A total of 274 primary outcome events occurred at 1 year: 25 deaths from CV causes, 210 nonfatal strokes, and 39 nonfatal acute coronary syndromes, which corresponded to a Kaplan-Meier estimate event rate of 6.2% (95% confidence interval [CI]: 5.5-7.0). Meanwhile, in secondary outcomes, 80 patients died from any cause, 533 patients had recurrent strokes or TIAs, 46 had acute coronary syndromes, and 87 patients experienced bleeding (including 16 patients with moderately severe bleeding and 18 with major bleeding).
If a patient had a higher ABCD2 score, the risk of stroke tended to increase, with the 1-year risk ranging from 0% (score of 0) to 9.6% (score of 7), and 22% of strokes occurred in patients with a score of less than 4.
At 1 year, the risk of the composite outcome of major fatal or nonfatal CV events was 6.2% and stroke risk was 5.1%, according to Kaplan-Meier estimates. Recurrent stroke risks at 2 days, 7 days, 30 days, 90 days, and 1 year was less than half than expected from historical cohorts. Investigators also observed a 3.7% risk for stroke and other vascular events (at 90 days) compared with 12% to 20% from previous studies.
Variables independently associated with 1-year stroke risk included multiple cerebral infarctions on brain imaging (hazard ratio [HR] for comparison with no infarctions: 2.16; 95% CI: 1.46-3.21; P<.001), an ABCD2 score of 6 or 7 (HR for comparison with score of 0 to 3: 2.20; 95% CI: 1.41-3.42; P<.001), and large-artery atherosclerosis (HR for comparison with undetermined cause: 2.01; 95% CI: 1.29-3.13; P=.002), according to multivariable Cox regression analysis. When the Cox regression model was refitted by introducing ABCD2 score as a continuous variable, the results remained similar.
“Despite a much lower event rate than in historical cohorts, we found that the ABCD2 score was still effective at stratifying risk in this urgently and intensively treated cohort,” researchers wrote, “but we also observed that 22% of recurrent strokes occurred in patients with ABCD2 scores of less than 4 and with preventable underlying causes such as atrial fibrillation and ipsilateral internal-carotid-artery stenosis of 50% or more.”
Given that finding, if clinicians were to limit evaluations only to patients with ABCD2 scores of 4 or more, they would miss approximately 20% of those with early recurrent strokes. It is also important to bear in mind other strong independent predictors such as multiple infarctions on neuroimaging and large-artery atherosclerotic disease.
Investigators were careful to note that the site selection was not random, but were chosen because they either had a TIA clinic or were capable of dedicating care to patients with TIA, with at least 100 TIAs evaluated per year during the previous 3 years.
The registry was also biased toward more specialized stroke physicians and therefore, may have included patients with characteristics differing from patients in a population-based study. However, those patients are probably being recruited by relevant clinical trials.
Finally, 1-year follow-up data are missing for more than 380 patients, which could have affected the 1-year event rate.
Where Do We Go From Here?
Interestingly, investigators also found that anticoagulant therapy in addition to risk factor control is so effective that if implemented, the residual risk of stroke is probably very low, in the event of cardiac disease (eg, atrial fibrillation). Blood pressure-lowering therapy is also effective when combined with other risk factor management and antiplatelet therapy.
These therapies and risk-factor control may help explain why investigators observed a lower rate in CV events after a TIA or minor stroke than historically reported.
“The findings from the current multicenter registry suggest that the low risk of stroke reported by single-center registries in patients who had a TIA or minor stroke and who received care in TIA clinics that were organized for fast-track evaluation … may be achievable in a large range of settings as long as patients are evaluated and treated for acute TIA and minor stroke on an urgent basis,” researchers concluded.
Amarenco P, Lavallée PC, Labreuche J, et al; for the TIAregistry.org Investigators. One-year risk of stroke after transient ischemic attack or minor stroke. N Engl J Med. 2016;374(16):1533-1542. doi: 10.1056/NEJMoa1412981.