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ECG artefact or life-threatening arrhythmia? A neonatal presentation of Long QT syndrome type 3 with a de novo SCN5A mutation

Published online by Cambridge University Press:  11 December 2025

Emine Gulsah TorunOpen the ORCID record for Emine Gulsah Torun[Opens in a new window],
Nevin ÖzdemiroğluOpen the ORCID record for Nevin Özdemiroğlu[Opens in a new window],
İsmail Çağrı AçıkgözOpen the ORCID record for İsmail Çağrı Açıkgöz[Opens in a new window],
Ahmet Cevdet CeylanOpen the ORCID record for Ahmet Cevdet Ceylan[Opens in a new window] and
Serhat KocaOpen the ORCID record for Serhat Koca[Opens in a new window]
Emine Gulsah Torun*
Affiliation:
Department of Pediatric Cardiology, Ankara Bilkent City Hospital, Ankara, Türkiye
Nevin Özdemiroğlu
Affiliation:
Department of Pediatric Cardiology, Ankara Bilkent City Hospital, Ankara, Türkiye
İsmail Çağrı Açıkgöz
Affiliation:
Department of Neonatology, Ankara Bilkent City Hospital, Ankara, Türkiye
Ahmet Cevdet Ceylan
Affiliation:
Department of Medical Genetics, Ankara Bilkent City Hospital, Ankara, Türkiye
Serhat Koca
Affiliation:
Department of Pediatric Cardiology, Ankara Bilkent City Hospital, Ankara, Türkiye
*
Corresponding author: Emine Gulsah Torun; Email: drgtorun@gmail.com
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Abstract

Electrocardiogram interpretation is critical in neonatal care, as artefacts may mimic life-threatening arrhythmias. We report the case of a preterm newborn girl, delivered at 31 weeks of gestation due to acute fetal distress, who developed tachycardia shortly after birth. The initial ECG showed chaotic electrical activity, initially raising suspicion of artifact; however, a subsequent tracing confirmed a life-threatening arrhythmia with wide QRS complexes, prolonged QTc, and torsades de pointes. As the patient remained haemodynamically stable, intravenous lidocaine and magnesium sulphate were administered, achieving pharmacological cardioversion. Propranolol was subsequently initiated, and the lidocaine infusion was tapered and replaced with oral mexiletine. Serial electrocardiograms showed QTc interval improvement, left ventricular function normalised, and the patient was discharged on the 39th postnatal day following stabilisation and supportive care for prematurity. Genetic testing identified a de novo SCN5A c.796C > G (p.L266V) mutation associated with Long QT syndrome type 3. At 1 year of age, the patient remains stable and asymptomatic while receiving combined therapy with propranolol and mexiletine.

Keywords

Long QT syndrome type 3SCN5A mutationtorsades de pointesneonatal arrhythmia

Information

Type
Case Report
Information
Cardiology in the Young , Volume 35 , Issue 12 , December 2025, pp. 2598 - 2601
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Copyright
© The Author(s), 2025. Published by Cambridge University Press

Introduction

Electrocardiogram interpretation is essential for identifying potentially life-threatening arrhythmias and guiding appropriate treatment. Reference Silvia, Carina and Andrea1,Reference Rafie, Kashou and Noseworthy2 However, differentiating true pathological rhythms from electrocardiogram artefacts—extrinsic distortions unrelated to cardiac activity—remains challenging. Artefacts may result from patient movement, electrode misplacement, or electrical interference, and they can closely mimic malignant arrhythmias, thereby increasing the risk of misdiagnosis and inappropriate interventions. Reference Littmann3 Recognising and distinguishing electrocardiogram artefacts from genuine life-threatening arrhythmias is therefore critical to ensure accurate management and to avoid unnecessary treatments, which is particularly important in vulnerable populations such as neonates. Reference Schulze-Bahr, Fenge and Etzrod4

This case report highlights the importance of precise electrocardiogram interpretation in a newborn with a de novo SCN5A nonsense mutation (c.796C > G, p.L266V) associated with Long QT syndrome (LQTS) type 3, who presented with torsades de pointes.

