June 25, 2009 -- The late pop legend Michael Jackson's reported cardiac arrest could have been from any one of a number of factors -- but heart experts say that emotional stress can be an important contributor to the often deadly condition.
Dr. Christopher Cannon, a cardiologist at Brigham and Women's Hospital in Boston, told ABCNews.com that stressful situations "definitely" increase the risk for cardiac arrest.
"Increased adrenaline levels and sympathetic nerve signals can increase the risk of arrhythmia and sudden cardiac arrest," he said.
It is too early to tell, however, the exact reasons behind the 50-year-old Jackson's death. Undiagnosed heart disease is the leading underlying cause of cardiac arrest. However, other risk factors like a family history of the condition, previous heart attack or heart failure, and drug abuse or excessive alcohol intake can increase the risk of its occurence.
Jackson's death came less than a month before the start of a scheduled series of so-called comeback concerts. From July 13 to March 6, 2010, Jackson was scheduled to perform 50 sold-out concerts at London's O2 Arena.
The would have been hist first major concert series since his HIStory tour that ended in 1997.
News of Jackson's death spread shortly after an ambulance arrived at his Los Angeles home and transported him to UCLA Medical Center.
Thus far hospital officials have released no details on the underlying cause of death. As was the case with Jackson, the prognosis for cardiac arrest is not a favorable one.
Cardiac arrest is a condition in which the electrical signals to the heart become abnormal, making it impossible for it to properly pump blood through the body. In over 90 percent of victims, death occurs.
The first sign that something was wrong with Jackson likely occurred when an ambulance arrived at his home and took him to the medical center just a few miles away. But even if paramedics responded immediately, Jackson's chances would not have been good.
"This is something where minutes count," said Cannon. "Survival tails off from 50 percent survival down to 1 percent over a 10-minute period."
Cannon said cardiac arrest is different from a heart attack, which is normally the result of a blockage in an artery that supplies the heart with blood.
The reasons for cardiac arrest vary, Cannon noted. "It can strike seemingly suddenly and without warning," he said. "Unfortunately this could be a relatively common situation, though it is more often among people with heart disease, especially those with weakened hearts."
While many heart problems primarily affect those older than Jackson, cardiac arrest generally strikes people in their mid-thirties to mid-forties, according to the National Institutes of Health. Men appear to be more likely to suffer from cardiac arrest. Each year, between 250,000 and 450,000 Americans have a cardiac arrest, NIH statistics show.
Jackson's recent physical appearance also led some to question whether he was up to the task of performing. Recent pictures had shown him being pushed in a wheelchair, appearing frail and gaunt and wearing a face mask while being helped across the street. In December, there were reports that Jackson was on his deathbed, suffering from a rare lung condition, which his publicist denied.
"Certainly from what I've read he was under great stress in the past several years which can play a great role as well [as other factors]," noted Dr. Douglas Zipes, professor emeritus of medicine, pharmacology and toxicology at the Indiana University School of Medicine in Indianapolis.
ABC News' Lauren Cox, Radha Chitale, Sheila Marikar and Luchina Fisher contributed to this report.