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. The 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 * arrhythmias * tachycardia * fibrillation, atrial * tachycardia, supraventricular rhythmia.2 Eight of these patients had paroxysmal atrial fibrillation defined by the following ECG criteria: (1) mean rate >100 beats per minute, (2) QRS morphology during tachycardia that is either normal or functional bundle branch block, (3) a grossly irregular ventricular rhythm, (4) the absence of P waves or the presence of fibrillatory waves in the baseline when P waves had been recorded during periods of sinus rhythm, and (5) episodic occurrence. There were 5 men and 3 women with mean+SD age of 54±t19 years in the paroxysmal atrial fibrillation group. A total of 5 of the patients had some associated heart or lung disease, including 3 with valvular heart disease, 1 with hypertension, 1 with premature ventricular beats, 1 with left bundle branch block, 1 with chronic obstructive lung disease, and 1 with a history of partial pneumonectomy. None of the patients with paroxysmal atrial fibrillation had the Wolff-Parkinson-White syndrome. Fourteen subjects had paroxysmal supraventricular tachycardia identified by ECG criteria: (1) a mean rate > 120 beats per minute, (2) QRS morphology during tachycardia that is either normal or functional bundle branch block, (3) <0.02-second variation in successive RR intervals, (4) no evidence of atrioventricular dissociation, and (5) episodic occurrence. The mechanism of the arrhythmia was atrioventricular nodal reentry in 1 patient, atrioventricular reentry in 3, and unknown in 10. There were 2 men and 12 women with mean±SD age of 42±13 years in the paroxysmal supraventricular tachycardia group. A total of 5 of the patients had associated heart or lung disease, including 1 with valvular heart disease, 1 with hypertension, 2 with asthma, and 1 with chronic bronchitis. The Wolff-Parkinson-White syndrome was present in 2 of the patients with paroxysmal supraventricular tachycardia. The study period for each patient lasted 29 days, during which all class I antiarrhythmic drugs, calcium channel blockers, f-adrenergic blockers, and digoxin were withheld, except verapamil was used in some patients with paroxysmal supraventricular tachycardia for acute treatment of symptomatic tachycardias; none of the patients had ever used a class III antiarrhythmic drug. During this entire period, patients used a portable monitor (Cardiobeeper Memory Monitor; Survival Technology, Bethesda, Md) to record their ECG when they had symptoms of tachycardia and to transmit the ECG to us using a toll-free telephone number. ECGs were received by a 24-hour-a-day automatic answering device, and we called patients back daily (7 days per week) if they transmitted ECGs. These ECGs were archived in laboratory log books. All patients were in sinus rhythm on the first day of the study. We also used 24-hour continuous ambulatory ECG monitors (QuikTrak; Zymed Medical Instrumentation, Camarillo, Calif) to record arrhythmias during the study period. These monitors recorded ECG leads V, and Vs. These continuous recordings were done on the first day of the study period and then once weekly for the next 4 weeks for a total of five recordings in 29 days. In this way, all patients had 29 days in which symptomatic arrhythmia events were recorded with the Cardiobeeper and 5 days in which asymptomatic arrhythmia events were also recorded using the continuous recorders. If the patient had a symptomatic arrhythmia while wearing the continuous recorder, we asked him or her first to push the event marker button on the continuous recorder and second to record the ECG with the Cardiobeeper. Continuous ambulatory ECG recordings were analyzed using a Zymed Model 1610 system. All arrhythmias lasting 5 or more beats were written on chart paper at 25 mm/s for review by a cardiologist who coded them in the following way: 1. A "sustained" asymptomatic event was defined as an arrhythmia lasting at least 30 seconds recorded by 24-hour continuous monitors in the absence of symptoms. This definition is arbitrary and based on the way "sustained" is often defined in the study of ventricular tachycardia by electrophysiological techniques.3'4 For a patient with an asymptomatic event of any length, sinus rhythm was considered "restored" after 5 consecutive sinus beats. 2. A "sustained" symptomatic event was defined as an episode of paroxysmal atrial fibrillation or paroxysmal supraventricular tachycardia that was documented using the Cardiobeeper. Events that were recognized and documented by the event marker on the 24-hour continuous ECG monitor but not documented by Cardiobeeper were excluded from analysis; that is, these latter events were not considered either symptomatic or asymptomatic. 