The study's authors attribute much of the sharp decline in acute myocardial infarctions (AMI) to a near-elimination of the rapid and harmful effects of secondhand smoke on blood platelets and the arteries that supply blood to the heart. Damage to these and other functions increases the likelihood and seriousness of a cardiovascular "event," they note.
In addition, smoke-free environments encourage smokers to stop or reduce smoking, which also reduces heart attack risk, they point out.
The findings were reported at the scientific sessions of the American College of Cardiology meeting in Chicago.
The study took place in Helena, Montana, where a smoke-free ordinance went into effect June 5, 2002 and was suspended in a legal challenge six months later. One hospital - St. Peter's Community Hospital - serves almost all cardiac patients in the region, with a population of 65,913.
The researchers compared hospital charts for patients admitted with primary or secondary diagnosis of AMI from the smoke-free Helena area with those from outside the area. They also compared records for the period of the smoke-free ordinance with records from more than four years before that ordinance went into effect. They accounted for seasonal differences so the records from the smoke-free period could be reliably compared with the records from other times of the year.
During an average six-month period, the number of hospital admissions for AMI from people living or working in Helena is just under seven per month. But during the six months that the ordinance was in force, the number of hospital admission for AMI in Helena declined to less than four per month - a drop of nearly 60 percent in the number of admissions. There was no significant change in the number of admissions from outside the Helena area.
The authors note that this is the first empirical evidence suggesting that smoke-free policies not only protect people from long-term dangers of secondhand smoke, but they also rapidly prevent heart attacks.
"This striking finding suggests that protecting people from the toxins in secondhand smoke not only make life more pleasant; it immediately starts saving lives," said Stanton Glantz, PhD, professor of medicine at UCSF Cardiovascular Research Institute and a statistics authority. "This work substantially raises the stakes in debates over enacting and protecting smoke-free ordinances."
Glantz, who serves as director of the Center for Tobacco Control Research and Education at UCSF, provided the study's statistical analysis.
Many important physiological effects of secondhand smoke on cardiovascular function occur within minutes of exposure and are nearly as large as they are for smokers, studies have shown. Within five minutes, the aorta becomes stiffer; within 30 minutes, blood platelets are activated, which makes the blood "stickier" and damages artery linings. In the same time period, the ability of blood vessels to dilate to get more blood to the heart and other organs is reduced. Within two hours of exposure to secondhand smoke, heart rhythm is disturbed, according to a number of studies.
The heart attack risk for smokers is known to drop in half within a year of quitting, and according to another analysis, smoke-free workplace and public place laws such as the one in Helena encourage people to stop smoking. These effects, combined with the effect of reduced exposure to secondhand smoke contributed to the rapid drop in the incidence of heart attack, the researchers suggest.
The study was undertaken in Helena by Richard P. Sargent, MD, and Robert M. Shepard, MD, physicians at the city's St. Peter's Community Hospital who serve on the hospitals health care quality board. It was presented by Sargent at the American College of Cardiology meeting.
The study was funded in part by the National Cancer Institute.