Importance: Accurate estimation of the association between transient ischemic attack (TIA) and risk of subsequent stroke can help to improve preventive efforts and limit the burden of stroke in the population.
Objective: To determine population-based incidence of TIA and the timing and long-term trends of stroke risk after TIA.
Design, setting, and participants: Retrospective cohort study (Framingham Heart Study) of prospectively collected data of 14 059 participants with no history of TIA or stroke at baseline, followed up from 1948-December 31, 2017. A sample of TIA-free participants was matched to participants with first incident TIA on age and sex (ratio, 5:1).
Exposures: Calendar time (TIA incidence calculation, time-trends analyses), TIA (matched longitudinal cohort).
Main outcomes and measures: The main outcomes were TIA incidence rates; proportion of stroke occurring after TIA in the short term (7, 30, and 90 days) vs the long term (>1-10 years); stroke after TIA vs stroke among matched control participants without TIA; and time trends of stroke risk at 90 days after TIA assessed in 3 epochs: 1954-1985, 1986-1999, and 2000-2017.
Results: Among 14 059 participants during 66 years of follow-up (366 209 person-years), 435 experienced TIA (229 women; mean age, 73.47 [SD, 11.48] years and 206 men; mean age, 70.10 [SD, 10.64] years) and were matched to 2175 control participants without TIA. The estimated incidence rate of TIA was 1.19/1000 person-years. Over a median of 8.86 years of follow-up after TIA, 130 participants (29.5%) had a stroke; 28 strokes (21.5%) occurred within 7 days, 40 (30.8%) occurred within 30 days, 51 (39.2%) occurred within 90 days, and 63 (48.5%) occurred more than 1 year after the index TIA; median time to stroke was 1.64 (interquartile range, 0.07-6.6) years. The age- and sex-adjusted cumulative 10-year hazard of incident stroke for patients with TIA (130 strokes among 435 cases) was 0.46 (95% CI, 0.39-0.55) and for matched control participants without TIA (165 strokes among 2175) was 0.09 (95% CI, 0.08-0.11); fully adjusted hazard ratio [HR], 4.37 (95% CI, 3.30-5.71; P < .001). Compared with the 90-day stroke risk after TIA in 1948-1985 (16.7%; 26 strokes among 155 patients with TIA), the risk between 1986-1999 was 11.1% (18 strokes among 162 patients) and between 2000-2017 was 5.9% (7 strokes among 118 patients). Compared with the first epoch, the HR for 90-day risk of stroke in the second epoch was 0.60 (95% CI, 0.33-1.12) and in the third epoch was 0.32 (95% CI, 0.14-0.75) (P = .005 for trend).
Conclusions and relevance: In this population-based cohort study from 1948-2017, the estimated crude TIA incidence was 1.19/1000 person-years, the risk of stroke was significantly greater after TIA compared with matched control participants who did not have TIA, and the risk of stroke after TIA was significantly lower in the most recent epoch from 2000-2017 compared with an earlier period from 1948-1985.