Findings

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Substantial variations in the nature, extent and availability of health care across geographical areas,^1, 2 without any clear association with outcomes, have long been observed. Two decades ago, such variations in the United States led to calls for guidelines to determine appropriateness in the delivery of services. Investments were made in Patient Outcome Review Teams^3-6 to develop clinical guidelines for deciding when a given surgical procedure or diagnostic imaging study is warranted. The underlying premise was that the wide variations might indicate that health care was being provided based on different protocols or with different benefits to patients.

This article presents data on geographical variations, so-called small area variations,^1, 2 in treatment and outcomes for heart attack (acute myocardial infarction) patients in Canada. Beyond simply showing that treatments—in this case, rates of revascularization—vary a great deal across subprovincial health regions,^7‑10 this study juxtaposes revascularization rates against a fundamental outcome: 30-day mortality (see The data).

Revascularization rising/Mortality falling

Overall, among acute myocardial infarction patients in the 46 health regions examined, revascularization rates rose and mortality rates fell between 1995/1996 and 2003/2004. The mean percentage who were revascularized within 30 days of hospital admission tripled from 12.8% to 39.8%, and the mean 30-day mortality rate dropped from 13.2% to 9.4% (Table 1).

Table 1
Age-sex standardized 30-day revascularization and 30-day mortality rates of acute myocardial infarction patients, health regions with at least 100,000 population, seven provinces, 1995/1996 and 2003/2004

Although revascularization rates rose in all health regions, those with a low rate in 1995/1996 also tended to have a relatively low rate in 2003/2004. Nonetheless, in both years, rates varied substantially among the regions—from 0.9% to 31.9% in 1995/1996, and from 20.8% to 65.6% in 2003/2004 (Table 1). Even in the same province, variability among health regions was considerable; for example, in one province in 2003/2004, revascularization rates ranged from 22% to 50% (data not shown).

By 2003/2004, 30-day mortality rates among acute myocardial infarction patients had fallen in 42 of the 46 health regions. However, in both years, mortality rates varied widely by region (Table 1), ranging from 7.5% to 18.4% in 1995/1996, and from 5.5% to 12.7% in 2003/2004. Even within the same province, mortality rates varied substantially among health regions; for example, in 2003/2004, in one province, the range was from 5.5% to 11.3% (data not shown).

For both 1995/1996 and 2003/2004, health regions have been classified into four groups (Sections) by comparing their revascularization and mortality rates with the median rates that year. Section A contains regions where both the revascularization and mortality rates were low (below the medians); Section B, regions where the revascularization rate was high (above the median) and the mortality rate was low; Section C, regions where the revascularization rate was low and the mortality rate was high; and Section D, regions where both rates were high. 

Despite a tendency for health regions with high revascularization rates to have lower mortality rates, this was not always the case (Table 1). In each year, about 20% of health regions had low revascularization rates and low mortality rates (Section A), and a similar percentage had high revascularization and high mortality rates (Section D). Moreover, during the eight-year period, health regions did not necessarily remain in the same Section—more than half of them were in a different Section in 2003/2004 than they had been in 1995/1996. 

Revascularization and mortality

Figure 1 brings together and juxtaposes the data on revascularization and mortality rates for each health region to illustrate the association (or lack thereof) between revascularization and mortality among acute myocardial infarction patients. Each point represents a health region: the open triangles pertain to 1995/1996, and the filled diamonds, to 2003/2004. The horizontal axis indicates the percentages of inpatient acute myocardial infarction cases that were treated by revascularization within 30 days; the vertical axis, the percentages who died within 30 days.

Figure 1
30-day revascularization and 30-day mortality rates of acute myocardial infraction patients, health regions with at least 100,000 population, seven provinces, 1995/1996 and 2003/2004

The dispersion of values in Figure 1 shows that high revascularization rates were not invariably associated with low mortality rates. For example, in 2003/2004, 11 health regions had high revascularization rates of 50% or more, yet mortality rates in these regions ranged from around 5% to more than 11%. On the other hand, for the same year, in 14 health regions, revascularization rates were relatively low at 30% or less, but mortality rates ranged from 7% to 13%.

Conclusion

Between 1995/1996 and 2003/2004, the overall 30-day revascularization rate among acute myocardial infarction patients in 46 of Canada’s largest health regions tripled, and the overall 30-day mortality rate decreased.

In principle, if revascularization was effective and beneficial, higher revascularization rates would be clearly and strongly correlated with lower mortality rates. However, the correlation within a single year was weak at best. In fact, the more recent 2003/2004 data show a weaker correlation between revascularization rates and mortality rates than do the 1995/1996 data. The weaker correlation in 2003/2004 may be due to diminishing returns, as there may be an upper limit to the percentage of patients who would benefit from revascularization.

The large variations in both procedure rates and survival rates across health regions may be associated with factors that could not be considered in the analysis because the relevant data were unavailable. There is clearly much more to treating heart attacks than revascularization. Geographical differences in a surgical procedure rate may reflect systematic variations in professional decision, diagnostic and practice styles, and in physicians’ training, experience and beliefs about the efficacy of a procedure. As well, hospital policies, practices and facilities may vary from region to region, as may the severity of heart attack cases. Clinical variables such as arrival time in hospital, use of secondary preventive medications^15, 16 and cardiac rehabilitation services¹⁷ may also differ. In addition, lifestyle factors can be important; for example, are heart attack patients in some regions more likely than those in other regions to be smokers, obese or sedentary?

No consensus has emerged in the literature as to what rate of revascularization is optimal for acute myocardial infarction patients. Greater use of the procedure in the United States^18-20 has not consistently been shown to improve mortality rates,^18, 19 although one study concluded that American patients survive longer than Canadian patients.²¹ As well, randomized trials such as TACTICS, FRISC and CADILLAC have demonstrated benefits of early revascularization,^22-26 and an excess of angina pectoris with resultant diminished quality of life has been reported for the lower Canadian surgery levels for acute myocardial infarction patients, compared with the United States.^19, 20

The results of this analysis suggest that research on the delivery of health care in Canada might focus on why wide geographical variations persist in the treatment and survival of heart attack patients. More data are required to extend the mortality follow-up beyond 30 days; to determine how much healthier patients are after the procedure; to identify other aspects of treatment and hospital characteristics that might influence the results; and to investigate patient risk factors such as obesity, physical fitness, smoking, hypertension, and blood lipid levels. Knowledge of the factors associated with the geographical differences could aid in the development of guidelines to help clinicians determine if a procedure, in this instance, revascularization, is likely to be beneficial. The analysis needs to be extended to enable us to tell the story of which factors—at the patient, care team, hospital or community level—are most important to health outcomes.