The Impella CP is a left ventricular assist device based on a microaxial pump and is licensed for use for several hours during high-risk percutaneous coronary interventions and up to four days in patients with cardiogenic shock. Successful clinical off-label use for several weeks has been previously reported [1]. Other models of Impella (Impella 5.0 and 5.5) are licensed for left ventricular support up to 14 days and are being progressively used when there is requirement for higher pump flows and an anticipated extended period for circulatory support. The purpose of the Impella CP is to improve cardiac output sufficiently to prevent secondary organ failure and to unload a failing left ventricle (LV). Impella devices are used clinically for temporary mechanical circulatory support during high-risk percutaneous coronary interventions, particularly for the left main coronary artery intravascular interventions, for myocardial infarction associated with severe cardiogenic shock due to the left ventricular failure, in acute viral myocarditis or pharmacologically-induced cardiotoxicity, during off-pump coronary bypass surgery, for post-cardiotomy shock, for supporting the heart in difficult weaning of patients from cardiopulmonary bypass after cardiac surgery, and when there are clinical requirements for left ventricular venting during peripheral veno-arterial extracorporeal oxygenation [2,3,4,5,6]. It is also used in large animal translational research models of mechanical circulatory support [7,8,9].

An Impella CP is usually inserted in humans percutaneously via femoral or axillary arteries using a modified Seldinger technique with a pigtail guidewire negotiated across the aortic valve into the left ventricle. Large animal models use femoral or carotid artery access. A diagnostic catheter is negotiated over the guidewire into the LV over the guidewire, which is then exchanged for the straight-tipped Impella guidewire. An Impella is then implanted over that guidewire so that the inflow of the device is positioned approximately 3.5 cm below the aortic valve within LV, and the outflow, together with the 14Fr pump motor, above the aortic valve. The 9Fr reinforced Impella catheter traverses the aortic valve, providing continuous flow of blood from the LV into the systemic circulation with a titratable flow rate commensurate with the native cardiac output, up to 3.7 l/min.

Dynamic radiography is the most frequent imaging used to guide the Impella implantation when it is performed in a cardiac catheterisation laboratory or hybrid operating theatre [10]. However, fluoroscopic guidance may not be immediately available in cardiac operating theatres or intensive care units. Fluoroscopy is associated with radiation exposure to the patient and the staff. Echocardiography is usually performed to confirm the device position after fluoroscopically guided placement. Correct positioning of the Impella is critical for optimization of flow and avoidance of complications. Of particular importance is the position of the inflow which may inadvertently impinge on the anterior mitral leaflet, mitral subvalvular apparatus, left ventricular wall or left ventricular outflow tract wall, or migrate into the aortic root. Transthoracic (TTE), transesophageal (TEE) and intracardiac (ICE) echocardiography techniques have been reported to provide adequate imaging for successful and uncomplicated Impella CP placement [11,12,13]. However, transthoracic and transesophageal echocardiography approaches frequently do not offer adequate views sufficient for safe navigation in ovine and porcine models. Transthoracic echocardiography is impractical in intraoperative cardiac surgery. Although widely utilized during cardiac surgery, in rare circumstances TEE may be inapplicable in the presence of co-existing pathologies, such as oesophageal strictures or recent oral or oesophageal surgery, or severely limited mouth opening, limiting probe insertion in humans. The immediately available epicardial probe can also provide additional views whenever TEE images are suboptimal. This is the case in large animal models where TEE views are often very limited and insufficient for the detailed assessment required for careful implantation of the Impella during cardiac surgery. Reports of intracardiac echocardiography remain scarce due to the lack of equipment and expertise in both clinical and translational research settings [13]. It is also the most invasive of all echocardiographic modalities and requires insertion of a large-bore venous access sheath to allow intracardiac placement of the echocardiographic probe.

Epicardial ultrasound scanning of the aorta is widely used in cardiac surgery prior to cannulation for cardiopulmonary bypass [14] and therefore is readily available in most cardiac surgery institutions, as well as in translational cardiac surgery laboratories. It is also used intraoperatively in coronary arterial surgery, congenital heart disease surgery and for placement of durable ventricular assist devices [15,16,17,18,19]. Detailed recommendations for the human epicardial echocardiographic scanning have been published [20]. The use of epicardial scanning in a large animal model has been previously reported [21].

We hypothesised that it is feasible to guide the implantation of the Impella CP using epicardial echocardiography without the need for fluoroscopy or other echocardiographic techniques.