Transient Ischemic Attack: Risk Stratification and Treatment
Cucchiara B, Ross M
Ann Emerg Med
This article offers a comprehensive review on an important topic for the emergency physician: transient ischemic attack (TIA). This paper reviews various methods to risk-stratify the TIA patient, including several clinical scoring tools to predict a TIA patient's short-term risk of stroke. These scores can help the emergency physician decide the appropriate disposition. The article also reviews current literature and recommendations for acute and long-term TIA therapy. One important fact to note is that this paper adopts the traditional definition of TIA: an episode of focal cerebral ischemia with symptom resolution within 24 hours.
The article discusses three TIA risk-stratifying scoring systems: The California score (JAMA 2000;284:2901), the ABCD score (Lancet 2005;366:29), and a composite of those two scoring systems termed the ABCD2 score (Lancet 2007;369:283). The California score examined 1,707 patients and their post-TIA risk of stroke at 90 days, valuable information for the patient and his primary physician. To better assist the EP with management and disposition decisions from the ED, however, it would be more helpful to examine outcomes at shorter intervals.
In 2005, Rothwell et al derived the ABCD score to investigate seven- and 90-day stroke risk after a TIA. (Lancet 2005;366:29.) According to the score, there are four predictive variables: age over 60, blood pressure higher than 140 mm Hg or diastolic pressure higher than 90 mm Hg, clinical features of unilateral weakness or speech disturbance without weakness, and duration of symptoms. Unfortunately, external validations of the ABCD score showed conflicting results.
In 2007, the authors of the California and ABCD rules combined their data and derived a composite scoring system called the ABCD2 score. (Lancet 2007; 369:283.) It is the same as the ABCD score except it adds diabetes as a critical variable. The ABCD2 score and the associated risk of post-TIA stroke after two, seven, and 90 days is summarized in the tables. Notably, patients with a TIA with an ABCD2 score of 3 or less have a two- and seven-day stroke risk of only one percent.
The article continues with a discussion on the acute treatment of TIA and long-term stroke prevention. Acutely, perhaps the easiest treatment to implement is simply to lower the patient's head from the traditional 30° to 0°, a maneuver shown to increase the mean flow velocity in the middle cerebral artery by 20 percent. (Neurology 2005;64:1354.) Using permissive hypertension is also recommended for acute TIA-stroke management by the American Heart Association and the American Stroke Association guidelines. The patient's blood pressure should be allowed to auto-regulate except where the risk of excessively elevated blood pressure poses an even greater immediate risk, such as aortic dissection, acute coronary syndrome, acute pulmonary edema, and hypertensive encephalopathy. Otherwise, no specific interventions to lower blood pressure should be made in the first 24 hours after a TIA or stroke unless the systolic blood pressure exceeds 220 mm Hg or the diastolic blood pressure exceeds 120 mm Hg. (Circulation 2007;116:1504.)
Once hemorrhage is ruled out with CT, anti-platelet therapy should be considered. Unfortunately, as the authors point out, there are only limited data from randomized control trials specifically involving TIA treatment within the first 24 to 48 hours after symptom onset. The International Stroke Trial (IST) and the Chinese Acute Stroke Trial (CAST) studied the effects of early aspirin therapy after nonhemorrhagic stroke, and each randomized about 20,000 patients within 48 hours of symptom onset to either aspirin therapy or placebo. Data from both studies found that aspirin reduced recurrent ischemic stroke significantly for weeks after the initial stroke without any significant increased risk of bleeding. A pooled analysis of the trials indicates aspirin reduced recurrent stroke by seven per 1,000 patients treated (p<0.0001) and reduced mortality by four per 1000 patients treated. (Stroke 2000;31:1240.)
Recently, clopidogrel for cardiac and neurovascular causes has been studied, with the Fast Assessment of Stroke and Transient Ischemic Attack to Prevent Early Recurrence (FASTER) study finding no additional benefit of combining aspirin and clopidogrel compared with aspirin alone in treating the event within 24 hours after symptom onset. Significantly more symptomatic bleeding was observed in the combination arm than the aspirin-alone arm. (Lancet Neurol 2007;6:961.) The authors also concluded there was no good evidence of benefit from anticoagulation in stroke or TIA patients, and that the risk of bleeding is significant. They do say, however, that anticoagulation for specific causes of TIA or stroke may be worth examining.
The authors also highlight how important it is for the emergency physician to consider underlying causes of TIA that have acute management implications, such as atrial fibrillation, carotid stenosis, and arterial dissection. In these cases, specific consultation and treatment plans may be required to improve long-term outcome.
A few studies also showed that the risk of stroke was less in admitted groups than in discharged ones. According to recent guidelines by National Stroke Association on TIA hospitalization, hospitalization is recommended not only for patients with appropriate ABCD scores, but also for crescendo TIA, duration of TIA symptoms longer an hour, symptomatic carotid stenosis greater than 50 percent, a known cardiac source of embolus, or a known hypercoagulable state. (Ann Neurol 2006;60:301.)
Comment: With recent technological advances in neuroimaging, the accepted definition of TIA is in a state of flux. In contrast to the historical definition of TIA — focal neurologic ischemia resolving within 24 hours — the AHA and ASA now define TIA as “a transient episode of neurological dysfunction caused by focal brain, spinal cord, or retinal ischemia without infarction.” (Stroke 2009;40:2276.) This new definition represents a fundamental shift in defining TIA based on imaging findings (or the lack of them) rather than on an arbitrary time period. Adoption of the new definition has been slow, and the historical definition is still widely used in clinical practice.
The AHA-ASA guidelines for evaluating TIA also support the use of a clinical scoring system, specifically the ABCD2 score, to assist in determining the need for hospitalization. Although external validation studies for the ABCD2 score showed conflicting results, the guidelines recommend hospitalizing TIA patients if they present within 72 hours of symptom onset with an ABCD2 score greater than or equal to 3.
The AHA-ASA guidelines appropriately take into consideration the variability in our nation's health care system to provide rapid follow-up, recommending that patients be admitted to the hospital if appropriate evaluation and workup cannot be rapidly completed within two days as an outpatient. This factor alone should weigh heavily on the emergency physician's decision on whether to send a TIA patient home.
To summarize key ED management points for the TIA patient:
* Keep the symptomatic patient supine while in the ED because it may improve cerebral blood.
* Remember permissive hypertension, and resist the urge to treat elevated blood pressure within the first 24 hours unless there is an overwhelming reason to decrease it.
* Make a diligent attempt to identify the source of ischemic symptoms, including an EKG to rule out an embolic source and listening for carotid bruits (which can be minimal when the degree of carotid stenosis is high).
* Once hemorrhage is ruled out with CT, give aspirin.
* Don't be fooled by TIA mimics like hypoglycemia, infectious endocarditis, complex migraines, and peripheral cranial nerve lesions, and seizure.
* Never forget the uncommon but important vascular sources of TIA like carotid, vertebral, and aortic dissections.
As with many other diagnoses in our specialty, often the most complex and relevant medical decision-making is whether to send the patient home. With prominent guidelines emphasizing clinical scores like the ABCD2, one may become tempted to rely solely on the score to determine disposition, but keep in mind that this score, like all clinical scoring rules in medicine, is merely an adjunct to our clinical judgment, not a replacement.
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