Discussion

Ivabradine may be used for heart rate control/heart failure therapy, but it also exhibits anti-arrhythmic properties. ^{Reference Oeffl, Schober and Faudon3} Cardiac graft denervation after heart transplantation causes inadequate sinus tachycardia, which is associated with a reduced survival. Rivinis et al. conducted a registry study analysing 104 adult patients receiving either ivabradine (n = 50) or metoprolol succinate (n = 54) within 5 years after cardiac transplantation. ^{Reference Rivinius, Helmschrott and Rahm4} Compared to baseline and metoprolol succinate, patients with ivabradine had a significantly lower heart rate, reduced left ventricular mass, lower left ventricular end-diastolic pressure, and reduced NT-proBNP level. Moreover, five-year post-transplant survival was significantly better in patients with ivabradine. ^{Reference Rivinius, Helmschrott and Rahm4}

Except for a single case report, there are no paediatric data available on the use of ivabradine for heart failure therapy/heart rate control after cardiac transplantation. Recently, Ogawa et al. reported on the use of ivabradine in a 10-year-old patient with graft failure after cardiac transplantation. ^{Reference Ogawa, Urata and Inuzuka5} Bonnet et al. conducted a randomised, double-blind, placebo-controlled study on ivabradine in children with dilated cardiomyopathy and symptomatic chronic heart failure. Of the 116 patients, 70 % reached the primary endpoint of a ≥ 20 % heart rate reduction (p < 0.0001), though response variability highlighted the need for dose titration. Improvements in left ventricular function, clinical status, and quality of life were noted. ^{Reference Bonnet, Berger, Jokinen, Kantor and Daubeney1}

Besides its role in heart failure therapy, ivabradine has been investigated as an antiarrhythmic agent in paediatric patients, mainly for tachyarrhythmias driven by increased automaticity. One of the first systematic investigations on paediatric ivabradine usage illustrated its potential to treat junctional ectopic tachycardia after CHD surgery in combination with amiodarone. ^{Reference Dieks, Klehs, Müller, Paul and Krause6} In addition, Janson et al. described four cases, where ivabradine helped control junctional ectopic tachycardia and ectopic atrial tachycardia in three patients, but was ineffective for a post-transplant supraventricular tachycardia, likely due to a microreentry mechanism. ^{Reference Janson, Tan, Iyer, Vogel, Vetter and Shah2} In addition, Krishna et al. examined ivabradine in postoperative junctional ectopic tachycardia in 26 patients, of which 54 % were successfully treated with ivabradine alone, 38 % required combination therapy with amiodarone, and 8 % received ivabradine alongside flecainide. ^{Reference Krishna, Kunde, Kumar and Balaji7} Furthermore, Younis et al. reported ivabradine use in refractory supraventricular tachycardia. Within the treatment-resistant subgroup (3 out of 79 patients), ivabradine was successful in two out of three cases. One patient was treated with ivabradine alone, another received a combination therapy with amiodarone. ^{Reference Younis, Abi-Saleh and Al Amin8} Safety and efficacy of ivabradine for heart failure and/or arrhythmia therapy have also been suggested during infancy by recent case series on ivabradine use within the first twelve months of age. ^{Reference Gómez-Ganda, Parramón-Teixidó, Giralt-García, Fernández-García, Ferrer-Menduiña and Cabañas-Poy9,Reference Ergul, Ozturk, Ozgur, Ozyurt, Cilsal and Guzeltas10}

In conclusion, we herein provide the first report on successful ivabradine usage for atrial arrhythmia in a paediatric cardiac transplant recipient. There is a mounting body of evidence that suggests safety and efficacy of ivabradine usage in paediatric patients. In addition, ivabradine shows promising results in adult cardiac transplant recipients in achieving both, heart rate control, and anti-arrhythmic treatment (when associated with increased automaticity). Further research is required to clarify its potential role in the vulnerable population of paediatric cardiac transplant recipients.