Read... As per epocrates: CAD (coronary disease) hypertension, heart failure, valvular disease, pericardial and pleural diseases, diabetes, thyroid disorders, disorders of the lung, and advanced age are known risk factors for the development of acute af. However, af may occur in the absence of any underlying cardiac or noncardiac diseases, for example, as a result of heavy alcohol intake.
Age/ MI. The incidence of af increases progressively with age, ranging from 2 to 3 new cases per 1000 population per year between the ages of 55 and 64 years, to 35 new cases per 1000 population per year between the ages of 85 and 94 years.  the overall number of men and women is equal and af is less common among black people than white people.
Htn. People with other cardiovascular diseases such as hypertension or CHF or have had an mi that has damaged the heart itself are all at risk for atrial fibrillation.