Comparing performance between coronary intervention centres requires detailed case-mix adjusted analysis

This study compares 12 month clinical outcomes and procedural costs at two interventional centres with significant differences in crude mortality and revascularization outcomes between 1997 and 1998. Percutaneous coronary intervention (PCI) registry data on 1046 consecutive patients treated contemporaneously at two university centres were linked to hospital discharge and death data to provide 12 month follow-up information on survival and repeat revascularization. Costs were determined by detailed analysis of equipment use, length of stay and staff from 100 contemporary cases at each centre to derive a procedural cost model. This model was then applied retrospectively to estimate cost per procedure. Stents were used more frequently at one centre (56 versus 26 per cent, chi(2) test, p < 0.001) resulting in greater procedural cost [mean (SE), pounds sterling 1970 (34) versus pounds sterling 1521 (39), t-test, p < 0.001). One year repeat target vessel PCI was significantly greater at the centre using more stents (10.3 versus 5.6 per cent, chi(2) test, p = 0.005) and the need for any repeat revascularization (PCI or coronary artery by-pass surgery) was also significantly greater at this centre (18.4 versus 10.8 per cent, chi(2) test, p < 0.001). Cox regression revealed that after correction for case-mix the difference in the need for repeat target vessel PCI between the two centres was no longer significant (p = 0.15). In the two centres studied, crude differences in cost per case, mortality and the need for revascularization were largely accounted for by significant differences in case-mix. Comparison of outcomes and costs between centres should not be published without careful adjustment for differences in case-mix.