Gurmeen Kaur, MBBS
Bergström L, Irewall AL, Söderström L, Ögren J, Laurell K, Mooe T. One-Year Incidence, Time Trends, and Predictors of Recurrent Ischemic Stroke in Sweden From 1998 to 2010: An Observational Study. Stroke. 2017
The risk of recurrent stroke has been on a decline as per estimates from different countries, including Italy, Taiwan and the “Western world.” Rikstroke is the Swedish Stroke Register where all Swedish hospital admissions because of stroke are recorded. The authors describe an excellent longitudinal study design where patients with ischemic strokes were followed up from 1998 to 2009. From the year 1998, all Swedish hospitals and rehab centers report their admissions to the Rikstroke registry, which had an astounding 85% coverage in the year 2009.
The recurrence of ischemic stroke events was calculated by amalgamating the Rikstroke registry with the Swedish National Inpatient Register (IPR), which contains data about diagnoses and dates of discharge from hospitalizations in Sweden.
A total of 196,765 patients were enrolled into 4 groups based on the year of inclusion into Rikstroke (1998–2000, 2001–2003, 2004–2006, and 2007–2009). The data in these 4 groups was compared with a reference group of 190,157 patients. All baseline parameters were noted and were found to be demographically similar to the Rikstroke population studied. Various regression models were used, and factors associated with an increased risk of recurrent ischemic stroke were identified.
The authors reported that the 1-year risk of recurrent ischemic stroke has decreased in Sweden between the time periods 1998 to 2001 and 2007 to 2010. There was a significant trend of increased chances of recurrence with well-known stroke risk factors. Additionally, several secondary preventive drugs were associated with a lower risk. In the Kaplan–Meier analysis shown in the Figure (below), a temporal trend towards decreasing cumulative incidence of stroke is seen over the years 1998 to 2007. Not unexpectedly, prior ischemic stroke or MI, diabetes and atrial fibrillation, not on warfarin were associated with higher hazard ratios and aspirin, dipyridamole, statin use, warfarin use in atrial fibrillation were associated with a lower risk of recurrent ischemic stroke in the next one year.
The Rikstroke data gives an important perspective on the recurrence risk of strokes because it is one of the largest population-based studies assessing temporal risk. A major limitation is that because the ICD9 code for ischemic stroke is used to look for recurrence, we do not have the ischemic stroke subtypes. Differences and improvements with treatment of risk factors are dependent on the etiology of ischemic stroke. However, the estimated decline in the risk of ischemic stroke with management of secondary risk factors is reassuring for a stroke clinician!