The platelet count has decreased from 210 ×10⁹/L (preop) to 130 (POD 1) to 88 (POD 2). Which of the following best describes the significance of this platelet trend?
Question 2 of 4
This patient received heparin during cardiac catheterization 7 days ago. How does this affect the timeline for HIT?
Question 3 of 4
Calculate the 4Ts score for this patient. Review the findings below and select the total score.
Category
Finding
Points
Thrombocytopenia
>50% fall, nadir ≥20 ×10⁹/L
2
Timing
Onset ≤1 day — prior heparin within 30 days (cath 7 days ago) enables rapid-onset immune response on CPB re-exposure
2
Thrombosis
No confirmed thrombosis; no acute systemic reaction documented
0
oTher causes
Post-CPB thrombocytopenia is a plausible alternative explanation — not definitively excluded
1
Total
?
Question 4 of 4 — Select all that apply
The 4Ts score is 5 (intermediate probability). What are your immediate next steps?
Key Teaching Points — Scenario 1
Post-CPB platelet nadir: Expected ~38–50% drop in first 48–72 hours, recovering by POD 4–5. This patient's 58% decline (88 ×10⁹/L) exceeds that threshold and continued declining rather than stabilizing — a pattern requiring investigation.
Early-onset HIT: Prior UFH within 30 days enables antibody formation. Re-exposure at CPB triggers a rapid 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% vs. ~1–3% in other cardiac surgery populations — driven by 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 here — 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 with normal hepatic function. Both require reduced starting doses post-cardiac surgery.
Lillo-Le Louët (LLL) score: An alternative/adjunct to 4Ts specifically designed for post-cardiac surgery patients — accounts for the confounding effect of CPB on platelet kinetics. Scoring is based on three variables:
Variable
Scenario
Points
Platelet count pattern
Pattern A: Platelets begin to recover after CPB, then fall again >4 days after CPB
2
Pattern B: Thrombocytopenia occurs immediately after CPB and persists >4 days without recovery
1
Time from CPB to index date
≥5 days
2
<5 days
0
CPB duration
≤118 minutes
1
>118 minutes
0
Score ≥2 suggests HIT is likely; score <2 suggests an alternative diagnosis.
Communication with the surgical team: Stopping heparin in an LVAD patient requires joint decision-making with cardiac surgery. Key points: (1) HIT suspicion and 4Ts score; (2) bivalirudin started — target aPTT range; (3) all line flushes converted to saline; (4) ELISA sent; (5) platelet transfusion is contraindicated. Surgeon must know anticoagulation has changed for any re-exploration or procedure.
⚠POD 4 — ELISA result returned. RV function deteriorating. Pharmacist asking for anticoagulant selection.
Platelets
62×10⁹/L
ELISA OD
2.4
LVAD Flow
3.8L/min ↓
SvO₂
52%
PA Catheter — POD 4
CVP/RAP18 mmHg ↑
PA pressures42/24 mmHg
PCWP14 mmHg
PAPi1.0 (low; <2.0 = RV failure)
CI1.9 L/min/m²
SvO₂52%
Echo Findings
RVModerate-severe dilation
RV:LV ratio>1.0
SeptumLeftward shift ↑
TRModerate-severe
IVC2.6 cm, non-collapsing
LVAD inflowPosition good
Labs — POD 4
PF4 ELISA OD2.4 (strongly +)
SRAPending (3–5 days)
Total bilirubin4.2 mg/dL ↑
AST185 U/L ↑
INR (baseline)1.4
Creatinine1.4 mg/dL ↑
Question 1 of 3
The ELISA OD is 2.4 and the SRA is pending. Can you wait for the SRA before stopping heparin and changing anticoagulation?
Question 2 of 3
Heparin has been stopped. The pharmacist needs to know which nonheparin anticoagulant to dispense. The patient has a bilirubin of 4.2 mg/dL, AST 185 U/L, and INR 1.4 — all consistent with congestive hepatopathy from RV failure. Which anticoagulant is most appropriate?
Question 3 of 3
The team initiates milrinone and inhaled nitric oxide for RV failure. Review the hemodynamic trend over the next 48 hours. What does this trajectory indicate about RV function and bivalirudin dosing?
Parameter
POD 4
POD 5
POD 6
CVP (mmHg)
18
15
12
PAPi
1.0
1.2
1.6
CI (L/min/m²)
1.9
2.1
2.4
SvO₂ (%)
52
58
64
LVAD Flow (L/min)
3.8
4.2
4.6
Total bilirubin (mg/dL)
4.2
3.5
2.8
Platelets (×10⁹/L)
62
68
78
Key Teaching Points — Scenario 2
ELISA OD >2.0: ~95% PPV for functional HIT. Do not wait for SRA results when clinical probability is high and ELISA is strongly positive.
Challenges in aPTT monitoring: Liver disease prolongs aPTT independently, causing aPTT to overestimate anticoagulant effect. Argatroban clearance is also impaired in hepatic disease, and its aPTT dose-response curve is nonlinear and plateaus at higher concentrations.
