The Diagnostic Yield of Implantable Loop Recorders Stratified by Indication: A “Real-World” Single-Center Experience

<b>Background/Objectives:</b> Implantable loop recorders (ILRs) are widely used for the diagnosis of unexplained syncope, palpitations, and cryptogenic stroke. While ILRs demonstrate clinical utility, data on their diagnostic yield and value in real-world settings remain limited. This study evaluates ILR performance, diagnostic yield, and clinical impact across multiple indications. <b>Methods:</b> We retrospectively analyzed 316 patients who underwent ILR implantation between 2017 and 2023 at a single center. Indications included unexplained syncope, palpitations, and atrial fibrillation (AF) detection. Diagnostic yield, defined as the ratio of positive diagnoses to implants, and diagnostic value, defined as diagnoses leading to therapeutic changes, were assessed. Diagnostic appropriateness, reflecting diagnoses consistent with implant indications, was also investigated. Continuous variables were analyzed using an independent samples <i>t</i>-test or ANOVA, when appropriate; dichotomous variables were analyzed using a chi-square test. <b>Results:</b> The overall diagnostic yield was 30%, with most diagnoses occurring within 24 months post-implantation. Bradyarrhythmias were diagnosed earlier (mean: 290 days) than tachyarrhythmias (590 days, <i>p</i> = 0.04). The diagnostic value was 29%, and the appropriateness reached 70%. The diagnostic-value-to-diagnostic-yield ratio was shown to be as high as 97%, suggesting that whenever a diagnosis was made, it was of clinical impact. Patients with presyncope showed a higher diagnostic yield, particularly for tachyarrhythmias. Device re-implantation showed limited utility, as only one diagnosis (classified as bystander) was achieved in 32 re-implanted patients. After 900 days, the diagnostic yield decreased significantly, with the number needed to follow (NNF) rising from 3.85 to 18 (<i>p</i> < 0.001). <b>Conclusions:</b> ILRs are effective for arrhythmia detection, demonstrating significant diagnostic and therapeutic impact, particularly within the first two years. The recurrence of presyncope and atrial dilation was associated with higher yields, while isolated syncope posed diagnostic challenges. Prolonged monitoring beyond 900 days and device re-implantation provided diminishing returns.