atrial fibrillation incidence in Framingham Study

the Lancet just published an article on the trends of atrial fibrillation (afib) over the past 50 years, based on the meticulous Framingham Study database (see afib prevalenceframingham lancet 2015 in dropbox, or doi.org/10.1016/S0140-6736(14)61774-8). they looked at 9511 study participants from 1958-2007, assessing afib prevalence, incidence, risk factors and mortality over 10-year blocks, stratified by sex, with 202,417 person-years of observation.  results:

--there were 1544 cases of new-onset afib (821 men and 723 women)

--between the first and last 10-year groupings

        --the age-adjusted prevalence of afib quadrupled from 20.4 to 96.2 per 1000 person-years in men, and from 13.7 to 49.4 cases per 1000 person-years in women (p<0.001)

        --the age-adjusted incidence of afib went from 3.7 to 13.4 per 1000 person-years in men, and from 2.5 to 8.6 cases per 1000 person-years in women​ (p<0.001)

        --for EKG-diagnosed afib, found on routine exams during the study, the age-adjusted prevalence per 1000 person-years increased from 12.6 to 25.7 in men (p=0.007)and 8.1 to 11.8 in women (p=0.009) -- of note, the pickup of afib over time decreased for those EKG-diagnosed during the routine exams and increased in those diagnosed by reviewing outside medical records (ie, more afib cases were diagnosed outside of the study and fewer during the study's routine exams)

        --but, there was no significant change in the age-adjusted incidence of afib by EKGs in the routine exams over time (increase was from 1.83 to 3.75 in men (p=0.06) and from 1.31 to 1.58 in women (p=0.23)

        --the prevalence of most risk factors changed over time in those with new-onset afib, as follows:

                --smoking decreased from 40.9% to 12.7%

                --moderate/heavy alcohol decreased from 10.2% to 5.4%

                --BMI>30 increased from 27.3% to 35.4%

                --systolic BP>160mmHg decreased from 38.6% to 16.9%

                --hypertension treatment increased from 22.1% to 59.8% 

                --diabetes increased from 5.7% to 19.6%

                --EKG-LVH decreased from 12.9% to 2.9%

                --prevalent heart failure decreased from 5.7% to 3.5%

                --significant heart murmur decreased from 20.0% to 8.1%

                --no significant change in prevalent MI

        ​--overall summary of the effects of these changes in risk factors: the population attributable risks for incident afib plummeted for systolic blood pressure (47.3 to -2.1), heart failure (7.8 to 1.4), significant heart murmur (21.9 to 3.1) and EKG-LVH (from 10.4 to 1.8), but increased for BMI (12.0 to 16.9) and diabetes (3.2 to 5.9). though systolic blood pressure decreased so dramatically, the attributable risk for treated hypertension (from 9.8 to 19.5) suggests that there is a residual effect of hypertension even if treated, but much less so than untreated hypertension (and,presumably, hypertension prevention would be even better, eg by diet and exercise, ....)

        ​--over a 20-year period after the development of afib, there was a 74% decrease in stroke (p=0.001) and a 25.4% decrease in mortality (p=0.003)

so, this study brings out some important points: many of the risk factors for afib are modifiable, and there have been some very impressive changes over the past 5 decades in several of them (especially the identification and treatment of hypertension, profound decreases in smoking, decreases in alcohol consumption), though these improvements have been somewhat overcompensated by the worsening in BMI and diabetes. the difference between prevalence and incidence are likely the result (for prevalence) of improved detection and the fact that people are living longer with afib (impressive decreases in strokes and mortality). for example, i do remember 20-30 years ago that it was not so clear that paroxysmal atrial fibrillation was as bad, and in need to treatment, as permanent afib. or that it was safe to use anticoagulants in older and somewhat frail people.  or that afib is as common as we now know it to be. the ascertainment ofafib by the screening EKGs during the study is probably the most consistent marker of real changes in incidence, and these were largely nonsignificant over time (in men it was pretty close to significant, but the point is that this confirms that the increase in BMI and diabetes makes up for the improvements in the other risk factors in the incidence of afib -- though, of course, there could be unidentified risk factors that play a role as well). and it is important to remember that the Framingham Study was based on white European immigrants.