Impella Heart Pump

In depth

The one-page summary above is what the PDF prints. These sections go further.

Hemodynamics in depth

The Impella is a continuous-flow axial pump in series with the LV: the inlet draws blood from the cavity and the impeller ejects it just above the aortic valve. Speed is fixed by the P-level, with no ECG or pressure trigger, so it pumps through VT, VF and asystole as long as the LV fills. An IABP adds about 0.5–1 L/min by displacement; a CP adds 3.5–4 L/min and a 5.5 up to 5.5 L/min of forward flow.

Unloading works at both ends of the coronary perfusion gradient: emptying the LV lowers LVEDP, PAOP and wall stress, so the pressure-volume loop shifts left and oxygen demand falls, while forward flow raises aortic diastolic pressure. Native ejection falls as support rises, so pulse pressure narrows; follow MAP, cardiac power output and LVEDP instead.

Flow at any P-level depends on the pressure difference across the pump, small in systole and large in diastole, so flow and motor current swing with every beat. The pump is preload dependent: hypovolemia, RV failure, tamponade or a large PE starve the inlet and cause suction. The RP Flex is the mirror image, moving blood from the right atrium to the pulmonary artery to lower CVP and raise LV preload; if the LV cannot accept the return, a left pump is needed too (BiPella).

Cardiac power output (W) = MAP × CO ÷ 451; below 0.6 W carried the highest mortality in the SHOCK trial registry (Fincke 2004). PAPi = (PA systolic − PA diastolic) ÷ RA pressure; below 0.9 with RA pressure above 12 mmHg points to RV failure that a left-sided pump cannot fix.

Device family and selection

The CP is for support in minutes: AMI shock, high-risk PCI, a bridge to a decision. The 5.5 is for more flow or more time: post-cardiotomy shock, myocarditis, chronic heart failure bridged to LVAD or transplant, or an upgrade from a CP; the axillary route frees the groin and lets the patient walk. The RP Flex is for isolated RV failure after LVAD, RV infarct, transplant or cardiac surgery, or joins a left pump when CVP climbs and the left pump keeps sucking.

• LV thrombus: the inlet would aspirate and embolize it
• Mechanical aortic valve or stenosis ≤0.6 cm²: the cannula cannot cross or jams the leaflets
• Moderate or severe aortic regurgitation: pumped blood leaks straight back and the leak worsens
• ASD or VSD: lowering LV pressure reverses the shunt toward the aorta
• Severe PAD: a 14 Fr sheath occludes a 5 mm artery; go axillary
• RV failure, tamponade, LV rupture: the LV cannot fill, so the pump only sucks

Insertion and position management

Femoral CP insertion: ultrasound-guided puncture of the common femoral artery, an angiogram to size the vessel (ideally ≥6 mm), pre-close sutures before the 14 Fr peel-away sheath, a 0.018-inch wire placed in the LV through a diagnostic catheter, the pump advanced over it under fluoroscopy and started at P-2. The peel-away sheath is then split off and the repositioning sheath advanced, leaving the 9 Fr shaft in the artery. The 5.5 needs a cutdown and a 10 mm graft on the axillary artery under TEE; the RP Flex passes from the right IJ or femoral vein through the tricuspid and pulmonary valves to the main PA.

Position is confirmed two ways. Fluoroscopy: inlet below the aortic annulus, pigtail free in the LV, cannula off the septum. Echo (parasternal long axis): annulus-to-inlet distance 3.5 cm for the CP and 5 cm for the 5.5, pump pointing at the apex, nothing caught in the mitral chordae. Record the shaft marker number at the sheath hub every shift.

Pumps migrate. Inward (hip flexion, coughing, a loosened sheath) puts the inlet against the wall or mitral apparatus: suction, hemolysis, a damped motor current. Outward (tension on the shaft, turning, transport) brings the outlet toward the valve: Placement Signal Low, then an in-ventricle or in-aorta alarm, finally a flat current. The nurse catches the change in marker, signal shape or flow and calls; only a credentialed clinician repositions, under echo or fluoroscopy, at P-2 during the move.

The SmartAssist screen

The home screen shows the alarm banner (red critical, yellow serious, white advisory), P-level and Impella flow, the placement signal and motor current waveforms, and purge and power status. The placement signal comes from an optical pressure sensor at the outlet; on the CP and 5.5 it is an aortic pressure, so it doubles as a second arterial line. From that pressure and the gradient implied by motor current the controller reconstructs LV pressure and displays LVEDP; entering a thermodilution or Fick cardiac output adds cardiac power output and native cardiac output (entered CO minus Impella flow).

Read the waveforms together. Aortic placement signal plus pulsatile current: the pump straddles the valve. Ventricular placement signal (low diastolic, wide swing) with pulsatile current: the outlet has slipped into the LV. Flat current: both ends are in one chamber, and the placement signal tells you which. A weak LV, arrest or VA-ECMO dampens both and produces Impella Position Unknown: examine the patient and get an echo. Flow is calculated, not measured, so it is wrong whenever the pump is malpositioned; a fall in flow at the same P-level is afterload, suction, malposition or clot until proven otherwise.

