Tromsø Study Documents Dramatic Decline in CHD in Norway

Pam Harrison

November 23, 2015

TROMSØ, NORWAY — The incidence of coronary heart disease (CHD) in Norway has declined substantially over the past 15 years, with almost two-thirds of the decline due to changes in modifiable risk factors like activity levels, blood pressure, and cholesterol, suggests a large population-based study[1].

In their report published November 18, 2015 in Circulation, Dr Jan Mannsverk (University Hospital of North Norway, Tromsø) and colleagues found that between 1995 and 2010, the age- and-sex-adjusted incidence of total CHD decreased by 3% each year (P<0.001).

This decline was largely driven by dramatic decreases in out-of-hospital sudden death due to probable MI as well as hospitalizations for ST-segment-elevation MI.

There was also a significant reduction in case fatality rates among patients hospitalized for MI; together, changes in the total incidence of CHD and case-fatality rates contributed 43% and 57%, respectively, to the decline in CHD mortality across the country.

Changes in coronary risk factors accounted for 66% of the observed decline in hospitalized and nonhospitalized fatal and nonfatal CHD, the most important contribution being a reduction in cholesterol, which, the group reports, accounted for almost one-third of the decline in CHD seen between 1995 and 2010.

"These results indicate that populationwide changes in risk-factor levels have a large potential for reducing MI incidence in a population," Mannsverk and colleagues write. "The association between risk factors and out-of-hospital sudden death indicate that primary prevention by modification of risk factors will influence both incident MI as well as case fatality in populations."

The author of an accompanying editorial[2], Dr Russell Luepker (University of Minnesota, Minneapolis, MN), heartwire from Medscape that the Norwegian group has clearly shown risk-factor modification contributed to a major portion of the observed decline in CHD events and sudden death.

"One of the things that was impressive here is that the Norwegians could pull all this information together—it's partly their system and it's partly their culture—but when we try to do this in the States, we discover it's very difficult because we don't have the same consistent, well–measured data available on our population, and that's what we need to know to understand what's going on," Luepker said.

The analysis comes from the Tromsø Study, population-based prospective cohort study of a range of diseases and health issues. The current analysis includes participants from surveys undertaken in 1994–1995, 2001–2002, and 2007–2008, comprising 29,582 subjects aged 25 years of age or older who participated in at least one survey.

A total of 1845 patients had an incident CHD event between 1995 and 2010, 78% of whom were hospitalized. Some 404 patients were not hospitalized, and among this group there were 332 out-of-hospital sudden deaths.

"Thus, 58% of all fatal incident CHD events occurred as an out-of-hospital sudden death," Mannsverk notes.

Mortality from CHD also dropped by approximately half between 1995 to 2010.

CHD Mortality Between 1995 and 2010 (Cases per 100,000 Person-years)

  1995 (cases) 2010 (cases) P
CHD mortality 137 65 <0.001
Out-of-hospital sudden death 89 42 <0.001
Mortality rates among hospitalized MI patients 50 28 <0.001
Hospitalized STEMI patients 132 80 <0.001

There was also a 7.6% annual decline in rate of out-of-hospital sudden deaths (P<0.001), according to the group. "And 65% of the decline in CHD mortality was due to a decrease in the rates of out-of-hospital sudden deaths."

Age- and sex-standardized mortality rates from CHD also fell by 7.3% a year, the incidence of total CHD by 3% a year, and the case-fatality rate among patients hospitalized for MI by 4% a year (all P<0.001).

Major risk factors for coronary disease also changed favorably throughout the study, with mean cholesterol levels, blood pressure, resting heart rate, and smoking all dropping while levels of physical activity increased. At the same time, overweight and diabetes both increased.

Changes in systolic blood pressure, smoking, resting heart rate, and physical activity each accounted for between 9% and 14% of the decline in CHD risk, while increases in body-mass index and the prevalence of diabetes increased CHD risk by 7% and 2%, respectively.

"This study demonstrates that primary prevention by modification of risk factors by means of a healthy lifestyle or medication will influence both incident CHD as well as case-fatality in populations, shown by the association between coronary risk factors and out-of-hospital sudden deaths," Mannsverk and colleagues conclude. "Thus, sudden death is a preventable condition."

Luepker said the analysis has lessons for practicing cardiologists. "We as cardiologists tend to focus on the acute things we do, whether it's catheterization or surgery, and sometimes we let the general practitioner worry about smoking and cholesterol and blood pressure," Luepker said.

"And while I think cardiologists need to focus on the very ill, they also need to learn from studies like this that there are other ways to prevent sudden death than just putting in a defibrillator."

 

The study was funded by the Research Council of Norway, the Norwegian Council on Cardiovascular Disease, the Northern Norway Regional Health Authority, the University of Tromso, the Norwegian Foundation for Health and Rehabilitation, and the Odd Berg Research Foundation. The authors had no relevant financial relationships, nor did Luepker.

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