Acquired Long QT Syndrome and Electrophysiology of Torsade de Pointes

Abstract

Congenital long QT syndrome (LQTS) has been the most investigated cardiac ion channelopathy. Although congenital LQTS remains the domain of cardiologists, cardiac electrophysiologists and specialised centres, the much more frequently acquired LQTS is the domain of physicians and other members of healthcare teams required to make therapeutic decisions. This paper reviews the electrophysiological mechanisms of acquired LQTS, its ECG characteristics, clinical presentation, and management. The paper concludes with a comprehensive review of the electrophysiological mechanisms of torsade de pointes.

Prolonged QT Interval in a Patient With Coronavirus Disease-2019: Beyond Hydroxychloroquine and Azithromycin

“…4 Acquired LQTS is mostly secondary to adverse effects of medications and electrolyte abnormalities, such as hypokalemia, hypomagnesemia, and hypocalcemia. 4,5 Phase 3 of the ventricular myocyte action potential is characterized by efflux of potassium ions predominantly through 2 subtypes of delayed rectifier potassium current, IKr (rapid), and IKs (slow), leading to myocardial repolarization. 4,5 IKr current proteins are encoded by the human ether-a-go-go-related gene (hERG).…”

Late Sodium Current Inhibitors as Potential Antiarrhythmic Agents

“…Many inherited and acquired diseases can lead to a longer ventricular repolarization, presented as long QT (LQT) syndromes (El-Sherif et al, 2019;Locati et al, 2019). The inherited LQT3 syndrome is caused by an increased I Na,late because of a mutant, much slower inactivating Na v 1.5 channel.…”

“…Even in normal hearts, both APD and I Na,late is greater in Purkinje fibers and in "M" cells than in the rest of the myocardium contributing to the physiological heterogeneity of repolarization. LQT syndromes increase both the spatial heterogeneity of repolarization (Maltsev et al, 2007) and the temporal variability of repolarization (El-Sherif et al, 2019) and therefore can present an arrhythmogenic substrate. This can be further exaggerated by bradycardia, where the APs are already long, and having larger heterogeneity (Szentandrassy et al, 2015).…”

Calcium Handling Defects and Cardiac Arrhythmia Syndromes

“…In addition to the congenital form, LQTS can also be acquired. The prevalence of acquired LQTS is greater than that of congenital forms (El-Sherif et al, 2019). It is generally caused by adverse, unwanted drug effects and/or electrolyte abnormalities and may predispose to the prolongation of the APD/QT interval, increase in dispersion of refractoriness and to a higher risk for generating EADs, being the substrates for VTs, especially for torsade de pointes VT (El-Sherif and Turitto, 1999).…”