<unk>  occurs as both an inherited (linked to at least 17 genes) and as an acquired form caused most often by drugs and/or electrolyte disorders that cause excessive lengthening of the QT interval. Common causes for<unk>  include drug-induced QT prolongation and less often diarrhea, low serum magnesium, and low serum potassium or congenital long QT syndrome. It can be seen in malnourished individuals and chronic alcoholics, due to a deficiency in potassium and/or magnesium. Certain drugs and combinations of drugs resulting in drug interactions are common contributors to<unk>  risk. QT-prolonging medications such as clarithromycin, levofloxacin, or haloperidol, when taken concurrently with cytochrome P450 inhibitors, such as fluoxetine, cimetidine, or particular foods including grapefruit, can result in higher-than-normal levels of medications that prolong the QT interval in the bloodstream and therefore increase a person's risk of developing<unk> . At least one mention of the common over-the-counter medication loperamide causing<unk>  has been made in the literature, although the dose preceding this particular cardiac event was well beyond the therapeutic range of the medication. In addition, patients with inherited long QT syndrome have a very high risk of episodes of<unk>  and that risk can be further increased by drugs and electrolyte disorders that further prolong QT. Medications as causes Knowledge that<unk>  may occur in patients taking certain prescription drugs has been both a major liability and reason for removal of 14 medications from the marketplace. Forty-nine drugs known to cause<unk>  and another 170 that are known to prolong QT remain on the market because the drugs provide medical benefit and the risk of<unk>  can be managed and mitigated by instructions in the drug label. Examples of compounds linked to clinical observations of<unk>  include amiodarone, most fluoroquinolones, methadone, lithium, chloroquine, erythromycin, azithromycin, pimozide, and phenothiazines. The anti-emetic agent ondansetron may also increase the risk of developing<unk> . It has also been shown as a side effect of certain anti-arrhythmic medications, such as sotalol, procainamide, quinidine, ibutilide, and dofetilide. In one example, the gastrokinetic drug cisapride (Propulsid) was withdrawn from the US market in 2000 after it was linked to deaths caused by long QT syndrome-induced<unk> . This effect can be directly linked to QT prolongation mediated predominantly by inhibition of the hERG channel and, in some cases, augmentation of the late sodium channel.
Torsades de pointes
Ventricular fibrillation
Pre-excitation syndrome
Brugada syndrome
Pacemaker syndrome
Takotsubo cardiomyopathy
Sudden arrhythmic death syndrome
Unstable angina