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Heart expert warns about using
UCSF doctor says jolt can interrupt pumping of blood
When 50,000 volts of electricity from a Taser surge across the body, it can instantly incapacitate a person -- more safely than a blow from a police baton or a blast of pepper spray, its manufacturer contends.
But cardiologists are concerned that, in certain cases, the device might also interrupt the rhythm of the human heart, throwing it into a potentially fatal chaotic state known as ventricular fibrillation.
Rather than pump blood in sequence through its four chambers, a heart in ventricular fibrillation writhes uncontrollably, wiggling like a bag of worms. It is a common cause of sudden death.
Dr. Zian Tseng, a cardiologist at UCSF, believes Tasers are potentially dangerous because a jolt of electricity, at just the right moment in the heartbeat cycle, can trigger ventricular fibrillation.
He ought to know. He uses a precisely timed jolt to throw the hearts of his patients into ventricular fibrillation on a regular basis.
Tseng installs implantable electric defibrillators into the chests of heart patients who are at risk of sudden cardiac arrest. The devices are miniature versions of the electric paddles used to jolt a stalled heart back into its proper rhythm. Vice President Dick Cheney is the most prominent American with such a device implanted in his chest.
Before Tseng can wheel a patient out of the operating room, he must test the new defibrillator by stopping the heart, and watching to see if the life- saving implant does its job.
"There are vulnerable periods in the cardiac cycle, when shocks can cause dangerous arrhythmias,'' Tseng said.
Known as a T-wave on the heart monitor, the brief pause in pumping takes up about 3 percent of a heartbeat's cycle. Tseng times his jolt of electricity for that moment, to stop a heart, so the defibrillator can automatically start it again.
People using Tasers, he said, risk jolting a person at precisely the wrong instant. "I think they are dangerous,'' he said. "If you are shocking someone repeatedly, it becomes a bit like Russian roulette. At some point, you may hit that vulnerable period."
Cardiologists also know that the window in which a jolt of electricity can halt a heart expands significantly when a patient is treated with certain drugs, or when the body is flooded with the fear hormone, adrenaline. Patients with underlying heart problems are also more vulnerable to the condition.
Executives at Taser International are aware of the heart's vulnerability to ventricular fibrillation, but they insist their device is safe. The electrical current used in an operating room to stop a heart is 30 times higher than that produced by a Taser, said Mark Kroll, an electrical engineer and board member of the Scottsdale, Ariz., firm. Medically induced fibrillation involves applying a current directly to the inside of the heart, he added, while a Taser's current is applied to the clothing and skin.
"The current delivered by a Taser is too weak to induce ventricular fibrillation,'' he said.
Kroll acknowledged that adrenaline does increase vulnerability to ventricular fibrillation, and that many subjects facing police arrest are pumped up with the hormone. But he said there is no evidence it lowers the threshold to a point that would make Tasers dangerous.
"If anything, a Taser is reducing deaths," Kroll said. "Many subjects are in a terminal stage of a drug overdose. The quicker police can get them under control, the quicker they can get medical help."
UCSF cardiologist Tseng said that, as a precaution, police should carry automatic electronic defibrillators in their cars, so they might revive someone whose heart has been stopped.
And while Kroll said Tasers are not responsible for stopping
hearts, he agreed with Tseng on that point: "I think cops should carry