3. Crisis Control: VA-ECMO – An Ischemic Leg!

CathMasters Drs. Nazli Okumus and Daniel Ambinder, along with expert faculty Drs. Ann Gage and Marwan Jumean, tackle the management of limb ischemia — one of the most feared complications of peripheral VA-ECMO (veno-arterial extracorporeal membrane oxygenation) and large-bore mechanical circulatory support (MCS). Through the case of a 50-year-old woman with ischemic cardiomyopathy on VA-ECMO and Impella CP who develops right leg ischemia, the team walks through bedside assessment of the ischemic limb, equipment and technique for placing a distal perfusion catheter (DPC) on an existing ECMO circuit, strategies to mitigate limb ischemia with Impella, assessment of vascular patency during large-bore access removal, and the recognition and management of compartment syndrome. Audio editing for this episode was performed by CardioNerds Intern, Dr. Julia Marques Fernandes. CathMasters is for educational purposes only. CathMasters is for educational purposes only. Music by Elijah K from Pixabay Pearls Limb ischemia on VA-ECMO is a clinical diagnosis made at the bedside. Compare the cannulated leg to the non-cannulated leg: assess color (pallor, mottling), temperature, capillary refill, and Doppler signals (dorsalis pedis and posterior tibial). Near-infrared spectroscopy (NIRS) provides continuous, objective monitoring — an absolute rSO2 20% drop from baseline, or a>15–20% difference between legs should prompt urgent evaluation. The distal perfusion catheter (DPC) should be the standard of care for all patients on femoral VA-ECMO. Prophylactic DPC reduces limb ischemia by ~60% (OR 0.31–0.41). When placing a DPC on a patient already on ECMO, use ultrasound-guided antegrade access into the superficial femoral artery (SFA) — the stick is more challenging with a large arterial cannula already in place, so patience and meticulous ultrasound technique are critical. For Impella CP, the 14F peel-away introducer sheath can be removed ("peeled away"), leaving only the smaller 9F repositioning sheath around the catheter. This simple maneuver may be sufficient to restore distal limb perfusion without the need for a separate DPC. After removing any large-bore access (TAVR sheath, Impella, ECMO cannula), consider performing completion angiography — ideally via radial or contralateral femoral access — to confirm vessel patency and rule out dissection, thrombosis, or stenosis before leaving the lab. Compartment syndrome on ECMO is paradoxically most dangerous after reperfusion, not during ischemia. When a DPC is placed in an ischemic limb, reperfusion causes cellular edema within fascial compartments. If compartment pressures exceed 20 mmHg (or are within 30 mmHg of diastolic blood pressure), emergency fasciotomy is required. Elevated CPK and lactate are late and concerning findings — do not wait for them. Notes 1. Assessment of an Ischemic Limb Limb ischemia occurs in approximately 10–20% of patients on peripheral VA-ECMO, historically 16.9% with fasciotomy needed in 10.3% and amputation in 4.7%. Contemporary data from high-volume centers using prophylactic DPC, smaller arterial cannulas, and ultrasound-guided access report limb ischemia rates as low as 3.5%. The mechanism is multifactorial: the large arterial cannula (15–20F) partially or completely occludes the common femoral artery, reducing antegrade flow to the ipsilateral leg. Contributing factors include peripheral arterial disease (PAD), hemodynamic instability/low cardiac output, vasoconstriction from vasopressors, and thromboembolism. Bedside assessment (compare cannulated vs. non-cannulated leg): Inspection: Pallor, mottling, cyanosis, or dusky discoloration. Late findings include blistering and gangrene. Palpation: Temperature differential (cool vs. warm), capillary refill time (>3 seconds is concerning), and palpation of pedal pulses. Doppler assessment: Check dorsalis pedis (DP) and posterior tibial (PT) artery signals. Absent or monophasic signals on the cannulated side with normal signals contralaterally are highly concerning. Hourly Doppler checks should be standard nursing protocol. NIRS monitoring: Near-infrared spectroscopy placed on the calves of both legs provides continuous, real-time tissue oxygen saturation (rSO2). An absolute rSO2 20% from baseline, or a difference >15–20% between legs should trigger urgent evaluation. Studies demonstrate that NIRS-guided DPC placement reduces limb ischemia requiring surgical intervention from 8.5% to 2.6% and eliminates the need for fasciotomy in monitored cohorts. Laboratory markers: Elevated serum creatine phosphokinase (CPK) and lactate levels are late and very concerning findings, indicating that muscle necrosis has already begun. These should not be relied upon for early detection. Risk factors for limb ischemia: PAD (OR 2.19), female sex, smaller vessel caliber, larger arterial cannula size, diabetes, and prolonged ECMO duration. 