Case presentation

A newborn girl was delivered at 31 weeks of gestation via caesarean section due to acute fetal distress and fetal bradycardia, with a birth weight of 1730 g. Following birth, her clinical condition deteriorated, necessitating intubation and transfer to the neonatal ICU. During cardiac monitoring, an electrocardiogram was obtained because of an unclear monitor rhythm and tachycardia at 220 beats per minute. The initial electrocardiogram demonstrated chaotic electrical activity (Figure 1(a)), suspected to represent an artefact, and a repeat electrocardiogram was performed. The second electrocardiogram revealed intermittent wide QRS complexes, a prolonged QTc interval, and episodes of torsades de pointes (Figure 1(b)).

Figure 1.

Electrocardiogram (ECG) showing chaotic electrical activity, initially suspected to represent an artefact. ( b ) ECG showing intermittent wide QRS complexes with a prolonged QTc interval and the onset of torsades de pointes. ( c ) Prolonged QTc interval on ECG following medical cardioversion.

As the patient was haemodynamically stable, intravenous lidocaine was administered at a bolus dose of 1 mg/kg, followed by continuous infusion at 30 µg/kg/min. Additionally, a single intravenous dose of magnesium sulphate (30 mg/kg) was given. After pharmacological cardioversion, the follow-up electrocardiogram demonstrated a prolonged QT interval (>500 ms) in sinus rhythm (Figure 1(c)). Echocardiography revealed impaired left ventricular systolic function.

The patient was subsequently evaluated for potential secondary and reversible causes, including hypoxia, hypovolemia, electrolyte disturbances (hyperkalemia, hypokalaemia, hypocalcaemia), hypothermia, acidosis, and toxins, all of which were excluded. Propranolol therapy was initiated at 2 mg/kg/day in three divided doses. The lidocaine infusion was gradually tapered and replaced with oral mexiletine at a dose of 10 mg/kg every 8 hours. Follow-up electrocardiograms demonstrated QTc interval improvement, and echocardiography confirmed normalisation of left ventricular function. After stabilisation and management of complications related to prematurity, including nutritional support and growth monitoring, the patient was discharged on the 39th postnatal day.

Genetic analysis revealed heterozygosity for the SCN5A c.796C > G (p.L266V) mutation, associated with Long QT syndrome type 3. This variant was not detected in either parent, confirming a de novo origin.

At 1 year of age, the patient remains asymptomatic under combined propranolol (3 mg/kg/day) and mexiletine (10 mg/kg/day) therapy, with normal QTc values on 12-lead electrocardiogram (Figure 2) and maximum QTc intervals consistently below 500 ms on 24-hour Holter monitoring.

Figure 2.

Reduction in QTc interval observed after initiation of combined therapy with mexiletine and propranolol.

Discussion

Accurate recognition of electrocardiogram artefacts is essential in clinical practice to prevent misdiagnosis and inappropriate management, particularly in critically ill neonates. Reference Silvia, Carina and Andrea1 Because artefacts may mimic life-threatening arrhythmias, they can result in unnecessary treatments and interventions. Reference Littmann3 In the present case, the initial electrocardiogram was suspected to represent an artefact; however, a subsequent recording clarified the diagnosis by demonstrating a pathological rhythm that required prompt medical intervention.

