occur in adults Junctional ectopic tachycardia (JET) Prevention Once an acute arrhythmia has been terminated, ongoing treatment may be indicated to prevent recurrence. However, those that have an isolated episode, or infrequent and minimally symptomatic episodes, usually do not warrant treatment other than observation and explanation. In general, patients with more frequent or disabling symptoms warrant some form of prevention. A variety of drugs including simple AV nodal blocking agents such as beta-blockers and verapamil, as well as antiarrhythmic drugs may be used, usually with good effect, although the adverse effects of these therapies need to be weighed against potential benefits. Radiofrequency ablation has revolutionized the treatment of tachycardia caused by a re-entrant pathway. This is a low-risk procedure that uses a catheter inside the heart to deliver radiofrequency energy to locate and destroy the abnormal electrical pathways. Ablation has been shown to be highly effective: around 90% in the case of AVNRT. Similar high rates of success are achieved with AVRT and typical atrial flutter. Cryoablation is a newer treatment involving the AV node directly. SVT involving the AV node is often a contraindication to using radiofrequency ablation due to the small (1%) incidence of injuring the AV node, then requiring a permanent pacemaker. Cryoablation uses a catheter supercooled by nitrous oxide gas freezing the tissue to −10 °C (+14.0 °F). This provides the same result as radiofrequency ablation but does not carry the same risk. If it is found that the wrong tissue is being frozen, the freezing process can be quickly stopped with the tissue returning to normal temperature and function in a short time. If after freezing the tissue to −10 °C the desired result is obtained, the tissue can be further cooled to a temperature of −73 °C (-99.4 °F) and it will be permanently ablated. This therapy has further improved the treatment options for AVNRT (and other SVTs with pathways close to the AV node), widening the application of curative ablation to young patients with relatively mild but still troublesome symptoms who might not have accepted the risk of requiring a pacemaker. Treatment Most SVTs are unpleasant rather than life-threatening, although very fast heart rates can be problematic for those with underlying ischemic heart disease, or the elderly. Episodes can be treated when they occur by Valsalva maneuver, adenosine injection or taking a AV node blocking agent as pill-in-pocket, but regular medication may also