Recently NEJM published the results from the german SHOCK II trial. The study suggests intraaortic balloon pumps (IABP) don’t work as well as we think. It has been interesting following the e-mail correspondance between our hospital cardiac intensivists and cardiologists. They went nuts.
Via a guidewire an IABP is inserted so that the balloon is placed in the proximal descending aorta. It then works in synchrony with the ECG and invasive blood pressures. It is timed to inflate at the onset diastole and deflate in systole.
In theory the diastolic counterpulsation increases diastolic pressures which in turn should improve diastolic myocardial blood flow in oxygenation. In theory the sudden systolic deflation should reduce afterload and increase forward blood flow.
Commonly it is used in patients with cardiac shock (CS) patients due to ischemic disease. It is the most commonly used form of mechanical support until the CS patients can be revascularized with PCI or CABG.
Using IABP in these scenarios is in european and US guidelines given class 1B and 1C recommendations (strong recommendations). Despite that there is no strong evidence proving it works and definitely no adequately powered randomised trials.
Some studies demonstrate increased coronary perfusion and reduced afterload but, as far as I can tell, no studies prove it actually improves cardiac output more than marginally (at best).
600 patients with CS after myocardial infarction were randomised. All were due for early revascularisation with either by-pass surgery or percutaneous coronary intervention. 301 received IABP-support while 299 received no IABP-support. 30 day mortality was the primary end-point.
The vast majority of patients had revascularisation within 24 hours. On average the patients in the IABP-group were on IABP for three days for 3 days.
At 30 days 119 (39,7%) patients in the IABP-group had died while 123 (41,3%) patients in the no-IABP groups had died.
IABP counterpulsation did not significantly reduce mortality in ischaemia related CS due for revascularisation.
Likewise, there was so significant difference in secondary outcomes like time to hemodynamic stabilization, length of ICU-stay, lactate levels and catecholamine therapy.Interestingly there was no improvement of blood-pressure or pulse rate in the IABP-group.
There is still no evidence IABPs are really doing anything for patients in cardiogenic shock CS due for revascularisation. Between these groups of 300 there was no difference in mortality.
However, in the small subgroup of patients <70 years old there is an interesting difference.
Study lives here. It is open access.:
Comment by Thomas D:
This randomised trial concludes with what I’ve always thought: Intra-aortic balloon pumps aren’t very helpful. The little fraction of extra blood pressure you get from the counter-pulsation doesn’t really help. The 30-day mortality was the same with or without the fancy machine. What these patients need is V-A ECMO.
And V-A ECMO isn’t more complicated than an IABP. If you can put in a central line, you can start patients up on ECMO. So why you would use an IABP, such a complicated, expensive and invasive machine that might help unload the heart in systole, and gives you a tiny 5-10 mmHg extra in diastole is beyond me (the Shock II trial actually reports no change/improvement in blood pressure in the IABP arm). If you’re going to be invasive, just go for the full monty and put them on ECMO instead.
What I can say for the IABP is that it does in fact relieve the heart of some of its work. As opposed to inotropes and pressors. So I think the IABP has a benefit – it’s just so small that you’ll need a really marginal patient to get a survival benefit from it. And that might be the problem with this study. The study looks good, but the patients might not have been sick enough to get a mortality difference from the tiny blood pressure lift of the IABP. If 10-20 mmHg is going to make any difference, it must be from the patients on the very edge of tolerable, survivable blood pressure. Maybe there is a small mortality gain in the more severe cardigenic shock patients?
Still, ECMO would help them more, and have the flexibility to support the whole range of these cardiogenic shock patients, until they’re ready to go off pump. Hopefully, ECMO could’ve helped lower the 40% mortality this study found. ECMO can fix anything.