Bivalirudin clearance: ~80% enzymatic proteolysis (organ-independent), ~20% renal. Safe in hepatic dysfunction. Short half-life (~25 min) allows rapid offset. Start 0.15–0.20 mg/kg/hr without bolus; titrate to aPTT 1.5–2.5× baseline.
LVAD flow as surrogate for RV function: In a fixed-speed LVAD, flow is preload-dependent. Declining flow at constant speed without device malfunction = decreased LV filling from RV failure. Pulsatility Index falls as native cardiac contribution diminishes.
LFT monitoring in RV failure: Congestive hepatopathy produces a cholestatic pattern (bilirubin, ALP, GGT > transaminases) with impaired synthetic function (prolonged PT). Markedly elevated transaminases in isolation suggest superimposed acute cardiogenic liver injury from hypoperfusion rather than congestion alone.
⚠POD 7 — SRA returned positive. New alert: left arm swelling. Duplex result pending.
Platelets
95×10⁹/L ↑
SRA
Positive
LVAD Flow
4.7L/min
MAP
70mmHg
Clinical Status — POD 7
SRAPositive — HIT confirmed
Bivalirudin0.14 mg/kg/hr
aPTT56 sec (therapeutic)
Total bilirubin2.8 mg/dL (↓)
Creatinine1.0 mg/dL
INR1.3
New Finding
SymptomL arm swelling + pain
L vs R armL arm 4 cm larger
Prior line siteL arm A-line removed POD 3
Duplex resultAcute non-occlusive L axillary/subclavian DVT
Lower extremitiesNo DVT
Question 1 of 4
The patient has confirmed HIT (positive SRA) and now has a new venous thrombosis. What is this condition called, and what is the minimum anticoagulation duration?
Question 2 of 4
Platelets are 95 ×10⁹/L and trending upward. Can warfarin be started now to simplify outpatient anticoagulation planning?
Question 3 of 4
When the time comes for warfarin transition, how does the bivalirudin-to-warfarin transition differ from argatroban-to-warfarin?
Question 4 of 4
Should vascular surgery be consulted urgently for this non-occlusive left axillary/subclavian DVT?
Key Teaching Points — Scenario 3
HITT incidence: 17–55% of untreated HIT patients. Post-cardiac surgery, arterial events (stroke, limb ischemia, MI) predominate, but venous thrombosis — especially at catheter sites — is common.
HITT anticoagulation duration: Continue parenteral anticoagulation until platelets ≥150 ×10⁹/L, then start warfarin for a total of ≥3 months (vs. ≥1 month for uncomplicated HIT).
Warfarin timing: Warfarin depletes Protein C before suppressing procoagulant factors. In active HIT with DVT, this creates a prothrombotic window that can cause venous limb gangrene or skin necrosis. Defer until platelets ≥150 ×10⁹/L.
Bivalirudin-to-warfarin transition: Overlap ≥5 days; stop bivalirudin once INR 2.0–3.0 on two measurements ≥24 hours apart. Argatroban significantly prolongs INR — requires holding the drug, rechecking at 4–6 hours, and confirming therapeutic INR off argatroban before stopping. Substantially more complex.
LVAD warfarin goal: INR 2.0–3.0 for HeartMate 3 — aligns with HITT treatment goals, simplifying long-term planning.
ℹPOD 14 — Platelets recovered. Warfarin started 3 days ago. INR 4.8. Discharge planning in progress.
Platelets
185×10⁹/L
INR (combined)
4.8
LVAD Flow
5.0L/min
MAP
75mmHg
Clinical Status — POD 14
Platelets185 ×10⁹/L (recovered)
Bivalirudin0.14 mg/kg/hr (ongoing)
Warfarin started3 days ago
INR on combined therapy4.8
Bilirubin / AST1.4 / 38 (near-normal)
Arm DVTImproving clinically
LVAD Console
Speed5,400 rpm
Flow5.0 L/min
Power4.2 W
PI4.0
Transplant listingStatus 4 (UNOS)
Question 1 of 3
The INR is 4.8 on warfarin + bivalirudin (3 days of overlap). Is it safe to stop bivalirudin now?
Question 2 of 3 — Select all that apply
Before discharge, what must be documented in the medical record? Select all correct items.
Question 3 of 3
The patient is listed for cardiac transplantation. What critical information must be communicated to the transplant team?
Key Teaching Points — Scenario 4
Bivalirudin-to-warfarin transition: Safe only after ≥5 days of overlap with INR 2.0–3.0 confirmed on two measurements ≥24 hours apart — ideally with bivalirudin briefly held to verify true warfarin effect. Combined-therapy INR does not reliably reflect warfarin alone.
Critical documentation for HIT patients: Flag HIT at the allergy level — not just in notes. Document: the alternative used (bivalirudin), why argatroban was avoided (hepatic dysfunction), and the CPB strategy implication for future surgery. Must be visible to ER physicians, anesthesiologists, and proceduralists at a glance.
Antibody clearance timeline: Antibodies typically undetectable 50–85 days after heparin cessation (median ~50 days) — this is the maximum re-exposure risk window. After confirmed SRA negativity, brief intraoperative heparin for CPB carries low reactivation risk.
