From the Guidelines
Torsades de Pointes (TdP) is primarily caused by prolongation of the QT interval on an electrocardiogram, and among the given options, hypokalemia, hypomagnesemia, and hypocalcemia are recognized causes of TdP. Common causes of TdP include certain medications such as antiarrhythmics (especially Class IA and III like quinidine, procainamide, amiodarone, and sotalol), some antibiotics (macrolides like erythromycin, fluoroquinolones like moxifloxacin), antipsychotics (haloperidol, thioridazine), and antidepressants (tricyclics, some SSRIs) 1. Other causes include electrolyte abnormalities (particularly hypokalemia, hypomagnesemia, and hypocalcemia), bradycardia, heart failure, congenital long QT syndrome, and structural heart disease. These factors affect cardiac repolarization by blocking potassium channels in heart cells, leading to prolonged action potentials and creating the substrate for early afterdepolarizations that can trigger TdP.
Key risk factors for drug-induced TdP include:
- Female gender
- Hypokalemia
- Bradycardia
- Recent conversion from atrial fibrillation
- Congestive heart failure
- Digitalis therapy
- High drug concentrations
- Rapid rate of intravenous drug administration
- Baseline QT prolongation
- Ventricular arrhythmia
- Left ventricular hypertrophy
- Congenital long QT syndrome
- Certain DNA polymorphisms
- Severe hypomagnesemia
- Concomitant use of 2 or more drugs that prolong the QT interval 1.
It's worth noting that drugs that shorten the QT interval are not typically associated with TdP, as the condition is primarily caused by QT interval prolongation. Similarly, hyperkalemia and hypermagnesemia are not typically associated with TdP, as the condition is more commonly associated with hypokalemia and hypomagnesemia. Marijuana use has not been established as a direct cause of TdP in the provided evidence.
In terms of management, withdrawal of any offending drugs and correction of electrolyte abnormalities are recommended in patients presenting with TdP 1. Additionally, acute and long-term pacing may be recommended for patients presenting with TdP due to heart block and symptomatic bradycardia 1.
From the Research
Causes of Torsades de Pointes
- Hypokalemia 2, 3, 4, 5
- Hypomagnesemia 2, 3, 5
- Hypocalcemia 3, 5
- Bradycardia 2, 3, 6
- QT prolonging drugs 2, 3, 4, 5, 6
Factors that do not cause Torsades de Pointes
- Drugs that shorten the QT interval 2 (these are actually used to treat Torsades de Pointes)
- Hyperkalemia (the opposite of hypokalemia, which is a known cause)
- Hypermagnesemia (the opposite of hypomagnesemia, which is a known cause)
- Marijuana use (there is no evidence in the provided studies to suggest that marijuana use is a cause of Torsades de Pointes)