Troubleshooting alarm by alarm

Suction means the inlet cannot get blood: the LV is empty (hypovolemia, bleeding, RV failure, tamponade, vasodilation) or the inlet is on the wall. Raising the P-level pulls harder on an empty chamber; drop one or two levels and fix the filling. Suction with rising CVP and falling PAPi is the RV (inotropes, pulmonary vasodilators, RP Flex); suction with hemolysis and a damped current is position.

Purge alarms follow one rule: at a fixed viscosity, pressure tracks resistance. Low pressure means fluid is escaping (loose luer, cracked cassette, empty bag) or is thinner than expected; high pressure means a kink, a closed clamp, thicker fluid, or protein and thrombus narrowing the purge gap in the motor. The controller adjusts purge flow between 2 and 30 mL/h to hold pressure, so a slow pressure rise with falling flow over a shift is the earliest sign of pump thrombosis. Call the MCS coordinator or perfusion for a purge alarm a kink check does not clear, the interventionalist for a position alarm, and Abiomed's Clinical Support Center (1-800-422-8666, 24 hours).

Complications

Hemolysis is shear injury in the impeller; its drivers are the suction list plus speed: inlet near a wall or the chordae, an underfilled LV, a high P-level in a small cavity, thrombus on the impeller. Recognize it by pink or dark urine, plasma free hemoglobin above 40 mg/dL (IBCC), rising LDH and bilirubin, low haptoglobin, and a falling hemoglobin without bleeding. Free hemoglobin scavenges nitric oxide and clogs tubules, so AKI follows; renal replacement therapy was needed in 41.9% of Impella patients versus 26.7% of controls in DanGer Shock. Management: echo the position first, then the lowest P-level that holds MAP and CPO, volume, the purge pressure trend for thrombus, and an upgrade to a 5.5 or removal if it persists.

Limb ischemia follows from a 14 Fr sheath in a common femoral artery of 6–7 mm, less in women, diabetics and peripheral disease; DanGer Shock recorded it in 5.6% of Impella patients versus 1.1% of controls. Prevention: ultrasound and angiographic sizing, downsizing to the repositioning sheath, and in small vessels a prophylactic antegrade perfusion sheath (5–7 Fr in the superficial femoral artery, fed from the introducer side arm). Assess hourly: Doppler at the dorsalis pedis and posterior tibial, color, temperature, capillary refill, motor and sensory function, calf tension; near-infrared oximetry on both calves falls before pulses disappear. Treatment escalates from a perfusion sheath or external bypass, to thrombectomy or fasciotomy, to removing the pump or moving to the axillary artery.

Bleeding comes from the access site, the retroperitoneum when the puncture was above the inguinal ligament (flank pain, falling hemoglobin, clean groin), the GI tract, and acquired von Willebrand syndrome from shearing of the large vWF multimers; new thrombocytopenia prompts a HIT workup because purge heparin is a continuous exposure. Aortic regurgitation worsens the longer the cannula sits across the valve, so serial echo looks at the valve as well as the position. Stroke, pump thrombosis (rising purge pressure and motor current, falling flow), site infection and ventricular arrhythmias complete the list; a patient in sustained VT with a working pump can keep a MAP of 65 mmHg, so treat per ACLS and drop the P-level only if suction alarms.

ECMO plus Impella (ECPELLA)

Peripheral VA-ECMO returns blood retrograde up the aorta, raising LV afterload when the LV is least able to eject: the ventricle distends, the aortic valve stops opening, blood stagnates in the LV and root, and the lungs flood. An Impella across the valve vents the LV directly; the combination is ECPELLA. In 255 propensity-matched pairs (Schrage, Circulation 2020) unloading was associated with lower 30-day mortality (HR 0.79, 95% CI 0.63–0.98) at the price of more severe bleeding (38.4% vs 17.9%), access-site ischemia (21.6% vs 12.3%) and renal replacement therapy (58.5% vs 39.1%). The randomized UNLOAD ECMO trial is still enrolling.

The console reads differently on ECMO: aortic pressure is set by the ECMO pump, so the placement signal is a near-flat line at the MAP; the LV is small, so motor current loses its swing and Impella Position Unknown is common; and flow at a given P-level is lower because the pump works against a higher aortic pressure. The target is the lowest P-level that keeps the LV decompressed: a pulse pressure on the arterial line, the aortic valve opening on echo, LVEDP or PAOP below about 18 mmHg, no new pulmonary edema. Too much Impella empties the LV (suction, hemolysis); too little leaves it distended with echo contrast and thrombus.

