Mechanical Circulatory SupportQuestion Bank

Correct answer: C — Transition to a direct thrombin inhibitor (bivalirudin or argatroban) while discontinuing all heparin exposure, including the Impella purge solution if present

When HIT is confirmed on ECMO, all heparin exposure must be eliminated, including systemic heparin, heparin flushes, and the heparinized Impella purge solution if an Impella is in place. The ISHLT/HFSA guideline recommends a direct thrombin inhibitor (bivalirudin or argatroban) outside the purge solution for patients with HIT on Impella support. For the Impella purge, a bicarbonate-based purge solution can replace the standard heparinized dextrose solution. The JACC Scientific Expert Panel recommends monitoring DTIs with aPTT targets of 50–60 seconds. Argatroban is hepatically cleared (important in liver dysfunction), while bivalirudin is cleared by proteolytic cleavage and renal excretion. Lubnow et al. found that HIT on ECMO, when treated promptly with argatroban, did not increase in-hospital mortality compared with non-HIT ECMO controls. Warfarin should never be initiated as the sole agent in acute HIT due to the risk of venous limb gangrene and skin necrosis.

Board pearl: In HIT on ECPELLA, all heparin must be eliminated — including the Impella purge solution, which should be switched to a bicarbonate-based alternative.

Correct answer: B — The purge solution contains heparin (typically 50 U/mL in 5% dextrose), and systemic heparin may also be required to achieve target aPTT or ACT

The ISHLT/HFSA guideline recommends an initial purge solution of heparin 50 U/mL in 5% dextrose. The device automatically adjusts purge flow (typically 2–30 mL/h) to maintain a pressure barrier of roughly 300–1,100 mmHg that prevents blood entry into the motor housing. Because the device determines the purge flow rate, frequent adjustment of systemic UFH may be required, with anticoagulant monitoring every 4–6 hours. If the heparin purge alone is insufficient to achieve anticoagulation goals, supplemental systemic UFH is added. Patients with axillary cannulation have demonstrated higher median heparin requirements compared with femoral cannulation. A survey of dozens of centers found that clinical practices varied considerably and often diverged from manufacturer recommendations, with a minority of centers having an alternative strategy for patients with heparin contraindications.

Board pearl: The purge provides local anticoagulation to protect the motor, but systemic heparin is often also needed — and the two must be managed together.

Correct answer: B — Two separate device circuits with different thrombotic surfaces, combined with the Impella purge contributing variable heparin delivery, create unpredictable systemic anticoagulation levels

ECPELLA combines the prothrombotic surfaces of both the ECMO circuit and the Impella device, each with distinct thrombotic risk profiles. The Impella purge solution delivers a variable amount of heparin systemically, which must be accounted for when titrating systemic anticoagulation for the ECMO circuit. Beavers et al. note that combining Impella with ECMO creates additional anticoagulation challenges because the purge heparin contribution is device-determined and not directly controllable by the clinician. Vandenbriele et al. emphasize that the combination of cardiogenic shock physiology, systemic inflammation, two foreign-body surfaces, and variable purge delivery creates a uniquely complex anticoagulation environment where both bleeding and thrombosis risks are amplified. Monitoring frequency should be increased, and close coordination between the ECMO and Impella management teams is essential.

Board pearl: In ECPELLA, the Impella purge delivers variable heparin that must be factored into the ECMO anticoagulation strategy — two devices, one patient, one coagulation system.

Correct answer: C — Acquired von Willebrand syndrome

Acquired von Willebrand syndrome (AVWS) is a frequent but often undetected complication of extracorporeal circuits, caused by shear-mediated degradation of high-molecular-weight vWF multimers. A reduced vWF activity-to-antigen ratio in a patient with mucosal bleeding, a normal platelet count, and therapeutic anticoagulation is the classic pattern. Kanji et al. note that AVWS frequently remains undetected on routine testing and recommend assessing the vWF activity-to-antigen ratio when mucosal or unexplained bleeding occurs on ECMO. The platelet function analyzer (PFA-100/200) can be used as a rapid screening tool with high negative predictive value. Treatment options include desmopressin (DDAVP), vWF-containing factor concentrates, or reduction of shear stress (e.g., reducing pump speed if clinically feasible). This complication is also relevant to durable LVADs — the HeartMate 3's reduced shear stress from magnetic levitation is one reason it has lower bleeding rates than the HeartMate II.

Board pearl: Acquired von Willebrand syndrome is common on ECMO and durable LVADs — check the vWF activity-to-antigen ratio when mucosal bleeding occurs with normal platelets and therapeutic anticoagulation.

Correct answer: B — Surgical-site and cannulation-site bleeding

An ELSO registry analysis by Chung et al. of VA-ECMO hemocompatibility-related adverse events (HRAEs) found that bleeding complications constituted nearly two-thirds of all HRAEs, occurring almost twice as frequently as thrombotic complications. Surgical-related bleeding (cannulation site and surgical site) represented the largest proportion of all events, accounting for nearly half of all HRAEs. However, while surgical bleeding was most common, the less frequent medical bleeding events (hemorrhagic stroke, pulmonary bleeding, GI bleeding) and ischemic stroke carried substantially higher mortality risk. Circuit-related thrombotic events, particularly clots in the circuit, were relatively frequent but had minimal impact on mortality — highlighting the importance of distinguishing between event frequency and clinical severity.

Board pearl: Surgical-site bleeding is the most common HRAE on VA-ECMO, but medical bleeding (hemorrhagic stroke, GI, pulmonary) and ischemic stroke carry the highest mortality.