BIO 3344 Assignment Case Study Long QT Syndrome
BIO 3344 Assignment Case Study Long QT Syndrome
The congenital long QT syndrome (LQTS) is characterized by abnormally prolonged ventricular repolarization due to inherited defects in cardiac sodium and potassium channels, which predispose the patients to syncope, seizure like activity, ventricular arrhythmias, and sudden cardiac death. Early diagnosis and preventive treatment are instrumental in preventing sudden cardiac deaths in patients with the congenital LQTS. The diagnostic criteria for congenital LQTS are based on certain electrocardiographic findings, clinical findings and findings of epinephrine stress test. Recently genotype specific electrocardiographic pattern in the congenital LQTS has also been described. Recent studies suggest feasibility of genotype specific treatment of LQTS and, in near future, mutation specific treatment will probably become a novel approach to this potentially fatal syndrome. We describe one case that fulfilled the electrocardiographic, historical diagnostic criteria and epinephrine stress test suggestive of LQT syndrome.
Introduction
The Long QT is a rare congenital disorder characterized by QT-interval prolongation and repetitive episodes of syncope and cardiac arrest related to rapid, polymorphic ventricular tachycardia. Genetic linkage mapping defines six types of LQTS (LQT1-LQT6) out of which, LQT1-LQT3 have been well characterized in clinical studies (1). Diagnosis of LQTS is based on clinical and electrocardiographic
BIO 3344 Assignment Case Study Long QT Syndrome CRACKERS
features (2). These EKG characteristics are useful for selecting which gene to investigate first, while performing genetic analysis. The identification of genotype specific EKG pattern is gaining importance, for its potential use in the management of LQTS, with favorable outcomes (3). Further, epinephrine stress test is important in unrevealing the underlying congenital LQTS.
The QT interval is a surface marker of cardiac electrical activity, specifically cellular repolarization. It is generally accepted that the absolute QT interval provides a surface rendering of the underlying cellular action potential durations. Despite overlap of the resting QTc between healthy persons and patients with LQTS, the 12-lead EKG remains one of the principal tools in the LQTS evaluation, and the baseline QTc is still one of the most important diagnostic criteria.
The congenital LQTS is a potentially life threatening condition, caused by mutations in genes encoding cardiac ion channels which result in prolongation of ventricular action potential. Genetic screening of symptomatic patients or their asymptomatic family members may identify patients at risk for life threatening arrhythmias and the type of LQT as it has important implications in the management. Out of the several forms of congenital LQTS, three forms LQT1, LQT2, and LQT3 have been well characterized. These three forms have also been described on the basis of their specific EKG morphology. Recent investigations suggest that even in patients with acquired LQTS (e.g. resulting from intake of QT-prolonging medicines), there are clinically silent gene mutations that lead to overt QT prolongation only with exposure to QT-prolonging medications (4)–(6).This explains why some patients seem to be more prone than others to have QT prolongation at a given dose of QT-Prolonging drugs, even after adjustment for other factors that could prolong QT-interval.