New risk score for development of AF

ROCHESTER, MINNESOTA. The risk of developing heart disease can be estimated using a scheme developed by the Framingham Heart Study and the risk of suffering an AF-related stroke can be estimated by the use of the CHADS2 or CHA2DS2-VASc score. Now a group of researchers from the Mayo Clinic reports the development of a scoring protocol for determining the 10-year risk of developing atrial fibrillation in black and white men and women. The study involved 14,546 individuals between the ages of 45 and 64 years of which 27% were black and 55% were women. All participants underwent an extremely comprehensive medical examination at baseline and then three additional examinations during the 10-year follow-up from 1989-1998. All examinations included 12-lead ECG and incidences of AF were also recorded if patients were admitted to hospital for AF or reported AF in telephone interviews. During the 10 years, 515 study participants developed AF, giving an annual incidence rate of around 0.35%.

By comparing the status of 12 variables vs. incidence of AF, the researchers were able to develop a score for predicting the risk of developing AF over the next 10 years. The most significant risk factors and their corresponding score are given below. Please note that all risk factors refer to status at enrolment.

  • 8 points - Age 60 to 64 years
  • 5 points - Early coronary artery disease (age 45 to 50 years)
  • 4 points - Age 55 to 60 years
  • 4 points - Height of 173 cm (5 ft 8 in) or greater
  • 4 points - Left ventricular hypertrophy and white race
  • 4 points - Early diabetes (age between 45 and 55 years)
  • 3 points - Age 50 to 55 years
  • 3 points - Systolic blood pressure above 160 mm Hg
  • 3 points - Use of hypertension medication
  • 3 points - Current smoker
  • 3 points - Coronary heart disease between ages of 50 and 60 years

The following conditions were associated with a 2 point risk score – systolic blood pressure between 140 and 160 mm Hg, precordial murmur, left atrial enlargement, and heart failure. Risk factors associated with a 1 point risk score were height between 164 and 173 cm (5 ft 5 in to 5 ft 8 in), systolic blood pressure between 120 and 140 mm Hg, former smoker, and age 55 to 60 years. The following variables confirmed no additional risk for AF development – age 45 to 50 years, height less than 164 cm (5 ft 6 in), blood pressure between 100 and 120 mm Hg, never having smoked, and left ventricular hypertrophy (if black). It was also observed that blacks have a significantly lower preponderance to develop AF, so they were automatically given a score of –4 just for their race alone.

Considering all the data collected, the researchers estimate the following actual risks of developing AF over a 10-year period as follows:

Risk Score
Estimated 10-year Risk
1 or less
less than 1%
2 - 6
1%
7 - 8
2%
9
3%
10 - 11
4%
15
11%
19 or higher
greater than 24%

The researchers recognize that the number of patients actually developing AF could be greater than recorded since some participants’ episodes may not have been caught on an ECG. They also point out that an individual’s risk factors were only measured at baseline. lf the individual made major lifestyle changes during the 10-year follow-up, that could obviously affect final outcome. Finally, it is now well known that certain genes can predispose to AF. This was not considered in the survey.

Chamberlain, AM, et al. A clinical risk score for atrial fibrillation in a biracial prospective cohort. American Journal of Cardiology, Vol. 107, 2011, pp. 85-91

Editor’s comment: This study is a good “first stab” at a risk score for developing atrial fibrillation. However, it could likely be improved by including other established risk factors such as alcohol abuse, recreational drug use, digoxin, thyroid disorder, hypoglycaemia, pheochromocytoma, hyperaldosteronism (Conn’s syndrome), electrolyte imbalances, frequent consumption of tyramine-containing foods, autonomic nervous system imbalances, and of course, chromosomal abnormalities (inherited AF).