History

The clinical diagnosis of long QT syndrome is prompted by a high degree of clinical suspicion, which arises from the presenting complaints.^[6]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)^[6]
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^[7]

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].
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].
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].
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] Epstein AE, DiMarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices) developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons. J Am Coll Cardiol. 2008 May 27. 51(21):e1-62. [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].
Maron BJ, Chaitman BR, Ackerman MJ, et al. Recommendations for physical activity and recreational sports participation for young patients with genetic cardiovascular diseases. Circulation. 2004 Jun 8. 109(22):2807-16. [Medline].
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].

Media Gallery

Marked prolongation of QT interval in a 15-year-old male adolescent 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.
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.
ECG of 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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