Canto JG, Rogers WJ, Zhang Y, Roseman JM, French WJ, Gore JM, Chandra NC.
The association between the on-site availability of cardiac procedures and the utilization of those services for acute myocardial infarction by payer group. The National Registry of Myocardial Infarction 2 Investigators.
Clin Cardiol 1999;22(8):519-24.

The purpose of this study was to determine whether there is a relationship between the utilization of cardiac procedures (arteriography) and the onsite availability of those services for patients with acute myocardial infarction (AMI) and to examine the role of payer status (insurance type, including commercial/PPO, Medicare, Medicaid, and uninsured) in this relationship. “Black race” was included as a potential confounder of this hypothesized association.

Data for the study were drawn from the National Registry of Myocardial Infarction 2 (NRMI2), which is a multi-site, voluntary database designed to collect, analyze and report cross-sectional data on patients admitted with myocardial infarction at participating hospitals. The current study includes reports from 1,388 hospitals that enrolled 275,046 patients during the period from June 1994 to April 1996.

The study found that the likelihood of undergoing cardiac arteriography was significantly higher when patients were initially admitted to hospitals having onsite facilities (OR=1.69, 95% CI =1.66-1.73). This relationship was significant for each insurance type and was strongest among patients with commercial/PPO insurance (OR=2.19, 95% CI = 2.07-2.31). This relationship was also significant in each insurance group when the analysis was restricted to only the most severe patients (those with recurrent ischemia, recurrent infarction, Killip class III and IV, ejection fraction <40%, sustained ventricular tachycardia, or ventricular fibrillation). Finally, this association remained statistically significant after adjusting for demographic and clinical factors (OR=2.08, 95% CI = 2.02-2.15). Black race was significant in the multivariate analysis. Blacks were less likely to receive arteriography after adjusting for other demographic and clinical factors, including presence of a CATH lab (OR=0.68, 95% CI=0.65-0.72).

Two major limitations of this study are its design and its lack of follow-up data. With regard to the design, as the authors point out, the optimal approach would be to compare procedures and outcomes of patients who presented with AMI’s at hospitals with onsite coronary arteriography laboratories with patients presenting at hospitals without such laboratories. However, the data used in this study did not track patients after hospital transfer. The authors conservatively assumed that all patients who were admitted for AMI and then transferred out eventually received coronary arteriography. The bias in making this assumption would be to underestimate the impact of presence of facility type. However, it is difficult to know for certain how this would influence the effect of race, as the distribution of transfers between blacks and whites was not reported.

With regard to follow-up data, it would be important to replicate this analysis using a longitudinal design in which patients’ presented following their first AMI. Furthermore, it will be important to follow patients over time to determine whether these tests lead to needed procedures and better clinical outcomes.