Concerns have been raised about high rates of mortality and major bleeding with the Impella  intravascular microaxial left ventricular assist device (LVAD) among patients undergoing PCI for acute MI complicated by cardiogenic shock.

An observational study published in JAMA involving 3360 patients receiving mechanical circulatory support has found that inhospital mortality rates were 11 percentage points higher (45% vs 34%) and major bleeding rates were 15 percentage points higher (31% vs 16%) with the Impella device compared with intra-aortic balloon pumps (IABPs)

The US study authors said the increase in mortality seen in their registry-based, propensity-matched study may be explained by an increased bleeding with intravascular microaxial LVAD as compared with IABP, consistent with prior studies.

An accompanying editorial said the mechanism of possible harm associated with the Impella device was likely an excess in device-related complications that might outweigh any hemodynamic benefit.

It said the adverse findings highlighted the issue of FDA approval of such devices and their increasing use despite a lack of adequately powered RCTs for any of the available active mechanical circulatory support devices in the setting of cardiogenic shock.

“Until reliable evidence from RCTs is available, the study … together with other registry studies, provide evidence to support a more restrictive use of these devices and as based on current guidelines, only in selected patients with refractory cardiogenic shock,” wrote the authors from the Leipzig Heart Institute, Germany

Cardiologist Dr Sidney Lowe from Liverpool Hospital, NSW, told the limbic that the study did not provide a realistic representation of what clinicians consider when evaluating patients in need of mechanical cardiac support devices, ie the choice between Impella and ECMO is usually brought into the equation once the balloon pump hasn’t worked.

“They didn’t compare [the ECMO group] with the Impella subgroup, because the question is that is the bleeding any worse in these two populations. And it is truly, the ECMO patients must be sicker, the sickest,” he said.

“The authors admitted that maybe these were sicker people, despite trying to correct for that with a propensity match. And the mortality rate for the balloon pump patients, the IABP patients, was lower than actually expected,” said Dr Lowe.

He said the loose definition of shock patients in studies within the field can mean it can be difficult for clinicians to determine if the results are enough to change their current use of such devices.

He compared it with the defined shock patients in the All New Zealand Acute Coronary Syndrome Quality Improvement (ANZACS-QI) registry study and the US National Cardiogenic Shock Initiative providing a pyramid on how to define shock in clinical trials.

“You can define shock in many different ways …. In this [new] paper, it’s very loose or what is a shock patient and so we don’t really know that’s what really is,” he said.

“We know that from other studies, like IABP-SHOCK II, that balloon pumps don’t really work very well in cardiogenic shock patients from STEMI or myocardial infarction. And, hence it led to a downgrade of its use in Europe, and in the US.”

“It’s all very complicated  … and we’d like to see a trial comparing Impella with ECMO. This data would suggest we might even want to see a trial comparing in Impella versus balloon pumps,” said Dr Lowe.