EDITORIAL

More light on QT interval measurement

L Toivonen

Correspondence to:
Correspondence to:
Lauri Toivonen, MD, Division of Cardiology, Helsinki University Central Hospital, Haartmaninkatu 4, PO Box 340, FI-00029 HUS, Helsinki, Finland;
lauri.toivonen@hus.fi

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The electrocardiographic QT interval can contain information on the risk of dying suddenly.

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Keywords: QT interval; long QT interval

A prolonged QT interval signifies a delay in the ventricular repolarisation phase, which renders the heart vulnerable to malignant arrhythmias such as torsade de pointes ventricular tachycardia. This sign of disease is sometimes subtle and may avoid recognition unless meticulously sought. In this issue of Heart, Malik and colleagues¹ draw attention to methodological difficulties in the measurement of the QT interval.

The action potential duration of the myocardium, reflected as the QT interval on the surface ECG, depends on heart rate which hampers estimation of the intrinsic myocardial repolarisation time. The relation of the QT interval and heart rate, or cardiac cycle length, is modified by a number of physiologic processes. The mechanism causing the change in heart rate may variably influence ventricular repolarisation. For example, an equal increase in heart rate shortens the QT interval less during sympathetic stimulation by cold pressor test² and during cardiac pacing³ compared . . . [Full text of this article]

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