The improvements in severity of heart attacks applied to men and women, blacks and whites. (CBC)

The severity of first heart attacks in the U.S. has dropped over 15 years, propelling a decline in heart disease deaths, researchers say.

"This landmark study suggests that better prevention and better management in the hospital have contributed to the reduction in deaths,' said cardiologist Dr. Merle Myerson of the Columbia University in New York, lead author of the study which appears in Circulation: Journal of the American Heart Association.

"Better control of risk factors for heart disease, such as blood pressure and cholesterol as well as improvements in hospital management may lessen the severity if somebody has a heart attack," Myerson said.

The researchers also considered whether people had less severity because they got to the hospital sooner, but that was not the case, the researchers said.

The study extends research released last month that found heart disease deaths in the United States have fallen 30 per cent in the past decade. Better control of cholesterol and blood pressure, declining smoking rates and better medical treatments were credited for the decline.

Myerson and her colleagues analyzed data from 1987 to 2002 for more than 10,000 first-time heart attack patients aged 35 to 74.

Improvements across the board

The researchers looked at markers for heart attack severity, such as enzyme levels in the blood that point to heart muscle damage, and changes in blood pressure.

The results suggested that improvements in severity of heart attacks applied to men and women, blacks and whites.

But there was some evidence of possible race-related differences between whites and blacks for the Q-wave, a measure on the electrocardiogram that was higher in blacks.

"When we see that particular pattern, it generally indicates more of the heart muscle was affected by the heart attack," Myerson told Reuters.

Over the course of the study, one measurement did not change: the percentage of patients who got to hospital in less than two hours after symptoms started remained at about 33 per cent.

Heart disease is the world's top killer, but cancer is set to overtake it by 2010, according to the World Health Organization.