Death of the Balloon Pump?

3/3/2014

This paper looks at whether inserting an IABP just before or after PCI for patients with cardiogenic shock due to an acute MI improves 30 day mortality.

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So my questions for this paper (take your pick) are:

90% of these patients were on inotropes (unsurprisingly, they had shock). Could the presence of an inotrope be expected to alter the results?

Is mortality the best endpoint for this study? Should infarct size or ejection fraction have been considered in the 30 day survival group?

What does this patient sample tell us about our patients? Only 1/3 of them were smokers for example. Just how well does a sample need to fit with your population for results to be meaningful?

They all had lesions at angiography, and in only 3.2% was revascularisation not completed – does this mean all MI patients with shock should go to the cath lab?

This group excluded those patients in coma (why do you think this might be? – remember the presumption is that patients in this study died of cardiogenic shock). NICE guidelines for acute STEMI specifically point out that coma should not be used as a contraindication to PCI (see the recommendations section). Do you agree with NICE?

The conclusions mention a trend towards increased VAD use. This phrase (a trend towards) is used quite a bit. Is a p value of 0.07 any more meaningful when looking for a difference than one of 0.12?

On a similar note is it appropriate to calculate relative risks when there is not a significant difference?

Is early revascularisation such a confounding feature that IABP, or any other therapy, becomes insignificant i.e. is your fate determined by the PCI and nothing else?

And finally….

Should we bin the IABP in the cath lab?

Will the pressure waveform for the IABP ever stop being an exam favourite (like the PA catheter trace)?!

As always you don’t have to base your response on these questions – these are just some of the things I thought about when reading the paper. I look forward to reading your thoughts.

8 Comments

Majid Saleem

6/3/2014 08:02:49 am

I think IABP would be mentioned in exams much more the PA Cathetars

Peter Hersey

6/3/2014 02:40:49 pm

Ok. Any thoughts on the paper?

Lynn Fairless

7/3/2014 04:36:01 am

A few comments on the paper...
Revascularisation is discussed throughout the paper, however, there is no mention as to how early, 'early' revascularisation is. The paper does not look at the time to revascularisation in either group, and whether there was a difference here? What if all the IABP patients had revascularisation at a later time than the other group - surely this would affect outcome? It's a shame it does not get mentioned.
Looking at their end points - is the use of urine output an appropriate outcome measure, is this not a little outdated? Would CO monitoring be more appropritae? A target of 30ml/hr is a little too low for some of their patient population who according to their tables, weighed up to 90kg.
I find it a little unusual to read a paper looking at the outcomes following ACS and revascularisation, to not look at actual cardiac function afterwards, or infarct size, or presence of systolic/diastolic dysfunction? There is no clinical mention of this either ie. functional performance afterwards, were they all still breathless or with ongoing angina? There is no mention of total in hospital stay duration - they may still be alive at 30 days, but are they home & well?
Only 3.2% didn't get revascularised - this is quite low? Do we now need to think about cath lab for more of our NSTEMI's, which seemingly don't get there?
I got a bit frustrated reading about VAD use, and non-VAD use. It seems that if the clinicians wanted to use one, they could, regardless of the trial. For an intervention with no proven survival benefit, it is right to use it in a non-standardised way, when looking specifically at the impact of another intervention on outcome?? I would suggest that the ad-hoc use of a VAD (unknown times is the IABP group), may have skewed the results and actually removing these patients from the analysis, would add statistical integrity to the analysis and make me more inclinced to extrpolate their results to our practice. They haven't commented on this.

Sam

8/3/2014 08:41:18 am

A little out of my depth with this but had a few thoughts.

It seems that the two most important interventions here are the early revascularisation and the use of inotropic support.

As mentioned above ~90% of patients were on inotropes prior to randomisation - does this suggest that the inotropes are so effective that IABP is unnecessary? Or does it just appear that way becuase they're measuring BP not cardiac function?

I also agree with the above point that death isn't a great outcome measurement for this study - although it is easy and cheap to measure - and they may have had more meaningful results if assessment of cardiac output or infarct etc were used.

With regards to the use of 'trending towards', my understanding is that a non-significant result is non-significant no matter what the value. It can't be nearly significant or 'trending towards' significant. Surely that is the reason that a value for 'significance' is needed?

With regards to calculating a relative risk, i'd had two thoughts
1) If there is no significant difference then there shouldn't be a difference in the absolute risks between the groups therefore a relative risk cannot be calculated.
2) If there is a difference in the two absolute risks, surely a statistical test needs to be applied to this to calculate whether the difference between the absolute risks is significant before you go on to calculate a relative risk

Hope this makes sense

8/3/2014 07:04:41 pm

Completely out of depth here but thought I would make an effort. A random thought from a junior so please feel free to bash me

Whilst reading about IABP I realise that there are different sizes of balloons available. This study does not state what size balloons are used. The size of balloon would depend on patients’ height but I thought it would be interesting to know, or is this too obvious and not worth mentioning?

There is a case report by Nair et al in 2011 which showed use of 50cc balloon instead of 40cc (patient's height was 162.6cm which means size 34cc or 40cc normally) produced better diastolic augmentation that resulted in improved hemodynamic….

Pete Hersey

11/3/2014 08:23:41 am

Less of the self deprication please! These are excellent comments raising some interesting an important points - thanks for your contributions so far.

Some of the thoughts raised could be answered by looking at the protocol (usually available with the online version of a published article). There is an english language section at the end but most of the detail from memory is in German so not hugely helpful.

Interested to see how the discussion develops....

Pete H

3/4/2015 09:04:41 am

here's a link to a meta-analysis that shows a lack of benefit, both in patients with and without shock:

http://archinte.jamanetwork.com/article.aspx?articleid=2210888&utm_source=TWITTER&utm_medium=social_jn&utm_term=161237894&utm_content=%7Carticle_engagement&utm_campaign=article_alert&linkId=13168138

Pete H

7/4/2015 04:28:19 am

And now a Cochrane review....

https://web.nhs.net/OWA/redir.aspx?SURL=u9_VDCs63s8YR5SSjCkawWybEuKzfsNnaBm5JSHiSbd8vO1-ND_SCGgAdAB0AHAAOgAvAC8AbwBuAGwAaQBuAGUAbABpAGIAcgBhAHIAeQAuAHcAaQBsAGUAeQAuAGMAbwBtAC8AZABvAGkALwAxADAALgAxADAAMAAyAC8AMQA0ADYANQAxADgANQA4AC4AQwBEADAAMAA3ADMAOQA4AC4AcAB1AGIAMwAvAGEAYgBzAHQAcgBhAGMAdAA7AGoAcwBlAHMAcwBpAG8AbgBpAGQAPQA4ADAAMQBDADUARgBCADYAMQA4ADQAOQAxADgAMwA4ADYAQgBFADAAMAAzADcAMwAxADUAQgA1ADMANAA3ADQALgBmADAAMgB0ADAAMgA.&URL=http%3a%2f%2fonlinelibrary.wiley.com%2fdoi%2f10.1002%2f14651858.CD007398.pub3%2fabstract%3bjsessionid%3d801C5FB6184918386BE0037315B53474.f02t02

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Death of the Balloon Pump?

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