Cigarette smoke worsens heart attacks.

People at risk of heart attacks should avoid smoke-filled rooms, a new study suggests. Researchers have found that lab rats were far less likely to survive a heart attack if they had regularly breathed secondhand cigarette smoke during the previous week.

The finding "was a real shock to us," notes cardiovascular physiologist Paul F. McDonagh of the University of Arizona Health Sciences Center in Tucson.

For a week, one of his colleagues exposed the rodents to smoke equivalent to that experienced by a person in a smoky bar for 3 hours a day, says McDonagh. Then the scientists temporarily clamped an artery of each rat, inducing heart attacks, and did the same to animals that had remained smokefree. Fully 80 percent of the smoke-exposed rats died within the hour and a half following the induced heart attack, but only 30 percent of the smokefree rodents died during that critical period.

McDonagh's team monitored the animals' blood before and during the heart attacks. The scientists found that blood platelets in the smoke-exposed rats attached themselves to white blood cells more frequently than did those in the other rats. Platelets play a role in clotting, and the white cells participate in inflammation.

The excessive linking of these two types of cells may have made the blood form more fatal clots, McDonagh speculates. Alternatively, he posits, immune cells activated by exposure to smoke in the lungs may have triggered the systemic release of chemical messengers, known as cytokines, that somehow aggravated the heart attacks.