What Is An Impella?

Impella® is a percutaneous axial heart pump placed retrograde across the aortic valve into the left ventricle (LV) utilizing fluoroscopy +/- echocardiography. Its indications include high-risk percutaneous coronary intervention (PCI, especially cardiogenic shock or signs of ongoing ischemia), post-cardiotomy failure, and myocarditis. In addition, it is routinely used as a bridge between other forms of circulatory support like intra-aortic balloon pumps (IABP), ventricular assist devices (VAD), artificial hearts, and extracorporeal membrane oxygenation (ECMO). In 2014, the (underpowered) RECOVER RIGHT study showed benefits with the Impella RP device to help those with right-sided heart failure refractory to medical therapy. For this post, I’ll only discuss the traditional left-sided Impella.

Without going into detail about the different power/rpm settings (P1 – P8), purge system, and other parameters, the intracardiac portion of the Impella consists of a pigtail to stabilize the catheter in the ventricle, an inflow where blood is suctioned from the LV, a radiopaque marker which is aligned with the aortic valve annulus under fluoroscopy, an outflow segment which propels blood into the ascending aorta, and a motor housing. The newer generation Impella 5.5 device does not have a pigtail, but instead, it advanced farther into the LV cavity (~5 cm versus 3.5 cm of previous generations).

This device accomplishes many hemodynamic goals:

• reduces left ventricular end-diastolic pressure (LVEDP) and volume (preload)
• reduces afterload
• reduces myocardial oxygen demand
• increases overall forward flow and mean arterial pressure (MAP)
• increases coronary perfusion

Impellas traditionally come in several flavors:

• Impella 2.5 (9 French catheter, 12 French motor) has a peak flow of 2.5 liters/minute and can be placed into the LV from the femoral artery.
• Impella CP (9 French catheter, 14 French motor) has a peak flow of 4.3 liters/minute and can also be placed from the femoral artery.
• Impella 5.0 (9 French catheter, 22 French motor) has a peak flow of 5.0 liters/minute but requires surgical placement (femoral artery cutdown, subclavian artery graft, etc.)
• Impella 5.5 has a peak flow of over 6 liters/minute and is placed surgically in the axillary artery.

In general, flow ~ [rpm (power) / (aortic diastolic pressure – LV diastolic pressure)]. Therefore, the sicker the left ventricle, the smaller the difference between the aortic and left ventricular diastolic pressures, and therefore, the higher the flow for a given power setting.

Sometimes we’ll use Impella devices as ventricular vents for patients on ECMO for many weeks. In other situations, patients will have them for longer than 4-6 days as their native heart function slowly recovers.

Placing these devices can lead to vascular injury, bleeding (from placement and because we need to heparinize), intracardiac injury (especially of the aortic valve and papillary muscles). In addition, the axial pump can “chew up” cells at higher speeds leading to some degree of hemolysis and thrombocytopenia. Additionally, microemboli and plaques can be dislodged leading to renal dysfunction, strokes, etc.

With this in mind, a few contraindications to Impella placement include a mechanical aortic valve, significant aortic stenosis/insufficiency, LV thrombus/rupture, cardiac tamponade, and severe peripheral artery disease.

I’m definitely a fan of axillary Impellas since patients can still ambulate, but femoral Impellas are very finicky regarding positioning. Because the inflow and outflow segments have to be properly positioned, if the patient moves their hip even slightly, they may move the catheter tip resulting in decreased cardiac output and suction events along the ventricular wall, valve, or chordae.

Drop me a comment below with questions! 🙂