Improving Survival When Cardiogenic Shock Complicates Acute MI

Abstract & Commentary

By David J. Pierson, MD, Editor, Director of Pulmonary and Critical Care Medicine, Harborview Medical Center, University of Washington, Seattle, is Editor for Critical Care Alert

Synopsis: This prospective 10-year study of 7356 patients with ST-elevation MI who presented in cardiogenic shock showed once again that early mechanical revascularization (as recommended by current guidelines) substantially increases survival; it also suggests that adherence to the guidelines needs to be further improved.

Source: Babaev A, et al. Trends in management and outcomes of patients with acute myocardial infarction complicated by cardiogenic shock. JAMA. 2005;294:448-454.

Based on the results of studies showing that early mechanical revascularization substantially reduces mortality among patients with acute myocardial infarction (AMI) complicated by cardiogenic shock, the American College of Cardiology and American Heart Association classified this intervention as a class I recommendation in their 1999 guidelines.1 In this study, Babaev and colleagues used the prospectively acquired database of the National Registry of Myocardial Infarction to determine trends in the early use of early mechanical revascularization—percutaneous coronary intervention (PCI) and coronary artery bypass grafting (CABG) surgery—in the participating hospitals from 1995 through 2004. Of 293,633 patients treated in the participating hospitals for ST-elevation AMI during the study period, 25,311 (8.6%) had cardiogenic shock. Babaev et al examined the use of PCI and CABG in relation to outcomes in the 7356 (29%) in the latter group who had cardiogenic shock on initial presentation.

During the 10-year observation period, the rate of cardiac catheterization in this patient population increased from 51.5% to 74.4%. There were concomitant increases in the rate of primary PCI from 27.4% to 54.4%, and of total PCI from 34.3% to 64.1%, during this time. Overall CABG surgery rates decreased from 11.5% to 8.8%; the change in the rate of immediate CABG surgery from 2.1% to 3.2% was not significant. Overall in-hospital mortality fell from 60.3% in 1995 to 47.9% in 2004 (P < 0.001), paralleling the rise in revascularization rates. Multivariable analysis of mortality adjusted for patient demographics, medical history, clinical presentation, hospital characteristics, year of discharge, and procedures performed showed PCI to remain strongly and independently associated with a lower mortality rate (adjusted odds ratio, 0.46; 95% CI, 0.40-0.53). Among the 7356 patients with cardiogenic shock at presentation, 238 (3.2%) died prior to the median door-to-PCI time without having received PCI.

Commentary

This large observational study of patients with AMI shows that the rate of cardiogenic shock has remained relatively constant, but also that there has been a substantial decrease in mortality in patients with this complication. It further shows that this improvement in outcome is strongly and independently correlated with concomitant increases in early mechanical revascularization—specifically, in the rate of primary PCI. Somewhat surprisingly, it does not show a parallel increase in the use of early CABG surgery, as might have been expected.

These findings strongly reinforce the message of the evidence-based ACC/AHA guidelines, and emphasize the importance of awareness and implementation of the latter. A doubling of the rate of primary PCI (from 27% to 54%) during the 10-year period of this study is encouraging. However, the fact that at the end of the study only about three-fourths of potentially eligible patients were undergoing cardiac catheterization, and only slightly more than half of them were receiving primary PCI, suggests that we still have a lot of work to do if current evidence is to be used to the maximum benefit of our patients.

Reference

1. Ryan TJ, et al. 1999 update: ACC/AHA guidelines for the management of patients with acute myocardial infarction. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Management of Acute Myocardial Infarction). J Am Coll Cardiol. 1999;34:890-911.