This is the first study, to our knowledge presenting follow-up data in patients initially diagnosed with paroxysmal atrial fibrillation from the perspective of a general practice setting, and we found the annual incidence of paroxysmal AF to be 1.0 per 1000 person-years. A slightly lower incidence rate (0.6 per 1000) has been reported in a study where paroxysmal AF patients attending hospital were identified [13
]. The incidence of paroxysmal AF was almost half the one we reported for chronic AF in the same source population [10
]. This is well in line with what has been reported previously – that paroxysmal episodes represent between 35% and 66% of all cases of AF, depending on the study population and the definitions used [1
]. It has been reported that the load of patients with atrial fibrillation is likely to increase substantially in the next years, explained only in part by the aging of the population [15
]. Our results show, as previously reported, that patients with paroxysmal AF are younger and have less comorbidity than patients with chronic AF [10
]. This age difference could reflect the progressive nature of AF. The differences in morbidity and mortality among the two forms of AF suggest the possibility that paroxysmal and persistent AF may be different diseases with different risk factors and different pathogenic substrates, although clearly overlapping in part [17
], paroxysmal being a more benign disease than chronic.
It is difficult to assess an underlying cause in all AF patients [3
]. In our study, the specific cause was not reported in 32% of paroxysmal AF patients. We observed that the most frequent underlying associated conditions in paroxysmal AF were coronary heart disease, rheumatic heart disease and hypertension. These causes have also been found for chronic AF [12
], although there appears to be a great variability between studies.
It has been recommended that pharmacological management of patients with newly discovered AF requires knowledge of its pattern of presentation (paroxysmal, persistent, or permanent) [4
]. Anticoagulation with warfarin has been proposed for patients with paroxysmal forms when there is underlying heart disease [9
], as no major differences in risk of stroke between chronic and paroxysmal AF have been reported. However it is not clear whether patients with limited episodes of paroxysmal AF require anticoagulation, and the decision must be individualized for each patient [4
]. We found that close to half of the patients attending general practice with initial paroxysmal AF were not given warfarin or aspirin in the three months after the first-detected episode – a higher proportion than the one we observed among patients with chronic forms of AF [10
]. This could be due in part to the fact that 37% of patients with paroxysmal AF presented a single episode of paroxysmal AF without any recurrence during the follow-up, and consequently anticoagulant or antiplatelet therapies may not be recommended in this subgroup of patients [19
Clinical experience suggests that paroxysmal AF is often perpetuated and frequently it progresses to chronic AF, with estimates ranging between 20% and 30% within a period of 1–3 years [1
]. A ten year follow-up study of paroxysmal patients in Trieste reported that 34% developed chronic AF [18
]. The rate of progression varied according to aetiology, with patients with rheumatic valve disease carrying the highest rate of progression (66%) [4
]. A recent 14 years follow up study on Japanese patients with initial paroxysmal AF, reported that 77% of them developed into its chronic form (5,5% of patients per year) [25
]. In our study, we found that 17% of paroxysmal AF patients progressed to chronic AF during an average follow-up of close to 3 years, and history of valvular heart disease and moderate to high alcohol consumption were identified as the major independent predictors of progression to chronic AF.
Only a few small studies have examined factors predicting progression from paroxysmal to persistent AF [23
]. The study by Abe et al. of 122 consecutive patients with paroxysmal AF reported a progression of 11% to chronic AF during a period of 2 years. They did not find any significant differences in age, sex or presence of organic heart diseases in the patients who developed chronic AF, compared with paroxysmal AF patients who did not progress[23
]. Another study reported an annual progression rate of 22% [24
]. Chronic and persistent forms of AF have been reported to carry a greater mortality than paroxysmal AF [17
]. Our study suggests that patients progressing to chronic AF had a slightly higher increased risk of mortality than those not progressing.
Some limitations need to be taken into account when interpreting our results. Our findings are the reflection of detection and management of patients with newly diagnosed AF in general practice. Furthermore, our data are based on physicians assessments of patients symptoms and when available results from diagnostic tests to determine if the atrial fibrillation was paroxysmal or chronic (we could not specifically distinguish between permanent or persistent), and consequently will not be as accurate as prospective studies based on events detected after Holter monitoring, pacemaker insertion or ablation surgery. Our study was observational based on the information recorded by general practitioners during their daily practice. This shares the limitations of insufficient information at times but has the advantage to study the occurrence and determinants of AF patients in the real world of general practice. Therefore, it is likely that we may not have ascertained all cases of paroxysmal atrial fibrillation occurring in the study population, resulting in some underestimation of paroxymal AF. We found that a large proportion of patients had a unique episode of PAF, but we could not verify whether this was due to effective treatment with antiarrhythmic drugs or was incomplete reporting of subsequent paroxysmal episodes.
As we rely on the judgment of the GPs as well as their records and tests, some information was missing, for example GP could not assign a specific aetiology in 32% of paroxysmal AF patients, and we could not distinguish between those who would truly be "lone AF" and those with an underlying etiology not recorded by the GP. Also the rate of progression from paroxysmal to chronic AF could have been underestimated as we did not obtain complete response for all followed-up patients.