Two traps. With femoral VA-ECMO and failing lungs the Impella pumps blood that has passed through the lungs to the coronaries and brain before the ECMO blood reaches them, so it delivers hypoxemic blood to the organs that matter most (north-south syndrome): monitor a right radial ABG and fix oxygenation first. Anticoagulation is one system: purge heparin counts toward the dose and a HIT diagnosis changes both circuit and purge. Weaning is usually ECMO first, leaving the Impella as the LV bridge.

Daily care, weaning and explant

• Each shift: neuro check, MAP, CPO, LVEDP, PA catheter numbers if present; P-level, flow, both waveforms, purge pressure and flow, purge fluid and additive, bag volume, cassette date, marker at the hub, backup controller at the bedside
• Hourly: urine output and color; limb Doppler, color, temperature, capillary refill, motor and sensory function; knee immobilizer and HOB ≤30° for femoral access; no cuffs or sticks on a 5.5 arm
• Labs: ACT 160–180 s per IFU, or aPTT or anti-Xa per protocol; hemoglobin and platelets every 6–12 h; creatinine, plasma free hemoglobin and LDH daily; purge heparin counts (25 units/mL at 10 mL/h is 250 units/h)
• Handling: one person holds the catheter when turning; femoral pumps stay in bed with the leg straight; axillary 5.5 and IJ RP Flex patients can walk with a trained team

Weaning starts when the cause has been treated and the numbers hold without escalation: MAP ≥65 mmHg on no or low-dose vasopressors, CPO >0.6 W, lactate cleared, LVEDP or PAOP under about 18 mmHg, urine output back, and an echo showing improving ejection. The CP comes down 2 P-levels at a time (the 5.5 one level), with 15–60 minutes or longer between steps depending on the program. Most programs hold at P-2 for 30 minutes to a few hours before explant; the IFU calls all of this guidance only.

For a femoral CP the interventionalist pulls the pump into the descending aorta at P-2, sets P-0 and removes the catheter; the sheath comes out when ACT is below 150 s, with 40 minutes of manual pressure per the IFU or closure of the pre-placed sutures, then about 6 hours of bedrest with the leg straight. The 5.5 comes out through the graft, which is then ligated; the RP Flex like a large venous sheath. Afterward: neurovascular checks every 15 minutes for an hour, then hourly; watch for hematoma, pseudoaneurysm and retroperitoneal bleeding; LDH and creatinine lag the pump by a day or two.

Evidence and controversies

DanGer Shock is the first randomized trial to show a survival benefit for any mechanical support device in cardiogenic shock. Number needed to treat at 180 days was about 8; number needed to harm for the composite of severe bleeding, limb ischemia, hemolysis, device failure or worsening aortic regurgitation was about 6, and dialysis rose from 26.7% to 41.9%. It succeeded where IMPRESS failed by enrolling STEMI with lactate ≥2.5 mmol/L and LVEF <45%, excluding comatose arrest survivors, RV failure and mechanical complications, and placing the pump before or during PCI. The 2025 ACC/AHA ACS guideline made this a class 2a recommendation for a microaxial pump in selected STEMI patients with severe or refractory shock, with class 3 for routine IABP. VA-ECMO showed no survival benefit in ECLS-SHOCK (2023: 30-day death 47.8% vs 49.0%), and PROTECT II was stopped for futility, so high-risk PCI support rests on weaker evidence.

Still open: whether the benefit extends to NSTEMI, non-ischemic shock or arrest survivors; whether centers without a limb-protection and hemolysis protocol can reproduce the net benefit; and how to weigh the registries that found more death and bleeding with Impella than IABP (Dhruva 2020: in-hospital death 45.0% vs 34.1% in 1,680 matched pairs). PROTECT IV (high-risk PCI) and UNLOAD ECMO are still enrolling. Practice also varies on heparin versus bicarbonate purge and on ACT 160–180 s per IFU versus aPTT or anti-Xa targets.

Exam pearls

• Correct position = aortic placement signal + pulsatile motor current; ventricular signal = outlet too deep; flat current = both ends in one chamber
• Suction = underfilled LV or inlet on the wall: lower the P-level, give volume, check the RV and position; never raise it
• Purge: dextrose with heparin 25 or 50 units/mL or bicarbonate 25 or 50 mEq/L, never saline, never both; low pressure = leak or dilute, high = kink, clot or strong
• Never P-0 or P-1 across the valve: blood flows backward into the LV; weaning stops at P-2 until explant
• Hemolysis: pink urine, plasma free hemoglobin >40 mg/dL, rising LDH, low haptoglobin; echo the position first, then lower the P-level
• CPO = MAP × CO ÷ 451, <0.6 W is inadequate; PAPi <0.9 with RA >12 mmHg is RV failure a left pump cannot fix
• DanGer Shock 2024: Impella CP in STEMI shock, 180-day death 45.8% vs 58.5%, more bleeding, limb ischemia and dialysis; 2025 ACC/AHA class 2a