2. Equipment for Adding a DPC to a Patient on ECMO Vascular ultrasound (linear probe) Micropuncture access kit (21G needle, 0.018" wire, 4–5F micropuncture sheath) 0.035" guidewire for exchange Antegrade sheath: 5–8F braided sheath (braided sheaths resist kinking in the antegrade orientation). A 6F or 7F sheath is most commonly used. Y-connector and arterial tubing to connect the DPC sheath side-arm to the arterial limb of the ECMO circuit Fluoroscopy (if available) to confirm wire position in the SFA and rule out inadvertent entry into the profunda femoris Sterile prep and drape for the ipsilateral groin/thigh Sheath size selection: The DPC sheath should be large enough to provide adequate flow but small enough to avoid further vascular compromise. A 6–7F sheath is standard. The donor vessel (ECMO arterial limb) should ideally be a larger French size than the recipient (DPC sheath) to promote flow via a high-to-low pressure gradient. 3. Procedure for Adding a DPC to a Patient Already on ECMO This is one of the more technically challenging sticks in interventional cardiology because the large arterial cannula already occupies the CFA, thereby limiting space and altering anatomy. Step 1 — Position and prep: The patient is supine. Sterile prep of the ipsilateral groin and thigh. Identify the SFA distal to the arterial cannula insertion site using ultrasound. Step 2 — Ultrasound-guided antegrade CFA-SFA access: Using a linear ultrasound probe, identify the SFA below the femoral bifurcation, distal to the ECMO arterial cannula. Perform an antegrade stick with a micropuncture needle. The key challenge is that the large cannula may compress or displace the SFA, and flow in the SFA may be diminished, making the vessel harder to visualize and access. Step 3 — Wire and sheath placement: Advance the micropuncture wire and confirm position with fluoroscopy, if available (ensure the wire is in the SFA, not the profunda femoris). Exchange for a 0.035" wire and place a 6–7F braided sheath in the antegrade direction. Step 4 — Connect to circuit: Connect the side-arm of the DPC sheath to the arterial limb of the ECMO circuit using a Y-connector and arterial tubing. This diverts a portion of oxygenated, pressurized blood from the ECMO circuit into the distal leg. Step 5 — Confirm perfusion: Reassess distal pulses by Doppler, check NIRS values, and assess clinical improvement (color, temperature, capillary refill). Improvement should be seen within minutes. Alternative approaches if antegrade SFA access is not feasible: Retrograde posterior tibial artery access with a 5–6F sheath Contralateral femoral-to-ipsilateral SFA internal bypass (up-and-over technique): Retrograde access of the contralateral CFA with a 7F sheath, advance a 4–5F sheath up and over the aortic bifurcation into the ipsilateral SFA or profunda Surgical cutdown with side-arm graft sewn onto the femoral artery 4. Ischemia Avoidance with Impella Limb ischemia with Impella CP occurs in up to 12.5% of cases, primarily due to the occlusive 14F introducer sheath in the CFA. Peel-away sheath technique: The Impella CP is inserted through a 14F peel-away introducer sheath. Once the device is positioned and secured, the outer 14F sheath can be "peeled away" (split and removed), leaving only the 9F repositioning sheath around the Impella catheter. This reduces the effective sheath size from 14F to 9F, which may be sufficient to restore adequate distal perfusion. DPC configuration for Impella: If peeling away the sheath is insufficient, a DPC can be placed using the same antegrade SFA technique described above. The donor vessel options include: Ipsilateral CFA: External bypass from the large-bore sheath side-port to the DPC sheath side-port using a male-to-male connector and arterial tubing Contralateral femoral artery: External bypass to the antegrade ipsilateral SFA sheath Contralateral femoral internal bypass: Up-and-over technique General principles: Minimize arterial cannula/sheath size when possible, use ultrasound-guided access to ensure a clean CFA stick, and continuously monitor distal perfusion with NIRS and perform hourly Doppler checks. 5. Assessing Vascular Patency During/After Large-Bore Access Removal Vascular complications after large-bore access removal (TAVR, Impella, VA-ECMO decannulation) are common and include thrombosis, dissection, stenosis, pseudoaneurysm, and distal embolization. Strategies for assessment: Pre-removal baseline: Document pedal pulses (Doppler DP and PT signals) and NIRS values on the ipsilateral leg before decannulation. Know what the baseline was so post-removal changes can be detected. Completion angiography: After achieving hemostasis, perform angiography of the access vessel — ideally via radial access or contralateral femoral access. This confirms vessel patency, rules out dissection/thrombosis/stenosis,...