History

The clinical diagnosis of long QT syndrome is prompted by a high degree of clinical suspicion, which arises from the presenting complaints.^[11]A detailed family history for similar symptoms is warranted. The presenting complaints may include the following:

Unexplained bradycardia - Especially in the newborn
Syncope - Especially when associated with a triggering event (eg, drowning, near drowning)^[11]
Epilepsy - Especially not controlled by conventional medications
Palpitations
Aborted or sudden cardiac death in the patient or family history of sudden cardiac death
Sudden infant death syndrome (SIDS)
Depressive symptoms^[12]

Physical Examination

Certain physical findings in long QT syndrome, such as skeletal abnormalities (eg, short stature, scoliosis), may suggest Andersen syndrome, whereas congenital heart diseases, along with cognitive and behavioral problems, musculoskeletal diseases, and immune dysfunction, may suggest Timothy syndrome. Congenital deafness is seen in JLN syndrome, although the incidence of long QT syndrome in patients with congenital deafness is very low.

Differential Diagnoses

Taggart NW, Haglund CM, Tester DJ, Ackerman MJ. Diagnostic miscues in congenital long-QT syndrome. Circulation. 2007 May 22. 115(20):2613-20. [Medline].
Schwartz PJ, Moss AJ, Vincent GM, Crampton RS. Diagnostic criteria for the long QT syndrome. An update. Circulation. 1993 Aug. 88(2):782-4. [Medline].
Simma A, Potapow A, Brandstetter S, Michel H, Melter M, Seelbach-Göbel B, et al. Electrocardiographic screening in the first days of life for diagnosing long QT syndrome: findings from a birth cohort study in Germany. Neonatology. 2020 Nov 12. 1-8. [Medline].
Saprungruang A, Khongphatthanayothin A, Mauleekoonphairoj J, et al. Genotype and clinical characteristics of congenital long QT syndrome in Thailand. Indian Pacing Electrophysiol J. 2018 Sep - Oct. 18 (5):165-71. [Medline]. [Full Text].
Chen XM, Guo K, Li H, et al. A novel mutation KCNQ1p.Thr312del is responsible for long QT syndrome type 1. Heart Vessels. 2019 Jan. 34 (1):177-88. [Medline].
Gupta A, Lawrence AT, Krishnan K, Kavinsky CJ, Trohman RG. Current concepts in the mechanisms and management of drug-induced QT prolongation and torsade de pointes. Am Heart J. 2007 Jun. 153(6):891-9. [Medline].
Hobbs JB, Peterson DR, Moss AJ, et al. Risk of aborted cardiac arrest or sudden cardiac death during adolescence in the long-QT syndrome. JAMA. 2006 Sep 13. 296(10):1249-54. [Medline].
Ozawa J, Ohno S, Hisamatsu T, et al. Pediatric cohort with long QT syndrome - KCNH2 mutation carriers present late onset but severe symptoms. Circ J. 2016. 80 (3):696-702. [Medline].
Goldenberg I, Moss AJ, Zareba W, et al. Clinical course and risk stratification of patients affected with the Jervell and Lange-Nielsen syndrome. J Cardiovasc Electrophysiol. 2006 Nov. 17(11):1161-8. [Medline].
Czosek RJ, Kaltman JR, Cassedy AE, et al. Quality of life of pediatric patients with long QT syndrome. Am J Cardiol. 2016 Feb 15. 117 (4):605-10. [Medline].
Albertella L, Crawford J, Skinner JR. Presentation and outcome of water-related events in children with long QT syndrome. Arch Dis Child. 2011 Aug. 96(8):704-7. [Medline].
Hintsa T, Keltikangas-Jarvinen L, Puttonen S, et al. Depressive symptoms in the congenital long QT syndrome. Ann Med. 2009 Jun 23. 1-6. [Medline].
Vyas H, Ackerman MJ. Epinephrine QT stress testing in congenital long QT syndrome. J Electrocardiol. 2006 Oct. 39(4 Suppl):S107-13. [Medline].
Monnig G, Eckardt L, Wedekind H, et al. Electrocardiographic risk stratification in families with congenital long QT syndrome. Eur Heart J. 2006 Sep. 27(17):2074-80. [Medline].
Cuneo BF, Strasburger JF, Yu S, Horigome H, Hosono T, Kandori A. In utero diagnosis of long QT syndrome by magnetocardiography. Circulation. 2013 Nov 12. 128(20):2183-91. [Medline].
Mitchell JL, Cuneo BF, Etheridge SP, Horigome H, Weng HY, Benson DW. Fetal heart rate predictors of long QT syndrome. Circulation. 2012 Dec 4. 126(23):2688-95. [Medline].
Moss AJ, Shimizu W, Wilde AA, et al. Clinical aspects of type-1 long-QT syndrome by location, coding type, and biophysical function of mutations involving the KCNQ1 gene. Circulation. 2007 May 15. 115(19):2481-9. [Medline].
Arnestad M, Crotti L, Rognum TO, et al. Prevalence of long-QT syndrome gene variants in sudden infant death syndrome. Circulation. 2007 Jan 23. 115(3):361-7. [Medline].
Tester DJ, Ackerman MJ. Postmortem long QT syndrome genetic testing for sudden unexplained death in the young. J Am Coll Cardiol. 2007 Jan 16. 49(2):240-6. [Medline].
[Guideline] Priori SG, Blomström-Lundqvist C, Mazzanti A, Blom N, Borggrefe M, Camm J, et al. 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 Nov 1. 36 (41):2793-867. [Medline]. [Full Text].
Bar-Cohen Y, Silka MJ. Congenital Long QT Syndrome: Diagnosis and Management in Pediatric Patients. Curr Treat Options Cardiovasc Med. 2006 Sep. 8(5):387-395. [Medline].
Vohra J. The Long QT Syndrome. Heart Lung Circ. 2007. 16 Suppl 3:S5-12. [Medline].
Hamang A, Solberg B, Bjorvatn C, Greve G, Oyen N. [Genetic counseling in congenital long QT syndrome]. Tidsskr Nor Laegeforen. 2009 Jun 11. 129(12):1226-9. [Medline].
Johnson JN, Ackerman MJ. Return to play? Athletes with congenital long QT syndrome. Br J Sports Med. 2013 Jan. 47(1):28-33. [Medline].
[Guideline] Priori SG, Wilde AA, Horie M, et al. HRS/EHRA/APHRS expert consensus statement on the diagnosis and management of patients with inherited primary arrhythmia syndromes: document endorsed by HRS, EHRA, and APHRS in May 2013 and by ACCF, AHA, PACES, and AEPC in June 2013. Heart Rhythm. 2013 Dec. 10 (12):1932-63. [Medline]. [Full Text].
[Guideline] Ackerman MJ, Priori SG, Willems S, et al. HRS/EHRA expert consensus statement on the state of genetic testing for the channelopathies and cardiomyopathies: this document was developed as a partnership between the Heart Rhythm Society (HRS) and the European Heart Rhythm Association (EHRA). Europace. 2011 Aug. 13 (8):1077-109. [Medline]. [Full Text].
[Guideline] Ackerman MJ, Zipes DP, Kovacs RJ, et al. Eligibility and disqualification recommendations for competitive athletes with cardiovascular abnormalities: Task Force 10: The cardiac channelopathies: a scientific statement From the American Heart Association and American College of Cardiology. Circulation. 2015 Dec 1. 132 (22):e326-9. [Medline]. [Full Text].
Chockalingam P, Crotti L, Girardengo G, Johnson JN, Harris KM, van der Heijden JF. Not all beta-blockers are equal in the management of long QT syndrome types 1 and 2: higher recurrence of events under metoprolol. J Am Coll Cardiol. 2012 Nov 13. 60(20):2092-9. [Medline].
Seth R, Moss AJ, McNitt S, et al. Long QT syndrome and pregnancy. J Am Coll Cardiol. 2007 Mar 13. 49(10):1092-8. [Medline]. [Full Text].
Barsheshet A, Moss AJ, McNitt S, Polonsky S, Lopes CM, Zareba W. Risk of syncope in family members who are genotype-negative for a family-associated long-QT syndrome mutation. Circ Cardiovasc Genet. 2011 Oct. 4(5):491-9. [Medline].
Hofman N, Wilde AA, Tan HL. Diagnostic criteria for congenital long QT syndrome in the era of molecular genetics: do we need a scoring system?. Eur Heart J. 2007 Jun. 28(11):1399. [Medline].
Page A, Aktas MK, Soyata T, Zareba W, Couderc JP. "QT clock" to improve detection of QT prolongation in long QT syndrome patients. Heart Rhythm. 2016 Jan. 13 (1):190-8. [Medline]. [Full Text].

