17.2 ECMO, Intravascular Lithotripsy & Distal Embolic Protection

ECMO, Intravascular Lithotripsy & Distal Embolic Protection

ARRT Cardiac-Interventional Procedures 2.A.10–A.13 cluster three advanced tools the R.T.(CI) still has to staff: extracorporeal membrane oxygenation (ECMO), intravascular lithotripsy (IVL), and distal embolic protection. They share a cath-lab zip code. They do not share physics. The Focus of Questions layer still applies — anatomy, indications, contraindications, imaging, access, ultrasound, equipment, complications, closure — and the hybrid OR conversation from 14.1 sits under ECMO more than under a coronary IVL balloon.

Quick Answer: VA-ECMO uses arterial plus venous cannulae and supports heart and lungs. Place a distal perfusion catheter so the arterial-cannula limb does not die. Differential hypoxia (North-South / Harlequin) is the VA teaching; recirculation is the VV cousin. VV-ECMO is respiratory-only. Anticoagulation keeps the circuit from clotting; air in the circuit is lethal. IVL (Shockwave-class) is a balloon with emitters that send sonic pressure waves to fracture calcium, 0.014" compatible in coronary and peripheral work, delivered in cycles. Transient VF/VT is a real risk, especially in the RCA — pads on. IVL complements atherectomy (15.3); it does not always replace it for nodules. Distal filters (Spider / FilterWire-class) are classic in SVG PCI; they need a landing zone and must be retrieved without spilling debris.

VA-ECMO versus VV-ECMO — get this binary right

Veno-arterial (VA) ECMO drains venous blood (usually a multistage femoral venous cannula to the RA), runs it through a pump and oxygenator, and returns it to the arterial tree (usually the femoral artery). That loop provides both cardiac and respiratory support. It is the configuration that appears when a CI case becomes cardiogenic shock, refractory arrest (ECPR), or high-risk PCI collapse.

Veno-venous (VV) ECMO drains and returns entirely on the venous side. It oxygenates and removes CO2. It does not support blood pressure. Isolated respiratory failure with a beating, adequate LV is a VV problem, not a CI mechanical-support problem. Know it so you do not call VV “the shock circuit.”

Cannulation and the room. Peripheral VA cannulae can go in at the table. Central cannulation (RA to aorta) and messy conversions belong in a hybrid OR with a perfusion path and the ability to open the chest without moving the patient (14.1). Map dedicated outlets and UPS the same way you would for an Impella console — the ECMO cart is not an extension-cord device.

Distal perfusion catheter. A femoral arterial return cannula is large enough to occlude the iliac or SFA. Limb ischemia is expected unless you add an antegrade distal perfusion catheter (commonly into the SFA) that feeds the leg. Check pulses and Doppler after cannulation, not at the end of the case. This is IABP limb-ischemia logic at extra-large French sizes.

Recirculation versus North-South (differential hypoxia)

Do not mash these two words together.

Recirculation is a VV-ECMO problem. If the drainage and return cannulae sit too close, newly oxygenated blood is immediately re-aspirated into the circuit. The circuit SvO2 looks beautiful; the patient’s brain does not. Fix it by separating the cannulae, not by turning the blender to 100% and hoping.

Differential hypoxia — North-South / Harlequin syndrome — is a peripheral VA-ECMO problem. ECMO blood enters the femoral artery and supplies the lower body. If the native LV recovers enough to eject, but the lungs are still wet or atelectatic, the LV ejects deoxygenated blood into the arch. The brain and coronaries (the “north”) see blue blood; the legs (the “south”) see pink ECMO blood. A right-radial ABG is the brain/coronary sample; a femoral ABG is the ECMO sample. They will not match. Teaching moves: improve native lung oxygenation, consider LV venting, raise ECMO flow, or convert the return (VAV / central) — those are operator decisions. Your job is to recognize that this is VA, not VV, and to sample the right radial.

ECMO circuit rules the R.T.(CI) can be failed on

Anticoagulation is required because a stagnant or slow circuit thromboses, and circuit clot embolizes into whichever bed the return cannula faces (arterial = brain and body; venous = lungs). Bleeding from large-bore sites is the other wall. This is a perfusion and ACT conversation, not “heparin off because we are also doing PCI” without a plan.

Air in the circuit is lethal. The oxygenator and the arterial return will deliver a massive air embolism into the aorta (VA) or the right heart (VV). Never leave a stopcock open to air. Prime completely. Emergency clamps live on the tubing, not in a drawer down the hall. If you see bubbles, clamp and call — do not “aspirate later.”

Other complications: bleeding, stroke, North-South hypoxia, recirculation (VV), cannula malposition, and the access-site disasters of 6.3 at extra-large French sizes. Closure of ECMO arterial access is surgical or a planned preclose — it is not a 6 Fr collagen-plug story.

Intravascular lithotripsy (Shockwave-class)

Mechanism. An IVL balloon carries emitters. Inflated to a low atmosphere (teaching 4 atm for energy delivery), it does not rely on high-pressure barotrauma. The emitters fire sonic / acoustic pressure waves that travel through soft tissue and fracture calcium at tissue–calcium interfaces — superficial and deep. Vessel compliance rises so a subsequent non-compliant balloon and stent can expand.

