Abstract 19329: Impact of Dipyridamole on Adenosine Dosing in Pediatric and Young Adult Patients After Heart Transplant

Introduction: Adenosine as an antiarrhythmic agent has been relatively contraindicated following heart transplant. Dipyridamole, often prescribed after transplant, is thought to potentiate adenosine. Adult guidelines recommend lower adenosine doses in patients on dipyridamole, based on limited evidence. In an initial prospective study, we demonstrated safety and efficacy of adenosine to induce atrioventricular (AV) block in pediatric and young adult patients; 42 patients were on dipyridamole, suspended ≥ 72 hours before testing. Safety and efficacy on dipyridamole is unknown. Methods: In a prospective follow-up study, we reassessed safety and efficacy of adenosine in healthy young patients after heart transplant on dipyridamole (4/2016 - 6/2017). Patients were eligible if they took part in the parent study, were on dipyridamole and returned for routine cardiac catheterization (39 patients). After cardiac biopsy, we placed a temporary ventricular pacing wire and dosed adenosine in stepwise increments until ≥ 1 P wave was blocked or max dose reached (200mcg/kg or 12mg). The primary outcome was clinically significant asystole (≥ 12 seconds). Secondary outcomes included the lowest adenosine dose causing AV block, block duration, cardiac ectopy and patient reported symptoms. Incidence and 95% confidence intervals for categorical outcomes were calculated. Paired outcomes from the current and parent study were compared. Results: Thirty patients (5 - 24 years) were tested. No patient (0%, CI 0 - 8%) experienced significant asystole. AV block occurred in 29 patients (97%, CI 86 - 100%). Seventeen patients (57%, CI 39 - 72%) required less adenosine to achieve AV block on dipyridamole; six (20%) required more. The median lowest dose causing AV block was 50mcg/kg (vs. 100mcg/kg off dipyridamole; P=0.013). No block occurred Conclusion: AV block occurs often at half the dose of adenosine in healthy pediatric and young patients after transplant on oral dipyridamole. Initial dosing of 25mcg/kg (max 0.8mg) with stepwise escalation poses low risk.