Post-CPB platelet nadir: Expected ~38% drop in first 48–72 hours, recovering by POD 4–5. This patient's 58% decline (88 ×10⁹/L) substantially exceeds that threshold.

Early-onset HIT: Prior UFH exposure within 30 days (cath 7 days ago) enables antibody formation. Re-exposure with CPB heparin triggers a rapid-onset immune response — platelet fall by POD 0–4 rather than the typical POD 5–10 window. ~10% of post-cardiac surgery HIT cases follow this pattern.

LVAD-specific HIT incidence: ~10–15% in LVAD patients vs. ~1–3% in other cardiac surgery populations — likely due to the combination of CPB exposure, ongoing UFH requirement, and device-related platelet activation.

Nonheparin anticoagulant options: Bivalirudin 0.15–0.20 mg/kg/hr IV without bolus (target aPTT 1.5–2.5× baseline) is preferred in this patient — early RV dysfunction and hepatic congestion make argatroban clearance unreliable. Argatroban 0.5–1.2 µg/kg/min (target aPTT 1.5–3× baseline) is appropriate when hepatic function is normal. Both require reduced starting doses post-cardiac surgery.

Lillo-Le Louët score: Alternative/adjunct to 4Ts specifically designed for post-cardiac surgery patients — accounts for the confounding effect of CPB on platelet kinetics.

Communication with the surgical team: Stopping heparin in an LVAD patient is a high-stakes decision that must be made jointly with cardiac surgery. Key points to convey: (1) clinical rationale for HIT suspicion and 4Ts score; (2) plan to start bivalirudin immediately and target aPTT range; (3) conversion of all line flushes to saline; (4) ELISA sent — result expected within hours; (5) platelet transfusion is contraindicated. The surgeon needs to know anticoagulation has changed in the event of re-exploration or procedure planning.

ELISA OD >2.0: Positive predictive value ~95% for functional HIT. Treatment should not be delayed for SRA results when clinical probability is high and ELISA is strongly positive.

The aPTT paradox with argatroban in hepatic dysfunction: Baseline aPTT is prolonged by coagulopathy — so the aPTT overestimates argatroban effect. Simultaneously, impaired hepatic clearance causes drug accumulation. The clinician cannot reliably distinguish drug effect from coagulopathy. Alternative monitoring (ecarin clotting time, diluted thrombin time) is more accurate but often unavailable.

Bivalirudin clearance: ~80% enzymatic proteolysis (organ-independent), ~20% renal. Safe in hepatic dysfunction. Short half-life (~25 min) allows rapid offset. Titrate to aPTT 1.5–2.5× baseline (0.15–0.20 mg/kg/hr without bolus in post-cardiac surgery patients).

LVAD flow as a surrogate for RV function: In a fixed-speed continuous-flow LVAD, flow is preload-dependent. A declining flow with unchanged speed and no device malfunction reflects decreased LV filling — most commonly from RV failure. Pulsatility Index falls as native cardiac contribution diminishes.

Congestive hepatopathy: Elevated CVP transmitted to hepatic veins causes a cholestatic pattern — elevated bilirubin, ALP, GGT > transaminase elevation — with impaired synthetic function. Resolves as CVP decreases with RV recovery.

Hemodynamic targets for post-LVAD RV failure: CVP <12 mmHg, PAPi >2.2, CI >2.2 L/min/m², SvO₂ >60%, MAP >65 mmHg.

HITT incidence: 17–55% of untreated HIT patients develop thrombosis. After cardiac surgery, arterial events (stroke, limb ischemia, MI) predominate, but venous thrombosis — especially at catheter sites — is common.

HITT anticoagulation duration: Minimum 4 weeks of therapeutic parenteral anticoagulation, then warfarin for a total of ≥3 months (compared to ≥1 month for uncomplicated HIT).

Warfarin timing: Protein C is depleted faster than procoagulant factors when warfarin is started. In active HIT, this creates a transient prothrombotic state — particularly dangerous with DVT — and can cause venous limb gangrene or skin necrosis. Defer until platelets ≥150 ×10⁹/L.

Bivalirudin-to-warfarin transition: Straightforward — bivalirudin has minimal effect on INR. Overlap ≥5 days; stop bivalirudin when INR 2.0–3.0 on two consecutive measurements ≥24 hours apart. The argatroban-to-warfarin transition requires holding argatroban, rechecking INR at 4–6 hours, and confirming therapeutic INR off the drug — significantly more complex.

LVAD warfarin goal: Target INR 2.0–3.0 for HeartMate 3 — this aligns with HITT treatment goals, simplifying long-term planning.

Bivalirudin-to-warfarin transition: INR on combined therapy does not reflect warfarin effect alone — bivalirudin has minimal but non-zero effect on INR. The transition is safe only after ≥5 days of overlap with confirmed INR 2.0–3.0 on two measurements ≥24 hours apart while bivalirudin is held briefly to verify true warfarin effect.

Critical documentation for HIT patients: HIT allergy must be flagged at the allergy level — not just in the notes. Future providers (ER physicians, anesthesiologists, interventional cardiologists) must be able to see this at a glance. Document the specific alternative used (bivalirudin), why argatroban was avoided (hepatic dysfunction), and the CPB strategy implication for future surgery.

Antibody clearance timeline: Anti-PF4/heparin antibodies typically become undetectable 50–85 days after heparin cessation (median ~50 days). This window defines the period of maximum re-exposure risk. After confirmed SRA negativity, brief intraoperative heparin re-exposure for CPB carries low reactivation risk.

Post-transplant anticoagulation: The LVAD is explanted at transplantation — long-term warfarin is no longer required for device anticoagulation. Post-transplant anticoagulation is determined by the HITT treatment course (DVT) and institutional protocol, not LVAD indication.

Subacute HIT: The most dangerous window for heparin re-exposure. Platelets have recovered but preformed anti-PF4/heparin antibodies are still circulating and functional. Median antibody clearance ~50 days — at 4 weeks, re-exposure risks fulminant HIT.

Bivalirudin CPB — operational requirements: Non-heparin-coated circuit; ACT target >400 seconds; absolutely no circuit stasis (bivalirudin is enzymatically degraded even in the CPB tubing — stagnant blood will clot); continuous surgeon irrigation of the operative field; no protamine.

When other strategies apply: TPE + heparin is reasonable if time permits (not with a 4-hour donor window). Heparin after confirmed negative SRA is acceptable for true remote HIT (>3 months, functional assay negative). Epoprostenol + heparin has ~50 reported cases; limited to specialized centers.

Strict postoperative heparin avoidance: All heparin exposures must be eliminated — IV heparin, flushes, heparin-bonded catheters, heparin in dialysis circuits, subcutaneous heparin. All IV lines flushed with saline only. Communicate to every team member and consulting service.

Post-transplant warfarin: The LVAD is explanted — long-term warfarin for device anticoagulation is no longer required. Anticoagulation decisions are now driven by the HITT treatment course (DVT completion) and institutional post-transplant protocol.

SRA timing: No benefit to repeating SRA immediately postoperatively — turnaround is 3–5 days and will not change immediate management. The pre-transplant SRA will return and should be reviewed when available.