Background Paroxysmal atrial fibrillation and paroxysmal supraventricular tachycardia are recognized clinically when patients seek treatment for symptoms due to recurrent arrhythmias; atrial fibrillation also increases the risk of stroke. The frequency with which asymptomatic arrhythmias occur in patients with these arrhythmias is unknown.Methods and Results Twenty-two patients with paroxysmal atrial fibrillation (n=8) or paroxysmal supraventricular tachycardia (n=14) were studied for 29 days with two different ambulatory ECG-monitoring techniques to measure the relative frequency of asymptomatic and symptomatic arrhythmias. All class I antiarrhythmic drugs, calcium channel blockers, ,8-blockers, and digitalis were withheld. Sustained asymptomatic arrhythmia events (defined as lasting at least 30 seconds) were documented using continuous ambulatory ECG monitoring once weekly for a total of 5 of the 29 study days; symptomatic arrhythmia events were documented using transtelephonic ECG monitoring for all 29 days of the study. In the group of patients with paroxysmal atrial fibrillation, asymp-P aroxysmal atrial fibrillation and paroxysmal supraventricular tachycardia are common arrhythmias that may be treated with antiarrhythmic drugs when patients have symptoms. Patients who are affected with these disorders have sinus rhythm that is punctuated by episodic recurrences of their arrhythmias. The sequence of these recurrent arrhythmia events can be described in mathematical terms as a "stochastic process," which is a series of events occurring in time in accordance with probabilistic laws.' In this study, we used methods developed to study stochastic processes to estimate the average rate of asymptomatic arrhythmia events in groups of patients with symptomatic paroxysmal atrial fibrillation and paroxysmal supraventricular tachycardia. MethodsThe study sample consisted of 22 ambulatory outpatients (7 men and 15 women with mean±SD age of 47±+17 years) who were being followed in the Clinical Research Unit Arrhythmia Clinic because they had a paroxysmal supraventricular ar- tomatic arrhythmia events occurred significantly more frequently than symptomatic arrhythmia events; the mean rates, expressed as events/100 d/patient (95% confidence interval), were 62.5 (40.4, 87.3) and 5.2 (2.7, 9.0) (P<.01); the ratio of the mean rates was 12.1 (5.8, 26.4). In contrast, in the group of patients with paroxysmal supraventricular tachycardia, asymptomatic arrhythmia events were significantly less frequent than symptomatic arrhythmia events; the mean rates were 0.0 (0.0, 5.3) and 7.4 (5.0, 10.6) (P=.02). The ratio of the mean rates was 0.0 (0.0, 0.8).Conclusions In a group of patients with paroxysmal atrial fibrillation, sustained asymptomatic atrial fibrillation occurs far more frequently than symptomatic atrial fibrillation. However, it is not known whether asymptomatic atrial fibrillation is a potential risk factor for stroke even when patients are not having symptomatic arrhythmias. (Circulton. 1994;89:.224-227.) Key Words * a...

This study suggests that atrial fibrillation will develop in approximately 12% of patients with paroxysmal supraventricular tachycardia during a 1-year follow-up period. The occurrence of atrial fibrillation is not related to the mechanism or heart rate of the paroxysmal supraventricular tachycardia.

Age is more important than other clinical variables, including the ECG classification of a paroxysmal supraventricular arrhythmia in predicting the occurrence of symptomatic arrhythmias. Arrhythmias documented by ECG during symptoms are often different from the arrhythmia documented at the time of referral, which may confound interpretation of antiarrhythmic drug effects.