PMC8422972_01
Mexiletine QTc shortening effect. ECG in the first day of life with QTc >530 ms (recording speed 25 mm/s) (A), ECG at age of 3 months, under mexiletine and propranolol treatment with QTc <450 ms (recording speed 50 mm/s) (B).
fped-09-674041-g0001.jpg
PMC8422972_01_fped-09-674041-g0001.jpg
F1
An electrocardiogram performed in the first day of life in an asymptomatic term female neonate (38+ weeks, spontaneous birth, BW 3.4 kg) due to family history of LQT3 syndrome revealed marked QTc prolongation with late appearing T waves, persisting in repeated ECG after 24 h (QTc values 530-550, Figure 1A). Mexiletine administration was associated with QTc shortening on 12 lead ECGs already at a daily dosage of 4 mg/kg/d with normalization of QTc values (<460 ms) observed at a dosage of 6 mg/kg/d (Figure 1B).
Neonatal 24-h ECG recording. Recording artifacts simulating ventricular arrhythmia -arrows (A) and presence of T wave alternans (B) during the first day of life in 24-h ECG recording.
fped-09-674041-g0002.jpg
PMC8422972_01_fped-09-674041-g0002.jpg
F2
Regular fetal echocardiograms during fetal life ruled out the presence of arrhythmias, while in repeated postnatal 24-h ECG recordings, only artifacts resembling ventricular tachycardia, as well as T wave alternans were documented (Figures 2A,B, respectively).
Family pedigree. Arrow, Proband; black filled symbols, Affected Y1795C mutation carrier; SD, Sudden death; CA, Cancer; negative/unknown, Y1795 mutation status; ICD, Intracardiac defibrillator; act +-, History of appropriate activation yes/no; Propr.+, Mexil.+, Propranolol/mexiletine treatment.
fped-09-674041-g0003.jpg
PMC8422972_01_fped-09-674041-g0003.jpg
F3
Affected family members have the LQT3 ECG phenotype and are currently on propranolol and primary intracardiac defibrillator (ICD) prophylaxis (Figure 3).
PMC8422972_02