This study was based on nationwide register data that included all CHD patients who underwent coronary revascularisation. It examined hospital treatment pathways leading to the operation in Finland between 1998 and 2007. More specifically, we examined the treatment pathways among CHD patients with diabetes during a period that saw a large increase in revascularisation operations. Overall, treatment practices changed substantially during the study period to favour performing revascularisation operations during the first hospital admission, whether it was an emergency admission or not. This was true for both men and women and for patients with and without diabetes. The large increase in PCIs is likely to be an important factor behind these changes, as it is likely that CABG will be more often planned for a subsequent hospitalisation than PCI.
However, patients with diabetes admitted to coronary revascularisation received relatively fewer operations in the first CHD hospital admission compared to their counterparts without diabetes. The differences remained rather stable during the whole study period. While suboptimal treatment pathways decreased substantially during the study period, pathways including two or more emergency admissions were still more common among patients with diabetes at the end of the study period. One explanation might be that health services provide a lower threshold for CHD admission among patients with diabetes. The average number of hospitalisations due to CHD was higher among patients with diabetes. However, distributions of categories for CHD hospitalisations were similar in both patient groups. Of all CHD admissions of men and women with and without diabetes, a quarter were due to MI, which was obviously diagnosed by the same criteria for all patients, that is using a blood test (troponin-T) with high sensitivity and specificity. In Finnish hospitals this test was introduced in 1997-2000 . Other emergency CHD admissions comprised a quarter of men's and a third of women's admissions among both diabetic and non-diabetic patients. Therefore we consider that it is unlikely that health services provide a substantially different threshold for CHD admissions for diabetic patients compared to non-diabetic patients. Neither do these differences in suboptimal treatment pathways seem to be solely due to a different case-mix among patients with and without diabetes, since taking into account differential comorbidity between the patient groups did not eliminate the differences. We also adjusted for the type of revascularisation in our models, and that did not explain the differences. Adjustment for region using conditional logistic regression assured that confounding due to cluster effects was adequately controlled.
We made further sensitivity analyses by adjusting for the MI during the two years period preceding the operation. These analyses revealed that persons with MI had clearly higher odds to undergo revascularisation at their first hospitalisation, and slightly higher odds for the suboptimal pathways leading to CABG. The differences between patients with and without diabetes, however, remained the same or slightly increased after adjustment for MI. The interpretations of the results did not change, but these sensitivity analyses suggest that our findings were rather conservative.
Adjusting for changes in the characteristics of the patient population over time, we modelled specific time periods at the beginning and end of study, comparing at both time points the non-diabetic patients to those with IDD or NIDD. Possible changes in the patient population included an increase in the number of patients with diabetes , a shift in CHD incidence towards elderly persons, an increased number of revascularisations, and a more precise technology used in determining the need for revascularisation.
The ten-year study period allowed us to examine changes in treatment practices among both diabetic and non-diabetic patient groups. Since the data cover all public and private hospitals, we were able to examine the total population of patients undergoing a coronary revascularisation operation during the study period.
The quality and coverage of the Finnish Hospital Discharge Register has been reported to be generally good and particularly good among patients with MI [16, 17]. Information on chronic diseases was also obtained from two other registers: a register on the reimbursement of prescriptive medicine costs and a register on persons eligible for elevated mandatory health insurance reimbursement of drug costs. Since the prescription register is an administrative register based on actual reimbursements of medicine costs, its coverage is likely to be very high. Eligibility for an elevated level of reimbursement requires a doctor's certificate confirming that the criteria set by the Social Insurance Institution are met, with the certificate reviewed by a medical specialist at the Social Insurance Institution. The use of all three registers allowed for a reliable identification of chronic diseases.
When interpreting the results, it is important to bear in mind that the study population is a retrospective cohort of hospitalized CHD patients who underwent a coronary revascularisation operation. Our study cannot therefore estimate whether access to revascularisation is inequitable among persons with diabetes compared with other coronary patients. An earlier study from Finland does suggest that diabetes decreases the likelihood of coronary revascularisation . Additionally, the diabetes population has clearly higher mortality compared to others [19, 20]. Based on our data, we cannot estimate the proportion of those in need of revascularisation, who died before the operation, or who were not revascularised in spite of a need. The issue of equitable access to revascularisation among patients with and without diabetes is complex, and there is an ongoing discussion on whether an initial strategy of revascularisation, or a conservative approach with drugs is most effective for coronary patients with diabetes .
Earlier studies have mainly examined differences in access to revascularisation instead of pathways to it and to our knowledge similar studies are scarce. A cohort study of MI patients admitted to Californian hospitals found both ethnic and payer group differences in treatment pathways; uninsured and minority patients were less likely to have treatment pathways leading to revascularisation. They were less likely to receive the operation at the first admission, to be transferred to a hospital offering revascularisation or to be readmitted to undergo revascularisation . Other retrospective studies of selection to health care in CHD (revascularisation and cardiac rehabilitation) suggest there are barriers in treatment pathways among older patients, women and lower socioeconomic groups [23–25].
Our retrospective study design enabled us to examine treatment pathways leading to revascularisation in different patient groups in terms of hospital care. Earlier research has reported socioeconomic differences in access to revascularisation among coronary patients in general as well as patients with diabetes [7, 18, 26, 27]. Further research is needed on the potential socioeconomic differences in pathways to operations among patients with diabetes.
Differences between patient groups in the revascularisations performed in the first treatment period may partly echo delays in clinical decision-making on referral for revascularisation. Due to complicating conditions requiring medical attention, diabetic CHD patients and especially patients with IDD may experience these delays more often than CHD patients without diabetes. The registers used in this study lack information on these clinical details. However, allowing for delays in decision-making, suboptimal treatment pathways should not be more common among patients with diabetes. Moreover, the differences in operations at the first CHD admission as well as in suboptimal pathways remained even after adjusting for observable comorbidities. In conclusion, our results suggest that the differences in the risk of suboptimal treatment pathways may partly be explained by treatment practices that are not in accordance with the evidence-based treatment guidelines that suggest that the benefits of revascularisation are similar in both patients groups.