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Ventricular tachycardia is an abnormal condition in which the ventricles of the heart beat abnormally fast. This rapid eartbeat is stimulated by electrical signals that arise from within specialized cardiac cells within the ventricles themselves, or it may be caused by electrical signals that do not follow the normal conduction system and stimulate more than one contraction. These are called reentrant signals.
In a normal heart, electrical signals arise from a specialize d “natural pacemaker” in the upper right atrium called the sinoatrial node (SA node). These signals first spread through the atria, then into the ventricles. During ventricular tachycardia, however, additional signals arise from the ventricles themselves or are caused by a defect in the heart's conduction system.
Ventricular tachycardias are classified by their duration (e.g., sustained or nonsustained) and whether they occur without cause or because of an underlying condition, such as coronary artery disease. Short, unsustained episodes of ventricular tachycardia generally do not produce symptoms and do not require treatment. However, longer, sustained episodes of VT, in the presence of an underlying heart disease, may cause a medical emergency. Over time, VT can lead to heart failure or degenerate into ventricular fibrillation, which can result in cardiac arrest.
The specific types of VT include:
- Nonsustained ventricular tachycardia. An episode of VT that lasts for at least three beats but less than 30 seconds.
- Sustained ventricular tachycardia. An episode of VT that lasts longer than 30 seconds.
- Monomorphic ventricular tachycardia. Fast but regular rhythm.
- Polymorphic ventricular tachycardia. Fast, irregular rhythm.
- Stable ventricular tachycardia. The heart is still pumping enough oxygen-rich blood to meet the body’s needs.
- Unstable ventricular tachycardia. The patient is showing signs of a lack of oxygen-rich blood circulating through the body.
- Torsade de pointes. A particularly rapid, dangerous form of VT that often occurs as a result of certain medications or in patients with congenital long QT syndrome.
- Accelerated idioventricular rhythm (also known as slow ventricular tachycardia). A slower and less dangerous form of VT.
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