3. When a patient had a symptomatic (recorded by Cardiobeeper) arrhythmia event, any symptomatic or asymptomatic event recorded within 1 hour of the termination was considered part of the preceding symptomatic event. The comparisons of average rates of asymptomatic and symptomatic arrhythmia events in the group of 8 patients with paroxysmal atrial fibrillation and the 14 patients with paroxysmal supraventricular tachycardia were based on theoretical properties of renewal processes, stochastic point processes in which the time intervals between successive point events are independent random variables with a common distribution. It has been shown previously that recurrences of symptomatic paroxysmal atrial fibrillation and paroxysmal supraventricular tachycardia typically behave as a Poisson process,56 a renewal process in which the interevent times are exponentially distributed and the number of events in a time interval of length t has a Poisson distribution with mean At where A is the rate of occurrence. To study the average rate of symptomatic (asymp-  Plots of mean rates of arrhythmia events. Sustained asymptomatic arrhythmia events were significantly (P<.01) more frequent than symptomatic arrhythmia events in the group of patients with paroxysmal atrial fibrillation (PAF, left). In contrast, sustained asymptomatic arrhythmia events were significantly (P=.02) less frequent in the group of patients with paroxysmal supraventricular tachycardia (PSVr, right). tomatic) arrhythmias in our groups of patients, we superimposed on one time line the collective symptomatic (asymptomatic) experience of the entire group for the 29-day (5-day) study period (see "Appendix"). In the group of 8 patients with paroxysmal atrial fibrillation, sustained asymptomatic atrial fibrillation occurred far more frequently than sustained symptomatic atrial fibrillation; in the group of 14 patients with paroxysmal supraventricular tachycardia, the exact opposite was found. In the group of 8 patients with paroxysmal atrial fibrillation, 25 sustained asymptomatic arrhythmia events were recorded in 5 days of continuous ambulatory ECG monitoring in each patient; 12 sustained symptomatic arrhythmia events were recorded in 29 days of transtelephonic ECG monitoring. All 8 patients contributed some type of arrhythmia event to the analysis: 7 of 8 had symptomatic events, 6 of 8 had asymptomatic events, and 5 of 8 had both symptomatic and asymptomatic events. The mean rate of arrhythmia events in the paroxysmal atrial fibrillation group (Fig,  left) , expressed as events/100 d/patient (95% confidence interval), was estimated to be 62.5 (40.4, 87.3) for asymptomatic events and 5.2 (2.7, 9.0) for symptomatic events (P<.O1). Thus, asymptomatic events were far more frequent than symptomatic events in patients with paroxysmal atrial fibrillation. The ratio of the mean rates was 12.1 (5.8, 26.4); asymptomatic events were estimated to be 12-fold more frequent than symptomatic events. To compare the heart rate during symptomatic and asymptomatic atrial fibrillation, the first event of each type was selected from the 5 patients who contributed both event types. The mean heart rate during symptomatic atrial fibrillation was 141 beats per minute, and the mean difference between this rate and the asymptomatic rate was -0.4 beats per minute (95% confidence interval, +12.6; n=5). The 14 patients with paroxysmal supraventricular tachycardia provided a striking contrast with respect to the occurrence of asymptomatic arrhythmia events (Fig,  right) . No  This study is important because it shows that in a group of patients with symptomatic paroxysmal atrial fibrillation, sustained asymptomatic atrial fibrillation occurred 12.1-fold as often as sustained symptomatic atrial fibrillatioin. The 95% confidence interval for this estimate indicated that the asymptomatic rate was at least 5.8-fold the symptomatic rate. In another group of patients with a different arrhythmia, paroxysmal supraventricular tachycardia, asymptomatic and symptomatic arrhythmias behaved quite differently. In this group of patients, sustained asymptomatic paroxysmal supraventricular tachycardia was never recorded during the study, and the estimated ratio of the mean rates (asymptomatic to symptomatic) therefore was 0.0; the 95% confidence interval showed that this ratio was at most 0.8. Thus, in the group of patients with paroxysmal supraventricular tachycardia, sustained asymptomatic arrhythmia events occurred much less often than symptomatic arrhythmia events. This behavior was in sharp contrast with the behavior of paroxysmal atrial fibrillation, in which asymptomatic events occurred many times more frequently than symptomatic events.
It increases the risk of stroke also REF .
Asymptomatic arrhythmias in patients with symptomatic paroxysmal atrial fibrillation and paroxysmal supraventricular tachycardia.
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