May 14 (HealthDay News) -- News media periodically report on people dying after being shocked by Tasers, better known as "stun guns."

But instead of immediately dropping to the ground, people often take as long as 13 minutes to collapse, new research shows.

And though the cause of death is often attributed to ventricular defibrillation, an often fatal heart arrhythmia believed to be caused by the electrical stimulation, other types of heart arrhythmias are a more common cause of death.

The research was to be presented Thursday at the Heart Rhythm Society's annual meeting in Boston.

Researchers examined emergency medical services reports, autopsy reports and electrocardiograms (EKGs) of 12 men with a median age of 36 who collapsed within 15 minutes of having a conducted energy weapon (CEW) used on them between 2001 and 2008. Taser is a brand name for a conducted energy weapon.

Initial EKGs, which record heart electrical activity, showed only one man had ventricular fibrillation, while 11 had other types of heart arrhythmias.

Ventricular fibrillation is an uncoordinated, rapid contraction or trembling of the heart's ventricles that causes the blood to stop circulating. Ventricular fibrillation can lead to death within minutes.

Medical records showed the other 11 men had a variety of abnormal heart rhythms, including six with asystole (less then five beats per minutes) and two with severe bradycardia (six to 29 beats per minute).

Nine of those who died were taking illegal drugs, and four had significant cardiomyopathy, or inflammation of the heart.

The man with ventricular fibrillation collapsed immediately after the Taser was discharged to the left chest, consistent with electrically-induced arrhythmia, researchers said.

In the remaining 11 men, the time from the last weapon discharge to collapse ranged from one to 13 minutes.

"In sudden deaths proximate to CEW discharge, collapse is rarely immediate, and VF [ventricular fibrillation] is uncommon," according to a Heart Rhythm Society news release. "While one case was consistent with electrically induced VF, it is not a common causal mechanism of these sudden deaths."

SOURCE: Heart Rhythm Society, news release, May 14, 2009