Despite relative scarce evidence to support their use, intra-aortic balloon pumps (IABPs) have received high-grade recommendations in both U.S. and European guidelines for use in the management of cardiogenic shock. In the October issue of The New England Journal of Medicine, Holger Thiele, MD, and the IABP-SHOCK II trial investigators conducted a controlled study to whether IABP counterpulsation is associated with improved survival for patients with acute myocardial infarction (AMI) and cardiogenic shock.
The IABP-SHOCK II trial was a prospective, multicenter, randomized trial conducted over a three-yr period at 37 centers in Germany. AMI patients were considered to be in cardiogenic shock if a systolic blood pressure of 90 mm Hg was observed for more than 30 minutes, with other signs of shock or need for catecholamine infusion. Patients were randomized to the IABP vs. no IABP in a 1:1 ratio. Randomization was performed centrally, all patients were accounted for in an intention-to-treat analysis, and clinical outcomes assessors were blinded to group assignments. There were no significant differences between the groups in terms of baseline characteristics, nor clinical course before randomization. Patients who crossed over from the control group to the IABP group were excluded. The major outcome of interest was 30-day, all-cause mortality; additional secondary endpoints were established a priori.
Three hundred patients were included in the IABP group and 298 in the control group. At 30 days, no statistically significant difference in relative risk for death was found between the groups (relative risk [RR] of death with IABP, 0.96; 95% confidence interval [CI], 0.79-1.17; p=0.69). There were no significant differences in secondary endpoints (i.e., lactate, C-reactive protein levels, renal function, Simplified Acute Physiology Score II). In a multivariate analysis, the relative risk remained non-significant for the primary endpoint of death. The authors concluded that IABP counterpulsation did not reduce 30-day mortality in patients with AMI and cardiogenic shock.
AMI complicated by cardiogenic shock has a disturbingly high (40%) attendant mortality. This randomized controlled study was appropriately powered and rigorously conducted; however, the results may not be generalizable to all populations. For example, the procedure used for revascularization was primary percutaneous coronary interventionin over 95% of all patients. In other countries, immediate bypass surgery may be more commonly performed. In the group aged <50, the IABP was associated with a lower risk of death (RR 0.44, 95% CI, 0.21-0.95), and this population might deserve further study. In populations with higher mortality (> 40%), it is unclear if the IABP might be of some benefit. In view of these limitations, this study provides evidence that challenges current high-grade recommendations for the use of IABP counterpulsation in AMI patients with cardiogenic shock.
Concise Critical Appraisal is a regular feature authored by SCCM member Samuel M. Galvagno Jr., DO, PhD. Each installment highlights journal articles most relevant to the critical care practitioner.