Torsades de pointes
| Torsades de pointes | |
|---|---|
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| 12-lead ECG of Torsades de Pointes (TdP) in a 56-year-old white female with low blood potassium (2.4 mmol/L) and low blood magnesium (1.6 mg/dL.) | |
| Classification and external resources | |
| Specialty | Cardiology |
| DiseasesDB | 29252 |
| eMedicine | med/2286 emerg/596 |
| Patient UK | Torsades de pointes |
| MeSH | D016171 |
Torsades de pointes or torsade de pointes (TdP or simply torsade(s)) (French: [tɔʁsad də pwɛ̃t], translated as "twisting of the points"), is a specific type of abnormal heart rhythm that can lead to sudden cardiac death. It is a polymorphic ventricular tachycardia that exhibits distinct characteristics on the electrocardiogram (ECG). It was described by Dessertenne in 1966. Prolongation of the QT interval can increase a person's risk of developing this abnormal heart rhythm.
Action potential of cardiac muscles can be broken down into five phases:
Repolarization of the cardiomyoctes occurs in phases 1-3, and is caused predominantly by the outward movement of potassium ions. In Torsades de pointes, however, the repolarization is prolonged; this can be due to electrolyte disturbances (hypokalemia, hypomagnesemia, hypocalcemia), bradycardia, certain drugs (Disopyramide, Sotalol, Amidarone, Amitryptine, Chlorpromazine, Erythromycins) and/or congenital syndromes (LQT1-LQT4 gene defect).
The prolongation of repolarisation may result in subsequent activation of an inward depolarisation current, known as an early after-depolarisation, which may promote triggered activity. Re-entry, due to a dispersion of refractory periods, is also possible; this is because M Cells (found in the mid myocardial layer) show a more prolonged repolarization phase in response to potassium blockage than other cells. In turn, this produces a zone of functional refractoriness (inability to depolarize) in the mid myocardial layer. When new action potential is generated, the mid myocardial layer will remain in a refractory period, but the surrounding tissue will depolarize. As soon as the mid myocardial layer is no longer in a refractory period, excitation from nearby tissue will cause a retrograde current and a reentry circuit that will result in a positive chronotropic cycle, leading to tachycardia.
Most episodes will revert spontaneously to a normal sinus rhythm. If this does not occur, however, possible adverse outcomes include palpitations, dizziness, lightheadedness (during shorter episodes), fainting (during longer episodes), and sudden cardiac death.
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