The heart is a muscle that contracts in rhythmic sequence for the duration of our lifetime. Each beat is stimulated by an electrical signal that is generated by the heart's conduction system. A normal heart beats 60 to 100 times per minute. Sometimes, a problem with the conduction system causes the heart to beat too fast, too slow, or to have an erratic or irregular beat. A test, called an electrocardiogram, or EKG, can measure and record the heart's electrical activity. In a normal heartbeat, the heart's signal follows a specific pathway through the heart. The signal begins in the sino-atrial node, or SA node, located in the right atrium. The SA node triggers the atria to contract, pushing blood into the ventricles. The electrical signal then travels through the atrio-ventricular node, or AV node, and into the ventricles. This signal now causes the ventricles to contract, pumping blood to the lungs and body. Tachycardia is a type of arrhythmia, or irregular heart rate, in which the heart beats in excess of 100 beats per minute. There are many types of tachycardia, but the most common and most severe form of tachycardia is ventricular tachycardia. Ventricular tachycardia occurs when the heart's electrical activity begins in the ventricles rather than in the SA node. When this happens, the ventricles beat faster than the atria. The normal, precise, rhythmic contractions between the atria and ventricles become interrupted, causing blood flow to the heart and body to be disrupted. Symptoms of tachycardia can include dizziness and fainting due to the interruption of blood flow to the brain. Tachycardia can be caused by many factors, including exercise or overexertion. However, damage can occur if the tachycardia is prolonged and persistent, and if the underlying cause is not treated. Treatments for tachycardia may include medication and/or surgical procedures. In some cases, an implanted defibrillator may be inserted in the patient's chest in order to regulate the heart rate.
