Objectives: According to the guidelines of the European Society of Cardiology a likely diagnosis of neurally mediated syncope (NMS) can be made when the patients have a consistent history and competing diagnosis are excluded. In the present study we validated the initial diagnosis of NMS by means of implantable loop recorder (ILR) documentation.
Methods and Results: In the Third International Study on Syncope of Uncertain Etiology (ISSUE-3) registry, 504 NMS patients ?40 years who had suffered, in the prior 2 years, ?3 syncopal episodes received a ILR and were followed-up for a mean of 15±11 months. A diagnosis was achieved in 187 of them with an estimated diagnostic yield of 31% (95% CI 27-36) at 1 year, 40% (95% CI 36-45) at 2 years and 47% (95% CI 40-53) at 3 years. NMS was confirmed in 162 (87%) patients (asystolic in 99 and likely hypotensive in 63) and was ruled out in other 25 (13%) who had an intrinsic cardiac arrhythmic cause (atrial tachyarrhythmias [#9], long pause at termination of tachyarrhythmia [#7], persistent bradycardia [#3], ventricular tachycardia [#2]) or a non-arrhythmic loss of consciousness (non-syncopal [#3], orthostatic hypotension [#1]). No clinical baseline feature was able to predict an intrinsic cardiac cause with the exception of a more frequent non-syncopal atrial tachyarrhythmias on clinical history which was present in 38 % of cardiac vs 5% of NMS patients (p=0.001). Treatment: pacemaker in 108 (101 NMS and 7 cardiac), education and counterpressure maneuvers in 61 NMS, catheter ablation in 6 cardiac, ICD in 2 cardiac, other treatments in 5 cardiac patients. Among established NMS patients, pacemaker therapy was more effective then no pacemaker therapy in preventing syncopal recurrence (26% vs 54% at 21 months of follow-up, p=0.01).
Conclusions: The accuracy of the diagnosis of NMS made at initial evaluation is 87%. A small not irrelevant number of patients have a different diagnosis, especially an intrinsic arrhythmic cause. Pacemaker therapy is effective in patients with NMS established by ILR documentation.