These two cases illustrate the effective use of POC TTE in rapid diagnosis of clinical problems related to cardiopulmonary mechanical support devices. In the first case, POC echocardiography was used to diagnose Impella malposition. While hemolysis is a documented complication of the Impella device, the underlying mechanism can be related to either the shear stress of the device or improper positioning [15, 16]. The improper positioning of the device can lead to hemolysis as turbulent flow is generated when the outflow of the cannula is too close to the aortic valve or when the outflow of the device is partially below the aortic valve (Fig. 1). Given the different mechanisms that could lead to hemolysis in these patients, it is mandatory to check the cannula position before any therapeutic interventions are undertaken. Unlike the case of malposition, hemolysis related to shear stress would warrant either removal of the device, dependent on the extent of hemolysis, or change in the anticoagulation plan. Bedside TTE thus provides the clinician with the ability to quickly determine if cannula malposition is the cause of hemolysis. The bedside availability of TTE for device placement is recommended by the European Expert Group although very few case reports in literature have described the utilization of bedside TTE for Impella device repositioning [17].
Case one also demonstrates the importance of real-time echocardiographic confirmation of device positioning even when device hemodynamic pressure signals do not display evidence of malposition. The Impella device is fitted with a display screen that continuously monitors device position using a waveform calculated from the pressure difference between the inlet and the outlet areas. Based on the changes in this waveform, a proximal or a distal migration of the device can be detected. As the distal pressures are monitored in an open area above the outlet port, migration of the device outlet area into the aortic valve is possible without a change in waveform [15]. We suspect this to be the case in our patient. In this case, even though the device console indicated appropriate device position, the device malposition was evident on the TTE exam.
The second case highlights the important role of bedside echocardiography in daily management of patients requiring VV-ECMO therapy. Traditionally, VV-ECMO support has been achieved via dual cannulation either through femoro-jugular or femoro-femoral venous cannulation. However, VV-ECMO support can now be achieved via single-vessel cannulation at the internal jugular vein with the use of Avalon Elite Bicaval Dual Lumen Cannula®. The advantages of this cannula include less recirculation, improved patient mobility, and decreased risk of infection. However, this catheter like other ECMO catheters when improperly positioned can lead to recirculation, arrhythmias, and a decrease in ECMO flows resulting in hypoxia [7, 8].
As highlighted by our case, echocardiography can assist in determining the cause of inadequate flows and allow clinicians to institute correct therapies. Due to underlying lung pathology, physicians treating these patients generally employ restrictive fluid strategy. This can result in a decrease in ECMO flows due to collapse of the IVC around the cannula. The collapse of the IVC around the catheter combined with signs of hypovolemia can be determined with real-time echocardiography and allow physicians to guide fluid therapy. However, ECMO catheter malpositioning can result in decreased flows as well, in which case the proper therapy would be to reposition the catheter in order to achieve adequate flows. As evidenced by this case, diagnosis of catheter malposition as the cause of decreased flows prevents excessive fluid administration that would otherwise risk worsening of pulmonary function due to volume overload. Additionally, cannula repositioning should always be performed under real-time fluoroscopy or echocardiography guidance as migration of the tip of the cannula into the right ventricle could lead to structural damage and poses risk of arrhythmias [7].