Platform. Coronary and peripheral IVL balloons are 0.014" compatible. They track like a balloon, not like a Rotablator burr. Peripheral shafts are longer and fatter; the physics of the wave is the same.

Cycles. Energy is delivered in prescribed pulse cycles, not as a continuous drill. Count cycles with the operator. Do not treat “one more cycle” as free after the balloon has already ruptured or the vessel has a new spiral flap.

Arrhythmia — pads on. The sonic pulse can trigger transient VF or VT, especially in the RCA (proximity to the AV node and right ventricle). Defibrillator pads go on before the first cycle, not after the first wide-complex beat. This is the IVL equivalent of rotational-atherectomy RCA bradycardia: you do not discover it.

IVL versus atherectomy. IVL is excellent at circumferential calcium that will not let a stent expand. Nodular, eccentric calcium that a balloon cannot appose may still need orbital or rotational atherectomy (15.3). Teach complement, not replacement. A lab that “does not do burrs anymore because we bought lithotripsy” will still meet a nodule.

Complications: dissection, perforation (less barotrauma than a high-pressure NC fight, not zero), balloon rupture, and the VF/VT above. After IVL, size and post-dilate as you would any calcium-modified vessel — IVL is not a finished PCI.

Contraindications are mostly balloon-in-vessel problems: an unprotected perforation already in progress, an inability to deliver the balloon, or a landing zone so small the balloon cannot inflate without jailing something you cannot recover. Uncorrected coagulopathy is a PCI problem, not an IVL-specific exception.

Distal embolic protection

Degenerated saphenous vein grafts (SVGs) are full of friable atheroma. Ballooning or stenting them without protection is a classic no-reflow / periprocedural MI setup. Distal filters (Spider-class, FilterWire-class) are the exam-classic answer for SVG PCI. The same idea appears in carotid stenting and in selected peripheral work; native-coronary distal protection is not the everyday teaching.

Landing zone. The filter must open in a relatively straight, disease-free segment distal to the lesion, large enough for the basket, not at a tight bifurcation, and not in a segment so distal the vessel is too small. No landing zone means no filter — and that may mean a different strategy, not a jammed basket in a 1.5 mm channel.

Two delivery flavors to recognize:

• Filter-on-a-wire (FilterWire-class): the protection wire is the lesion wire.
• Bare-wire then filter (Spider-class): you may keep a workhorse wire and deliver the basket over it — useful when the graft was already wired.

Retrieve without spilling. At the end, recapture the basket into the recovery sheath under fluoro. A full filter dragged through a stent and dumped at the sheath tip is how you cause the no-reflow you were hired to prevent. If the basket will not recapture, stop yanking and tell the operator — force plus a loaded filter equals distal embolization.

Unique risks: filter thrombosis, spasm at the landing zone, inability to retrieve, vessel injury from the hoop, and debris spill on recovery. An occlusion-balloon plus aspiration system is a different, less-used class (inflate distal, aspirate, deflate); do not confuse it with a filter that is supposed to keep antegrade flow.

Table: device / classic indication / unique risk

Imaging, access, ultrasound, closure

ECMO: fluoro or TEE confirms cannula depth (venous to RA, not in the RV; arterial not dissecting the iliac). Ultrasound guides both sticks. Closure is large-bore or surgical.

IVL: treat it as a balloon — markers on fluoro, 0.014" wire, coronary or peripheral guide that will accept the profile. Pads on. After cycles, IVUS or OCT can show fractured calcium and whether a nodule remains.

Filters: fluoro the landing zone before you commit. On retrieval, cine the recapture. Access is whatever the SVG or carotid case already used; the filter does not change the stick, it changes the distal choreography.

Worked case

A degenerated SVG to an obtuse marginal is the PCI target. There is a clean 4 mm landing zone before the distal anastomosis. A FilterWire-class basket opens there, the stent goes in, and the basket comes back into the sheath — not dragged full through the hemostatic valve. Same patient, later: a proximal RCA with circumferential calcium. Pads on, IVL balloon at teaching 4 atm, cycles delivered, then an NC balloon. A nodular island still waists the NC balloon — that is atherectomy, not “ten more lithotripsy cycles until VF.”

A different room: STEMI shock, VA-ECMO femoral–femoral. No distal perfusion catheter, and the right foot is mottled. That is a predicted complication, not bad luck. Meanwhile the right-radial PaO2 is 48 mm Hg while the femoral looks pink: North-South, not “the oxygenator failed,” and not VV recirculation.

Exam traps

• VV is not the shock circuit; VA is.
• Recirculation is not North-South. One is VV cannula spacing; the other is VA differential hypoxia.
• Forgetting the distal perfusion catheter.
• Air in an ECMO circuit is not a tiny coronary air bubble.
• IVL is not a diamond burr and not high-pressure NC physics.
• RCA IVL without pads.
• Treating IVL as a replacement for every nodule.
• SVG PCI without a landing-zone plan.
• Retrieving a full filter like a spent balloon.