Mechanism of syncope without prodromes with normal heart and normal electrocardiogram

Background " Unexplained syncope, no prodromes, and normal heart " has been described as a distinct clinical and biological entity. Objective The purpose of this study was to assess the mechanism of syncope. Methods In this prospective multicenter study, 58 patients presenting with unexplained syncope, no prodromes, and a normal heart received an implantable loop recorder (ILR) and were followed up until a diagnosis was established. Their outcomes were compared with those of 389 patients affected by reflex syncope with prodromes who received an ILR. Results During a mean observation period of 16 ± 13 months, a diagnostic event was documented by the ILR in 29 patients (50%); an asystolic pause of 11 ± 5 seconds (range 3.5–22 seconds) was present at the time of the diagnostic event in 19 patients (66%). Compared with patients affected by reflex syncope with prodromes, patients with unexplained syncope, no prodromes, and a normal heart more frequently had an asystolic syncope (66% vs 47%; P = .001), and this was more frequently due to idiopathic paroxysmal atrioventricular block (47% vs 21%; P = .04). Ten patients with asystolic pauses underwent cardiac pacing, and 8 patients underwent oral theophylline treatment. During the subsequent 17 ± 12 months of follow-up, syncope recurred in 1 patient on theophylline and presyncope occurred in 1 patient with pacemaker. Conclusion A long asystolic pause, frequently due to idiopathic paroxysmal atrioventricular block, played a role in the mechanism of syncope in two-thirds of patients who had electrocardiographic documentation of a diagnostic event. When a specific therapy was administered in patients with asystolic syncope, the short outcome was favorable.