Does the Presence of an On-site Cardiac Catheterization Facility in a Hospital Alter the Long-term Outcome of Patients Admitted With Acute Myocardial Infarction?
In this issue of Circulation, Every et al1 present an analysis of a longer follow-up to their 1993 analysis2 of a registry of patients admitted to 19 hospitals in the Seattle, Wash area for acute myocardial infarction between 1988 and 1994.
As the authors reported in 1993, patients admitted to any of 10 hospitals with on-site cardiac catheterization facilities were more likely to undergo coronary angiography than those admitted to 9 hospitals without such facilities. Transfer for coronary arteriography was quickly and readily accomplished in Seattle. As a result, coronary arteriography was performed in 67% of 7984 patients admitted to hospitals with cardiac catheterization laboratories and in 39% of 4219 patients admitted to hospitals without such laboratories.
Acute reperfusion therapy was performed in 33.9% of patients admitted to hospitals with cardiac catheterization laboratories but in only 23.3% of patients admitted to hospitals without cardiac catheterization laboratories. Unfortunately, it is not possible to determine how many patients were treated by thrombolysis, direct angioplasty, surgery, or more than one technique.
In the present report, the authors conclude that the more conservative approach was not associated with any observed increase in mortality during the period of follow-up, which averaged 2.3 years (maximum follow-up, 6 years). It is of interest, however, that if one considers the subgroup of 4412 patients who presented with ST-segment elevation and who represented only 35.8% of the 12 330 patients, the hospital mortality rate was significantly lower (6.8%) for 3007 patients admitted to hospitals with cardiac catheterization laboratories than for 1405 such patients admitted to hospitals without catheterization laboratories (8.8%). The authors found, however, that after adjustment for baseline characteristics, there was no association between admission to hospitals with on-site catheterization laboratories and hospital mortality. Of interest, the 3-year mortality rate for patients with ST-segment elevation originally admitted to hospitals with cardiac catheterization laboratories was 18.5% versus 23.0% for patients admitted to hospitals without such facilities.
In a subgroup analysis of high-risk patients admitted to hospitals without on-site cardiac catheterization facilities, 24% were transferred during the index admission, and after multivariate adjustments, there was no difference in 3-year mortality rates between patients initially admitted to hospitals with or without on-site cardiac catheterization laboratories.
Because this report is based on registry data, the conclusions that can be made are very limited. The data were derived from patients treated in a nonrandomized manner and were incomplete, primarily due to a lack of sufficient funding for more complete data collection. The data are further limited by crossover, the Achilles’ heel of many clinical trials. In this report, crossover is represented by the 39.2% of patients who were admitted to hospitals without on-site cardiac catheterization laboratories but who had coronary arteriography performed and by the 30% of patients admitted to such hospitals who were transferred to hospitals with on-site cardiac catheterization laboratories.
As one might expect with registry data, many important patient characteristics were apparently not available for analysis, including the following: the time interval between the onset of chest discomfort and the arrival of the patient at the hospital, the criteria used by the patient or paramedics to select different hospitals, the number of patients with a contraindication to thrombolytic therapy, the criteria used to select patients for coronary arteriography, the exact criteria used for the diagnosis of acute myocardial infarction at each institution, and whether or not all the hospitals with on-site cardiac catheterization laboratories had these laboratories staffed 24 hours a day by physicians qualified in coronary angioplasty. It would also be of interest to know the medical qualifications of the physicians who assumed primary responsibility for each patient.
Although the authors adjusted for a number of factors that can influence long-term mortality after acute myocardial infarction, numerous other factors can influence this mortality. Among these are the use of aspirin, lipid-lowering drugs, β-blockers, ACE inhibitor drugs, and tobacco.
As the authors acknowledge, the conclusions of the present report are limited by the lack of randomization, potential problems introduced by unknown patient selection bias, unmeasured patient factors, patient crossover, and the short follow-up period. In addition, the data are from a geographic area with very short transfer times between hospitals and may not be generalizable to other hospitals that lack on-site cardiac catheterization facilities.
In conclusion, it would appear that in an area of the United States with prompt and readily accomplished transfer of patients between hospitals, there appeared to be a greater use of procedures in patients who were originally admitted to a hospital with on-site cardiac catheterization facilities than in patients who were originally admitted to a hospital without such facilities. It was not possible to document a decrease in hospital or 3-year mortality rates with the increased use of procedures. Unfortunately, the data are from a registry, and therefore only limited conclusions can be made. As with many clinical studies, the most important conclusion is that further studies are needed.
The opinions expressed in this editorial are not necessarily those of the editors or of the American Heart Association.
- Copyright © 1997 by American Heart Association
Every NR, Parsons LS, Finn SD, Larson EB, Maynard C, Hallstrom AP, Martin JS, Weaver WD, for the MITI Investigators. Long-term outcome in acute myocardial infarction patients admitted to hospitals with and without on-site cardiac catheterization facilities. Circulation. 1997;96:1770-1775.
Every NR, Larson EB, Litwin PE, Maynard C, Fihn SD, Eisenberg MS, Hallstrom AP, Martin JS, Weaver WD, for the Myocardial Infarction Triage and Intervention Project Investigators. The association between on-site cardiac catheterization facilities and the use of coronary angiography after acute myocardial infarction. N Engl J Med. 1993;329:546-551.