A case of idiopathic ventricular fibrillation in which implanted loop recorder was useful in application decision for implantation of implantable cardioverter-defibrillator.

Establishing a symptom-rhythm correlation in patients with unexplained syncope is complicated because of its sporadic, infrequent, and unpredictable nature. Recently, an implantable loop recorder (ILR) has become available to evaluate undiagnosed recurrent arrhythmic episodes particularly in unexplained syncopes, and its usefulness has been reported in patients with recurrent syncopes that remain unexplained after conventional work-up. A 65-year-old man was referred to our hospital for loss of consciousness with nocturnal paroxysmal seizures. He had experienced several similar episodes. No family history of sudden death was evident, and apparent structural heart disease was absent. Coronary angiography with intracoronary ergonovine provocation showed vasospasm in left coronary artery without organic stenosis. Ventricular tachyarrhythmias were not induced by programmed electrical stimuli. According to the guideline, he was at once categorized as having class IIb indication for implantable cardioverter defibrillator implantation. However, his symptoms were not relieved despite administration of anti-anginal medications including nitrates and calcium antagonist. Implantation of an ILR was performed and revealed an episode of ventricular fibrillation during generalized-convulsion attack during sleep. ILR is useful in determining the presence of fatal arrhythmias during syncope, although conventional diagnostic testing, such as electrocardiogram, Holter monitoring, and external loop recording, is inconclusive.