Tetanus vaccine, also known as tetanus toxoid (TT), is a toxoid vaccine used to prevent tetanus. During childhood, five doses are recommended, with a sixth given during adolescence.After three doses, almost everyone is initially immune, but additional doses every ten years are recommended to maintain immunity. A booster shot should be given within 48 hours of an injury to people whose immunization is out of date. For people with high-risk injuries who are not fully immunized, tetanus antitoxin may also be recommended.Confirming that pregnant women are up to date on tetanus immunization during each pregnancy can prevent both maternal and neonatal tetanus. The vaccine is very safe, including during pregnancy and in those with HIV/AIDS.Redness and pain at the site of injection occur in between 25% and 85% of people. Fever, feeling tired, and minor muscle pain occurs in less than 10% of people. Severe allergic reactions occur in less than one in 100,000 people.A number of vaccine combinations include the tetanus vaccine, such as DTaP and Tdap, which contain diphtheria, tetanus, and pertussis vaccines, and DT and Td, which contain diphtheria and tetanus vaccines. DTaP and DT are given to children less than seven years old, while Tdap and Td are given to those seven years old and older. The lowercase d and p denote lower strengths of diphtheria and pertussis vaccines.Tetanus antiserum was developed in 1890, with its protective effects lasting a few weeks. The tetanus toxoid vaccine was developed in 1924, and came into common use for soldiers in World War II.
: 837–838  The tachyarrhythmias can be further classified as Ventricular fibrillation (V-fib) and pulseless or sustained Ventricular tachycardia (V-tach), both of which are rapid and erratic arrhythmias that alter the circulatory pathway such that adequate blood flow cannot be sustained and is inadequate to meet the bodys needs. : 837–838 The mechanism responsible for the majority of sudden cardiac deaths is ventricular fibrillation. Ventricular fibrillation is a tachyarrhythmia characterized by turbulent electrical activity in the ventricular myocardium leading to a heart rate too disorganized and rapid to produce any meaningful cardiac output, thus resulting in insufficient perfusion of the brain and essential organs. In ventricular tacycardia, the heart also beats faster than normal, which may  prevent the heart chambers from properly filling with blood. Some of the electrophysiologic mechanisms underpinning ventricular fibrillations include ectopic automaticity, re- entry, and triggered activity. Structural changes in the diseased heart as a result of inherited factors (mutations in ion-channel coding genes for example) cannot explain the suddenness of sudden cardiac death.Both ventricular fibrillation and ventricular tachycardia can result in the heart ineffectively pumping blood to the body. Ventricular tachycardia is characterized by an altered QRS complex and a heart rate greater than 100 beats per minute. When V-tach is sustained (lasts for at least 30 seconds), inadequate blood flow to heart tissue can lead to cardiac arrest.Bradyarrhthmias occur following dissociation of spontaneous electrical conduction and the mechanical function of the heart resulting in pulseless electrical activity (PEA) or through complete absence of electrical activity of the heart resulting in asystole.