The one-year mortality rates were 34.3 percent for Americans and 34.4 percent for Canadians. The data tell a different story when death rates were measured for 30 days--21.4 percent of Americans died and 22.3 percent of Canadians--suggesting a small but statistically significant short-term edge for American cardiac care. The findings appear in the May 22 issue of The New England Journal of Medicine.
Despite the initial benefit of the American approach, the researchers say the data overall seem to favor the more conservative Canadian practices. But they warn that before firm conclusions can be drawn, further investigations are needed that correlate in greater detail patient characteristics and the medical treatments they receive, as well as focus on other issues like quality of life and cost of care.
The research team looked at patients age 65 and older in the U.S. and Canada who had suffered a new myocardial infarction in 1991. Myocardial infarction, or heart attack, is a leading cause of death and disease in both the U.S. and Canada. The team compared the use of three cardiac procedures within 30 days of the attack and patient mortality rates in the two countries. The procedures were coronary angiography, a diagnostic technique using a contrast medium to produce x-ray images of the coronary arteries; percutaneous transluminal coronary angioplasty, insertion of a balloon catheter through the skin and into the channel of a coronary artery to dilate a narrowed section of the artery by inflating the balloon; and coronary-artery bypass graft surgery, a procedure to graft a section of vein between the aorta and a blocked coronary artery to reroute blood flow around the obstruction. The subjects included 224,258 elderly Medicare recipients in the U.S. and 9,444 elderly patients in Ontario--Canada's most populous province.
The study found that the Americans were much more likely to undergo the invasive procedures: For coronary angiography, the figures were 34.9 percent of the American patients vs. 6.7 percent of the Canadians; for percutaneous transluminal coronary angioplasty, 11.7 percent vs. 1.5 percent; and for coronary-artery bypass graft surgery, 10.6 percent vs. 1.4 percent. The differences in use of the procedures decreased only a small amount during 180 days of follow-up.
"The results of our study are likely to stimulate debate about the costs and effectiveness of the more aggressive U.S. approach S," write lead author Jack V. Tu, Barbara McNeil, and colleagues. Tu was in the Department of Health Care Policy at Harvard Medical School (HMS) at the time of the study and McNeil is chair of the department and the Ridley Watts Professor of Health Care Policy. Tu is currently at the Institute for Clinical Evaluative Sciences (ICES).
Unlike the U.S. with its variety of private and public health-care plans, Canada has publicly administered universal health-care coverage. The researchers explain that one interpretation of their findings may be that the better short-term outcomes in the U.S. are a result of the country's more timely and aggressive approach to cardiac procedures, and "the better long-term outcomes in Canada may reflect greater access to primary care, prescription drugs, and long-term care, which are universally provided to the elderly with minimal copayments, or none, under the Canadian health-care system."
An important aspect of the current study is its use of large patient populations. The initial set of American subjects included all elderly Medicare patients with a principal diagnosis of acute myocardial infarction during calendar year 1991. The initial Canadian population was made up of all elderly patients in Ontario with a primary diagnosis of acute myocardial infarction during fiscal 1991 (beginning April 1). The researchers used a set of exclusion criteria to ensure that the populations were comparable and that both were representative of the U.S. elderly population. Patients under age 65, for example, or those who had end-stage renal disease were eliminated.
Two similar studies comparing the care of heart-attack patients in the U.S. and Canada suggested that in the U.S., the higher rates of catheterization and bypass surgery might lead to a slight improvement in the quality of life. One of the weaknesses of these studies--called Survival and Ventricular Enlargement (SAVE) and Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries (GUSTO)--is that the number of patients studied was relatively small. As a result, statistically significant differences in mortality rates were difficult to identify. In addition, the two studies involved randomized clinical trials in which the subjects were not representative of the patient population in the two countries. The patients in Ontario who took part in GUSTO, for example, were younger, had fewer coexisting illnesses, and were more likely to undergo a cardiac procedure than patients not in the trial.
"Elderly patients constitute the majority of patients with myocardial infarctions in both countries but are often excluded from clinical trials of new therapeutic strategies," write the authors of the current study.
In an accompanying editorial in The New England Journal of Medicine, Harlan M. Krumholz of Yale University School of Medicine points out that no other country in the world matches the rate of cardiac procedures performed in the U.S., rates that have grown dramatically since 1980. "The relatively high rate of use of procedures may have been fostered by a health care delivery system that, until recently, almost uniformly favored their use," he writes.
This does not necessarily mean that there is little benefit. Krumholz says the effects of these procedures cannot be measured by mortality rates alone. Quality of life issues are significant. The SAVE study, for example, found that Canadian patients had a higher rate of activity-limiting angina. "Patients could be deriving substantial benefit from these procedures without there being a survival benefit at one year," he says. Furthermore, economic ramifications have to be determined. An early cardiac intervention may have no net cost--or a net savings--if it reduces length of hospital stay, minimizes the need for additional tests, or eliminates the need for future hospitalization.
The other authors of the recent study, which was supported by the U.S. Agency for Health Care Policy and Research, are Chris L. Pashos (Abt Associates and HMS), C. David Naylor (ICES and the University of Toronto), Erluo Chen (ICES), Sharon-Lise Normand (HMS and Harvard School of Public Health), and Joseph P. Newhouse (HMS, Harvard School of Public Health, and Kennedy School of Government).