Hospitalization rates for heart attacks are going down, so prevention efforts may be paying off.

Two studies published in 2010 show that the American heart attack rate is continuing to decline. The first, published in Circulation, was based on Medicare data. The main finding was that hospitalization rates for heart attack dropped by about 23 percent between 2002 and 2007, which by the authors' calculations might have translated into 100,000 fewer hospitalizations a year for the 45 million Americans enrolled in the Medicare program.

The second study, published in The New England Journal of Medicine, was based on the hospitalization records of 3 million people ages 30 and older enrolled in the Kaiser Permanente Northern California health plan. Again, the overall finding was the decline in hospitalizations for heart attack at a clip—24 percent—that was nearly identical to that found in the Medicare study, and for a time period, 1999 to 2008, that was roughly the same.

Postponement vs. prevention

As the accompanying editorial in Circulation pointed out, there's been a steady decline in heart attack deaths in the United States since 1970. Yet heart disease became more common as more Americans were diagnosed with the disease, treated for it, or survived what previously might have been a fatal heart attack. One of the ironies of modern medicine is that conditions sometimes become more common as efforts to find and treat them become more successful.

Another quirk in the heart disease statistics is that even as mortality numbers went down, hospitalizations for heart attacks and related problems like angina increased for people ages 65 and older between the mid-1960s till about 2000. It seems that heart disease wasn't being so much prevented as postponed to an older age.

But this Circulation study—as well as some others—shows declines in hospitalization for heart attacks in recent years for the Medicare population, even among those 85 and older. Hospitalization rates for all conditions have been going down for years for many reasons, but the rate for heart attacks seems to be falling much faster.

The researchers offered several possible explanations. Are more people perhaps dying of heart attacks before ever reaching the hospital? Data from several studies suggest that's not the case. Could doctors be classifying heart attacks under other heart-related diagnoses for Medicare billing purposes? They checked, and hospitalization rates for conditions like unstable angina and heart failure are also going down, so it doesn't seem "code shifting" is occurring.

So they settled on a true decline in the number of heart attacks as the most likely reason for hospitalizations going down. Maybe decades of efforts to eat right and exercise more, stop smoking, lower LDL cholesterol levels, and control blood pressure are working.

A milder kind of heart attack

The Kaiser study separated heart attacks into two categories: the more severe ones caused by a blockage of a coronary artery that results in significant damage to the heart muscle (myocardium) and the milder ones in which the blockage isn't as complete, so the infarct—tissue damaged by lack of blood—isn't as large. Doctors call the serious heart attacks ST-segment elevation myocardial infarcts—STEMIs for short—because of the shape of the electrocardiogram. The parlance for milder ones is non-STEMIs. Blood tests that detect proteins released by injured heart muscle—one called troponin has proved to be especially useful—have made it possible to detect the milder, non-STEMI event.

The Kaiser data showed a 62 percent decrease in hospitalizations for the serious brand of heart attacks, the STEMIs. The number of hospitalizations for the non-STEMIs increased through 2004, almost certainly because of increased troponin testing, before declining, although not by as much as the STEMIs. In 1998, the Kaiser data indicate that the number of serious and mild heart attacks were about the same. By 2008, there were three times as many hospitalizations for the milder non-STEMI heart attacks as there were for the STEMIs.

The STEMI fits the classic image of the heart attack. The blocked artery needs to be opened as soon as possible with angioplasty and possibly placement of a stent or, if that isn't available, a clot-busting drug. Any delay can mean even more dead or damaged heart muscle.

There isn't the same degree of immediate peril to the heart from the non-STEMI heart attack. In fact, prior to troponin testing, many cases were diagnosed as angina. Rather than rushing to open an artery, doctors often treat the non-STEMI patient with an assortment of medications: aspirin, nitrates, beta blockers, and sometimes heparin.

So the Kaiser study and others like it suggest that we're into a new era of heart attack when milder cases, detected by ever more sensitive tests, are outnumbering the devastating "widow makers" of old. - Harvard Health Letter