a transient ischemic attack is less than 2 hours but that occasionally prolonged symptomatic episodes may occur without infarction. Because the revised definition of transient ischemic attack uses a tissue-based criterion rather than a time-based criterion, stroke and transient ischemic attack rates with the new definition will not be directly comparable to such rates under the prior definition. Diagnostic certainty under the new definition will also depend on the extensiveness of the diagnostic evaluation and the availability of advanced neuroimaging, so estimates of stroke and transient ischemic attack incidence will vary by whether and when advanced neuroimaging studies are performed. Because some infarcts will not be visualized even with state-of-the-art imaging techniques, patients should still be diagnosed as having a stroke if they have persistent symptoms lasting several days that are consistent with a small deep infarct, even in the absence of neuroimaging confirmation of a new ischemic lesion.
In some patients it will be difficult to know whether to label the problem as a transient ischemic attack or a stroke. For example, in patients with symptoms of relatively brief duration (ie, lasting 2 to 24 hours), it may be difficult to determine the correct diagnosis in the absence of a detailed diagnostic evaluation. Similarly, in patients with acute cerebrovascular symptoms who have not had neurodiagnostic testing, it is not yet known whether the symptoms will resolve or persist. Although the authors of the present report stopped short of proposing a specific terminology for such situations, they did suggest that it would be "reasonable" to refer to such situations as "acute neurovascular syndromes" analogous to terminology used in cardiology, pending clarification with further observation and/or advanced neuroimaging.