Media Gallery

Pediatric Long QT Syndrome. Marked prolongation of QT interval in a 15-year-old male with long QT syndrome. Abnormal morphology of repolarization can be observed in almost every lead (ie, peaked T waves, bowing ST segment). Bradycardia is a common feature in patients with long QT syndrome. R-R = 1 s; QT interval = 0.56 s; QT interval corrected for heart rate (QTc) = 0.56 s.
Pediatric Long QT Syndrome. Genetically confirmed long QT syndrome with borderline values of QT corrected for heart rate (QTc) duration in a 12-year-old girl. Note the abnormal morphology of the T wave (notches) in leads V2-V4. R-R = 0.68 s; QT interval = 0.36 s; QTc = 0.44 s.
Pediatric Long QT Syndrome. Electrocardiogram from a 13-year-old female who had a syncopal event while running to a school bus. She awoke after a few seconds, and her subsequent clinical course was uneventful.

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Table 1. Genetic Basis of Long QT Syndrome, Including Jervell and Lang-Nielsen (JLN) Syndrome

Type of Long QT Syndrome	Chromosomal Locus	Mutated Gene	Ion Current Affected
LQT1	11p15.5	KVLQT1or KCNQ1 (heterozygotes)	Potassium (I_Ks)
LQT2	7q35-36	HERG, KCNH2	Potassium (I_Kr)
LQT3	3p21-24	SCN5A	Sodium (I_Na)
LQT4	4q25-27	ANK2, ANKB	Sodium, potassium and calcium
LQT5	21q22.1-22.2	KCNE1 (heterozygotes)	Potassium (I_Ks)
LQT6	21q22.1-22.2	MiRP1, KNCE2	Potassium (I_Kr)
LQT7 (Andersen syndrome)	17q23	KCNJ2	Potassium (I_K1)
LQT8 (Timothy syndrome)	12q13.3	CACNA1C	Calcium (I_Ca-Lalpha)
JLN1	11p15.5	KVLQT1or KCNQ1 (homozygotes)	Potassium (I_Ks)
JLN2	21q22.1-22.2	KCNE1 (homozygotes)	Potassium (I_Ks)

Table 2. Genetic Basis of Long QT Syndrome

Group	Prolonged QTc (s)	Borderline QTc (s)	Reference Range (s)
Children and adolescents (< 15 y)	>0.46	0.44-0.46	< 0.44
Men	>0.45	0.43-0.45	< 0.43
Women	>0.46	0.45-0.46	< 0.45

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