What is the indication and management of the Impella (Intra-Aortic Balloon Pump) cardiac device in patients with severe heart failure or cardiogenic shock?

Impella Cardiac Device Overview

Device Classification and Mechanism

The Impella is a nondurable, percutaneous, continuous-flow axial pump that provides temporary mechanical circulatory support by actively unloading the left ventricle while simultaneously augmenting cardiac output and systemic perfusion. 1

The device works by pulling blood from the left ventricle through an inlet near the catheter tip and expelling it into the ascending aorta, with the motor current reflecting the work required to overcome the pressure gradient during this process. 1 This mechanism differs fundamentally from IABP, which relies on passive diastolic augmentation, making Impella capable of providing greater left ventricular support. 1

Available Models and Flow Capacities

• Impella 2.5: Provides up to 2.5 L/min of flow, inserted percutaneously in the catheterization laboratory 1
• Impella CP: Most commonly used model (53.8% of cases in bridge-to-decision scenarios), offers intermediate flow capacity 2
• Impella 5.0: Provides up to 5.0 L/min, typically requires surgical insertion via axillary artery approach 3
• Impella RP: Specifically designed for right ventricular support 1

Primary Clinical Indications

Cardiogenic Shock Following Acute Myocardial Infarction

The most established indication is cardiogenic shock complicating acute myocardial infarction, though evidence remains mixed. 4, 1 The Detroit Cardiogenic Shock Initiative reported 85% survival to device explantation when Impella was used early (66% before revascularization) in patients with acute MI-related cardiogenic shock, compared to 51% historical survival. 4 However, a European multinational registry showed no mortality difference at 30 days compared to IABP (48.5% vs 46.4%), with higher rates of severe bleeding (8.5% vs 3.0%), vascular complications (9.8% vs 3.8%), and sepsis (35.3% vs 19.4%). 4

High-Risk Percutaneous Coronary Interventions

Impella is used prophylactically during high-risk PCI procedures to maintain hemodynamic stability. 1 The device allows straightforward percutaneous insertion with rapid initiation of circulatory support. 1

Bridge-to-Decision Strategy

In patients with severe cardiogenic shock (INTERMACS level 1-2), Impella serves as a bridge-to-decision device to stabilize hemodynamics and end-organ perfusion while determining candidacy for more definitive therapies. 4, 2 In one series, 68.8% of patients survived to next therapy: durable MCS (40.9%), heart transplant (36.4%), or recovery (22.7%). 2 The median duration of support was 7 days (IQR: 3-14 days). 2

Absolute Contraindications

The device is contraindicated in patients with: 1

• Left ventricular thrombus
• Severe aortic stenosis or significant aortic insufficiency
• Severe peripheral artery disease
• Aortic dissection or significant aortic disease

Anticoagulation Protocol

Initial Management

Administer unfractionated heparin bolus of 100 U/kg (maximum 5000 units) at the time of implantation to prevent pump thrombosis. 1 This is critical as pump stoppage can result in stagnant blood flow and thrombus formation, with restarting after prolonged stoppage risking stroke or systemic thromboembolism. 5

Post-Removal

After device removal, antiplatelet therapy should be considered based on the patient's underlying condition and risk factors. 1

Bleeding Risk

Severe or life-threatening bleeding occurs in 8.5% of Impella patients versus 3.0% with IABP, requiring careful balance of thrombotic and bleeding risks. 1

Device Management and Monitoring

Hemodynamic Assessment

Monitor the following parameters continuously: 1

• Cardiac output and cardiac index measurements
• Mean arterial pressure (target >65 mmHg)
• End-organ perfusion markers (lactate, urine output, mental status)
• Motor current, which reflects the work required to overcome the pressure gradient

Suction Event Management

When suction alarms occur: 5

1. Verify all power cables are properly connected and confirm adequate battery power
2. Assess device function by placing a stethoscope over the pump to confirm mechanical hum
3. Check for adequate arterial flow using clinical examination or Doppler
4. Consider exchanging the controller for the backup controller if alarm persists
5. Avoid excessive tension, kinking, or cutting of the percutaneous lead

If pump malfunction persists despite troubleshooting, transport the patient immediately to the nearest center with MCS experience. 5

Escalation Strategies for Inadequate Support

When Patient Deteriorates Despite Impella

Immediately assess for device malfunction, inadequate flow capacity for the degree of shock, and consider escalation to higher-flow Impella models or alternative mechanical circulatory support. 1

For biventricular failure or inadequate systemic support: 1

• Add VA-ECMO while maintaining the Impella as an LV venting mechanism to prevent left ventricular distension and pulmonary edema
• Avoid excessive inotrope use that increases myocardial oxygen demand

For predominant right ventricular failure: 1

• Add Impella RP to create biventricular support with bilateral Impella pumps
• Consider TandemHeart Protek-Duo percutaneous right ventricular assist device

Vasopressor Selection

When additional vasopressor support is needed, vasopressin or norepinephrine are preferred as they increase systemic afterload without significantly increasing pulmonary vascular resistance. 1

Weaning Protocol

Echocardiographic Assessment

Serial echocardiographic evaluations should assess for: 1

• Improvements in left ventricular systolic function
• Resolution of any mechanical complications
• Adequate cardiac output with reduced device support

For patients who fail initial weaning attempts, consider longer support duration (median 7 days, up to several weeks) or transition to more durable mechanical circulatory support devices. 1, 2

Complications and Limitations

Major Complications

• Vascular complications: 9.8% (vs 3.8% with IABP) 4
• Severe bleeding: 8.5% (vs 3.0% with IABP) 4
• Sepsis: 35.3% (vs 19.4% with IABP) 4
• Pump thrombosis: 14% in some series 3
• Device displacement requiring repositioning 3

Flow Limitations

The maximum flow capacity, particularly for Impella 2.5, may be inadequate for patients with large body mass index or severe cardiogenic shock. 1 In such cases, consider upgrading to Impella CP or 5.0 models.

Outcomes Data

Bridge-to-Decision Outcomes

In patients with severe heart failure (48.4% INTERMACS 1,51.6% INTERMACS 2): 2

• 30-day survival: 67.2%
• 60-day survival: 65.6%
• Survival conditional on reaching next therapy: 94.1% at 30 days, 91.2% at 60 days
• Survivors were less likely to be on ventilators (p=0.049) or continuous renal replacement therapy (p<0.001)

Non-Ischemic Cardiogenic Shock

Impella CP can be used effectively in non-ischemic cardiogenic shock with comparable outcomes to ischemic shock, showing a trend toward better 30-day survival (48% vs 30%, p=0.126) despite similar severity of illness at presentation. 6

Comparison with Other Temporary Support Devices

• Versus IABP: Impella provides greater left ventricular support and direct cardiac output augmentation, though IABP-SHOCK II trial showed no mortality benefit for IABP in cardiogenic shock 4, 1
• Versus TandemHeart: Impella has simpler design and implantation procedure 1
• Versus VA-ECMO: VA-ECMO provides biventricular support but may require additional LV venting with Impella to prevent left ventricular distension 1