Copyright 1999 American Medical Association. All Rights Reserved. Applicable FARS/DFARS Restrictions Apply to Government Use.1999
Figure 1. An electrocardiogram shows a heart rate of 53 beats/min, with a QT interval of 0.6 seconds and a corrected QT interval of 0.52 seconds.
The association of a long QT interval and congenital sensorineural deafness was described by Jervell and Lange-Nielsen1 in 1957. The estimated incidence of this rare syndrome, with an autosomal recessive mode of inheritance, is 1.6 to 6 cases per million.2 A more common form of long QT syndrome (LQTS) without congenital deafness, known as the Romano-Ward syndrome, is inherited through an autosomal dominant mode and has an estimated incidence of 1 case per 10,000 persons.3
The QT interval is prolonged in both inherited conditions, but it may be normal at rest, and variability in the interval may be found in the same individual at different times of measurement. In this disorder, the QT interval usually does not shorten appropriately with exercise. The corrected QT interval has been used to correct for heart rate (corrected QT = QT/√RR). A value greater than 0.44 seconds is considered prolonged.
Congenital prolongation of the QT interval must be differentiated from secondary forms that may occur with hypocalcemia, hypomagnesemia, hypokalemia, liquid protein fast diet, acute myocarditis, inflammation of the epicardial ganglia, and drug toxicity (tricyclic antidepressants, phenothiazines, quinidine sulfate, disopyramide phosphate, or procainamide hydrochloride).4
Most patients with LQTS are unaware of having the abnormality. The disorder is usually discovered by a routine electrocardiographic tracing following an evaluation for a syncopal episode, or in the evaluation of family members of individuals who have been found to have LQTS. Syncope associated with LQTS is almost always the result of a transient malignant arrhythmia, and sudden death is a frequent presentation of this disorder, usually the result of a torsade de pointes type of ventricular tachycardia. The arrhythmia may be precipitated by exercise, sudden loud noise or fright, and during anesthesia.5 Compelling evidence for prolonged QT interval playing a role in the sudden infant death syndrome has recently been presented.6
The LQTS should be considered a possibility in children with unexplained syncope, ventricular arrhythmias, sudden life-altering events, and, perhaps, nonfebrile seizures. In a prospective study of 350 congenitally deaf children, 2 (0.6%) were found to have significant prolongation of the QT interval.7
At least 5 genes have been shown to be involved in the pathogenesis of inherited LQTS. The genes involve chromosomes 11p15.5, 7q35-6, 3p21-24, 4q25-27, and 21.7 Four of these genes have been found to encode ion channel proteins, 3 involving potassium and 1 involving sodium. The cardiac ion channels play a key role in myocellular repolarization. The Romano-Ward syndrome occurs as a result of heterozygous mutations in these genes, while the Jervell and Lange-Nielsen syndrome is thought to result from a homozygous mutation of one of the genes encoding a cardiac potassium channel.3,4
Once an individual is determined to have primary LQTS, a decision must be made as to possible treatment because of the risk of sudden death. Medical treatment is indicated in any patients with prolonged QT syndrome who develop syncope or have an aborted cardiac arrest, those with congenital deafness, or those who have a family history of sudden death at a young age.8 Three possible therapeutic options are available to prevent life-threatening arrhythmias: β-blocking agents, pacemakers, and left cervicothoracic sympathetic ganglionectomy.8 Propranolol hydrochloride is the first line of therapy.
Parents and children should receive instruction regarding triggering factors of arrhythmias and should also be taught basic cardiopulmonary resuscitation. Genetic counseling should be offered to all family members, even if they are asymptomatic. Screening electrocardiograms and hearing tests should be considered.
Accepted for publication September 18, 1998.
Reprints: Hassib Narchi, MD, Al-Hasa Specialty Services Division, Saudi Aramco-Al-Hasa Health Center, Saudi Aramco Medical Services Organization, Box 6030, Mubarraz 31311, Saudi Arabia.
Picture of the Month. Arch Pediatr Adolesc Med. 1999;153(4):425-426. doi: