BACKGROUND:

Paroxysmal arrhythmias are a group of disorders in which sudden abnormalities of the cardiac rhythm occur without warning. Despite the abundant information available from studies on the mechanisms of tachycardias, there was hardly a shred of objective data in 1989 to establish how the occurrence of symptomatic tachycardias was influenced by various mechanisms. In fact, there were very few objective data describing the occurrence of symptomatic tachycardia among the patients who were afflicted with various paroxysmal tachycardias. For example, were patients in normal sinus rhythm likely to remain free of their tachycardia for one day, one week, one month, or longer? The suddenness and apparent unpredictability of attacks of paroxysmal tachycardias have been substantial obstacles to quantitative description of their occurrence. These studies used careful documentation of spontaneous tachycardia to establish the epidemiology of symptomatic arrhythmias.

DESIGN NARRATIVE:

Baseline electrophysiologic methods, including intracardiac recording and programmed electrical stimulation, were used to determine the mechanism of paroxysmal supraventricular tachycardia. All patients had antiarrhythmic medications stopped. In most cases, the diagnosis of atrial fibrillation was established by scalar electrocardiographic criteria. At the time of entry into follow-up each patient was given a cardiobeeper and instructed to record and transmit any symptomatic arrhythmia when it occured. Descriptive information about each patient was entered into a baseline data file which included information on the time interval between attacks, age, sex, mechanism of arrhythmia, types of associated heart diseases, ECG data during sinus rhythm, and date and time of call. The purpose of the outpatient follow-up was to obtain objective documentation of spontaneously occurring, symptomatic tachycardia for quantitative analyses. Holter monitoring was used in patients with paroxysmal tachycardias to establish that asymptomatic tachycardia did not occur so often that it constituted an important, unrecognized feature of these clinical conditions.

Ten consecutively referred patients with paroxysmal supraventricular tachycardia and ten consecutively referred patients with atrial fibrillation underwent untreated surveillance with telephone/ cardiobeeper monitoring for symptomatic arrhythmias and had four 24-hour ambulatory ECGs recorded at weekly intervals to detect symptomatic and asymptomatic arrhythmias. The Cox proportional hazards model was used to test the hypothesis that the mechanism of tachycardia was the most important predictor of the tachycardia-free period during an untreated observation period.