Continuing Education Activity

There are now percutaneous inserted ventricular assist devices available. This device is a non-pulsatile axial flow pump that is placed across the aortic valve and pumps blood from the left ventricle (LV to aorta). This activity reviews types, indications, contraindications, and complications of such a device. It is a type of mechanical circulatory support device that requires a team of health professions, well trained in managing high-risk patients that require ventricular support.

Objectives:

• Define percutaneous inserted ventricular assist devices and explore the different types of these devices.
• Outline the indications of percutaneous inserted ventricular assist device placement.
• Summarize the pertinent clinical trials regarding percutaneous inserted ventricular assist devices.
• Describe the effect of the interprofessional team on the outcome of patients with percutaneous inserted ventricular assist device placement.

Introduction

Percutaneous mechanical support devices have been used widely in clinical practice. The first use of mechanical support was in the 1960s with the intra-aortic balloon pump.[1] This device had seen wide use as it was relatively small and easy to place; however, it offered limited support, augmenting cardiac output by only 0.5 L/min. Until recently, percutaneous options for mechanical support have been limited until the advent of the percutaneously inserted axial flow pump ventricular assist device. 

The percutaneously inserted ventricular assist device (LVD) is a nonpulsatile axial flow pump that crosses the aortic valve and pumps blood from the left ventricle (LV) to the aorta.[2] The FDA has approved percutaneously inserted LVD for partial circulatory support since 2008. There are multiple different types of percutaneously inserted LVD that provide different levels of support. A percutaneously inserted LVD that provides a maximum flow rate of 2.5 L/min first device approved. Another percutaneously inserted LVD a maximum rate of 5 L/min for full circulatory support, however requiring surgical cut down for implantation. Finally, an intermediate level device was developed to offer an intermediate level of support of 3.0 to 4.0 L/min and can be placed percutaneously.[3][4]  

The percutaneously inserted LVD has impactful effects on the hemodynamic by decreasing the load on the left ventricle and myocardial oxygen consumption, subsequently improving cardiac output and reducing left ventricular end-diastolic pressure, leading to improvement in the coronary perfusion and systemic mean arterial pressure. Additionally, by improving forward output, percutaneously inserted LVD reduces left atrial pressures leading to right ventricle afterload reduction.[5] 

Other variations of the percutaneously implanted assist devices have since undergone development to aid providing mechanical circulatory support. The percutaneously inserted right ventricle assist device (RVD) was designed to be used in right ventricular (RV) failure and is a 22 french nonpulsatile axial flow pump mounted on an 11 Fr catheter and positioned via femoral venous access. The inflow of percutaneously inserted right ventricle assist device (RVD) is placed in the inferior vena cava and the outflow in the pulmonary artery and can provide up 4 L/min flow to help support a failing RV.[6]

Anatomy and Physiology

Through single femoral arterial access, the percutaneously inserted LVD crosses the aortic valve in a retrograde fashion with the inflow placed in the left ventricle and the outflow in the ascending aorta.[3] 

While the percutaneously inserted RVD requires femoral venous access, the device advanced and positioned across the tricuspid and pulmonary and ejects blood from the inferior vena cava to the pulmonary artery.[7] 

Indications

• High-risk percutaneous intervention, there is no precise definition for high-risk percutaneous coronary intervention (PCI), and many factors should be taken into consideration like impaired LV function, left main stenosis,  ostial stenoses, heavily calcified lesions, and cardiogenic shock.
• Acute myocardial infarction. Some patients with (STEMI) and non-ST-elevation myocardial infarction (NSTEMI) would benefit from circulatory support to unload the LV and improve the coronaries perfusion; however, no evidence of the benefit of the mechanical circulatory support in decreasing the myocardial injury in the setting of acute occlusion.  
• Cardiogenic shock and advanced heart failure to stabilize critically ill patients and serves as a bridge to recovery, surgical, mechanical circulatory support, or transplant.[4] 
• Selected high-risk patients undergoing percutaneous aortic valvuloplasty or aortic valve replacement.[8]
• Patients with severe LV dysfunction undergoing electrophysiologic procedures as these high-risk patients will be intolerant to prolonged ventricular arrhythmia during the procedure.[9]
• Right ventricular failure using percutaneously inserted RVD. RECOVER RIGHT trial demonstrated the safety and the immediate hemodynamic stabilization in the patients with acute RV failure.[6]

Contraindications

• Significant peripheral vascular disease
• Aortic stenosis (less than 1.5 cm) or insufficiency
• Ventricular septal defect. The percutaneously inserted LVD increases the left to right shunt significantly 
• Left ventricular thrombus [3]

In the presence of one or more of the mentioned contraindications, another modality of mechanical circulatory support should be considered.

