Our study found that while increases in overall capacity for coronary angiography did result in significant increases for most patients hospitalised with AMI in Ontario, physicians referred some patient subgroups disproportionately. Specifically, referral rates for post-MI angiography have risen most predominantly among the elderly, the more affluent, and those being managed by cardiologists as compared with non-cardiology attending physicians. In contrast, increases in utilisation rates of coronary angiography were similar among men and women and among patients admitted to centres with or without onsite revascularisation facilities. Intergroup differences in one year mortality have progressively narrowed between indices of risk and levels of socioeconomic status, have widened between attending cardiology and non-cardiology specialties, and have remained unchanged between age categories, sex, and hospital subgroups.
Our findings are consistent with previously published data showing more aggressive invasive cardiac procedural utilisation rates among elderly patients over time.3,4
Despite the significant temporal relation between angiography use and age, sex specific differences were inconsistent and did not vary significantly over time. While women were less likely to undergo angiography after an AMI in the early 1990s, sex gaps narrowed during the mid 1990s, only to widen again towards the end of the decade. Given that women are generally older than men at AMI presentation,33
such inconsistent findings may not be surprising, since any potential sex related temporal differences may have been overshadowed by the temporal increases in angiography use among the elderly.
Our results are also consistent with studies showing persistent inequities in socioeconomic related access to medical care despite increasing funding and supply.34,35
The finding that socioeconomic related disparities in the utilisation of post-MI coronary angiography widened with time may suggest that physicians preferentially select more affluent patients for discretionary procedures when faced with increasing supply or capacity. Indeed, one recent study found that socioeconomic disparities decreased with increasing angiography supply when funding was allocated based on models that accounted for markers of medical need.36
While it is possible that the phenomenon of supply induced preferential access observed in our study was confined to those with lower levels of clinical urgency or necessity,21
our findings may suggest that increases in supply alone may perpetuate rather than eliminate access inequities to specialised cardiac services when resources are implicitly rather than explicitly managed. Thus, we believe that our findings support the need for reform initiatives that refine the methods by which patients are selected and referred for coronary angiography in Ontario. Indeed, such initiatives may include the earmarking of funds to specific sociodemographic or clinical subgroups.
Physicians may utilise increasing supply differently across specialties. In our study, cardiologists became increasingly more aggressive in referring patients for coronary angiography compared with non-cardiologists. Moreover, this physician specialty effect may explain why angiography rates rose similarly at hospitals with and without onsite revascularisation facilities, given exponential increases in the number of cardiologists practising at community based hospitals with no onsite revascularisation facilities throughout the decade. Many studies have illustrated that cardiologists have become increasingly more aggressive in referring patients for catheter based interventions over time.3,4
Non-cardiologists may be less aware of recent studies favouring aggressive interventional approaches in patients after an AMI or they may be less capable of influencing angiography rates. This in part may relate to perceived differences in the efficacy of newer adjunctive technologies used in combination with catheter based interventions,37
given that recent evidence suggests that variations in the use of established evidence based treatments may be diminishing with time.2
Intergroup differences in coronary angiography did not correlate ecologically with variations in mortality over time, supporting the observations of other population based studies illustrating that the two outcomes are independent of one another.4,38
Indeed, for socioeconomic status the relation between angiography trends and mortality trends were discordant. For example, despite relative increases in angiography use among the most affluent, mortality rates declined more dramatically among the poor. Nonetheless, coronary angiography may be serving as a proxy for other evidence based treatments whose trends are also changing disproportionately in some subgroups relative to others.4
For example, age differences seen in the use of thrombolytic agents and angiography were also seen in the use of β blockers and calcium channel blockers in a cohort of elderly AMI patients in a Medicare database.4
Moreover, it is unknown whether variations in access to angiography account for differences in softer outcomes such as quality of life within subgroups.39
There are two important limitations in our study. Firstly is the use of linked administrative data, which limited our ability to characterise the patients in our cohort, either in regard to their own baseline health status or in regard to the specific nature of the care they received during the index hospitalisation or in follow up. In particular, we were unable to assess whether trends and variation in the use of cardiac procedures over time were appropriate or inappropriate. Nonetheless, we did control for many important prognostic variables, such as age, sex, presence or absence of coexisting conditions, and the presence or absence of complications, such as cardiogenic shock, at the time of the index admission. Secondly, we incorporated ecological rather than individual level markers of socioeconomic status. It is unknown whether such access disparities would have persisted had we used individual socioeconomic indicators. Nonetheless, these limitations must be traded off against the comprehensiveness of our sample, which itself is highly representative of the Canadian population.
Our findings suggest that, despite universal health care, not all types of patients have benefitted equally from increases in overall service capacity for coronary angiography. Further study is required to discern whether increased supply will decrease previously noted biases in the absence of formal policies directed towards certain disadvantaged groups. It will also be important to determine who would be most likely to benefit from increases in supply. Wider implementation of data monitoring and explicit management systems may be required to ensure that appropriate utilisation of specialised cardiac services is allocated to patients who are most in medical need.