Saturday, September 1, 2012

The End of IABP?

Adding to the "don't do anything, just stand there!" file, another relatively frequently used cardiovascular support tool – intra-aortic balloon counterpulsation – might be on the chopping block.

Typically used in cases of severe cardiogenic shock secondary to acute myocardial infarction, IABP is used to reduce strain on the stunned myocardium.  The first IABP-SHOCK pilot of 45 patients showed no mortality difference, but a significant improvement in BNP levels with IABP use.  This is the follow-up study, enrolling 600 patients to IABP or best available medical therapy.

Both groups were similarly ill – the IABP group had 6% more anterior STEMIs – and had nearly identical outcomes.  There were 1.5% more survivors in the IABP group, but the p value was 0.69.  Adverse events were similar – although the control group tended towards increased sepsis, which seems a little odd.  There was an expected random assortment of subgroups favoring one therapy or another, but nothing that would seem to be specifically hypothesis generating.

In the end, the authors rather grimly state that, despite some surrogate markers appearing to be improved in the IABP group, there is no evidence to support routine use of IABP in cardiogenic shock secondary to acute myocardial infarction.

"Intraaortic Balloon Support for Myocardial Infarction with Cardiogenic Shock"
http://www.nejm.org/doi/full/10.1056/NEJMoa1208410

3 comments:

  1. Hi Ryan,

    Balloon pump proponents might argue that based on mortality, the study sample weren't as sick as expected. The study authors point this out.

    Also the the study was powered for a 12% difference in mortality at 30 days. Apart from therapeutic hypothermia there are not many RCT-proven interventions that effective.

    One could argue that balloon pumps might still be beneficial in more severe patients with cardiogenic shock and that there could be a smaller benefit that this study wasn't powered to detect.

    Also one wonders if balloon pumps might still have a role if access to interventional cardiology is delayed, e.g. retrieval from remote locations.

    Nevertheless, it is correct to say "there is no evidence to support routine use of IABP in cardiogenic shock secondary to acute myocardial infarction."

    cheers,
    Chris

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  2. You mention the power to detect a 12% difference - and, yes, in this sense, it's hard to power a study to detect smaller differences. The flip side is, if the difference of a costly intervention is small, how clinically significant is it? In this study, where the outcome is mortality, that's very clinically significant. The authors plan to follow the patients out beyond 30 days - as the long-term mortality is much more important than short-term.

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  3. I think following longer term mortality is unlikely to be any different - longer term mortality is more likely to be determined by PCI in any patient that survives long enough to receive that intervention.

    If balloon pumps were found to have a 5% mortality benefit I expect they'd be hailed as a great success. This study wasn't designed to detect that. I won't be holding my breath for the study to come out that is powerful enough to do so either!

    Chris

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