In Canada, cardiovascular events represent a major health burden similar to what is observed in other developed countries. Myocardial infarction (MI) accounts for a large percentage of these events 1. Although practice guidelines regarding MI management have been widely published 23, regional disparities in managed cares and outcomes are still observed in Canada 456789101112131415, as well as in other countries 1617181920212223.

Early percutaneous transluminal coronary angioplasty (PTCA) has been given much greater priority in recent years 3. According to Health Canada, the number of PTCA done in Canada increased of 36% between 1994/95 and 2000/01 24. Moreover, patients suffering from a MI, who received an invasive cardiac procedure such as coronary angiography or revascularization during the first hospitalization, were less likely to be readmitted later for cardiac reasons 25. Invasive cardiac procedures require technical facilities and a professional expertise available only in specialized cardiology centers, logically privileging people living closer. In fact, both the availability of these services in the hospital initially admitting the patient and the geographical proximity to these services are factors determining their use 526. Thus patients from rural areas are disadvantaged as they are less likely to get a diagnostic and cardiac procedures 27, or must wait longer to access these procedures 28.

To our knowledge, only few studies have been published reporting results on the gap in revascularization rates according to the distance of patient's location and specialized cardiology centers (SCC). Amongst these, Scott et al 29 analyzed access to potential intravenous thrombolysis for stroke using crow-flight distances of 32, 64 and 105 km around Canadian hospitals. Vanasse et al 4 studied management and outcomes of acute coronary syndrome stratified by distance to SCC. This latter study showed that distances to SCC have an impact on the likelihood of receiving an invasive cardiac procedure at index hospitalization for patients suffering from an acute coronary syndrome. However, no one has studied the evolution of the gap over a one year period.

We hypothesize that MI patients living within a short distance from SCC will have a greater proportion of revascularization procedures compared to patients living farther, and that the gap will decrease with time, as patients living farther will have access to SCC on an elective basis in the year following their first hospitalization.

The aim of this paper is to test if the early gap observed in the revascularization rates according to distance between the patients' location and the closest SCC remains on a long term basis. The first objective of this study is to describe and compare the revascularization rates (PTCA or coronary artery bypass graft (CABG)) of patients with MI, according to distance categories (<32 km, 32–64 km, 64–105 km and ≥105 km). The second objective is to measure the evolution of the gap between groups over time (3, 6, 9, and 12 months).

A total of 12,646 individuals were hospitalized for MI in Quebec between January 1^st 1999 and December 31^th 1999. Of those, some patients were excluded: 9 because they were less than 25 years old, 289 because they had a MI the year prior to index hospitalization, 544 because they were living in the sparsely populated northern region or in the Outaouais region, and 2 because there was an error in their code of residence. Therefore, the study population totalled 11,802 individuals, of which 66% (n = 7733) were men. The average age was 66.5 years (± 13.8). The one-year incidence rate was 244 individuals per 100,000 inhabitants.

The age and sex adjusted revascularization rates differed significantly (p < 0.0001) amongst groups and over time (Figure 1), varying from 20.1% to 28.2% at index hospitalization and from 30.3% to 36.5% one year after. Higher rates of revascularization are found in the patients' group closer to a SCC at all points in time. At index hospitalization, statistically significant gaps can be observed between the patients' group living close to a SCC (<32 km) and the other groups (p < 0.0001). During the first year, a reduction of the gap can be found but only for patients living at an intermediate distance from the specialized center (64–105 km). In fact, the gap in revascularization rates between patients living at less than 32 km and those living between 64 and 105 km from a SCC is not statistically significant after 3 months (p = 0.4812), but significant differences can be observed for the two other patients' groups (p < .0001), creating a halo pattern of low revascularization rates by patients living between 32 and 64 km from a SCC. This halo pattern is more easily demonstrated with the cartographic representations in Figure 2 and Figure 3.

Revascularization rates in the province of Quebec in 1999, as found in this study, are similar to others previously presented in Quebec 12. The results showed above support the first part of our hypothesis. In fact, the gap in the revascularization rates between the four groups of patients at index hospitalization benefits patients living at less than 32 km from a SCC. A frequent explanation put forward in the literature to account for use of invasive cardiac procedures is accessibility to facilities performing such procedures 37.

The negative relationship between revascularization rates and distance to specialized centers has also been noticed in different countries 16202123 including Canada 571113. However the second part of our hypothesis is found to be partly true. Indeed, we can observe a complete closure of the gap for one of the groups living farther but the two others remain unchanged at one year. In fact, only the patients' group living within intermediate distances (64–105 km) to a SCC will close the gap over time. Strangely enough, the patients' group living between 32 and 64 km will experience the same lasting gap than the group of patient living farther than 105 km. This result cannot be attributed to a demographic difference between the four groups as age and sex adjusted rates have been presented. To our knowledge, it is the first time that the halo pattern revealed by the map has been described. Therefore, more comprehensive studies to fully understand this phenomenon are needed.

Piché et al argued that the relation between distance and access to care varies with the medical situation (severity, urgency, etc.) 3839. If we can logically hypothesize that patients in the 64–105 km radius of location may be easily transferred by their local physicians for non urgent revascularization than the patients living farther, no evident explanation can be offered for patients living in the 32–64 km radius.

In order to reduce bias in the comparison of each group, death rates were also measured at each point in time and were found to be not statistically different at the index hospitalization (p = 0.2628) and at one year (p = 0.1659) (data not presented). Bias can also result from an underestimation of deaths at index hospitalization in groups living farther and may possibly explain some of the differences. In fact, sicker people living in remote regions possibly die before even being admitted to the hospital. Increase in the time between onsets of symptoms to treatment (onset-to-door) has previously been reported in rural regions 40.

To better understand geographical disparities in healthcare management, more comprehensive exploration of socio-demographic variables' contribution is needed. Rurality is one of these variables that seems important to consider 41. Indeed, rural populations differ from urban ones not only in geographical access to care 42 but also by their cultural and socioeconomic backgrounds. Other possible variables that can explain heterogeneity in MI management include social and material deprivation indices 43, medical care and professional attributes including academic affiliation and year of graduation for family physicians and cardiologists 15.

The use of administrative data has some limitations. Even though Quebec's hospital discharge register has been used for epidemiological studies on acute myocardial infarction 3031, the follow-up of the hospital's care episode spread out over different care institutions requires an algorithm for which the accuracy needs to be further validated. Another limitation to take into account is the use of the crow-flight distance as estimated traveling time between the place of living and the care center 4445. The use of this proxy may not be valid for all regions in the province.

According to distance categories, significant gaps were observed in revascularization rates after a MI at index hospitalization. The gaps remained significant during the first year after a MI, except for patients living at an intermediate distance (64–105 km) from the cardiology center. This halo pattern can be easily noticed on a thematic map.

This project has benefited from an unrestricted grant by Merck Frosst Canada Ltd.

AV, TN conceived the study, JC and TN performed the analyses. AV, TN and JC wrote the manuscript and AH produced the maps. All authors read and approved the final version of the manuscript.