Impella device

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Tarek Nafee, M.D. [2]

Overview

The Impella device is a percutaneously inserted ventricular assist device (pVAD) that is used to temporarily support left or right ventricular function in patients with cardiogenic shock complicating acute myocardial infarction who undergo high-risk percutaneous coronary intervention (PCI) or open heart surgery. Cardiogenic shock occurs in approximately 6% to 12% of patients with STEMI and 17% of patients with NSTEMI. In these patients, cardiogenic shock results in a 30% to 50% in-hospital mortality after the ischemic event. pVADs utilize a small mechanical pump to give short term support to the ventricles. pVADs aim to improve outcomes through three primary mechanisms: (1) increase the mean arterial pressure (2) reduce in ventricular diastolic pressure (3) increase in coronary perfusion.

Structure and Function

The axial flow pumps of the Impella device are mounted on a 12Fr (Impella 2.5LP), 13Fr (Impella CP), or 21Fr (Impella 5.0) support catheter and are usually inserted through the femoral, subclavian, or axillary arteries. The micro-axial catheter is placed into the ventricle in retrograde fashion and the circulating impeller transfers oxygenated blood from the inlet in the ventricle to the outlet in the ascending aorta. This mechanism effectively and rapidly increases mean arterial pressure which increases coronary and peripheral perfusion, and unloads left ventricular volume and pressure which decreases myocardial oxygen demand.

The following video describes the function of the impella device: {{#ev:youtube|HmH709RXmNE}}

Indications

High Risk PCI Patients

Impella is used to prevent hemodynamic compromise in high-risk patients by unloading the left ventricle and reducing end-diastolic wall stress [Meyns]. Additionally, the Impella device works to decrease the pulmonary capillary wedge pressure. Compared with the intra-aortic balloon pump, there is a trend toward improved 90-day outcomes among patients receiving the Impella 2.5 device [cite O’Neill study]. Studies have also shown the Impella to be effective for increasing LVEF in patients undergoing high-risk PCI [ Cite Maini, Dixon, Burzotta, Gaudard].

The PROTECT II Trial was designed to assess the differences between Impella and IABP in regard to major adverse events (MAEs) at one month in patients undergoing high-risk PCI [O’Neill]. The study demonstrated that Impella use resulted in a trend toward significance in lower out-of-hospital MAEs compared with IABP (40.6% vs 49.3%, P=0.066) in the intent-to-treat population at 90 days, whereas the per-protocol population showed significant differences between Impella and IABP (40.0% and 51.0%, respectively, P=0.023).

In patients undergoing complex revascularization, there is a risk for periprocedural and postprocedural acute kidney injury (AKI). There is a subsequent higher risk for mortality, major bleeding, and MI in these patients. Patients with low LVEF often require longer procedures and greater contrast use which places them at higher risk of acute kidney injury (AKI). One study examined AKI outcomes among patients with an average LVEF of ≤35% receiving partial Impella 2.5 hemodynamic support during high risk PCI (HRPCI). Impella support was associated with significantly fewer AKI events than control patients not receiving the device (5.2% vs 27.8%, p < 0.001).

Cardiogenic Shock

One of the prime indications for use of the Impella device is for cardiogenic shock, a condition in which the Impella has consistently demonstrated favorable post-interventional outcomes. In the USpella Registry, patients with cardiogenic shock (CS) complicating an acute myocardial infarction (AMI) receiving the Impella 2.5 prior to PCI demonstrated superior outcomes to patients receiving the device after PCI, showing the importance of early support in this setting [O’Neill]. Patients with severe refractory cardiogenic shock may also experience a beneficial short-term effect of device placement [Casassus]. The Impella 5.0 may also allow for more rapid weaning of inotropes in this patient population [Gaudard]. The IMPRESS trial, a small, exploratory study comprising a heterogeneous patient population with severe cardiogenic shock complicating acute myocardial infarction, compared patients receiving either Impella CP or IABP. Researchers found 30-day mortality was similar between Impella CP and IABP (46% vs 50%, respectively). The issue with this trial was its severely ill patient population. Since anoxic brain injury was the main cause of death, mechanical support may not even have been the most optimal treatment in this population. Additionally, the study didn’t take into account timing of device placement. Early Impella support prior to initiation of PCI is considered optimal for improved outcomes [cVAD] and absence of this information hinders the generalizability of the findings to clinical practice.

Bridging to Transplantation or Durable Device Placement

Impella 5.0 may provide an effective bridge to further therapy (transplantation or durable left ventricular assist device [LVAD]). A small study consisting of 40 critically ill patients with heart failure undergoing Impella 5.0 support found that 75% of patients were able to survive to next therapy with no observed events of major bleeding or stroke [cite Lima study]. There was a 68% survival rate to discharge and/or 30 days, demonstrating that hemodynamic support with the Impella device may allow for an effective and safe bridge to a definitive decision strategy in heart failure patients.

