. It starts the heartbeat by spontaneously contracting, causing the rest of the heart to contract in a wave. The wave spreads through the atria before reaching the atrioventricular node, or AV node, located just above the right ventricle. The AV node focuses the wave into the ventricles, contracting the ventricles. Should the SA node fail, the AV node can take over as the primary pacemaker at a rate of forty to sixty beats per minute. Should both the SA node and the AV node fail, there is a tertiary pacemaker, the perkinje fibers. Perkinje fibers are located near the bottom of the ventricles and can stimulate contraction at a rate of twenty to forty beats per minute. If the perkinje fibers or the AV node becomes irritated, they can begin contraction of the ventricles at speeds well above normal. Other causes of ventricular tachycardia include heart disease and medications. When the ventricles are contracting at a rate greater than one hundred beats per minute, the heart becomes inefficient. Blood cannot properly fill the ventricular chambers before it is forced out. This decreases the amount of oxygenated blood circulating through the body. The lack of oxygen in the body causes the heart to attempt to pump more blood, forcing the ventricles to work even harder. Should the ventricular rate rise above one hundred fifty beats per minute, patients usually require cardioversion.Cardioversion is electric shock treatment. It acts like a reset button, stopping all action so that the heart can begin normal beating again. Cardioversion, or defibrillation, should be done up to three times in increasing strength, no less than two hundred joules and no more than three hundred sixty joules. If the patient is still in ventricular tachycardia, defibrillation is used in conjunction with certain medications.The first medication given to a patient in ventricular tachycardia is epinephrine. One milligram is administered rapidly, every thre...
