Mechanical Circulatory Support

The Impella 5.0: A Brief Overview

Hamza Zaheer Ansari1, Azam Hadi2,1Resident Physician, Indiana University Health, Indianapolis, Indiana; 2Assistant Professor, Division of Heart Failure, Krannert Institute of Cardiology, Indiana University Health, Indianapolis, Indiana

Hamza Zaheer Ansari1, Azam Hadi2,1Resident Physician, Indiana University Health, Indianapolis, Indiana; 2Assistant Professor, Division of Heart Failure, Krannert Institute of Cardiology, Indiana University Health, Indianapolis, Indiana

This article received a double-blind review from members of the Cath Lab Digest editorial board.

Disclosure: The authors report no conflicts of interest regarding the content herein.

The authors can be contacted via Dr. Hamza Zaheer Ansari at hzansari@iupui.edu.

Background 

Cardiogenic shock is associated with a mortality of 35% to 80%.1,2 Lately, there has been a shift in reliance upon aggressive pharmacological therapy alone to a more hybrid approach, incorporating innovative mechanical therapy to conventional pharmacological management. It is well established that pharmacological support with inotropic agents in cardiogenic shock results in an increasing oxygen demand from myocardial tissue, as well as the development of free radicals that cause further, irreversible injury to already compromised myocardial tissue.3 Furthermore, an increase in pharmacological support results in the development of a systemic, inflammatory-like illness, leading to the production of cytokines such as IL-1, IL-6, TNF-alpha and c-reactive peptide, and further compromising the myocardium.3,4 Despite high-risk percutaneous coronary intervention (PCI) with early revascularization, no significant improvement in the rates of cardiogenic shock post-ST-elevation myocardial infarction (STEMI) has been seen. There appears to be a paradigm shift toward the use of mechanical devices, believed to play an important role in protecting the myocardium and breaking the downward spiral of cardiogenic shock.  

Rationale

The benefits of mechanical circulatory support devices, which include the Impella (Abiomed), TandemHeart (Cardiac Assist), and extracorpororeal membrane oxygenation (ECMO), are considered to be twofold. First, cardiac output is increased, which is necessary to maintain constant perfusion of vital organs and prevent multi-organ failure, a feared complication of cardiogenic shock. Second, mechanical circulatory support devices allow for decompression of the left ventricle, reduce myocardial wall stress, improve perfusion of the coronary arterial circulation, assist with formation of coronary collateralization, and help break the vicious cycle of neurohormonal activation and cytokine production that contributes to worsening myocardial contractility.5-7 

Introduction

In this article, we will focus on the Impella 5.0 microaxial pump. It was first developed at Impella Cariotechnik AG by Dr. Thornsten Siess and colleagues. Initial experimental work was performed in sheep with ventricular fibrillation and the pumps were used to provide biventricular support. The pump was initially applied intra-operatively to provide support during coronary artery bypass grafting and was the platform that future miniature versions were based upon, especially the Impella 2.5 and the 5.0 support systems. There are two forms of the Impella 5.0 currently available: the Impella LD (Left Direct) 5.0 (commonly referred to as the “Impella LD”), requiring direct insertion into the left side of the heart by way of the aorta, through open surgical access, and the Impella LP (Left Percutaneous) 5.0 (commonly referred to as the “Impella 5.0”), placed via a percutaneous route after the arterial site is exposed following a surgical cut down.

Description 

The Impella 5.0 (Figure 1) is a microaxial, catheter-mounted pump that works on the principle of Archimedes’ screw.8 It is able to generate a total output of 4.0-5.0 L/min at an RPM of 33,000, a step up from its predecessor, the Impella 2.5, which generates a maximum of 2.0-2.5 L/min. The Impella 5.0 sits with its distal end inside the ventricle, across the aortic valve, with its outlet in the proximal aorta (Figure 2). The distal end consists of a 7 French (Fr) pigtail that helps anchor the device inside the left ventricle (LV) and an inlet (proximal to the pigtail) with up to 5 openings, connected to a nitinol-based 21 Fr catheter that houses the motor at the proximal end. Distal to the encapsulated motor housing is the outlet where blood is ejected into the aorta, while distal to the outlet is the differential pressure sensor that assists with positioning the Impella across the aortic valve. The Impella is then connected to a controller system (outside of the body) that helps regulate its function, including manual adjustments of up to 9 different iterations of rotational speed, with commensurate changes in flow and resultant change in cardiac output. The controller system also houses the purge system that infuses dextrose and heparin through the Impella, preventing the blood from contaminating the motor and also preventing clotting.

Indications 

Current algorithms indicate a stepwise pattern of up-regulation of therapy in heart failure patients, graduating from pharmacological therapy to pharmacological + mechanical support if the clinical status of the patients begins to deteriorate; however, interestingly, no specific guidelines have been developed or published that indicate appropriate use of Impella 5.0 (or 2.5).9 In most cases, use of a circulatory support device is based on physician preference, as well as the degree of cardiogenic shock. Indications for device use in available literature include cardiogenic shock directly related to various etiologies, for example, postcardiotomy, acute and post myocardial infarctions, acute on chronic ischemic cardiomyopathy, myocarditis, cardiac transplant-related acute graft failure, etc. In addition, it has also been successfully implemented as a bridge “in-between” treatments, i.e., transition from one form of support to another, such as ECMO to Impella, Impella 2.5 to 5.0, intra-aortic balloon pump to Impella, etc. 

