Effect of atenolol versus ivabradine on heart rate variability in patients of schizophrenia with clozapine-induced tachycardia: a randomized controlled trial

BACKGROUND A third of schizophrenia cases are resistant to antipsychotics, where clozapine is the only FDA-approved medication. Clozapine use is often limited by intolerable adverse effects. Persistent tachycardia occurs in approximately 25-54% patients receiving clozapine. Heart rate variability (HRV) is a non-invasive, clinically relevant marker of autonomic nervous system functioning. Atenolol and Ivabradine are usually prescribed for clozapine-induced tachycardia (CIT), although evidence guiding their optimal use remains limited. AIM This study aimed to compare the effects of atenolol versus ivabradine on HRV in patients with treatment-resistant schizophrenia (TRS) receiving clozapine. METHODS This open-label randomised clinical trial, conducted at a tertiary-care center over 20 months, involved TRS patients on clozapine for more than three months and having persistent tachycardia. Twenty patients received atenolol 25mg once-daily, while twenty received ivabradine 5mg twice-daily for two months. The primary outcome was the change in the frequency domain of HRV, while the secondary outcomes were time-domains, central and peripheral blood pressure, pulse rate and treatment-emergent adverse events (TEAE). RESULTS While both drugs significantly reduced pulse-rates (atenolol: -20.56±13.00, p<0.001; ivabradine: -21.855±12.873, p<0.001). Within-group analysis showed that, the atenolol group had significant improvements in high-frequency [HF] power (p=0.048) and LF/HF ratio (p=0.044), along with a non-significant trend towards increased total power (p=0.053); no significant within-group changes were observed in the ivabradine group. CONCLUSION No significant between-group differences in HRV parameters were established between atenolol and ivabradine. Ivabradine could be a viable option in patients where atenolol is either contraindicated or not tolerated. Future larger multicentric studies are needed for greater generalisability. TRIAL REGISTRATION ClinicalTrials.gov identifier: NCT06505668.