Key result
Among 15 paediatric patients with Long QT syndrome, 13.3% experienced an adverse cardiac event (syncope or ICD therapy) over 52.7 patient-years of follow-up.
Why the study?
Long QT syndrome confers profound ramifications in paediatric patients, yet these individuals are often under-represented in registries.
Observational (n=15)
No
Paediatric patients with LQTS display high penetrance and a non-benign clinical course, with frequent device implantation and adverse cardiac events.
Introduction Long QT syndrome (LQTS) confers significant long-term clinical implications. The ramifications are even more profound in paediatric LQTS, yet patients are often under-represented in registries. The aim of this study was to retrospectively evaluate the presentation, penetrance and outcomes of LQTS paediatric patients (<18 years) in a Mediterranean island nation. Methodology Paediatric individuals diagnosed with LQTS <18 years and followed up in the inherited arrhythmia clinic were included. A long QT was defined as per conventional guidelines. Those with a concealed phenotype (normal QT, gene positive G+) were also included. Genetic variants were classified as a VUS, likely pathogenic (LP) or pathogenic (P) as per ACMG criteria. Data was analysed with SPSS v23. A p-value of <0.05 was statistically significant. Results 67 patients with a LQTS diagnosis are followed up in clinic. Just over a fifth (n=15, 22.4%) were <18 years at diagnosis (8 families). Most were male (n=10, 66.7%), mean age 11.5±5.2 years at diagnosis. Half (n=8, 53.3%) were athletes (competitive sports and/or >4 hours of high intensity exercise weekly). Three (20.0%) reported symptoms at baseline (syncope n=2, palpitations n=1). None reported a family history of SCD. A third (n=5, 40.0%) were probands, with 11 (73.3%) having ≥1 affected relative. A diagnosis was often made at family (n=9, 60.0%) or athletic screening (n=3, 20.0%), followed by symptoms (n=2, 13.3%) or as an incidental finding (n=1, 6.7%). Most (n=13, 86.7%) had a Schwartz score of ≥3.5. All patients had at least 1 ECG documenting QT prolongation, longest QTc (resting or provocation) recorded at 561±72 ms. The longest recorded QTc was longer in probands (613±33 ms vs 535±73 ms, p=0.044). Most had a QTc ≥500ms (n=11, 73.3%). T wave anomalies were also frequently present (n=8, 53.3%) (n=5 notching, n=2 late peaking with T wave inversion, n=1 biphasic). 8 of 14 (57.1%) had abnormal ambulatory ECG monitoring. exhibiting >500 SVE/24hr (median SVE count of 650 beats (IQR 202-1474)). No atrioventricular block or malignant arrhythmias were ever recorded on holter monitoring (n=0/14) or exercise testing (n=0/13). Four families (4/8, 50.0%) harboured a genetic variant (n=2 KCNQ1 [1 LP, 1 VUS], n=1 KCNH2 [P], n=1 CALM1 [P]). 9 (60.0%) were G+. The degree of QT prolongation was independent of genetic status (p=0.498). Subjects with T wave morphology anomalies were more likely G+ (p=0.001). All patients were on a beta blocker (n=11 Nadolol, n=4 Propranolol). 40% were implanted with a device (n=5 ILR, n=1 ICD). During 52.7 patient-years of follow up, 2 patients (13.3%) experienced an event (n=1 syncope, n=1 ICD appropriate therapy). Conclusion Paediatric patients diagnosed with LQTS often display a high degree of penetrance (QT >500ms / T wave anomalies). Device implantation and adverse cardiac events are not infrequent, suggesting that the clinical course is rarely benign.
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Abela et al. (2026) conducted an observational in Long QT syndrome (n=15). Long QT syndrome was evaluated on Adverse cardiac events (syncope or ICD appropriate therapy). Among 15 paediatric patients with Long QT syndrome, 13.3% experienced an adverse cardiac event (syncope or ICD therapy) over 52.7 patient-years of follow-up.
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