A large cohort study has found that the strongest risk factors for atrial fibrillation in both men and women were a history of palpitations and hypertension. While hypertension is a well known risk factor for atrial fibrillation, Nyrnes et al (investigators of the study) note that “the impact of self-reported palpitations on later occurrence of atrial fibrillation has not been documented earlier”.
Results from the Tromsø Study, a large prospective follow-up of the general population of this region of Norway, were published on 15 May in the European Journal of Preventive Cardiology. The emergence of palpitations as a risk factor for atrial fibrillation was reported in the study. Participants were recruited in 1994-95 and included all inhabitants in the region over the age of 25. After exclusions, 22,815 people aged between 25 and 96 were included and followed up for a mean time of 11.1 years. Mean age at baseline was 46 years.
Information on palpitations was included at baseline along with measurements of height, weight, blood pressure, heart rate, total cholesterol and high-density lipoprotein cholesterol. All subjects were cross-linked to the local diagnostic registry and to the national death register for information on atrial fibrillation documented by electrocardiogram. Hospital records were searched for subjects with diagnoses of cerebrovascular or cardiovascular events but without a recorded registry diagnosis of arrhythmia.
Results showed that atrial fibrillation was recorded in 361 women (3.0%) and 461 men (4.2%) during the 11.1 years of follow-up, an incidence rate of 2.71 per thousand per year for women and 3.87 for men. Age, self-reported palpitations and hypertension were the strongest risk factors for atrial fibrillation.
Palpitations, which the investigators described as “frequent” in the total study group, increased the risk of atrial fibrillation in women by 62% (a hazard ratio of 1.62) and in men by 91% (HR 1.91).
The investigators also examined separately the predictors for palpitations and for atrial fibrillation (in order to exclude any common overlapping risk factors). This analysis found that for palpitations (but not for atrial fibrillation) several significant risk factors were related to lifestyle, while the most prominent risk factors for atrial fibrillation were biological (such as age, blood pressure, height, body mass index and diabetes). And although height, antihypertensive treatment and coronary heart disease were found to be risk factors for both palpitations and atrial fibrillation, the investigators nevertheless concluded “that palpitations are probably causally associated with atrial fibrillation”.
“Although the occurrence of palpitations was assessed before a diagnosis of atrial fibrillation and the association remained significant even after adjustment for other atrial fibrillation risk factors, we cannot conclude with certainty that the association is causal,” said first author Audhild Nyrnes, Department of Community Medicine, University of Tromsø, Norway.
“However, in this case it is not unreasonable to propose a causal relationship. ‘Palpitations’ are used subjectively to describe irregular heartbeats or accelerated heart rate, and it is likely that a proportion of palpitations also represent cases of irregular heart rhythm, which is a main characteristic of atrial fibrillation.”
A US study (Weber BE et al, Am J Med 1996; 100: 138-148) of 190 patients presenting to hospital with palpitations concluded that cardiac arrhythmias were diagnosed in 40%, with the remainder of varied – or unknown – cause. This and other studies suggest that palpitations can represent heterogeneous mechanisms, with highly different clinical implications.
“However,” said Nyrnes, “palpitations per se are not harmful. They are in fact mostly harmless; the challenge is to detect those which might signify an underlying condition and future atrial fibrillation.
“Thus, while palpitations might be reduced by modifying lifestyle factors, such as alcohol consumption and smoking, both of which increase heart rate, it is still unclear if this will reduce the risk of atrial fibrillation. It was interesting that our study found no significant association between lifestyle factors and future atrial fibrillation – and only with palpitations.”
However, the study did confirm that hypertension is a significant risk factor for atrial fibrillation. Raised blood pressure at baseline (defined as above 140/90 mmHg) almost doubled the risk of atrial fibrillation in women (HR 1.98) and increased by 40% (HR 1.40)) in men. The clinical implications of this, say the investigators, would be “to emphasise the importance of adequate treatment of high blood pressure”. They also add that subjects with palpitations could have paroxysms of atrial fibrillation, and should also be investigated further, with prolonged ECG monitoring.
