Case report

At 31 weeks of gestation, a woman was referred for a foetal echocardiography due to irregular heartbeat of the fetus. M-mode showed ventricular tachycardia, and the woman was started on digoxin i.v.. After 2 days without improvement, the foetal scan showed AV-valve regurgitation and incipient foetal hydrops. Medication was switched to flecainide, but shortly after that a C-section was necessary due to progressive heart failure of the fetus. A 2.06 kg boy was born, intubated, and received surfactant due to prematurity. On the basis of a 2:1 av block, he was bradycardic at around 60–70 bpm and the corrected QT interval was 590 ms. Echocardiography showed a structurally and functionally normal heart. Except for two episodes of non-sustained torsade-de-point, the boy was hemodynamically stable and could be extubated. As for treatment of the av block and the long QT interval, an epicardial pacemaker (SJM Microny II SR plus VVI, rate 120 bpm) with an epigastric device was implanted and propranolol (3 mg/kg/day) was started. After almost 6 weeks in the hospital (mainly due to prematurity), the boy was discharged.

In the following years, the boy was seen regularly in our outpatient clinic. There were no syncopes, no cardiac events or pacemaker problems documented. During these years, he was on propranolol (2–3 mg/kg/day) and regularly acquired 24-hour electrocardiograms never showed ventricular arrhythmias. Genetics later confirmed mutation p.G628S in gene KCNH2, a pathogenic variant confirming long QT syndrome type 2.

In March 2019, the same boy, now 10 years old, collapsed on a chair in school after a short period of feeling unwell. There were no obvious triggers such as QT-prolonging drugs, infection, or others. According to his parents, he was very compliant in taking his medication. His teacher performed cardiopulmonary resuscitation. The first rhythm seen when paramedics arrived 15 minutes later was interpreted as ventricular fibrillation and a shock (about 3 J/kg) as well as adrenalin was administered. After that, pulseless electric activity was seen and cardiopulmonary resuscitation was continued. After 45 minutes, return of spontaneous circulation with sinus rhythm was documented. On arrival in the trauma unit the boy was intubated, cardiopulmonary stable without inotropic support and in sinus rhythm at around 95 bpm (pacemaker set at a backup rate of 90 bpm). Read-out of the pacemaker showed ventricular fibrillation at the time of syncope, lasting for about 20 minutes. Subsequently, it exhibited sinus rhythm. Unfortunately, the exact mechanism leading to tachycardia could not be determined in the read-out due to the pacemaker settings. The prior medication with propranolol was continued at a higher dose of 4 mg/kg/day, potassium and magnesium were substituted, and the VVI-pacemaker was set at a rate of 100 bpm (before 90 bpm). In the following 24 hours, the boy repeatedly had non-sustained and sustained ventricular fibrillation as well as torsade-de-pointes, which did not respond to magnesium and required three resuscitations and several defibrillations. Hence, propranolol was stopped and isoproterenol was commenced and titrated up to 0.12 ug/kg/minute resulting in sinus tachycardia at around 110–120 bpm, but without improvement of the ventricular arrhythmias. Therefore, the pacemaker was explanted and an implantable cardioverter-defibrillator device (Medtronic) set to DDD 100 bpm was implanted. The procedure was successfully conducted. In the next days, there were repeated episodes of torsade-de-pointes and ventricular fibrillation that were adequately terminated by the implantable cardioverter-defibrillator. Propranolol was restarted (4 mg/kg/day) and the ICD paced at 110 bpm. As a last option before sympathetic denervation was considered, mexiletine (8.6 mg/kg/day) was commenced. The corrected QT interval at baseline was between 554 and 570 ms and with mexiletine reduced to 534–540 ms. Under this dual therapy, no more arrhythmias were documented.

Consecutively, the boy recovered slowly from the hypoxic brain injury he suffered during resuscitation and left the hospital for neurodevelopmental rehabilitation after 6 weeks. When visiting outpatient clinic 6 month later, the boy walked with a moderate ataxia, was able to talk, and also was attending a school for students with extra needs. In the following 2 years of check-ups, there have been no adverse cardiac events under propranolol (3–4 mg/kg/day) and mexiletine (8.3–8.6 mg/kg/day). Mexiletine has been well-tolerated without side effects.