In a patient who is not in cardiac arrest and is supported with an Impella device and an extracorporeal membrane oxygenation (ECMO) circuit, what does the absence of pulsatile flow indicate?

What Does No Pulsatile Flow Mean in a Patient with Impella and ECMO?

In a patient supported by both Impella and ECMO who is not in cardiac arrest, the absence of pulsatile flow is an expected physiologic finding that indicates the mechanical circulatory support devices are providing the majority of cardiac output, effectively bypassing native ventricular ejection. This does not necessarily indicate cardiac arrest or device malfunction if other hemodynamic parameters remain adequate 1.

Understanding Non-Pulsatile Flow in ECPELLA Configuration

Normal Physiologic State with Dual Support

When a patient is supported by both VA-ECMO and Impella (ECPELLA configuration):

• VA-ECMO generates continuous, non-pulsatile flow by design, as contemporary ECMO systems use centrifugal pumps that create constant arterial flow rather than the physiologic pulsatile pattern 2
• The Impella device draws blood directly from the left ventricle into the aorta, creating parallel circulation that can further reduce or eliminate pulsatility 3
• Complete LV unloading (LV uncoupling) occurs when the Impella completely bypasses ventricular ejection, resulting in non-pulsatile aortic pressure with no aortic valve opening 4

Critical Distinction: Adequate vs. Inadequate Circulation

The absence of a palpable pulse does NOT equal cardiac arrest in patients on VA-ECMO. The most recent UK guidelines (2025) explicitly state that "in VA ECMO, there can often be no pulsatile blood flow and therefore no pulse detectable. In fact, there may be no detectable heart rhythm or even ventricular fibrillation with a preserved circulation" 1.

Assessment Algorithm for Non-Pulsatile Flow

Step 1: Verify Adequate Circulation Parameters

According to 2025 British Societies guidelines, adequate circulation is confirmed by 1:

• MAP > 55 mmHg (ensure transducer is functioning and leveled appropriately)
• ECMO flow > 2 L/min
• Oxygen saturation > 88%

If these parameters are met, non-pulsatile flow is expected and acceptable.

Step 2: If Circulation is Inadequate

When MAP < 30 mmHg with no ECMO flow and no recordable saturations, this represents inadequate circulation requiring immediate intervention 1:

1. Increase Impella P setting if able and follow Impella-specific algorithms 1
2. Maximize VA-ECMO flows to highest tolerated level 1
3. Initiate CPR if inadequate circulation persists despite device optimization 1

Step 3: ECMO Troubleshooting

If device dysfunction is suspected 1:

• Expose and inspect the circuit for kinks, cannula malposition, or color change between drainage and return tubes
• Check ECMO flow rates: Flow < 2 L/min indicates access insufficiency requiring RPM adjustment and fluid bolus (2.5 ml/kg crystalloid)
• Verify gas flow to oxygenator (many ECMO devices lack alarms for loss of gas flow)
• Rule out catastrophic complications: air embolus, motor failure, decannulation, or circuit rupture

Clinical Implications of Complete LV Unloading

Hemodynamic Benefits

Research demonstrates that complete LV uncoupling (no blood ejection from LV) with non-pulsatile aortic pressure significantly increases coronary arterial flow 4:

• Left anterior descending coronary artery peak velocity and velocity-time integral markedly increase
• Blood flow becomes continuous throughout the cardiac cycle rather than phasic
• This enhanced coronary perfusion may benefit injured myocardium

Potential Complications

Long-term non-pulsatile flow carries vascular risks 2:

• Disrupts endothelial homeostasis and nitric oxide signaling
• Increases risk of both hemorrhagic and thrombotic complications
• Can lead to pathological angiogenesis and accelerated von Willebrand Factor denudation

Thrombus formation risk with prolonged Impella use 5:

• Thrombi can form around the Impella shaft in mixed flow areas
• Often develop distal to the aortic arch and may be overlooked
• Can cause fatal acute arterial occlusion

Common Pitfalls to Avoid

1. Do not assume cardiac arrest based solely on absent pulse - verify with MAP, ECMO flow, and saturations 1

2. Do not rely on end-tidal CO₂ alone - the ECMO oxygenator removes CO₂, leading to artificially low ETCO₂ readings that do not reflect cardiac output 1

3. Do not delay LV decompression - retrograde arterial flow from femoral VA-ECMO increases LV afterload and can cause pulmonary edema; the Impella serves this decompression function 6

4. Do not overlook thrombus surveillance - use multiple imaging modalities during long-term ECPELLA support and prepare revascularization strategies before device removal 5

5. Ensure proper transducer leveling - confirm MAP readings are accurate before making clinical decisions 1

Management Priorities

For stable patients with non-pulsatile flow and adequate circulation parameters: Continue current support, perform routine A-to-E assessment, and monitor for complications 1.

For unstable patients: Follow the structured troubleshooting algorithm prioritizing device optimization before escalating to advanced resuscitation 1.

The 2020 AATS/ISHLT guidelines emphasize that decompression of the compromised LV is mandatory with femoral VA-ECMO, and the Impella serves this critical function in the ECPELLA configuration 6.