In what is the biggest study of its kind, Kaiser Permanente researchers say their ability to reduce and control enrollees' cardiovascular risk factors such as cholesterol levels and blood pressure has led to a decrease in the worst kind of heart attack, called an ST-segment elevation myocardial infarction or STEMI, among Northern California enrollees over a 10-year period.
"I'm convinced that is at least part of the reason, because we systematically tried to rule out many of the other possible explanations, but I can't say for sure it's all of the reason," says Alan S. Go, MD, director of the Comprehensive Clinical Research Unit at the Kaiser Permanente Division of Research in Oakland and lead investigator of a report published today.
Go said that the results are not caused by a trend toward healthier workers who are covered by Kaiser resulting from the economic downturn, which may have removed older, sicker workers from the workforce without health coverage. They looked at a subset of their study sample that was with Kaiser during the 10-year duration and found the same reductions, Go says.
Using the system's electronic medical records, Kaiser researchers evaluated 46,087 myocardial infarction hospitalizations among its 3 million Northern California enrollees during the 18.7 million person-years of follow-up between 1999 and 2008.
While the age and sex-adjusted incidence of MI increased from 274 cases per 100,000 person- years in 1099 to 287 cases in 2000, it decreased each year thereafter, to 208 cases in 2008, a 24% decrease.
Most importantly, the occurrence of STEMI heart attacks, in which more of the heart muscle is permanently damaged and there's a higher risk of death, decreased from 133 cases per 100,000 person years in 1999 to 50 cases in 2008, or by 62%. And, 30-day mortality was significantly lower in 2008 than in 1999.
The researchers tracked the number of all kinds of heart attacks among their enrollees, regardless of whether they were brought to Kaiser for care, or were taken to another hospital or died before they were able or while they were able to obtain cardiac care.
During the same study period, "substantial reductions in levels of blood pressure and LDL cholesterol occurred during this period" within Kaiser's Northern California population, "as compared with other providers, according to reports form the Healthcare Effectiveness Data and Information Set."
The Kaiser report is published in today's New England Journal of Medicine.
Go says that identifying patients at risk for cardiovascular disease, specifically those with hypertension, high cholesterol and diabetes, and getting their blood pressure, lipid levels and A1C numbers under control was what he believes is the primary reason for the decline in STEMIs.
Also, he says, several Kaiser programs, notably PHASE (Preventing Heart Attacks and Stroke Everyday) may be partly responsible because of the program's way of actively encouraging people with known heart disease risk to eat more healthy foods and exercise.
"When you look across that decade, the control of blood pressure has improved, so that 80% of known hypertension patients were meeting the target blood pressure levels," Go said. Also, "Multiple methods to get to (target) cholesterol levels were achieved in the majority of patients, with overall levels lowered (from 129 mg per deciliter) to 113. And the proportion of patients with stroke has also gone down, although not as much as we would have liked."
To date, efforts also are ongoing to encourage patients to lose weight, but Go says Kaiser cannot produce data showing weight loss was significantly down. However, he says, that even in obese patients who have higher heart attack risks, methods to control blood pressure and lipid levels appear to be having an impact.
The report also is the first to note the influence of using a cardiac biomarker such as troponin to determine whether a person was having a heart attack, a test that may have increased sensitivity for capturing more patients, and in effect increased the number of heart attacks captured in the data. "Thus, the observed decreases in myocardial infarction since 20000 are even more striking" the authors wrote.
The Kaiser study received financial support from the Permanente Medical Group and from a Schering-Plough Future Leaders in Cardiovascular Medical Research Grant. Go's collaborating researchers, all of Kaiser Permanente, include Robert Yeh, MD; Stephen Sidney, MD, Malini Chandra, Michael Sorel, and Joseph Selby.
Heart disease is the biggest cause of U.S. mortality, with 631,636 in 2006.
In an accompanying Perspective article in the Journal, Jeremiah R. Brown, Ph.D., and Gerald T. O'Connor, of the Dartmouth Institute for Health Policy and Clinical Practice, wrote that the Kaiser paper demonstrates "the likely association between the increased use of statins, beta-blockers and angiotensin-converting-enzyme inhibitors or angiotensin-receptor blockers and a reduction in the rates of fatal and non-fatal heart attacks."
Go emphasizes that he and his colleagues who produced the report aren't absolutely sure that Kaiser's aggressive prevention efforts are responsible for the reductions in fatal and non-fatal heart attacks, although he believes that it must be partially responsible. "There are still unmeasured factors we aren't able to account for," such as inflammatory factors that could not be measured.
But, he said Kaiser is "in the process of analyzing through a collaboration, called the Cardiovascular Research Network, on trends documented within 15 participating health plans across the country. "We're looking to see if there are in fact similar trends during the same period of time," he says.
That project is funded by the National Heart Lung and Blood Institute.