After its initial diagnosis, atrial fibrillation (AF) may progress from paroxysmal to chronic AF (CAF). The rate of progression and risk factors for progression are not clearly defined.

The Canadian Registry of Atrial Fibrillation (CARAF) enrolled patients from 6 Canadian cities at the time of their first electrocardiographic diagnosis of AF. Comprehensive clinical and echocardiographic data were collected and patients were followed annually, carefully documenting clinical outcomes, recurrence of paroxysmal AF, and progression to CAF. Baseline clinical, electrocardiographic, and echocardiographic variables were evaluated by univariate Cox proportionate hazards analysis. A stepwise approach was used to model the association between echocardiographic and clinical variables with progression to CAF.

A total of 757 patients with a baseline diagnosis of paroxysmal AF were evaluated. Median follow-up was 8.0 years (range 2 days to 11.1 years). The probability of progression to CAF by 1 year was 8.6% and thereafter there was a slow but steady progression to 24.7% by 5 years. By 5 years, the probability of documented recurrence of any AF (chronic or paroxysmal) was 63.2%. Increasing age, significant aortic stenosis or mitral regurgitation, left atrial enlargement, and diagnosis of cardiomyopathy were independently associated with progression to CAF. A more rapid heart rate during AF was associated with decreased risk of progression.

After the initial diagnosis of paroxysmal AF, there is a slow but steady progression to CAF. Baseline echocardiographic variables, age, cardiomyopathy, and heart rate were independently associated with progression to CAF.