Results

Over the three year period 36 838 patients were admitted to hospital with a diagnosis of AMI. Of these, 21 925 (60%) were male and 14 913 (40%) were female. Their median age was 68 years and 20% belonged to the lowest two deprivation categories. Overall, 4831 (13%) underwent angiography within two years, 587 (2%) underwent PTCA, and 1825 (5%) CABG.

On univariate analysis, there were significant trends across the age groups for the use of both angiography and revascularisation procedures (χ² for trend, p < 0.0001), with older patients undergoing lower rates of all interventions (table 1). Similarly, women had significantly lower rates of all three modalities (χ², p < 0.0001) (table 1). However, age and sex themselves were related, with women tending to be admitted at an older age than men. Stratification by age produced more comparable rates between the sexes (table 2). There were no significant univariate associations between deprivation category and any of the procedures (table 1).

Variations were demonstrated between health board area of residence (table 1). There was a twofold variation in the crude percentages of AMI patients progressing to angiography and CABG (p < 0.001), and a threefold difference in those undergoing PTCA (p < 0.001).

On multiple logistic regression analysis women were significantly less likely to undergo angiography (p < 0.001) and CABG (p < 0.001) but more likely to undergo PTCA (p < 0.05) (table 3). Older patients were less likely to undergo all three interventions (p < 0.001). Unlike on univariate analysis, socioeconomic deprivation was associated with a reduced likelihood of both angiography and CABG (p < 0.001) but not PTCA. There were significant geographical variations in all three modalities (p < 0.001) (fig 1).

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Figure 1

Age, sex, and deprivation category standardised percentages of admissions for AMI which were followed by angiography, PTCA, or CABG within two years by health board area of residence. For names of health boards see table 1.

Discussion

Variations in crude population procedure rates can be difficult to interpret since they may be justified if associated with variations in incidence, risk, or benefit. The incidence of CHD is known to vary by age, sex, area of residence, and deprivation level. Therefore, comparisons within these categories must take account of incidence.

A number of studies have attempted to overcome this problem by using CHD mortality rates as a proxy measure of incidence, and comparing variations in procedure rates with variations in mortality rates. However, CHD mortality rates include patients dying outside hospital for whom coding of the cause of death is likely to be less accurate. Furthermore, mortality is a proxy measure of the community incidence of CHD rather than the hospital incidence. The latter is dependent not only on community incidence but also referral patterns, and it would be inappropriate to hold hospital physicians accountable for the management of those patients who are not known to them.

Therefore, new patients referred to hospital with definite CHD may be a more appropriate denominator for comparing hospital practice. In this study, this was further refined to AMI admissions because of the lack of consistency in applying other CHD codes, and the fact that elective admissions reflect referral thresholds and waiting times as much as they do incidence. A minority of AMI patients have normal coronary arteries but such patients would also be included if a clinical history of angina or a positive exercise test were used to identify CHD patients.

The results of this study provide evidence that the variations in provision of cardiac investigations and treatments across Scotland cannot be fully explained by variations in need. Compared with other countries, primary PTCA is a relatively uncommon procedure in all Scottish hospitals. Therefore the variations observed relate primarily to the management of patients with chronic stable angina and unstable angina.

Older CHD patients were demonstrated to be significantly less likely to be both investigated and treated after adjustment for sex, socioeconomic status, and area of residence. This supports the findings of previous studies.17 This may reflect a belief that revascularisation procedures pose a greater risk in these patients or that their benefit is reduced. A number of studies have demonstrated higher early mortality rates following revascu larisation,18-20 although these findings are not unanimous.21 Older patients can nonetheless gain significant symptomatic benefit from revascularisation.18 ,22

On univariate analysis women were significantly less likely to be investigated than men. However, there was a clear association between sex and age with the peak number of women admitted for AMI occurring 10 years after that in men, and age stratified procedures rates were relatively comparable between the sexes. Nonetheless, adjustment for age, deprivation, and area of residence in the multivariate analysis revealed a significant independent association between sex and access to angiography and CABG. Other studies have similarly demonstrated lower rates of angiography and revascularisation in women,6-9 even at comparable levels of morbidity.23 Lower CABG rates in women with CHD may be justified by their lower rate of severe stenoses,8 the fact that they have relatively low rates of CHD mortality compared with angina,24 and their higher use of PTCA. However, lower angiography rates are more difficult to explain in light of women tending to have more severe symptoms and greater functional disability than men.6

As with other studies,10-13 ,25 socioeconomic deprivation was demonstrated to be associated with reduced access to angiography and CABG. The lack of a significant association with PTCA is likely to reflect the smaller numbers of patients undergoing this procedure, since the odds ratios nonetheless showed a clear trend across deprivation categories.

Significant geographical variations were demonstrated for all three modalities. Previous studies have also demonstrated geographical variations which cannot be explained by need.9-11 ,26These differences can, in part, be attributed to ease of access, with patients resident close to facilities most likely to be referred to them.9-11

Because PTCA and CABG are both preceded by angiography, variations in angiography tend to perpetuate as variations in revascularisation.5-8 Therefore, access to angiography needs to be addressed before variations in revascularisation can be reduced.

Variations in practice can reflect both unnecessary interventions and unmet need. Studies from England and the USA have suggested that 25–50% of angiograms may be inappropriate.27 ,28However, the much higher prevalence of CHD in Scotland means that a comparable level of over provision is unlikely to be the case. In light of Scotland having one of the highest rates of CHD deaths in the world,29 ,30 it is likely that much of the demonstrated variation in practice reflects unmet need in some areas.