Risk factors for lone atrial fibrillation

BARCELONA, SPAIN. While much research is being done to find new, improved methods of treating atrial fibrillation (AF), very little research is done to determine the causes of the AF epidemic. Hopefully, work undertaken at the University of Barcelona will help reverse the balance. The Spanish researchers determined height, physical activity level, and left atrial size in a group of 107 lone atrial fibrillation (LAF) patients and compared their results to those in a group of age- and sex-matched healthy individuals without AF. In their discussion, the researchers make the following statements of particular interest:

  • “The rise (in atrial fibrillation cases) is not due exclusively to population aging or to the higher prevalence of obesity.”

  • “The prevalence of LAF ranges from around 2-10% in the AF population and may reach 30% in patients seeking medical attention.”

  • “LAF was defined as AF in the absence of any identifiable cause of the arrhythmia.”

  • “Atrial fibrillation was considered of ‘vagal’ origin when it occurred at least 80% of times during sleep and/or in post-prandial situation and ‘adrenergic’ when it occurred at least 80% of the time during high physical exertion and/or in situations of stress. The remaining patients were classified as suffering ‘random’ AF.”

The researchers measured the height, weight, and left atrial size of each study participant and also had all participants complete a validated questionnaire to determine their accumulated lifetime physical activity. Physical activity was classified into four levels – sedentary, light, moderate, and heavy. Light activities included standing and slow walking; moderate included activities that increased heart rate slightly and perhaps resulted in light perspiration, but which did not result in exhaustion; heavy activities included vigorous exercise that significantly increased heart rate. The accumulated lifetime hours of all occupational and exercise/sports activities for each level were calculated for each participant, taking into account their duration and frequency.

Forty-three percent of the LAF patients were admitted to the emergency department with a first episode of AF, while the remaining 57% had experienced previous episodes. Average age at admission was 48 years (NOTE: Our survey of 625 afibbers recorded an average age of 48 years at diagnosis). The majority (69%) of the participants were male and most (70%) had vagal AF.

The researchers observed a strong correlation between height and LAF prevalence with taller individuals (average height of 186 cm) being up to 17 times more likely to experience LAF than shorter individuals (average height of 160 cm). NOTE: Our first LAF survey in 2001 found an average height of 183 cm among male afibbers. PC’s later survey (LAFS-11) found an average height of male afibbers of 181 cm as compared to a population mean of 175 cm. Thus, the correlation between height and LAF risk is well established and is likely associated with the larger atrial size accompanying tallness.

A larger left atrium (left atrial anteroposterior diameter) was associated with a 40% increased risk of LAF. The most striking finding was the association between LAF risk and accumulated moderate and heavy physical activity. Those with a lifetime accumulated moderate plus heavy physical activity of more than 9300 hours had 15 times the prevalence of LAF than did those with less than 2100 hours accumulated. More than 564 hours of accumulated heavy, vigorous physical activity was associated with a 7 times increased prevalence of LAF.

The researchers speculate that the negative effects of moderate and particularly vigorous physical activity may be related to the chronic volume and pressure overload caused by the increased activity. They conclude, “The fact that physical activity is a risk factor for AF does not argue against exercise as a way of preventing coronary artery disease. It only offers a word of caution suggesting that the benefits obtained by physical activity, if excessively intense and over a great many hours, may be counteracted by the risk of AF.”

Mont, L, et al. Physical activity, height, and left atrial size are independent risk factors for lone atrial fibrillation in middle-aged healthy individuals. Europace, Vol. 10, 2008, pp. 15-20