Eighteen-year trends in stroke mortality and the prognostic influence of comorbidity

Objectives: To examine 18-year trends in short-term and long-term stroke mortality and the prognostic influence of comorbidity.

Methods: We conducted a nationwide population-based cohort study. Using the Danish National Registry of Patients, covering all Danish hospitals, we identified all 219,354 patients with a first-time hospitalization for stroke during 1994–2011. We computed standardized 30-day, 1-year, and 5-year mortality by sex. Comorbidity categories were defined by Charlson Comorbidity Index scores of 0 (none), 1 (moderate), 2 (severe), and 3 or more (very severe). Calendar periods of diagnosis (1994–1998, 1999–2003, 2004–2008, and 2009–2011) and comorbidity categories were compared by means of mortality rate ratios based on Cox regression.

Results: Over time, the 30-day mortality rate ratio adjusted for age, sex, and comorbidity decreased by approximately 45% for ischemic stroke (standardized risk decreased from 17.2% in 1994–1998 to 10.6% in 2009–2011) and by 35% for intracerebral hemorrhage (from 43.2% to 33.8%). The absolute mortality reduction occurred for all levels of comorbidity. Five-year mortality risk decreased from 56.4% in 1994–1998 to 46.1% in 2004–2008 for ischemic stroke and from 66.1% to 61.0% for intracerebral hemorrhage. Comparing very severe comorbidity with no comorbidity, 30-day and 5-year mortality rate ratios were both approximately 2.5-fold increased for ischemic stroke and 1.7-fold increased for intracerebral hemorrhage.

Conclusions: Short- and long-term mortality improved considerably between 1994 and 2011 for all types of stroke. Short-term mortality improved regardless of comorbidity burden. However, comorbidity burden was a strong prognostic factor for both short- and long-term mortality.