WASHINGTON (Reuters) - A woman whose defibrillator activated one week to the hour after her father died, and recorded the event, may provide the first documented evidence of "anniversary reaction," doctors reported.

The defibrillator acted as a pacemaker, perhaps saving the 50-year-old woman's life. Its function of keeping a precise record of when it was activated made it possible to establish the precise time of the event, the doctors reported.

In a dramatic extra twist to the story, the patient was standing by the open grave of her sister-in-law, who had herself died when she heard the news of the father's death.

Dr. Michael Sweeney of Brigham and Women's Hospital and Harvard Medical School in Boston and Dr. Michael Quill of the University of Rochester School of Medicine in New York reported on the occurrence in the journal HeartRhythm.

"We have all, almost to the point of being urban legend, heard stories of people literally dropping dead upon receipt of tragic news ... or a widower dying on the anniversary of his deceased spouse's (death)," Sweeney said in a telephone interview.

No one could really prove it, but the case of the woman, who had had the defibrillator implanted after an earlier heart attack, may provide good evidence, he said.

Sweeney said he learned of the story when the woman came into his office for a routine checkup. He noticed that the defibrillator -- a device that sits quietly in a patient's body until an abnormal heart rhythm activates it -- had provided a mild shock to her heart five months after it was implanted.

"My patient ... had an event which, had she not had a defibrillator, she would have fallen into the grave," Sweeney said.

She was also not aware that the defibrillator had fired, as it gave her heart just a gentle pulse and not an overwhelming shock. Because it fired at almost the precise hour of her father's death, but one week later, Sweeney and Quill believe it was this shock, and not the funeral of the sister-in-law, that precipitated the abnormal heart rhythm.

"The concept of anniversary reaction is that it is a response to the unconscious sense of time. Just because you aren't thinking that it is exactly seven days later ... a part of your mind ... is thinking that," Sweeney said.

The event also suggests a possible biological cause for "anniversary reaction" -- a change in the heart's beating pattern, Sweeney said.

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