The dependence on heart rate of the QT interval has been investigated for many years and several mathematical formulae have been proposed to describe the QT interval/heart rate (or QT interval/RR interval) relationship. While the most popular is Bazett's formula, it overcorrects the QT interval at high heart rates and under-corrects it at slow heart rates. This formulae and many others similar ...

To assess the influence of diurnal changes in the autonomic nervous system on the QT interval, 24 hour dynamic electrocardiographic monitoring was performed in six pacemaker dependent patients with normally innervated hearts, in six cardiac transplant patients with anatomically denervated hearts (but which respond to circulating catecholamines), and in nine diabetic patients with confirmed auto...

“Not to correct QT, but how to, that is the question”. The QT interval is a reflection of the action potential in the cardiac cells. Homogenous or heterogenous changes in the action potential duration lead to alteration of QT interval (in addition to morphological changes of T & U waves) 1. Such changes can be due to change in heart rate & autonomic tone. They can also be markers of abnormal re...

Human heart electrophysiology is complex biological phenomenon, which is indirectly assessed by the measured ECG signal. ECG trace is further analyzed to derive interpretable surrogates including QT interval, QRS complex, PR interval, and T wave morphology. QT interval and its modification are the most commonly used surrogates of the drug triggered arrhythmia, but it is known that the QT interv...

We examined the relationship between changes in heart rate and the measured QT interval of the electrocardiogram in healthy subjects after exercise and during breath holding, hyperventilation, the dive reflex, the Valsalva maneuver, and the cold-pressor test. The tachycardia of exercise was accompanied by the familiar shortening of the QT interval, but substantial heart rate changes encountered...

BACKGROUND/AIMS QT dispersion is a sign of heterogeneity of ventricular myocardial wall and is associated with cardiac mortality and morbidity. Data regarding with the persistence of QT interval changes in cases with acute pancreatitis (AP) that required clinical follow-up, are insufficient. Therefore, in this study, we aimed to evaluate the QT interval changes during attack and after remission...

BACKGROUND Following an abrupt change in heart rate (HR), QT adaptation is achieved within a delayed time frame. HYPOTHESIS The exclusion of electrocardiograms (ECGs) showing rapid HR changes influences the level of a drug-induced QT prolongation. METHODS Continuous 12-lead ECG-Holter monitoring was performed in 31 healthy subjects. Using the "bin" method, we evaluated moxifloxacin effects ...

Methods to correct the QT interval for heart rate are often in disagreement and may be further confounded by changes in autonomic state. This can be problematic when trying to distinguish the changes in QT interval by either drug-induced delayed repolarization or from autonomic-mediated physiological responses. Assessment of the canine dynamic QT-RR interval relationship was visualized by novel...

BACKGROUND The magnitude of QT prolongation in response to bradycardia, rather than the bradycardia per se, determines the risk for torsade de pointes during atrioventricular block (AVB). However, we do not know why some patients develop more QT prolongation than others, despite similar bradycardia. We hypothesized that in patients who develop significant QRS vector changes during AVB, the effe...