The primary echocardiographic measurement for an Impella device is the distance from the aortic valve annulus to the pump’s inlet area, which should sit approximately 3.5 cm below the valve. Beyond that single distance, a complete echo assessment includes confirming the catheter’s orientation, evaluating flow with color Doppler, and screening for complications like suction events or right ventricular failure.
Where the Inlet Should Sit
The Impella is advanced into the left ventricle so that the inlet area of the pump sits about 3.5 cm below the aortic valve, with the pigtail tip directed toward the apex. This measurement is the single most important number to confirm on echo. If the inlet migrates too close to the valve, it can straddle the aortic annulus and deliver blood right back into the ventricle instead of the aorta. If it drops too deep, it risks contact with the ventricular wall or papillary muscles.
To measure this distance, use a long-axis view (parasternal long axis on TTE, or the mid-esophageal long-axis view on TEE). Identify the aortic valve annulus, then measure down along the catheter shaft to the inlet area, which appears as the region where the catheter widens slightly. The pigtail at the very tip should point toward the apex without curling against the wall or septum.
TTE vs. TEE: Choosing the Right Approach
Transthoracic echo (TTE) is the first-line tool for routine checks at the bedside. It works well for confirming gross positioning, assessing ventricular filling, and screening for pericardial effusion. However, the metal components of the Impella catheter create acoustic shadowing that can obscure nearby structures, particularly the aortic valve. One documented concern is that color Doppler artifact from the device can mask aortic regurgitation on TTE, making a significant valve injury harder to detect.
Transesophageal echo (TEE) provides better spatial resolution of the device, the aortic valve, and surrounding flow. TEE is preferred during initial placement (especially in the operating room or cath lab), whenever the clinical picture doesn’t match expected hemodynamic improvement, and when TTE images are inconclusive. If a patient on Impella support isn’t improving and the TTE looks unremarkable, TEE should be strongly considered to rule out complications that artifact may be hiding.
Using Color Doppler to Verify Flow
Color Doppler is essential for confirming that the device is actually working as intended. You’re looking for two things: flow entering the inlet inside the left ventricle and flow exiting the outlet in the ascending aorta.
At the inlet, color Doppler should show organized flow converging toward the pump from the ventricular cavity. Turbulent or disturbed flow patterns near the inlet suggest partial obstruction, often from the device sitting too close to the septum or free wall. At the outlet (just above the aortic valve in the ascending aorta), you should see a jet of forward flow during device operation.
Also check the aortic valve itself. In a well-supported patient, the native aortic valve may open minimally or not at all because the Impella is doing most of the work. That’s expected. But if you see a regurgitant jet at the valve that wasn’t present before device insertion, that raises concern for iatrogenic valve injury, and TEE may be needed for a closer look.
Recognizing Suction Events on Echo
Suction events happen when left ventricular preload drops too low and the pump essentially tries to pull more blood than the ventricle can supply. On echo, the hallmarks are straightforward: the inlet area appears pressed against the septum or ventricular wall, and the left ventricle looks collapsed or significantly underfilled. The Impella console will usually alarm simultaneously, but echo confirms the mechanism and guides repositioning.
Color Doppler during a suction event often shows disturbed flow at the inlet, consistent with partial obstruction. You may also notice that the aortic valve has minimal or no opening, reflecting the low-output state. The fix typically involves volume resuscitation to improve preload, reducing the pump speed, or repositioning the catheter if it has migrated into the wall.
Assessing Right Ventricular Function
An Impella supports the left ventricle, but it depends entirely on the right ventricle to deliver blood to the left side. Right ventricular failure is one of the most common reasons an Impella-supported patient fails to improve, and echo is the primary way to catch it.
Look for moderate to severe RV dilation with reduced systolic function, significant tricuspid regurgitation, and septal flattening. Septal flattening gives the left ventricle a D-shaped appearance on short-axis views and indicates elevated right-sided pressures. This can be quantified with the left ventricular eccentricity index: a value above 1.1 is abnormal and suggests the right ventricle is pushing the septum leftward.
This matters practically because a leftward septal shift compresses the left ventricle, reducing filling and undermining exactly what the Impella is trying to accomplish. In severe cases, aggressive fluid administration can actually worsen the problem by further dilating the right ventricle, increasing tricuspid regurgitation, and pushing the septum even further into the left side.
Screening for Cardiac Tamponade
Pericardial effusion and tamponade are serious complications of any percutaneous cardiac device. Echo is the go-to diagnostic tool. On each assessment, sweep through standard views looking for new pericardial fluid. The hemodynamic signs of tamponade on echo include collapse of the right atrium during ventricular contraction and collapse of the right ventricle during filling (diastole). A rapidly accumulating effusion in a patient whose hemodynamics are deteriorating despite adequate Impella output should prompt immediate intervention.
Dealing With Device Artifact
The Impella’s metal catheter and motor housing create significant acoustic shadowing, which is the dark stripe behind the device where ultrasound can’t penetrate. This artifact is unavoidable but manageable with a few techniques. Use multiple imaging windows rather than relying on a single view. On TTE, combine parasternal long-axis, apical four-chamber, and apical five-chamber views to piece together a complete picture. Adjusting transducer angle slightly off-axis can sometimes shift the shadow away from the structure you need to see.
When applying color Doppler, be aware that the device itself generates high-velocity flow that can create color artifact mimicking regurgitation or turbulence. Compare findings across views and correlate with spectral Doppler when something looks abnormal. If TTE artifact prevents you from answering the clinical question, particularly regarding the aortic valve or device inlet position, escalate to TEE.
Putting It All Together: A Systematic Check
A structured approach ensures nothing gets missed. Each echo assessment of an Impella patient should cover these elements in sequence:
- Inlet position: Measure the distance from the aortic valve annulus to the inlet area, confirming it sits around 3.5 cm below the valve with the pigtail aimed at the apex.
- Catheter orientation: Verify the device crosses the aortic valve cleanly without excessive angulation against the septum, free wall, or mitral apparatus.
- Color Doppler flow: Confirm organized inflow at the inlet and outflow above the aortic valve. Flag any turbulence at the inlet or unexpected regurgitation at the valve.
- LV filling: Assess whether the ventricle has adequate volume. A collapsed or slit-like cavity suggests suction physiology.
- RV size and function: Look for dilation, reduced contraction, tricuspid regurgitation, and septal flattening (eccentricity index above 1.1).
- Pericardial space: Screen for new or worsening effusion on every study.
Running through this checklist on every echo, whether it’s a quick bedside check or a formal study, catches positioning problems and complications early, before they show up as hemodynamic collapse on the monitor.