How the Impella Microaxial Blood Pump Works
The Impella is a catheter-based microaxial flow pump that is inserted across the aortic valve, actively drawing blood from the left ventricle and expelling it into the ascending aorta, thereby simultaneously unloading the ventricle and augmenting systemic cardiac output. 1
Mechanical Design and Placement
The Impella operates as a continuous-flow axial pump with an external controller, featuring a simple design that allows for straightforward percutaneous insertion 1. The device is positioned retrograde through the femoral artery, crosses the aortic valve, and rests with its inlet in the left ventricle and outlet in the ascending aorta 2, 3.
Mechanism of Action
The pump works through two simultaneous physiological mechanisms:
Direct Hemodynamic Support
- Actively pumps blood from the left ventricle to the ascending aorta at rates of 2.5 to 5.5 L/min depending on the model 1, 4, 5
- Provides immediate and sustained increases in mean arterial pressure, cardiac output, and peripheral tissue perfusion 6, 2
- Enhances coronary blood flow through improved systemic perfusion 7, 6
Left Ventricular Unloading
- Reduces left ventricular end-diastolic pressure and wall stress 8
- Decreases myocardial oxygen demand, facilitating recovery of damaged cardiac muscle 4, 7
- This unloading effect distinguishes Impella from passive support devices like the intra-aortic balloon pump 6, 8
Device Variants and Flow Capacity
Different Impella models provide varying levels of support:
- Impella 2.5/CP: Delivers up to 2.5 L/min via percutaneous femoral access (14F) 1, 3
- Impella 5.0: Provides 5 L/min but requires surgical cut-down on peripheral artery 1
- Impella 5.5: Delivers up to 5.5 L/min, typically implanted via axillary artery, enabling full left ventricular support 5
- Impella RP: Specifically designed for right ventricular support 9
Clinical Implications
The flow limitation of smaller devices (2.5 L/min) may be inadequate for patients with large body mass index or profound cardiogenic shock requiring higher flow rates 1. The Impella 5.0 and 5.5 address this limitation but require more invasive access 1, 5.
Important Caveats
Complications include bleeding (up to 44%), limb ischemia (up to 18%), hemolysis (up to 32%), and stroke (up to 13%) due to the large-bore femoral access requirements and mandatory anticoagulation 1, 6. Despite widespread use exceeding 14,000 patients in Japan alone 4, randomized controlled trials have not demonstrated mortality benefit compared to intra-aortic balloon pump in cardiogenic shock 9, 6.
The device requires continuous monitoring for proper positioning across the aortic valve, adequate flow rates, and early detection of complications 5. Real-time monitoring technologies like SmartAssist and Impella Connect facilitate device management 5.