The heartbeat is controlled by the electrical system of the heart (Fig. 1). This system is made of several parts that tell the muscle of the heart when to contract. The SA node starts the heartbeat causing the atria, or upper chambers of the heart, to contract. The signal then travels through the AV node, the Bundle of His, Bundle Branches, and Purkinje fibers. This causes the ventricles, the lower chambers of the heart, to contract. The flow of electrical signals produces a normal heartbeat (Fig. 2). Normal heartbeats can be seen on an electrocardiogram, or ECG.
Ventricular Tachycardia is a heart arrhythmia, or irregular heartbeat. In ventricular tachycardia, abnormal electrical pulses in the lower chambers, or ventricles, disrupt the normal firing of the SA node, causing the heart to beat rapidly (Fig. 3). These signals can be seen in an Electrocardiogram or ECG (Fig. 4). A rapid heartbeat does not give the heart enough time to refill with blood before pumping, which causes diminished blood flow to the rest of the body. This may lead to symptoms of dizziness, lightheadedness, unconsciousness and cardiac arrest.
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