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The QTc interval is longer in females, as well as having a stronger response to IKr-blocking agents. In males, the presence of testosterone upregulates IKr channels and therefore decreases QT interval. [2] Stated otherwise, estrogens prolong the QT interval, while androgens shorten it and decrease the response to IKr-blocking agents. [citation ...
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] However, treatment with beta blockers markedly reduces the risk of death, as does, in selected cases, implantation of a defibrillator. [11]
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]
Class II agents are conventional beta blockers. They act by blocking the effects of catecholamines at the β 1-adrenergic receptors, thereby decreasing sympathetic activity on the heart, which reduces intracellular cAMP levels and hence reduces Ca 2+ influx. These agents are particularly useful in the treatment of supraventricular tachycardias.
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 ...
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.
Medications that further prolong the QT interval such as sotalol should be avoided, lists of which can be found in publicly accessible online databases. [8] Beta blockers such as propranolol or nadolol blunt the effects of adrenaline on the heart and thereby reduce the risk of arrhythmias. [8]
Quinidine is an inhibitor of the cytochrome P450 enzyme 2D6, and can lead to increased blood levels of lidocaine, beta blockers, opioids, and some antidepressants. Quinidine also inhibits the transport protein P-glycoprotein and so can cause some peripherally acting drugs such as loperamide to have central nervous system side effects, such as ...