Evolution of the Volume-Outcome Relation for Hospitals Performing Coronary Angioplasty

Abstract

Background —Hospitals performing more surgical procedures tend to yield better outcomes. This study examines the evolution of this volume-outcome relation over time. Methods and Results —The relation between the number of percutaneous transluminal coronary angioplasty (PTCA) procedures performed at hospitals (volume) and in-hospital bypass surgery and death for 353 488 patients treated in California between 1984 and 1996 was examined. Descriptive statistics and logistic regression were used to compare outcomes for 3 periods: 1984 to 1987, 1988 to 1992, and 1993 to 1996. The in-hospital mortality rate was 2.5% for hospitals performing <200 PTCA procedures per year but only 1.3% for hospitals performing >400 procedures per year in 1984 to 1987. By 1993 to 1996, mortality rates in these 2 volume categories narrowed to 1.7% and 1.3%, respectively. Bypass surgery rates also narrowed and fell in low-volume (<200 procedures) versus high-volume (>400 procedures) hospitals from 12.4% versus 6.9% in 1984 to 1987 to 4.6% versus 3.3% in 1993 to 1996. In a logistic regression, PTCA procedures significantly predicted in-hospital mortality and bypass surgery rates in all 3 time periods. However, coefficient estimates indicate that improvements over time in outcomes for hospitals performing <200 procedures were comparable to the predicted benefits of increasing volume above 400 procedures within time periods. Conclusions —Over time, the disparity in outcomes between low- and high-volume hospitals has narrowed, and outcomes have improved significantly for all hospitals. Given these improvements, lower minimum volume standards may be advisable in less populated areas, where the alternative is no angioplasty at all.