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July 2011, Volume 61, Issue 7

Evidence Based Medicine

My patient just had a transient ischaemic attack. Can I predict his risk for stroke? Is stroke inevitable or preventable?

Maria Khan  ( Fellow International Cerebrovascular Translational Clinical Research Training Program, Stroke Service, Aga Khan University Hospital, Karachi, Pakistan. )
Ayeesha Kamran Kamal  ( Director Stroke Service and Vascular Fellowship Program, Aga Khan University Hospital , Karachi, Pakistan. )

Transient Ischaemic Attack:
Transient Ischaemic attack or TIA has traditionally been defined as a discrete neurological deficit lasting for < 24 hours. The new definition of a TIA is that of a brief neurological dysfunction caused by focal brain or retinal ischaemia and lasting for < 1 hour without signs of infarction on brain MRI. Hence, a tissue based rather than a time based definition is being proposed.
What is the risk of recurrent TIA after an index TIA? What is the risk of stroke?
TIA puts a patient at a higher risk of subsequent stroke with a 2-day risk being quoted at 5-6%, 90-day stroke risk estimated at 10.5% and a 6-month stroke risk estimated to be 17%. It is important to realize that a subset of patients is at a higher risk of recurrent TIA as opposed to a subset which is at higher risk for a subsequent stroke. Those older than 60 years are at higher risk for both TIA and stroke. Additionally those with Diabetes, those with motor weakness and those with speech impairment are at a higher risk of subsequent stroke and therefore need to be managed more aggressively.
Risk stratification after a TIA — The ABCD-2 score:
ABCD 2 score is now a well recognized prognostic score for predicting individuals at high risk for stroke. BP in excess of 140/90, unilateral weakness and duration of symptoms >60 min are the strongest risk factors for recurrent events.
Based on this score, low risk is defined as a score of less than 4 (stroke risk 1·0% at 2 days, 1·2% at 7 days, and 3·1% at 90 days), moderate risk is a score of 4 or 5 (stroke risk 4·1% at 2 days, 5·9% at 7 days, and 9·8% at 90 days), and high risk is a score of greater than 5 (stroke risk 8·1% at 2 days, 11·7% at 7 days, and 17·8% at 90 days).


What investigations are warranted once a TIA is diagnosed?
Recommended acute approaches in patients with TIA include, brain imaging, preferably MRI with MR angiography, ECG to rule out rhythm abnormality and echocardiography to exclude cardio-embolism and carotid imaging for significant stenosis. Expedited testing based on ABCD2 score appears to be the way for high risk patients.
What therapy is indicated after a TIA?
For TIAs of cardioembolic origin, warfarin is irrefutably the only therapeutic option at present. For non-cardioembolic TIAs, there is very little direct evidence to guide management after and index TIA. The available evidence comes from two recent trials, FASTER and EARLY.
FASTER was a pilot trial designed to test early aggressive use of dual anti-platelets aspirin and clopidogrel after TIA or minor stroke. It showed that the early high risk can be decreased with the combination without the excess risk of haemorrhage.
EARLY is the other trial that investigated the benefit of combination anti-platelets (aspirin and dipyridamole in this case) when started within 24 hour of symptom onset as opposed to starting at 7 days. The trial showed that it is just as safe and efficacious to start early than late with no significant differences in terms of disability. In total, these early phase trials suggest that early dual anti-platelet therapy may be safe after a TIA.

Conclusion

All patients presenting with TIA must be risk stratified using the ABCD-2 score and investigated promptly. It may be safe to start dual anti-platelets for the initial one week. Future trials in Pakistani patients to validate the TIA scores locally would be useful.

Acknowledgement

Dr Maria Khan is a neurovascular fellow whose training is currently funded by Award Number D43TW008660 from the Fogarty International Center. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Fogarty International Center or the National Institutes of Health.

Recommended Reading

1.Ovbiagele B. Antiplatelet therapy in management of transient ischemic attack: overview and evidence-based rationale. J Emerg Med 2008; 34: 389-96.
2.Dengler R, Diener HC, Schwartz A, Grond M, Schumacher H, Machnig T, et al. Early treatment with aspirin plus extended-release dipyridamole for transient ischaemic attack or ischaemic stroke within 24 h of symptom onset (EARLY trial): a randomised, open-label, blinded-endpoint trial. Lancet Neurol 2010; 9: 159-66.
3.Kennedy J, Hill MD, Ryckborst KJ, Eliasziw M, Demchuk AM, Buchan AM; FASTER Investigators. Fast assessment of stroke and transient ischaemic attack to prevent early recurrence (FASTER): a randomised controlled pilot trial. Lancet Neurol 2007; 6: 961-9.
4.Johnston SC, Rothwell PM, Nguyen-Huynh MN, Giles MF, Elkins JS, Bernstein AL, et al. Validation and refinement of scores to predict very early stroke risk after transient ischaemic attack. Lancet 2007; 369: 283-92.

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