AbstractAimβ-blockers are the first line of treatment in patients with congenital long QT syndrome (cLQTS) (class I or II recommendation) in order to prevent malignant arrhythmias. Hence, we examined long-term β-blocker adherence and associated risk factors among patients with cLQTS.Methods and resultsDanish patients with cLQTS claiming a prescription for any β-blocker after their cLQTS diagnosis were identified using data from nationwide registries and specialized inherited cardiac disease clinics (1995–2017). Patients were followed for up to 5 years. Treatment breaks >60 days were assessed (i.e. proxy for reduced adherence). Multivariable Cox regression was used to identify risk factors associated with breaks of >60 days in β-blocker treatment. Overall, 500 out of 633 (79%) patients with cLQTS claimed at least one prescription for any β-blocker after cLQTS diagnosis. During follow-up, 38.4% had a treatment break. Risk factors significantly associated with treatment breaks were implantable cardioverter defibrillator (ICD) [hazard ratio (HR) = 1.65, 95% confidence interval (CI): 1.08–2.53], β-blocker side effects (HR = 2.69, 95% CI: 1.75–4.13), and psychiatric disease (HR = 1.63, 95% CI: 1.04–2.57). In contrast, patients presenting with ventricular tachycardia/syncope as cLQTS disease manifestation were less likely to have a treatment break compared with asymptomatic patients (HR = 0.55, 95% CI: 0.33–0.92).ConclusionReduced β-blocker adherence was common with more than a third of patients having a treatment break >60 days after cLQTS diagnosis. Patients with psychiatric disease, self-reported β-blocker side effects, and an ICD were more likely to display reduced adherence, whereas a severe cLQTS disease manifestation was associated with optimal β-blocker adherence.