August 27th, 2012

IABP Randomized Trial Delivers a Shock

We asked the lead author of the IABP-SHOCK II trial to shed further light on his study group’s findings.


Six hundred patients patients with acute MI complicated by cardiogenic shock were randomized, in unblinded fashion, to either intraaortic balloon counterpulsation (IABP) or no IABP. All patients were expected to undergo early revascularization (PCI or bypass surgery) and to receive the best available medical therapy.

The 30-day mortality rate (primary endpoint) was 40% in the IABP group and 41% in the control group – a nonsignificant difference. The two groups also did not differ significantly in any other endpoints, including major bleeding, peripheral ischemic complications, sepsis, stroke, renal function, and length of ICU stay.

See news coverage on CardioExchange and analysis from Beat Meyer on Journal Watch.


Q: Is it time to overturn – or at least reconsider – the class I guideline recommendation that patients with acute MI complicated by cardiogenic shock undergo IABP? Or should we wait for longer-term mortality data before the guidelines are re-envisioned?

Thiele: I believe that the class I recommendation was always too optimistic because no evidence from randomized trials showed that IABP can improve outcomes. Only registry data have even suggested the possibility of higher mortality if IABP were used in conjunction with primary PCI, and IABP’s benefit was mainly in patients who underwent thrombolysis or no reperfusion. The German/Austrian S3 guidelines, first published in 2011, took this into account and recommended only that the IABP may be used. Those guidelines also stated that we need a randomized trial, which we now have with the IABP-SHOCK II trial, and our findings challenge the current U.S. and European guidelines. I do not believe that at longer follow-up the results of the 30-day outcome will change. Nevertheless, we are very interested in the long-term results.

Q: Was the high number of endpoint events in your trial enough to outweigh the modest sample size of 600 patients? Why or why not?

Thiele: Indeed, we only included 600 patients, which is nonetheless the largest trial performed yet in cardiogenic shock. Trials in cardiogenic shock usually do not need very high patient numbers because of the high event rates. The only minor difference in mortality between the two groups — together with the lack of difference in any of the secondary endpoints or process-of-care measures, – which are usually much more sensitive for detection of meaningful clinical changes — make any clinically relevant effect of IABP unlikely. Therefore, even if we had a larger sample size, a change in the results is extremely unlikely.

Q: As a practical matter, given your finding of no advantage for IABP in acute-MI patients with cardiogenic shock, how would you act tomorrow if confronted with such a patient?

Thiele: What we have learned from IABP-SHOCK II is that approximately 60% of the patients will survive if we treat them according to guidelines — namely, early revascularization in all and dedicated intensive care. The German/Austrian S3 guidelines give very clear recommendations on how to treat cardiogenic shock patients, and we were surprised by the high adherence to the guidelines in our trial. For example, only a few patients were treated with dopamine, and the majority of those patients got norepinephrine plus dobutamine if catecholamines were required. This might be one reason why the mortality was at the lower end of the range that has been reported previously. Another important aspect is that many will now reflexively assume that we will need more and earlier left-ventricular assist devices. I believe that this is not the way to go. We will have to identify patients who might benefit from LVADs, those who might be harmed by these devices, and those who don’t need one at all. We will need good risk scores to predict outcomes for cardiogenic shock patients. This is one of the many areas in which we must move forward in the scientific work on cardiogenic shock.

What’s your view in the IABP SHOCK-II trial results?

One Response to “IABP Randomized Trial Delivers a Shock”

  1. Matthew Carr, MD says:

    This study was quite well done in my opinion. As a frequent user of the IABP in sicker MI pts, I would like tto see more thorough subgroup analysis to help select the proper pts. (if any). Specifically, the groups that were resuscitated before treatment, vs other; the group placed on iabp within 2 hours of MI vs those placed later on . The group with 1 hour of shock before rx vs those with 10 hours of shock These ae not spelled out in the orignal article, but may be quite interesting to look at, especially if one wishes to compare iabp vs impella, cs cardiohelp etc.