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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 ...
In long QT syndrome it takes longer for this repolarisation to occur, shown in individual cells as a longer action potential while being marked on the surface ECG as a long QT interval. [11] The prolonged action potentials can lead to arrhythmias through several mechanisms. The arrhythmia characteristic of long QT syndrome, torsades de pointes ...
The effect of quinidine on the ion channels is to prolong the cardiac action potential, thereby prolonging the QT interval on the surface ECG. Other ECG effects include a wide notched P wave, wide QRS complex, depressed ST segment, and U waves. These are the results of both slowed depolarization and repolarization.
So we have a QT of 400 milliseconds divided by the square root of 0.66 seconds over 1 second, which is 400 milliseconds divided by 0.81, which is unitless, and we get a corrected QT interval of 493 milliseconds, which is greater than 440, so actually, a 400 milliseconds QT interval at 90 beats per minute is considered long.
According to the FDA, sotalol should not be used in people with a waking heart rate lower than 50 beats per minute. [8] It should not be used in people with sick sinus syndrome, long QT syndrome, cardiogenic shock, uncontrolled heart failure, asthma or a related bronchospastic condition, or people with serum potassium below 4 meq/L. [8] It should only be used in people with a second and third ...
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]
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]
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 ...