A rare cause of syncope

A 52-year-old woman presented with syncope 6 months earlier. Ambulatory electrocardiography revealed sinus arrest, leading to a diagnosis of sinus node dysfunction and implantation of a right atrial leadless pacemaker. Subsequently, she developed palpitations and transient visual disturbances. A right ventricular Aveir leadless pacemaker was implanted (Panel A; Supplementary S1), but symptoms persisted, predominantly after physical activity. Ambulatory electrocardiography showed a pacing burden of 0.23%, 3123 premature atrial contractions, and 40 premature ventricular contractions (PVCs) with two morphologies. Device interrogation revealed no malfunction. Echocardiography showed no significant structural disease or systolic dysfunction. Exercise electrocardiography documented non-sustained ventricular tachycardia coinciding with syncope (Panel B). At rest (heart rate, 72 beats/min; LVEF 60%), exercise stress echocardiography showed limited mobility of the atrial leadless pacemaker without definite tricuspid-valve interaction (Supplementary S2). With increasing workload and heart rate above 90 beats/min, excursion of the free end progressively increased. At peak exercise (heart rate, 131 beats/min; LVEF 72%), the free end intermittently contacted the septal tricuspid leaflet, coinciding with increased PVC frequency (Panels C and D; Supplementary S3).