Long QT interval in resting electrocardiogram – and what next? Sports cardiologist’s point of view. Part 1. From electrophysiology to diagnostics

1 Laboratory of Sports Cardiology at the Department of Paediatrics, Preventive Cardiology and Immunology of Developmental Age, Medical University of Łódź, Poland.
Head of the Laboratory: Zbigniew Krenc MD, PhD, Head of the Department: Professor Krzysztof Zeman, MD, PhD
2 Department of Paediatrics and Immunology with Nephrology Division, Institute of the Polish Mother’s Health Centre in Łódź. Head of the Department: Professor Krzysztof Zeman, MD, PhD
Correspondence: Zbigniew Krenc MD, PhD, Department of Paediatrics, Preventive Cardiology and Immunology of Developmental Age, Medical University, Institute of the Polish Mother’s Health Centre,
Rzgowska 281/289, 93-338 Łódź, e-mail: zbigniew.krenc@umed.lodz.pl

Pediatr Med Rodz Vol 10 Numer 3, p. 244–252
DOI: 10.15557/PiMR.2014.0027

Electrocardiography is the most common and available cardiovascular diagnostic procedure and an important tool in everyday clinical practice of a family physician. Electrocardiogram interpretation is therefore an invaluable clinical skill. Resting 12-lead electrocardiogram allows to detect asymptomatic patients, especially athletes, with life-threatening heart diseases in order to protect them from sudden cardiac death. The vast majority of sudden cardiac deaths in young athletes (under 35 years of age) are due to hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy. Three to four per cent of young athletes who die suddenly have no evidence of structural heart disease and the cause of their cardiac arrest is a primary electrical heart disease such as inherited cardiac ion channel defects (channelopathies), including long QT syndrome. Long QT syndrome is a leading cause of sudden death in the young. It is characterised by prolongation of the QT interval and by the occurrence of syncope, due to torsade de pointes ventricular tachycardia, cardiac arrest and sudden death. Although these life-threatening cardiac events are usually associated with physical effort or emotional stress, they may also occur during rest or sleep. The diagnosis of long QT syndrome is mainly based on the QTc measurement. When using a  prolonged QTc to diagnose long QT syndrome, it is necessary to exclude secondary causes of QTc prolongation that can occur with drugs, acquired cardiac conditions or electrolyte imbalance. Preventive measures for cardiac events include, i.a., pharmacotherapy (β-blockers) and electrotherapy (implantation of implantable cardioverter-defibrillator). The aim of this paper is to provide family doctors with some practical guidance useful in the interpretation of a resting electrocardiogram with prolonged QT interval. Genetic and acquired causes of prolonged QT interval, diagnostic criteria for congenital long QT syndrome are discussed as well.

Keywords: prolonged QT interval, resting electrocardiogram, congenital and acquired causes, diagnostics