The study included 962 heart failure subjects (mean age of cases 75.4 years; 53.7% women). Women were older than men (mean age 78.3 years versus 72.1 years, p<0.001). By definition, the 962 controls had a similar age and sex distribution.
Frequency of Heart Failure Risk Factors Among Case Subjects
Hypertension was most common, followed by smoking (). Among ever smokers, 24.0% were light smokers, while 76.0% were heavy smokers. The mean number of heart failure risk factors per case subject was 1.9 ± 1.1; 29.4% had 1, 62.0% had 2 or more, while only 8.6% had none. The prevalence of risk factors by sex was similar for diabetes and obesity, but men had a greater frequency of coronary disease and smoking, while women had a greater frequency of hypertension. The number of risk factors per heart failure case increased over time with mean risk factors of 1.61, 1.89, 1.98, and 2.13 from 1979–84, 1985–90, 1991–96, and 1997–2002, respectively (p for trend <0.001). The prevalence of hypertension obesity, and smoking increased over time (). While the proportion of patients who had ever smoked prior to heart failure diagnosis increased over time, the proportion of current smokers at the time of diagnosis declined (17%, 20%, 15%, and 12% from 1979–84, 1985–90, 1991–96, and 1997–2002, respectively).
Prevalence of Risk Factors Among Heart Failure Cases 1979–2002
Change in Prevalence of Risk Factors over Time Among Heart Failure Cases 1979–2002
Time from Exposure to Development of Heart Failure
The duration of exposure prior to heart failure differed according to the risk factor. Heart failure developed only a few years after coronary disease diagnosis, contrasting with longer durations of exposure for other factors (). After adjusting for age, women developed heart failure more rapidly after being diagnosed with coronary disease than men. While men tended to develop heart failure more quickly after being diagnosed with hypertension or diabetes, the results were not significant (p=0.10 for hypertension, p=0.08 for diabetes).
Time from Risk Factor to Development of Heart Failure Among Cases
Risk of Heart Failure According to Risk Factor
The risk of heart failure associated with each exposure and the PARs are presented in . A history of coronary disease was associated with the greatest risk, followed by diabetes. While ever smoking was associated with an increased risk of heart failure (OR 1.37, 95% CI 1.13–1.68), when stratified by smoking burden, heavy smoking was associated with greater risk (OR 1.87, 95% CI 1.46–2.39) than light smoking (OR 1.02, 95% CI 0.74–1.40). There was no sex differences in the association between each risk factor and the development of heart failure (exposure*sex interaction term p>0.20 for all). The PARs were highest for coronary disease and hypertension, with each accounting for 20% of heart failure cases. Despite the weaker association between hypertension and heart failure relative to other factors, the PAR was high given its high prevalence. In women, hypertension had the highest PAR of the risk factors examined (28%), followed by coronary disease (16%). In men, coronary disease was responsible for the highest proportion of cases (PAR 23%), followed by smoking (22%). We examined whether the PAR for each risk factor changed over time. There was no evidence for a change for coronary disease, diabetes, and smoking. By contrast, the PAR for hypertension increased from 15% (1979–84) to 29% (1979–02), and for obesity from 8% (1979–84) to 17% (1997–02). These differences did not reach statistical significance. After adjusting for the risk associated with all five risk factors, the summary PAR was 52%. This suggests that these five risk factors are responsible for 52% of incident heart failure cases in the population.
Association Between Heart Failure and Risk Factors From Case/Control Analysis