Volume of coronary angioplasty procedures and mortality rates

To the Editor: The article by Jollis et al. (Dec. 15 issue)¹ concerning the relation between the annual volume of percutaneous transluminal coronary angioplasty (PTCA) procedures and mortality is incomplete and misleading. Data on Medicare admissions for PTCA from October 1991 through June 1994 in New Hampshire suggest that Jollis et al. disregarded robust risk factors that explain most of the variation in outcome attributed to hospital volume. Consequently, the findings are systematically biased against hospitals that perform fewer procedures. Key unexamined claims data include the type of admission, whether the surgery was elective or nonelective, and the risk associated.