No clinical outcome benefit from IABP support

The IABP-SHOCK II trial is the largest randomized trial of intra-aortic balloon pump (IABP) counterpulation support in cardiogenic shock.  At 30-days follow-up, this trial demonstrated no mortality reduction.  The current paper reports the longer term outcomes from this trial, given that the benefits of IABP may not be evident in early follow-up.

The IABP-SHOCK II trial was a randomized, open-label, multi-center trial of 600 with cardiogenic shock complicating acute MI and undergoing early revascularization.  At one-year, IABP did not mortality (relative risk [RR] 1.01; 95% confidence interval [CI] 0.86-1.18; p=0.91), reinfarction (RR 2.60; 95% CI 0.95-7.10; p=0.05) recurrent revascularization (RR 0.91, 95% CI 0.58-1.41; p=0.77) or stroke (RR 1.50; 95% CI 0.25-8.84; p=1.00).  Additionally, IABP use did not result in significant differences in quality-of-life measures.  Negative trial results often raise questions about power.  However, as the authors note, the absolute risk difference of 0.4% for mortality between the two groups is very small, there were no indications of benefit in any other outcome variable, and there was a trend toward higher risk of reinfarction in the IABP group.    These together make it unlikely there was a type II error in this study.

Conclusion:

This large trial of IABP counterpulsation for patients with cardiogenic shock complicating acute MI showed no reduction in long-term mortality and raise questions about the clinical utility of IABPs.  Similar trials of newer technologies for left ventricular support are needed to understand if larger increases in cardiac output support may overcome the lack of benefit seen with IABP support.

  •  Thiele H, Zeymer U, Neumann F-J, et al. Intra-aortic balloon counterpulsation in acute myocardial infarction complicated by cardiogenic shock (IABP-SHOCK II): final 12 month results of a randomised, open-label trial. The Lancet. 2013;382(9905):1638–1645.

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