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Most patients with drug-induced QT prolongation are asymptomatic and are diagnosed solely by EKG in association with a history of using medications known to cause QT prolongation. [6] A minority of patients are symptomatic and typically present with one or more signs of arrhythmia, such as lightheadedness, syncope, or palpitations. [6]
Torsades occurs as both an inherited (linked to at least 17 genes) [6] and as an acquired form caused most often by drugs and/or electrolyte disorders that cause excessive lengthening of the QT interval. [7] Common causes for torsades de pointes include drug-induced QT prolongation and less often diarrhea, low serum magnesium, and low serum ...
EADs can be triggered by hypokalemia and drugs that prolong the QT interval, including class Ia and III antiarrhythmic agents, as well as catecholamines. [1] Afterhyperpolarizations can also occur in cortical pyramidal neurons. There, they typically follow an action potential and are mediated by voltage gated sodium or chloride channels.
A more common cause is excessive loss of potassium, often associated with heavy fluid losses that flush potassium out of the body. Typically, this is a consequence of diarrhea, excessive perspiration, losses associated with crush injury, or surgical procedures. Vomiting can also cause hypokalemia, although not much potassium is lost from the ...
The diagnosis of hypokalemia (not enough potassium) can be suspected when there is a history of diarrhoea or malnutrition. Loop diuretics may also contribute. The electrocardiogram may show flattening of T waves and prominent U waves. Hypokalemia is an important cause of acquired long QT syndrome, and may predispose the patient to torsades de ...
As hypokalemia progressively worsens, the T wave becomes more flattened while the U wave becomes more prominent, with progressively deeper ST segment depression. For digitalis toxicity, there will be a sagging QT interval, flattened T wave, and prominent U wave with a shortened QT interval.
[1] [2] Electrocardiography (ECG/EKG) may show tachycardia (a fast heart rate) due to the thyroid disease, abnormalities due to cardiac arrhythmia (atrial fibrillation, ventricular tachycardia), and conduction changes associated with hypokalemia (U waves, QRS widening, QT prolongation, and T wave flattening). [2]
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]