Long QT Syndrome Priori SG, Schwartz PJ, Napolitano C, et al.: Risk stratification in the long-QT syndrome. N Engl J Med 2003;348(19):1866-74.
Vincent GM: The long-QT syndrome-bedside to bench to bedside. N Engl J Med 2003;348(19):1837-38.
Moss AJ: Long QT syndrome. JAMA 2003;289(16):2041-44.
Al-Khatib SM, LaPointe NM, Kramer JM, et al.: What clinicians should know about the QT interval. JAMA 2003;289(16):2120-27.
Mutations in six genes can produce abnormal cardiac sodium or potassium channels and result in QT interval prolongation. These changes increase the risk of fatal ventricular arrhythmia. However, sudden death only occurs in about 4% of affected persons; 50% of carriers never have symptoms. The QTc (QT interval, adjusted for heart rate) is considered prolonged when it is more than 0.45 seconds in men and more than 0.46 seconds in women and children (top 1% of normal distribution).
Al-Khatib and coauthors reviewed registries and case series, focusing on outcomes associated with prolonged QT intervals and medication errors that may have predisposed for prolonged QT interval. Patients at risk or taking other QT prolonging drugs should avoid quinolone antibiotics.
Priori and coauthors studied 647 at-risk patients and reported that sex, genotype, and QTc duration independently predict risk. For certain genotypes, strenuous exercise can trigger symptoms; for others, emotions or loud noises are more likely triggers. Although beta-blocking drugs have little effect on QT duration, they are the treatment of choice for asymptomatic and symptomatic patients with long QT syndrome. Complete compliance is essential when on a beta-blocker regimen. Life-threatening arrhythmias can occur when these medicines are stopped due to rebound receptor catecholamine hypersensitivity.
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