Cardiac electrophysiological characteristics of silent paroxysmal atrial fibrillation: What causes asymptomaticity?

BACKGROUND: A diagnosis of silent paroxysmal atrial fibrillation (AF) is highly challenging due to its asymptomatic and intermittent nature. The goal of the present study was to clarify its asymptomaticity with the use of a comprehensive electrophysiological approach. METHODS: We prospectively compared (a) 24-hour Holter monitoring data, (b) invasive cardiac electrophysiological properties, (c) AF inducibility, and (d) outcome of radiofrequency catheter ablation between patients with symptomatic paroxysmal AF and those with silent paroxysmal AF, defined as transient asymptomatic AF detected by chance. RESULTS: Patients with silent paroxysmal AF (N = 57) were more likely than patients with symptomatic paroxysmal AF (N = 282) to be male (75.4% vs 56.7%; P = .009), and to have a previous stroke (17.5% vs 6.7%; P = .008), more prolonged atrio-His interval (114.9 +/- 29.1 vs 105.5 +/- 24.1 ms; P = .01), longer atrioventricular nodal effective refractory period (352.3 +/- 103 vs 318.2 +/- 77.2 ms; P = .007), slower Wenckebach cycle length (488.5 +/- 83.9 vs 443.3 +/- 74.9 ms; P < .001), and lower maximum heart rate during AF (128.7 +/- 31.9 vs 143.9 +/- 29.6 beats/min; P = .02). Atrial ectopy (median [interquartile range], 385 [88, 2430] vs 207 [73.8, 870.8] beats/24 h; P = .02) and pharmacological AF induction (66.7% vs 43.2%; P = .02) were more common in silent paroxysmal AF patients. There was no difference in the 1-year freedom from AF following the ablation between the two patient groups. CONCLUSIONS: The more attenuated atrioventricular conduction properties in silent paroxysmal AF patients may explain their asymptomatic nature, and their higher likelihood of atrial arrhythmias may increase the chance to detect AF episodes. Whether or not they benefit from catheter ablation is uncertain.