Coronary revascularisation: why do rates vary geographically in the UK?

OBJECTIVE To explain the reasons for geographical variation in the use of coronary revascularisation in the United Kingdom. DESIGN This was a cross sectional ecological study. SETTING NHS and independent hospitals performing coronary revascularisation for the 11.6 million residents of the south east Thames, East Anglian and north western health regions in England plus Greater Glasgow, Lanarkshire, Ayr and Arran health boards in Scotland were included. SUBJECTS All residents aged > or = 25 years in 1992-93 who underwent coronary artery bypass grafting (CABG) or percutaneous transluminal coronary angioplasty (PTCA) in either the public or private sector were included. MAIN MEASURES Crude and age-sex standardised intervention rates for residents of the 42 constituent districts and boards were determined. Variation was measured using the systematic component of variation. RESULTS Considerable systematic variations in district rates of CABG and PTCA existed. These variations mostly arose from differences in supply factors. Higher rate districts were characterised by being close to a regional revascularisation centre and having a local cardiologist. Demand factors such as the level of need in the population (measured by coronary heart disease mortality) and the lack of use of alternative treatments not only failed to explain the observed variation but were inversely associated with the rate of intervention--an example of the inverse care law. The finding that the residents of more socially deprived districts experienced higher intervention rates was probably subject to confounding due to their close proximity to specialist centres. CONCLUSIONS If greater geographical equity of use for the same level of need is to be achieved, attention must be paid to the supply factors that determine levels of utilisation. As responsibility for purchasing these procedures is decentralised, utilisation might become even more unequal.