Role of echocardiography in ECMO

Introduction: Echocardiography (ECHO) plays a fundamental role in the management of patients supported with extracorporeal membrane oxygenation (ECMO).¹ It is particularly useful for the detection of cardiac complications that may arise during ECMO. It helps in many ways during the ECMO run, as presented in Table 1.

Table 1.

Indications for ECMO therapy.³

ECMO is a rescue therapy used to provide cardiac and/or respiratory support for critically ill patients in whom maximal conventional medical management has failed

VV ECMO provides adequate oxygenation and carbon dioxide removal in isolated refractory respiratory failure

VA ECMO is used when support is required for cardiac and/or respiratory failure.

ECHO helps to identify or exclude new reversible pathology, which could be the actual cause of patient hemodynamic deterioration (cardiac tamponade/undiagnosed valvular lesions and left ventricular (LV) dysfunction), thus avoiding the need for ECMO support. It also helps to provide information about contraindications, for example aortic dissection. Identification of significant aortic regurgitation (AR) is a relative contraindication in veno-arterial (VA) ECMO, in which the LV afterload is increased, leading to a further increase in AR. It also provides information on aortic atherosclerosis, thus guiding the intensivist in deciding the cannulation sites (central versus peripheral) or the technique (surgical versus percutaneous). ECHO also helps to evaluate the right heart morphology for any structural abnormality, which could impede the positioning of venous cannula for veno-venous (VV) ECMO or VA ECMO. ECHO aids in diagnosing complications during ECMO: The diagnosis of upper limb hyperperfusion relies heavily on clinical features, with imaging utilized more to determine etiology. Transthoracic echocardiography (TTE) may add incremental value to the diagnosis of arterial upper limb hyperperfusion during ECMO support with an axillary artery, and it can be easily and quickly performed at the bedside.²

ECHO has a crucial role during ECMO cannulation as it guides the correct placement of the ECMO cannulas. TTE may not have the adequate spatial resolution to guide ECMO cannulation, and therefore transesophageal echocardiography (TEE) is essential. There should be a direct communication between the operator and the echocardiologist as to the site of the indented cannula insertion. For example, in VV ECMO, when one cannula is used for access and another to return the blood, the position of the access cannula tip is in the proximal inferior vena cava (IVC), just before the entry into the right atrium (RA). On the other hand, the optimal position for the return cannula is in the mid-RA, but well clear from the interatrial septum and the tricuspid valve. This can be determined with ECHO.

ECHO is critical in the detection and management of specific complications that may arise during ECMO support. Because TTE has limited spatial resolution, TEE is usually used to detect these complications. ECHO enables rapid assessment of cannula positioning, cardiac filling, cardiac function, and evidence of chamber compression from tamponade. The detection of cardiac tamponade and the assessment of the significance of pericardial effusion or collection can be difficult in patients supported with ECMO as the heart is in a partially bypassed state.

Complications in any part of the ECMO circuit can be well seen on ECHO as well as thrombosis on 2D or 3D ECHO. Conclusion: ECHO is mandatory during the initiation of ECMO, cannula insertion, hemodynamic monitoring, and detection of complications during weaning.