New US research suggests a lot of people may ignore potentially lifesaving warning signs hours, days, even weeks before they collapse.
Cardiac arrest claims about 350,000 US lives a year. It's not a heart attack but worse: The heart abruptly stops beating, its electrical activity knocked out of rhythm.
CPR can buy critical time, but so few patients survive that it's hard to tell if the long-time medical belief is correct that it's a strike with little advance warning.
An unusual study that has closely tracked sudden cardiac arrest in Portland, Oregon, for over a decade got around that roadblock, using interviews with witnesses, family and friends after patients collapse and tracking down their medical records.
About half of middle-aged patients for whom symptom information could be found had experienced warning signs, mostly chest pain or shortness of breath, in the month before suffering a cardiac arrest, researchers reported Monday.
The research offers the possibility of one day preventing some cardiac arrests if doctors could figure out how to find and treat the people most at risk.
"By the time the 911 call is made, it's much too late for at least 90 per cent of people," said Dr Sumeet Chugh of the Cedars-Sinai Heart Institute in Los Angeles, who led the study reported in Annals of Internal Medicine.
"There's this window of opportunity that we really didn't know existed."
Importantly, a fraction of patients considered their symptoms bad enough to call 911 before they collapsed, and they were most likely to survive.
That's a reminder to the public not to ignore possible signs of heart trouble in the hope it's just indigestion, said University of Pittsburgh emergency medicine specialist Dr Clifton Callaway, who wasn't involved in Monday's study but praised it.
"Chest pain, shortness of breath - those are things you should come in the middle of the night to the emergency department and get checked out," said Callaway, who chairs the American Heart Association's emergency care committee.
Previous heart attacks, coronary heart disease, and certain inherited disorders that affect heartbeat all can increase sudden cardiac arrest risks.
People known to be at high risk may receive an implanted defibrillator to shock the heart back into rhythm. But cardiac arrest is such a public health problem that the Institute of Medicine last summer urged a national campaign to teach CPR, so more bystanders can help.
