Incidence and predictors for early (<1 month) etiology diagnosis in unexplained syncope patients: a multicenter study

Introduction ESC Guidelines recommend using implantable cardiac monitors (ICM) in patients with unexplained syncope upon thorough diagnostic workup. Recently, ICM implant in early workup stage was recommended, based on studies showing its benefit over ‘traditional’ workup.1,2,3 Thus, ICM use increased dramatically over the last decade. Nevertheless, ICM is an invasive procedure and is associated with non-negligible costs. At times, syncope diagnosis is made shortly after ICM implant, suggesting that external loop recorders (ELR) may suffice and reduce need for ICM. Purpose Evaluate the prevalence and predictors for early ICM-based syncope etiology diagnosis, defined as diagnosis within <1 month from ICM implant. Methods Retrospective cohort of all unexplained syncope patients implanted an ICM during 2019-2022 in two large tertiary centers. Syncope was defined as unexplained following a non-diagnostic initial workup including a comprehensive clinical history, physical examination, ECG, 24-h ECG Holter, and TTE. Cases considered of neurocardiogenic or other probable etiologies after initial evaluation were excluded. Study endpoint was an early (<1 month) ICM-based diagnosis of syncope etiology. Predictors for early diagnosis were identified via uni- and multivariable analysis. Results Study included 145 unexplained syncope patients implanted with an ICM. During a median follow-up of 30 [8-42] months, 48/145 (33.1%) received an ICM-based diagnosis. Fourteen of these 48 ICM-based diagnoses (29.2%) were achieved within <1 month from ICM implant, including 7 cases of high-degree atrio-ventricular block (AVB), 4 cases of definitive vagal etiology, and 3 with non-arrhythmic etiology. Univariate analysis demonstrated that older age (≥70 y/o), presence of bundle branch block (BBB) on initial ECG, and diabetes were significantly associated with early AVB diagnosis, while young age (≤35 y/o), normal initial ECG, and normal TTE were significantly associated with early vagal or non-arrhythmic syncope. Conclusions Around a third of all ICM-based syncope diagnoses were early, achieved within <1 month from ICM implant, suggesting that an initial ELR may obviate the need for ICM. Accordingly, 1-month ELR may still have a role in unexplained syncope initial workup before proceeding to ICM.