The successful management of this case underscores the importance of recognising and appropriately treating prolonged QT intervals. LQTS predisposes patients to life-threatening arrhythmias, and genetic analysis is crucial for identifying the underlying pathogenic mutations. Long QT syndrome type 3, a rare subtype in neonates, results from mutations in the SCN5A gene, which encodes the cardiac sodium channel. These mutations impair channel function, leading to delayed repolarisation and increased susceptibility to malignant arrhythmias such as torsades de pointes and ventricular fibrillation. Early diagnosis is essential for effective management, typically involving beta-blockers such as propranolol and sodium channel blockers such as mexiletine, which help shorten the QT interval and reduce arrhythmic risk. In refractory or high-risk cases, implantation of a cardioverter-defibrillator may be required. Reference Brugada, Blom and Sarquella-Brugada5,Reference Mazzanti, Maragna and Faragli6 Although the patient remains clinically stable at 1 year of age, the long-term risk of arrhythmic events persists in Long QT syndrome type 3, underscoring the need for regular follow-up with serial electrocardiograms and Holter monitoring.

The identification of the c.796C > G (p.L266V) mutation in SCN5A adds significantly to the current body of knowledge on Long QT syndrome type 3. This finding broadens the spectrum of known genetic variants associated with Long QT syndrome type 3 and provides valuable insights into genotype–phenotype correlations, underscoring the pivotal role of genetic analysis in the diagnosis and management of unexplained arrhythmias, particularly in neonates. Recognition of this mutation contributes to a better understanding of the underlying pathophysiology of Long QT syndrome type 3, informs future research and therapeutic strategies, and facilitates the early diagnosis of similar cases, thereby improving outcomes through timely intervention. Furthermore, it yields important information for family members who may be at risk, highlighting the ongoing need for genetic research, counselling, and surveillance in clinical practice. Reference Mazzanti, Maragna and Faragli6

In conclusion, accurate differentiation between electrocardiogram artefacts and true pathological findings is crucial in neonatal care. Early recognition and timely management of ventricular arrhythmias can markedly improve clinical outcomes. Furthermore, the identification of the de novo SCN5A mutation in this case contributes to the existing literature by expanding the spectrum of genetic variants associated with Long QT syndrome type 3.

Financial supports

This research received no specific grant from any funding agency, commercial, or not-for-profit sectors.

Competing interests

The authors declare none.

References

Silvia, GP, Carina, BL, Andrea, M et al. ESC Scientific Document Group. 2015 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: The Task Force for the Management of Patients with Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death of the European Society of Cardiology (ESC). Endorsed by: Association for European Paediatric and Congenital Cardiology (AEPC). Eur Heart J 2015; 36(41): 2793–2867.Google Scholar
Rafie, N, Kashou, AH, Noseworthy, PA. ECG interpretation: clinical relevance, challenges, and advances. Hearts 2021; 2(4): 505–513.CrossRefGoogle Scholar
Littmann, L. Electrocardiographic artifact. J Electrocardiol 2021; 64: 23–29.CrossRefGoogle ScholarPubMed
Schulze-Bahr, E, Fenge, H, Etzrod, D et al. Long QT syndrome and life-threatening arrhythmia in a newborn: molecular diagnosis and treatment response. Heart 2004; 90: 13–16.CrossRefGoogle Scholar
Brugada, J, Blom, NA, Sarquella-Brugada, G et al. Pharmacological and non-pharmacological therapy for arrhythmias in the pediatric population: EHRA and AEPC-Arrhythmia Working Group joint consensus statement. Europace 2013; 15(9): 1337–1382.CrossRefGoogle Scholar
Mazzanti, A, Maragna, R, Faragli, A et al. Gene-specific therapy with mexiletine reduces arrhythmic events in patients with Long QT syndrome type 3. J Am Coll Cardiol 2016; 67: 1053–1058.CrossRefGoogle ScholarPubMed
Figure 0

Figure 1.Electrocardiogram (ECG) showing chaotic electrical activity, initially suspected to represent an artefact. (b) ECG showing intermittent wide QRS complexes with a prolonged QTc interval and the onset of torsades de pointes. (c) Prolonged QTc interval on ECG following medical cardioversion.

Figure 1

Figure 2.Reduction in QTc interval observed after initiation of combined therapy with mexiletine and propranolol.