The number of in-custody sudden deaths rose dramatically during the first year California law enforcement agencies began using stun guns, raising questions about the safety of the devices, according to a new study at UCSF. Tasers are not as safe as thought," said Dr. Byron Lee, one of the cardiologists involved in studying the death rate related to Tasers, the most widely used stun gun. "And if they are used, they should be used with caution." The researchers analyzed sudden death data from 50 law enforcement agencies in the state that use Tasers. They compared the death rate pre- and post-Taser deployment - analyzing data for five years before each agency began using Tasers and five years afterward. They found a sixfold increase in sudden deaths during the first year of Taser use - amounting to nearly 6 deaths per 100,000 arrests. California does not have a statewide training standard for stun guns, which have been used in the state for decades. Tasers, known as "conducted energy" devices, send out high-frequency pulses which can cause a very rapid, dangerous heart rhythm, said senior author Dr. Zian H. Tseng, an assistant clinical professor in cardiology. "Maybe a simple change of technique is what is necessary," he said. "The longer you hold the trigger, the higher the danger to the heart. ... The fewer pulses the better." Two years ago, Amnesty International reported 156 stun gun-related deaths of people in the United States during the previous five years.