The patient's ECG showed a prolonged QT interval (Figure 1). The corrected QT (QTc) was 0.56 second. In addition, a biphasic T wave was seen in the precordial leads. His father's ECG (Figure 2) also showed a prolonged QT interval (QTc, 0.55 second) and a high-amplitude, rounded T wave in leads V2 and V3. On the ECG of the patient's 8-year-old brother (Figure 3), the QTc was 0.52 second, and T/U wave abnormalities in leads V2 and V3 were also detected.
In the context of the patient's history of recurrent fainting and the family history of "seizures" and sudden death, the prolonged QT intervals noted were very suggestive of intermittent ventricular arrhythmias caused by congenital long QT syndrome (LQTS).
LQTS is an electrical disease of the ventricular myocardium that is characterized by prolonged ventricular repolarization, which results in prolongation of the QT interval on the surface ECG and an increased risk for sudden death. It is characteristically associated with the potentially life-threatening cardiac arrhythmia known as torsade de pointes, which is a form of polymorphic ventricular tachycardia.
A prolonged QT interval may be acquired (usually resulting from drugs or electrolyte disturbances) or congenital. The congenital form is caused by mutations in the gene coding for the cardiac potassium, sodium, or calcium ion channels; about 400 mutations in 10 gene loci have been identified. The distinct genetic types are designated LQT1-LQT10. LQT1, LQT2, and LQT3 account for over 90% of cases of LQTS, with some estimated prevalences of 45%, 45%, and 7%, respectively. The specific genotype influences the clinical course, the kinds of triggering events that may initiate arrhythmias, the prognosis, and the recommended form of treatment. An underlying genetic predisposition has been identified in some patients with the acquired form of LQTS.
Traditionally, congenital LQTS has been characterized as two clinical entities:
Romano-Ward syndrome, which is inherited in an autosomal dominant fashion and only has cardiac manifestations.
Jervell and Lange-Nielsen syndrome, which is inherited in an autosomal recessive fashion and is associated with sensorineural deafness.
Most of the epidemiologic and clinical data on congenital LQTS come from reports from the International LQTS Registry. The registry, which began in 1979 and is still ongoing, is a major source of data on the incidence, natural history, and prognosis of patients with congenital LQTS.
The incidence of congenital LQTS is difficult to determine, but it is estimated to be 1 case per 2500-10,000 population, with most estimates around 1 case per 5000 population. The range is broad because a large number of cases go undiagnosed; about 20%-50% of affected patients may not demonstrate QT prolongation on resting ECG. Technical difficulties and methodological controversies in accurately measuring the QT interval are in part to blame. It is nonetheless one of the most common causes of autopsy-negative, unexplained sudden death.
Women are more commonly affected than men. Patients with congenital LQTS usually present in childhood, adolescence, or early adulthood, and they usually present with palpitations, syncope or near syncope, seizures, or cardiac arrest. Syncopal episodes associated with secondary seizures may be misdiagnosed as primary seizure disorders. The seizures are probably secondary to hypoperfusion of the brain during arrhythmic events.
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Cite this: Shatha M. Khatib. A 10-Year-Old Boy With Fainting Spells and Seizure Activity - Medscape - Sep 25, 2019.