Approved Devices

The following impella devices are approved for circulatory hemodynamic support:

Left Ventricular Heart Failure

• Impella 2.5 The impella 2.5 delivers a maximum of 2.5L/min of blood flow from the left ventrical to the ascending aorta. Current FDA-approved indications for temporary use include:
  • Cardiogenic shock (≤4 days) that occurs <48 hours after acute myocardial infarction (MI) or open heart surgery
  • Protected PCI (≤6 hours) in elective or urgent cases of hemodynamically stable patients with depressed left ventricular ejection fraction (LVEF) and severe coronary artery disease (CAD)

Impella CP The Impella CP received expanded FDA approval for its use in High-Risk Percutaneous Coronary Intervention (PCI) Procedures in 2016. This device pulls blood from the left ventricle into the ascending aorta at a maximum rate of 3.5L/min. The indications for use are the same for Impella 2.5 and 5.0.

Impella 5.0 The Impella 5.0 is an intravascular microaxial blood pump that delivers up to 5.0 L/min of forward flow blood from the left ventricle to the aorta. The indications are the same as the Impella 2.5 and CP devices.

Right Ventricular Heart Failure

Impella RP The Impella RP provides right-sided support in patients who experience right-sided heart failure after either left-sided support, a heart attack, heart transplantation, or after heart surgery. This Impella device delivers blood from the inlet area in the inferior vena cava and through the cannula to the device outlet opening in the pulmonary artery.

Clinical Practice Guidelines

Year	Guideline	Recommendation	Class	Level of Evidence
2011	ACCF/AHA/SCAI Guideline for Percutaneous Coronary Intervention	A hemodynamic support device is recommended for patients with cardiogenic shock after STEMI who do not quickly stabilize with pharmacological therapy.	I	B
2012	Recommendations for the Use of Mechanical Circulatory Support: Device Strategies and Patient Selection	Urgent nondurable MCS is reasonable in hemodynamically compromised HF patients with end-organ dysfunction and/or relative contraindications to heart transplantation/durable MCS that are expected to improve with time and restoration of an improved hemodynamic profile	IIa	C
2013	AHA/ACC Guideline for the Management of ST-Elevation Myocardial Infarction	The use of mechanical circulatory support is reasonable in patients with STEMI who are hemodynamically unstable and require urgent CABG.	IIa	C
		Alternative LV assist devices for circulatory support may be considered in patients with refractory cardiogenic shock.	IIb	C
2013	ACCF/AHA Guideline for the Management of Heart Failure	MCS is beneficial in carefully selected patients with stage D HFrEF in whom definitive management (e.g., cardiac transplantation) or cardiac recovery is anticipated or planned.	IIb	B
		Nondurable MCS, including the use of percutaneous and extracorporeal ventricular assist devices (VADs), is reasonable as a “bridge to recovery” or “bridge to decision” for carefully selected patients with HFrEF with acute, profound hemodynamic compromise.	IIb	B
2013	The 2013 International Society for Heart and Lung Transplantation Guidelines for mechanical circulatory support	Reasonable to use temporary mechanical support for patients with heart failure awaiting transplantation who have multi organ failure.	I	-

Alternative Devices

Left Ventricular Heart Failure

• LVAD
• IABP
• VA-ECMO
• TandemHeart

Right Ventricular Heart Failure

• TandemHeart RVAD

Clinical Trials

PROTECT II Trial

The trial was discontinued early due to futility. A press release from the manufacturer Abiomed stated the following:

"Abiomed announced completion of the PROTECT II study based on a futility determination at the planned interim analysis regarding the primary end-point, which the company views as likely to be due to unanticipated confounding variables related to the use of rotational atherectomy² in the study. The decision to end the study followed the recommendation of the Data Safety Monitoring Board. The study was designed to measure major adverse events at 30 days in high risk percutaneous coronary intervention (PCI) patients randomized to receive hemodynamic support during the procedure with the Impella versus intra-aortic balloon (IAB)."

Summary and Conclusion of Protect II:

• For the entire study population, Impella significantly reduced out of hospital major adverse events (MAE) by 52% compared to IAB for the duration of the 90 day monitoring (p=0.02, N= 302).
• There was an overall positive trend in the majority (88%, n=267) of patients in the study at the interim analysis, in which Impella reduced the major adverse event rate by 26% over the IAB (Impella 32% MAE vs. IAB 43% MAE, p=0.11).
• Impella provided a 47% reduction in major adverse events over IAB in a subgroup that represents 70% of the protocol study population (Impella 23% MAE vs. IAB 43% MAE, p=0.009). An analysis of a “PROTECT” score will be presented at the upcoming ACC in April.
• When using atherectomy, Impella significantly reduced repeat revascularization (p=0.02).
• The data revealed confounding variables in the treatment between the two arms with the most significant differences related to two times more frequent use (p=0.04) and two times the number of passes per use (p=0.003) of rotational atherectomy in the Impella arm compared to the IAB arm, accounting for 12% (n=38) of total PROTECT II patients at the interim. Use of atherectomy during PCI has been previously shown to increase CK-MB release (heart enzyme) following PCI, triggering an endpoint in PROTECT II.

“Atherectomy was an unanticipated variable which resulted from the operators’ decision to ‘do more with Impella.’ Our investigators had unblinded knowledge of the treatment arm after randomization,” said William O’Neill, M.D., University of Miami and Principal Investigator of the PROTECT II study. “It is interesting that operators felt that they could do more complex interventions once randomized to Impella and this in and of itself is an important finding.”