MONDAYS MOST LIKELY TIME FOR HEART ATTACKS.

Byline: Lee Condon Daily News Staff Writer

If Mondays weren't bad enough, it turns out that most heart attacks occur on the first day of the workweek - even for the unemployed.

Doctors examining the timing of heart attacks also found that most strike in the winter - even in Los Angeles and other warm climates - and are more likely to be fatal if they occur at night, according to findings presented Tuesday at the annual meeting of the American Heart Association in Dallas.

Although doctors still can't predict heart attacks, doctors said the studies will help in the development of new drugs and better patient care.

``The better we understand how, when and where these things happen, the better we can treat them,'' said Dr. Russell V. Luepker of the University of Minnesota.

Doctors have known for several years that heart attacks are more likely on Mondays. However, Dr. Michael K. Kruska of Hanusch Hospital in Vienna found that the usual explanation - the stress of heading back to work - cannot account entirely for this peak.

He reviewed about 1,500 cases of fatal cardiac arrest in Vienna. About one-quarter of the victims were retired. Their risk Mondays was about 20 percent to 40 percent higher than usual. Kruska theorized that going shopping and resuming other stresses of the weekly routine are to blame.

The winter study was done by Dr. Robert A. Kloner of Good Samaritan Hospital in Los Angeles. Kloner reviewed 220,000 deaths in Los Angeles between 1985 and 1996. The risk begins to climb sharply around Thanksgiving, peaked at New Year's and then gradually tapers off. January turned out to be the worst month. The risk in winter was 33 percent higher than in summer.

``There's a theory that extreme heat or cold triggers a heart attack, but Los Angeles is relatively mild in the winter, so we were very surprised to see this difference,'' he said.

Kloner's theory: It's holiday stress and overindulgence, especially too much alcohol, that make this time of the year so bad for the heart.

Still, temperature might play a role in colder climes. Dr. Philippe Amouyel of Lille University in France found that the lower the temperature, the worse for the heart. For every fall of 18 degrees Fahrenheit in a day's average temperature, the risk of a first heart attack increases by 13 percent.

``I think temperature is the marker,'' Amouyel said in an interview Wednesday. ``When you have colder conditions you modify your way of life. You're more active in the summer. People get fatter, have weight increases in the winter.''

Dr. Lawrence O'Connor, a cardiologist at Glendale Memorial Hospital, said he has noticed that the winter theory holds up at his hospital, despite the mild winter weather. He said he is interested in examining Kloner's work.

``We know for a fact our cardiac admissions go up when it gets colder,'' O'Connor said.

Already there is a high blood pressure drug on the market that is timed to provide more relief in the morning because studies show the risk of heart attack is greater then, said Dr. Ben Cohen, a University of California, Los Angeles, cardiologist.

Cohen said he believes that such information is of greatest benefit in the development of drugs, rather than for patients trying to avoid heart attacks.

``We see heart attacks at all times of the day,'' Cohen said, adding, however, ``They do seem to happen more in the morning, from 6 a.m. to noon.''

Other findings include:

Researchers at Brigham and Women's Hospital in Boston found that people with chest pain who came to the hospital between 6 p.m. and 6 a.m. were more likely to have a heart attack than those who showed up with the same symptoms during the day.

While heart attacks are less common at night than during the day, another study shows a nighttime occurrence is more likely to be fatal. Dr. C. Michael Gibson of Allegheny General Hospital in Pittsburgh looked at 1,246 heart attack victims. He found that those whose symptoms started at night were almost twice as likely to die or have a second heart attack in the hospital. Those whose symptoms start at night take about a half-hour longer to get to the hospital, but this delay does not entirely explain why late-night incidents are worse.

``It may have to do with differences in the way the body responds to a heart attack at night,'' Gibson said.

The Associated Press contributed to this story.