Long QT: The art of measurement

Abstract

The QT interval represents the time it takes for the ventricles to depolarize and repolarize. Accurate measurement is essential for many clinical decision-making situations, which can significantly affect patient outcomes. Prolonged QRS duration in cases such as paced rhythm, LVH and conduction abnormalities pose significant challenges in accurately measuring the QT interval. This review will focus on how to accurately measure the QT interval and how to avoid common pitfalls. *Correspondence to: Ali Naderi, Department of Cardiology, Case Western Reserve, MetroHealth Medical Center in Cleveland, Ohio, USA, E-mail: naderi.m@gmail.com Received: June 08, 2019; Accepted: June 19, 2019; Published: June 24, 2019 Introduction and background QT interval measurement is one of the most important aspects of any electrocardiogram (ECG) evaluation. It has significant clinical importance, as there is a correlation between the QT interval length and the risk of developing ventricular tachyarrhythmias. The importance of the QT interval did not come to light for several decades after the invention of the ECG by Willem Einthoven in the early 20th century. Louise Wolff, an American cardiologist who described the WPW syndrome with Parkinson and White, was probably the first person to measure the QT interval [1]. However, the clinical importance of the QT interval was not fully understood until further work by Jervell and Lange-Nielsen in the late 1950s, and Romano, Gemme, Pongiglione, and Ward in the 1960s [2,3]. Several types of long QT syndrome have since been described, and the awareness and knowledge of the relationship between QT prolongation and torsades de pointes has since grown. In 2007, the FDA formed an Internal Review Team (IRT) with the responsibility to oversee the clinical assessment of QT prolongation for all drugs that the agency reviewed. Assessment of QT prolongation has rapidly become an essential part of the development of new drugs [4]. It is now common practice to measure and monitor the QT interval with the use of many drugs, especially the antiarrhythmic agents. Despite the advent of many computer-assisted algorithms and software programs, the accurate measurement of QT interval remains a challenge for many clinicians. A survey of 334 practitioners, the majority of whom specialize in cardiology (81%), showed that 61% were able to identify what represented the QT interval on an ECG and only 36% were able to measure the QT interval [5].