Current data 

Hemodynamics. Since Abiomed received FDA approval for the Impella, various trials and studies have been evaluating the use of the device. Studies have shown that within the first 24 to 48 hours of Impella insertion, there is significant improvement in hemodynamic parameters, i.e., right atrial pressures, pulmonary artery pressures, pulmonary capillary wedge pressures (PCWP), and increase in cardiac output. These physiologic outcomes resulted in improvement of end-organ perfusion, as well as reductions in blood lactate levels.10 In the RECOVER trial, mean arterial pressure increased from 71.4 ± 12.5 mm Hg to 83.1 ± 7.5 mm Hg. In a study by La Torre et al, cardiac index increased from 1.9±0.4 to 3.1±0.6, PCWP decreased from 27.6±4.4 to 15.4±5.9, and central venous pressure decreased from 20.8±2.8 to 12.2±3.1 after initiation of therapy.10 

Duration of use and outcomes. The FDA has approved use of Impella for 6 hours, but current data has revealed off-label use in patients for a variable duration, ranging from a few hours to an average of 12 days, with the longest recorded duration at 35 days in a single documented case.11-15 In a 2011 Canadian study, Higgins et al looked at use of the Impella 5.0 (along with a few cases of the Impella 2.5) in patients with acute myocardial infarction (AMI), postcardiotomy cardiogenic shock (PCCS), and dilated cardiomyopathy. Patients had the device in place for an average of 3.7±3.0 days, with an overall mortality of 40% at 30 days and 49% at 6 months.12 

Lemaire et al, in 2013, recorded the use of the Impella 5.0, along with a few cases of Impella 2.5 (27 vs 9 cases), in patients with PCCS, AMI, chronic ischemic cardiomyopathy, and myocarditis-induced shock. Duration of device use was found to be 4.5±3.9 days. Mortality was 28% at 30 days, 36% at 90 days, and 39% at 1 year.13 In 2013, the RECOVER trial looked primarily at Impella 5.0 LD. In 16 patients with PCCS, overall survival was 94% at 30 days, 81% at 3 months, and 75% at 1 year.11 These results are in contrast to those presented by Engstrom et al, in a 3-center European study, where 46 patients were implanted with the Impella 5.0 for management of underlying treatment refractory PCCS, with a mortality of 60.5% at 30 days.12 

Duration of stay. The average duration of stay for patients after removal of the Impella has also been variable, but as is expected, patients do end up staying for extended periods of time after explantation. In the study by Higgins et al, patients stayed in the hospital for 19±34 days (median 11 days) after device removal (in the group that survived). In other cases, patients have been reported to stay in the hospital for, on average, 3-4 weeks before being discharged.16

The eventual outcomes vary in the literature, with the Impella 5.0 used in complete recovery of ventricular function in some patients (as a “bridge to recovery”), while in others, it has been used in cases where implantation of permanent ventricular assist devices such as the HeartMate (Thoratec) or a transplant has occurred (a “bridge to destination”). 

In patients who do not survive percutaneous ventricular assistance, or do not make it to destination therapy, mortality is frequently due to multi-organ failure. Infrequent cases have also pointed towards device malfunction, intractable arrhythmias, intracranial hemorrhage, and thrombocytopenia as some of the causes of death. 

Complications

The complications associated with the Impella 5.0 are also well documented and include the development of anemia in 5% to 10% of patients, most often due to blood loss secondary to heparinization, along with hemolysis in a small subset of patients, seen most often during the first 24 hours and with higher rotational speed of the device. Most published data has, however, shown the return of free hemoglobin levels to normal after the first 24 hours of device insertion. Other complications that have been reported in the literature include aortic injury and aortic valve insufficiency, arrhythmias, bleeding, cardiac tamponade, cerebral vascular accident (CVA), functional mitral stenosis, limb ischemia, mitral regurgitation secondary to chordal rupture, etc.9,12,17,18 Device malfunction is predominantly due to device thrombosis.

Contraindications

Similar to the Impella 2.5, the Impella 5.0 is contraindicated in certain situations. In those patients with peripheral arterial disease that would preclude insertion of the Impella 5.0, it is not advisable to use it, because the sheath required for insertion is fairly large. Also, in those patients with aortic valvular pathologies, such as severe aortic valve calcification, where the device can trigger embolization of calcium fragments since it sits across the aortic valve, the Impella is not a good supportive modality. Similarly, in patients with aortic regurgitation, prosthetic aortic valves, aortic dissection, left ventricular thrombi, ventricular septal defects, severe sepsis, and bleeding diathesis, it should not be used.19  

Conclusion 

The quest to find the most suitable treatment modality for cardiogenic shock is far from over. Data on the current available percutaneous ventricular assist devices are still very limited but is continuing to grow. Sometimes a clear. early exit strategy to break the cycle of shock is not always available in these patients, and what the Impella provides is a window for the cardiac team; buying time to perform a thorough work-up and plan for an appropriate long-term treatment strategy. Therefore, in this acutely ill population that tends to be intubated and on extensive inotropic and pressor support at the time of device insertion, the Impella has shown consistent hemodynamic improvement, and effectively functions as a bridge to recovery, bridge to bridge, or bridge to further destination therapy modality. 

Though data are limited, percutaneous ventricular assist devices such as the Impella 5.0 appear to be a viable option for acute heart failure therapy, one that the field seems to be cautiously embracing. The timely and appropriate use of percutaneous ventricular assist devices can indeed improve outcomes. In the meantime, we as cardiologists, cardiothoracic surgeons, and vascular surgeons, along with members of the cardiac cath lab teams, must strive for the effective use of these devices, including forming a task force of highly experienced interventional physicians and staff to develop appropriate practice guidelines for the use of this technology. n

References

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