What is an Impella device and how is it used in patients with severe cardiac dysfunction or failure, such as those experiencing cardiogenic shock or myocardial infarction, particularly in adults with a history of cardiac disease like coronary artery disease (CAD) or heart failure?

Impella Device Overview

The Impella is a percutaneous, continuous-flow, microaxial pump that provides temporary mechanical circulatory support by directly unloading the left ventricle while simultaneously increasing systemic perfusion and coronary blood flow. 1, 2

Device Mechanism and Classification

The Impella functions as a transvalvular axial flow pump that pulls blood from the left ventricle through an inlet near the catheter tip and expels it into the ascending aorta, with an external controller managing pump function. 2 This mechanism achieves three critical hemodynamic goals:

• Direct left ventricular unloading reduces ventricular workload and myocardial oxygen demand 2, 3
• Increased mean arterial pressure improves peripheral organ perfusion and promotes recovery from multiple organ failure 3
• Enhanced coronary perfusion occurs through the combination of increased MAP and decreased left ventricular end-diastolic pressure 3

Available Models and Flow Capacities

Different Impella models provide varying levels of circulatory support based on patient needs:

• Impella 2.5: Provides up to 2.5 L/min of flow via percutaneous femoral access, suitable for moderate support 2
• Impella CP: Similar percutaneous approach with enhanced flow capacity 4
• Impella 5.0/5.5: Delivers 5.0-5.5 L/min of flow, enabling complete left ventricular support but requires surgical conduit placement (typically axillary artery) 2, 5
• Impella RP: Specifically designed for right ventricular support in patients with predominant RV failure 4, 2

Primary Clinical Indications

Cardiogenic Shock Following Acute Myocardial Infarction

The strongest evidence supports early Impella use in cardiogenic shock complicating acute myocardial infarction, with observational data showing 85% survival to device explantation when deployed early, compared to 51% historical survival. 4, 6 The Detroit Cardiogenic Shock Initiative demonstrated that 66% of patients received the Impella before revascularization, emphasizing the importance of early deployment. 4

High-Risk Percutaneous Coronary Intervention

Impella can be used prophylactically during high-risk PCI procedures in patients with severe left ventricular dysfunction to maintain hemodynamic stability and prevent cardiovascular collapse. 2, 6

Bridge-to-Decision Strategy

Impella serves as a bridge-to-decision device in severe cardiogenic shock, with 68.8% of patients surviving to next therapy (durable mechanical circulatory support, heart transplant, or recovery) with a median support duration of 7 days. 2, 6

Absolute Contraindications

The following conditions preclude Impella use:

• Left ventricular thrombus (risk of systemic embolization) 2, 6
• Severe aortic stenosis or significant aortic insufficiency (device cannot function properly) 2, 6
• Severe peripheral artery disease preventing femoral access 2, 6
• Aortic dissection 2, 6

Anticoagulation Requirements

Initiate anticoagulation with unfractionated heparin bolus of 100 U/kg (maximum 5000 U) at the time of implantation to prevent pump thrombosis. 1, 2 This is a critical step that cannot be omitted, as pump thrombosis represents a serious complication.

Comparison with Alternative Mechanical Support Devices

Versus Intra-Aortic Balloon Pump (IABP)

Impella provides superior hemodynamic support compared to IABP through direct left ventricular unloading and cardiac output augmentation, whereas IABP only augments diastolic coronary perfusion. 1, 2 The IABP-SHOCK II trial demonstrated no mortality benefit with IABP in cardiogenic shock (39.7% vs 41.3% mortality; P=0.69), and current guidelines do not recommend routine IABP use. 4

Versus VA-ECMO

VA-ECMO provides biventricular support but critically does not unload the left ventricle and may actually increase left ventricular afterload, potentially causing ventricular distension and worsening pulmonary edema. 4, 2 When VA-ECMO is used, it often requires an additional LV venting mechanism—the Impella device itself can serve this purpose. 4, 1

Versus TandemHeart

Impella has a simpler design and implantation procedure compared to TandemHeart, allowing for more rapid deployment in emergency situations. 1, 2

Management of Biventricular Failure

For patients with biventricular failure, two strategies exist:

• Bilateral Impella pumps (left-sided Impella plus Impella RP for right ventricular support) 4
• VA-ECMO with Impella maintained as LV venting mechanism to prevent left ventricular distension 4, 2

Complications and Risk Profile

Vascular complications occur in 9.8% of Impella patients (vs 3.8% with IABP), severe bleeding in 8.5% (vs 3.0% with IABP), and sepsis in 35.3% (vs 19.4% with IABP). 4, 2 These higher complication rates must be balanced against the superior hemodynamic support provided.

Additional complications include:

• Device malfunction and suction events when the inlet becomes obstructed 2
• Aortic insufficiency with prolonged support 2
• Limb ischemia requiring continuous monitoring of distal perfusion 2
• Pump thrombosis despite anticoagulation 7

Weaning Protocol

Assess for device removal using echocardiographic evaluation of left ventricular function recovery, hemodynamic improvement, lactate clearance, and end-organ function restoration. 1, 2 For patients who fail initial weaning attempts, consider longer support duration or transition to more durable mechanical circulatory support devices. 1

Critical Evidence Gaps and Ongoing Trials

Despite widespread use, no randomized controlled trial has provided evidence supporting routine use of any short-term mechanical circulatory support platform, including Impella. 4 The DanGer trial is currently randomizing 360 patients with acute myocardial infarction complicated by cardiogenic shock to Impella CP versus guideline-driven therapy. 4 Multiple VA-ECMO trials are also ongoing (EURO SHOCK, ECLS-SHOCK, ECMO-CS, ANCHOR). 4

Recent registry data comparing Impella to IABP showed no difference in 30-day mortality (48.5% vs 46.4%; P=0.64) but higher complication rates with Impella. 4 This contrasts with the favorable outcomes from the Detroit Cardiogenic Shock Initiative and RETROSHOCK registry, highlighting the importance of patient selection and timing of device deployment. 4

Practical Implementation Considerations

The axillary artery approach for Impella 5.0/5.5 facilitates earlier ambulation and improved nutritional status compared to femoral access, making it the preferred approach when prolonged support is anticipated. 2 Strict adherence to best vascular access and closure practices is critical to prevent complications. 2

When additional vasopressor support is needed, vasopressin or norepinephrine are preferred as they increase systemic afterload without significantly increasing pulmonary vascular resistance. 2