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Excessive QT prolongation can trigger tachycardias such as torsades de pointes (TdP). QT prolongation is an established side effect of antiarrhythmics, but can also be caused by a wide range of non-cardiac medicines, including antibiotics, antidepressants, antihistamines, opioids, and complementary medicines.
Long QT syndrome (LQTS) is a condition affecting repolarization (relaxing) of the heart after a heartbeat, giving rise to an abnormally lengthy QT interval. [7] It results in an increased risk of an irregular heartbeat which can result in fainting, drowning, seizures, or sudden death. [1]
QT interval dispersion (QTd) is the maximum QT interval minus the minimum QT interval, and is linked with ventricular repolarization. [40] A QTd over 80 ms is considered abnormally prolonged. [ 41 ] Increased QTd is associated with mortality in type 2 diabetes. [ 41 ]
Long QT syndrome, or LQTS, is when somebody’s QT interval is longer than normal, which should typically be less than half of a cardiac cycle. In fact, for a heart rate of 60 beats per minute, the QT interval’s generally considered to be abnormally long when it’s greater than 440 milliseconds in males or 460 milliseconds in females.
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Romano–Ward syndrome is principally diagnosed by measuring the QT interval corrected for heart rate (QTc) on a 12-lead electrocardiogram (ECG). Romano–Ward syndrome is associated with a prolonged QTc, although in some genetically proven cases of Romano–Ward syndrome this prolongation can be hidden, known as concealed Long QT syndrome. [13]
The risk of arrhythmias is higher for those with Jervell and Lange-Nielsen syndrome than other forms of long QT syndrome. [10] Although this risk is dependent on the underlying genetic defect and degree of QT prolongation, without treatment more than 50% of those affected will die before the age of 15. [11]
Torsades de pointes is associated with long QT syndrome, a condition whereby prolonged QT intervals are visible on an ECG. Long QT intervals predispose the patient to an R-on-T phenomenon , wherein the R-wave, representing ventricular depolarization, occurs during the relative refractory period at the end of repolarization (represented by the ...