Atrial fibrillation, AF is the commonest reason for taking warfarin. Today we will be talking about AF and a study from a medical journal of the trends over the past 50 years.
So what is AF?
AF is a disorder of heart rhythm.
In a normal beat, the atria contract first, (shown by the purple arrow as the p-wave on the ECG below) leading to a regular contraction of the ventricles (shown as the regular, spikey QRS complex). In AF, the atria are usually enlarged and floppy, contracting erratically, like a ‘bag of worms’, unable to produce a p-wave on the ECG. Instead they produce an irregular signal to the ventricles (shown by the red arrow as the juddery baseline to the AF ECG) and the ventricles contract irregularly.
Comparison between ECGs showing normal heart rhythm and atrial fibrillation, AF.
How do people know they have AF?
The majority don’t know they have AF and it is only picked up as an irregular pulse or abnormal ECG. However, some people get palpitations or shortness of breath.
Why is AF important?
A blood clot can form in the poorly contracting atria. Part of the clot can break away and lodge in an artery in the brain causing a stroke. Taking warfarin reduces this risk by more than 80%.
Which medical journal paper are we studying?
“50 year trends in atrial fibrillation prevalence, incidence, risk factors, and mortality in the Framingham Heart Study: a cohort study.” – an American study, using data from the Framingham heart study, published in the Lancet in July 2015.
Why was the study done?
Although it’s been suggested that the incidence of AF is increasing, the authors state that “comprehensive long-term data on AF trends are scant”. To address this, they examined data from 9511 patients in the Framingham heart study from 1958 to 2007, to see if there was a genuine increase in AF, to look at risk factors and to identify reasons for any increase. They also wanted to see if anti-coagulant and other treatments had influenced mortality and the incidence of stroke.
What were the results?
Of the 9511 patients surveyed, 1544 developed AF. From this, the authors calculated a four-fold increase in the age-adjusted prevalence of AF from the decade beginning 1958 to the decade beginning 1998. Over this time, there was also a 74% decrease in stroke and 25% decrease in mortality.
The authors concluded, “Over the course of 50 years of observation of a community-based sample, we observed an increasing prevalence and incidence of atrial fibrillation accompanied by improved survival and reduced risk of stroke after onset of atrial fibrillation”.
It’s interesting that the prevalence of atrial fibrillation is increasing in spite of the fact that many risk factors have decreased; less people smoke and we have better treatment for hypertension, high cholesterol and heart disease. The rise in the prevalence of AF is in part, due to better screening for AF, but the authors conclude there is a genuine increase in prevalence with no clear explanation. Two risk factors were important: hypertension and obesity, but it is age that influences the prevalence most.
The authors speculate that the improved survival and reduced risk of stroke after onset of atrial fibrillation are due to improved therapies for cardiovascular disease and better use of anti-coagulation.
What’s the study reference?
Lancet, 2015 Jul 11;386(9989):154-62. doi: 10.1016/S0140-6736(14)61774-8. Epub 2015 May 7.
50 year trends in atrial fibrillation prevalence, incidence, risk factors, and mortality in the Framingham Heart Study: a cohort study.
Schnabel RB, Yin X, Gona P, Larson MG, Beiser AS, McManus DD, Newton-Cheh C Lubitz SA, Magnani JW, Ellinor PT, Seshadri S, Wolf PA, Vasan RS, Benjamin EJ, Levy D.