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ARIC: US stroke incidence, mortality rates declined from 1987 to 2011
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The rates of stroke incidence and stroke mortality in the United States declined from 1987 to 2011, according to new data from the Atherosclerosis Risk in Communities study.
The decline was consistent across sex and race, but the decline in incidence was driven by those aged at least 65 years and the decline in mortality was driven by those younger than 65 years, according to the researchers.
“More successful control of risk factors in the last decades (mainly hypertension control starting in the 1970s and later hypertension treatment combined with smoking cessation, control of diabetes and dyslipidemia, and treatment of atrial fibrillation) may have resulted in lower stroke incidence and less severe strokes, which may account for the observed lower mortality rates,” Silvia Koton, PhD, MOccH, and colleagues wrote.
The Atherosclerosis Risk in Communities (ARIC) study was a prospective cohort study of 14,357 participants aged 45 to 64 years and free of stroke at baseline recruited from four US communities. Baseline interviews and examinations were conducted between 1987 and 1989, and researchers identified stroke hospitalizations and deaths for participants through 2011.
Koton, of the Stanley Steyer School of Health Professions, Sackler Faculty of Medicine, Tel Aviv University, and colleagues found that 7% of participants had incident stroke during the study period. Of the 1,051 participants who had a stroke, 929 had ischemic stroke and 140 had hemorrhagic stroke (18 had both).
Incidence decreased over time
According to the researchers, crude incidence rates were as follows: 3.73 (95% CI, 3.51-3.96) per 1,000 person-years for total stroke, 3.29 (95% CI, 3.08-3.5) per 1,000 person-years for ischemic stroke and 0.49 (95% CI, 0.41-0.57) per 1,000 person years for hemorrhagic stroke.
They found that stroke incidence decreased over time in white and black participants (age-adjusted incidence rate ratios per 10-year period, 0.76; 95% CI, 0.66-0.87; absolute decrease, 0.93 per 1,000 person-years overall).
The decrease in age-adjusted incidence was evident for those aged 65 years and older (age-adjusted incidence rate ratios per 10-year period, 0.69; 95% CI, 0.59-0.81; absolute decrease, 1.35 per 1,000 person-years) but not for those younger than 65 years (age-adjusted incidence rate ratios per 10-year period, 0.97; 95% CI, 0.76-1.25; absolute decrease, 0.09 per 1,000 person-years; P for interaction=.02), Koton and colleagues found. There was no difference by sex in the decrease.
Of those who had incident stroke, 58% had died by 2011, with the mortality rate being higher for hemorrhagic stroke than for ischemic stroke (68% vs. 57%), the researchers found.
Overall mortality after stroke decreased over time (HR=0.8; 95% CI, 0.66-0.98); absolute decrease, 8.09 per 100 strokes after 10 years per 10-year period), according to the researchers.
They found that the decrease in mortality was mainly attributable to those younger than 65 years (HR=0.65; 95% CI, 0.46-0.93; absolute decrease, 14.19 per 100 strokes after 10 years per 10-year period) and was consistent across race and sex.
Risk factors better controlled
Ralph L. Sacco
The study permits comparisons of time-varying vascular risk factors that can help explain reasons for the decline in stroke incidence in mortality, Ralph L. Sacco, MD, and Chuanhui Dong, MD, PhD, both from the department of neurology at the Miller School of Medicine, University of Miami, wrote in a related editorial.
First, they wrote, those who were aged 55 to 64 years between 1996 and 1998 were more likely to use cholesterol-lowering medications compared with those who were aged 55 to 64 years between 1987 and 1989 (12.9% vs. 3.8%) and had an average of 20 mg/dL lower LDL; this is important because of an association between cholesterol medication use and lower rate of incident stroke (RR=0.8; 95% CI, 0.68-0.93).
Second, participants were more likely to use antihypertensive medications between 1996 and 1998 compared with between 1987 and 1989 (43.4% vs. 29.5%), and the increase was mainly seen in those aged 65 years and older, which could explain the higher rate of decline in stroke incidence among older patients, Sacco and Dong wrote.
Third, participants were less likely to smoke between 1996 and 1998 than they were in 1987 to 1989, Sacco and Dong wrote. “Successes in the control of cholesterol levels, [BP] and smoking habits over the last decades are likely partially responsible for the decline in stroke incidence,” they stated.
However, they noted, “formidable challenges to address stroke disparities and successfully control risk factors and lifestyle behaviors across race, ethnicity and regions persist.”
For more information:
Koton S. JAMA. 2014;312:259-268.
Sacco RL. JAMA. 2014;312:237-238.
Disclosure: The study was funded by the NHLBI. The researchers, Dong and Sacco report no relevant financial disclosures.
Perspective
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A.M. Barrett, MD
This is a great study in that it showed a decrease in stroke events. That is what has been emphasized and is very exciting. However, there is always more to the story.
One important point is that the number of strokes that occur is not the same as the burden or disability of stroke. Burden or disability tends to get swept to one side when we are thinking about stroke, but it really is what matters to our society. Another point is that this was not a study of the general population over time; it was a study of one group of people over a period of time. Thus, the study results may not mean that strokes decreased over time in the general population, but rather in a particular group that was recruited at one point in time and then got older as the study progressed. This may limit how generally the study results should be taken.
Of concern is that more than 14,000 people were seen three times, and the last time they were seen was 1996-1998. Then, these people were followed up at a distance via paperwork until 2011. During that time, the researchers were only able to know if someone had a stroke via secondary reports. They weren’t actually examining the patients.
We know that a lot of strokes are silent. In our lab, we study hidden disabilities after stroke. Many people who have right-brain strokes — the right brain being the visual, spatial and nonverbal hemisphere — are never diagnosed as having a stroke. One study found that 12% to 15% of people who had right-brain strokes were not accurately diagnosed, even in a stroke center (Foerch C. Lancet. 2005;366:382-383).
It is very possible that many people who had hidden disabilities or silent strokes were missed with this method. There may have been people with problems of memory and functional vision who were not diagnosed and treated and were not accounted for in this study, yet were still experiencing limitations on their ability to do things in the world as a result. People assume that we can diagnose 100% of strokes when they happen with techniques like FAST; however, it is very difficult when people have strokes that affect their functional vision only, and that happens relatively frequently. We have to be very careful not to miss those patients in every stage of care.
In future studies, it would be good to get a sense of the proportion of people with left-brain and right-brain strokes, so we can compare with previous studies and determine whether some of those people who had silent, right-brain stroke fell through the cracks.
When people have a stroke, approximately three of four will know they had a stroke based on something that is different that affects their activity (what they can do) and participation (how they can serve their roles). Depending on how those two factors are measured, as many as 80% say they are not doing what they used to do or enjoying the same roles. I understand that the researchers did not set out to answer that question, but if we are talking about the cost of stroke, we cannot ignore that question. From a personal and social perspective, that’s where most of the cost of stroke comes from. Before we congratulate ourselves on doing better with cholesterol lowering and BP lowering, we have to look at whether we are doing better at getting people all the way back to participation in their lives.
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