Equipment

• LVD mounted on 9 Fr catheter
• Console to control the performance of the device and to display the pressure gradient between the inflow and the outflow
• Purge solution through the sidearm at the distal end of the 9 Fr catheter
• Pressure monitoring tubing

Personnel

Interventional cardiologists place low flow, and intermediate flow assist devices percutaneously under fluoroscopy guidance. The high flow assist devices require surgical cutdown for placement and thus require positioning by cardiothoracic surgeons.

Technique

The low flow LVD (2.5 L/min)  is a 12F pump mounted on a 9F catheter shaft, and advanced via femoral artery access and positioned across the aortic valve into the LV under fluoroscopic guidance. The high flow LVD  (5.0 L/min) also mounts on the same 9F catheter shaft, and the pump is 21F in diameter. Due to its size, the high flow LVD requires a surgical cutdown via the axillary or femoral artery.

The 9F catheter includes the purge and the pressure lumens, and the proximal end of the 9F catheter consists of a hub for console cable attachment and side arms for purge solution and pressure monitoring tubing 

The console allows the pump speed management (9 levels of performance) and displays the pressure difference between the inflow and the outflow.

Intravenous heparin is recommended during the device deployment to achieve activated clotting time between 250 to 500 seconds and activated clotting time between 160 to 180 seconds after the placement to prevent clots formation.[10] 

Complications

• Hemolysis due to mechanical erythrocyte shearing
• Acute kidney injury secondary to persistent hemolysis 
• Limb ischemia
• Vascular injury including hematoma, pseudoaneurysm,  fistula, and retroperitoneal hemorrhage
• Bleeding requiring blood transfusion
• Pericardial tamponade[11]

Clinical Significance

Percutaneously inserted LVDs (2.5 L/min) have been studied in comparison with the intra-aortic balloon pump. In ISAR-SHOCK trial, 25 patients with acute myocardial infarction and severely reduced LV function randomly allocated to either percutaneously inserted LVD or IABP arm, The cardiac index after 30 min of support was greater in patients with the percutaneously inserted LVD (2.5 L/min)  compared with patients with intra-aortic balloon pump (IABP), however, no difference in the 30-days mortality between both arms.[12]

In PROTECT II, A total of 448 high-risk patients undergoing percutaneous coronary intervention (PCI) were randomized, 223 to IABP, and 225 to the percutaneously inserted LVD (2.5 L/min). The study terminated early. There is no difference in the 30-day incidence of major adverse events for patients with IABP or percutaneously inserted LVD (2.5 L/min). However, on per-protocol analysis,  improved outcomes were observed for percutaneously inserted LVD (2.5 L/min)-supported patients at 90 days driven mostly by a reduction in the need for repeat revascularization.[13]

On the other hand, the RECOVER RIGHT trial studied prospectively 30 patients with refractory RV failure (12 patients with myocardial infarction and 18 patients after cardiac surgery). It demonstrated the safety and efficacy of percutaneously inserted RVD  in improving the central venous pressure and the cardiac index immediately after activation. The overall survival in the trial at 30 days was 73.3%.[6][14]

Enhancing Healthcare Team Outcomes

The initiation of mechanical circulatory support therapy (whether temporarily or destination therapy left ventricular assist device) requires an interprofessional team of different health care professionals including and not limited to: cardiologists, cardiothoracic surgeons, nurse coordinators, social worker, and palliative care, all sharing their findings, monitoring as appropriate, and making adjustments to the treatment plan as conditions indicate. This interprofessional collaboration will lead to better patient outcomes when using these implantable devices. [Level 5]

Early identification of the need for mechanical circulatory support may improve outcomes. The implementation of a cardiogenic shock team (multidisciplinary team) is recommended for early diagnosis, structured protocols, risk stratification and, early application of the appropriate mechanical circulatory support device is recommended.[15][16][15] [Level 3, Level 2]