Long QT Syndrome
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Long QT syndrome (LQTS) is characterized by prolongation of the QT interval on the surface electrocardiogram (ECG), syncope, and sudden death as a result of malignant ventricular arrhythmias. The electrical instability is due to an abnormality of ventricular repolarization associated with a cardiac ion channelopathy.
Prevalence of LQTS is estimated to be approximately 1 in 2,500.
- Autosomal dominant (Romano-Ward syndrome)
- Autosomal recessive, sometimes associated with congenital nerve deafness (Jervell and Lange-Nielsen syndrome)
- Genetic linkage analysis studies have demonstrated that >400 genetic mutations among 13 cardiac ion channel genes account for nearly 3/4 of LQTS.
- Genotype-phenotype–based research studies have identified gene-specific electrocardiographic profiles, gene-specific arrhythmia triggers, gene-directed treatment strategies, and gene-specific risk stratification.
- Preventive measures focus on screening for the electrocardiographic abnormality, especially in individuals who appear to be at risk of having the diagnosis.
- Patients who have been diagnosed are advised to avoid exposure to stimulants, medications that are known to prolong the QT interval or provoke ventricular arrhythmias, and situations that may aggravate the cardiac rhythm or induce torsades de pointes.
Two hypotheses have been proposed to explain the pathogenesis of congenital LQTS syndrome:
- An abnormality or imbalance in sympathetic innervation to the heart, which helps explain the findings of sinus bradycardia, abnormal repolarization, adrenergic dependence of arrhythmias, and response to adrenergic antagonist medications associated with the syndrome
- Intrinsic cardiac ion (potassium and sodium) channel defects appear to be the mechanism responsible for cardiac repolarization abnormalities. Because some identified gene mutations that result in congenital LQTS occur at loci that also encode a cardiac ion channel protein, ion channel dysfunction has been proposed as the intrinsic abnormality that is responsible for abnormal repolarization.