Does Impella Unload the Left Ventricle?
Yes, the Impella device directly and effectively unloads the left ventricle by actively pumping blood from the left ventricle into the ascending aorta, reducing ventricular workload and myocardial oxygen demand. 1
Mechanism of Left Ventricular Unloading
The Impella functions as a transvalvular axial flow pump that is positioned across the aortic valve, drawing blood directly from the left ventricle through an inlet area near the device tip and expelling it into the ascending aorta. 2 This mechanism results in:
- Immediate and sustained reduction in left ventricular end-diastolic pressure by actively removing blood from the ventricle before it must be ejected 3, 4
- Decreased myocardial oxygen consumption by reducing the heart's workload 1
- Increased systemic cardiac output while simultaneously decreasing ventricular wall stress 4
- Physiological flow pattern that maintains forward circulation in parallel with native cardiac function 3
Clinical Evidence of Unloading Capacity
The degree of unloading varies by Impella model, with flow capacities ranging from 2.5 L/min (Impella 2.5) to 5.0-5.5 L/min (Impella 5.0/5.5), providing substantially greater left ventricular support than intra-aortic balloon counterpulsation. 1, 2
The American Heart Association specifically identifies left ventricular unloading as a primary rationale for Impella use in acute myocardial infarction complicated by cardiogenic shock, stating that mechanical circulatory support reduces ventricular workload, increases systemic perfusion, and enhances myocardial perfusion. 1
Comparison to Other Support Devices
Impella provides complete left ventricular unloading, which distinguishes it from other mechanical support options:
- IABP: Provides minimal hemodynamic support and does not actively unload the ventricle, only augmenting diastolic coronary perfusion 1, 5
- VA-ECMO: Does not unload the left ventricle and may actually increase left ventricular afterload and wall stress, potentially causing ventricular distension and worsening pulmonary edema—often requiring addition of an Impella or other venting mechanism 1, 2, 3
- TandemHeart: Provides left ventricular unloading but requires more complex transseptal implantation 2
Clinical Implications of Unloading
The unloading effect translates to specific hemodynamic improvements:
- Reduction in pulmonary capillary wedge pressure through decreased left ventricular filling pressures 3
- Improved end-organ perfusion by maintaining adequate mean arterial pressure (>65 mmHg) 2
- Prevention of hemodynamic deterioration during high-risk percutaneous coronary intervention in patients with severe left ventricular dysfunction 1, 5
Important Caveats
While Impella effectively unloads the left ventricle, several limitations exist:
- Flow capacity constraints: The Impella 2.5 may provide inadequate support for patients with large body mass or severe cardiogenic shock requiring higher cardiac output 2
- Contraindications that prevent placement: Left ventricular thrombus, severe aortic stenosis, significant aortic insufficiency, and severe peripheral artery disease all preclude Impella use 1, 2
- Potential for aortic valve injury: Prolonged support can lead to aortic insufficiency, which paradoxically increases left ventricular volume load 2, 6
- Does not address right ventricular failure: Isolated left-sided Impella support may be insufficient in biventricular failure, requiring addition of Impella RP or alternative right ventricular support 1, 2