Post-transplant anticoagulation: LVAD explanted at transplantation — long-term warfarin for device anticoagulation no longer required. Anticoagulation is now driven by the HITT treatment course (DVT) and institutional transplant protocol.
🔴DONOR HEART AVAILABLE — Patient called in for transplantation. Estimated OR time: 4 hours from now.
Platelets
220×10⁹/L
ELISA OD
1.1(↓ from 2.4)
SRA
Pending
Time since HIT
~4 wks
Current Status — 4 Weeks Post-HIT
MedicationsWarfarin (INR 2.3), ASA 81 mg
ELISA OD1.1 (down from 2.4)
SRAPending (sent 2 days ago)
Hepatic functionNormal (bili 0.9, AST 28)
Creatinine0.9 mg/dL
LVAD5,400 rpm / 5.1 L/min
Surgical Plan
ProcedureOrthotopic heart transplant
ApproachRedo sternotomy
CPB requiredYes — unavoidable
UrgencyCannot be delayed
Listing statusStatus 4 (UNOS)
Question 1 of 5
The ELISA OD is 1.1 at 4 weeks, and the SRA is pending. How should the patient's HIT status be classified?
Question 2 of 5
The surgery cannot be delayed. Review the four CPB anticoagulation strategies below and select the most appropriate one for this patient given the urgency of transplantation and the pending SRA.
Strategy 1 — Bivalirudin for CPBACCP Grade 2C
Bolus 1.0 mg/kg IV → infusion 2.5 mg/kg/hr; prime circuit with 50 mg bivalirudin. ACT target >2.5× baseline (~400 sec). No reversal agent — short t½ (~25 min) allows natural offset. Requires continuous circuit flow; no stasis in surgical field. Team has prior bivalirudin experience from ICU course.
Strategy 2 — TPE + IVIG then standard heparin/protamineAlternative if time permits
Preoperative TPE (1–3 sessions) reduces antibody titers. IVIG 1 g/kg blocks Fc-mediated platelet activation. Confirm antibody reduction before proceeding. Allows familiar heparin/protamine system with full reversal. At some centers (including Duke), TPE is performed in the OR immediately before CPB for HIT patients requiring urgent cardiac surgery — making this a case-by-case decision based on institutional expertise and time constraints. Requires 2–4 hours per session — might not be feasible within a tight donor organ ischemia time window.
Strategy 3 — Heparin + epoprostenol or tirofibanLimited evidence
Epoprostenol 4–8 ng/kg/min 30 min before heparin through CPB + 1 hour post-protamine. Inhibits platelet activation via cAMP. Standard heparin/protamine reversal. Risks: systemic hypotension; increased bleeding. ~50 reported cases in literature.
Strategy 4 — Heparin with confirmed negative SRANot applicable here
If SRA is confirmed negative, brief heparin re-exposure for CPB carries low recurrence risk. Requires strict postoperative heparin avoidance. NOT applicable: SRA is pending and ELISA is still positive — proceeding without confirmed functional assay negativity is unsafe.
Question 3 of 5
You have selected bivalirudin for CPB. The perfusionist needs the protocol. Complete the pre-bypass checklist — check off each item to confirm it has been addressed.
Confirm pharmacy has adequate bivalirudin supply (estimate 500–750 mg for a 4-hour case in an 80 kg patient)
IV bolus: 1.0 mg/kg administered 5 minutes before cannulation
Continuous infusion: 2.5 mg/kg/hr via dedicated IV line
CPB circuit prime: add 50 mg bivalirudin to prime solution
ACT monitoring: baseline ACT, then every 15–30 min on bypass; target >2.5× baseline (~400 sec)
Continuous flow protocol: no circuit stasis; surgeon irrigates field to prevent blood pooling
No protamine — document that protamine reversal does not apply and will not be given
Blood products on standby: platelets, FFP, cryoprecipitate, PCCs or rFVIIa as rescue
Modified ultrafiltration planned for post-bypass period
Cell saver approved for use (bivalirudin washed out during cell salvage processing)
0 of 10 items confirmed
✓ Bivalirudin CPB Protocol Confirmed
The lack of a reversal agent is the primary disadvantage of bivalirudin for CPB. However, its short half-life (~25 minutes) means anticoagulant effect dissipates rapidly after stopping the infusion. Post-bypass bleeding is managed with time, blood products, and modified ultrafiltration. In published case series, bivalirudin for CPB in HIT patients has been associated with acceptable bleeding rates, though higher than with heparin/protamine.
Question 4 of 5
After successful transplantation, the patient is in the cardiac surgery ICU. The surgical resident asks: "Can we start a heparin drip for postoperative anticoagulation?"
Question 5 of 5 — Select all that apply
What postoperative monitoring plan should be implemented after cardiac transplantation in this patient?
Key Teaching Points — Scenario 5
Subacute HIT: Highest-risk window for re-exposure. Platelets recovered but antibodies still circulating. Median clearance ~50 days — at 4 weeks, fulminant HIT on re-exposure remains a real risk.
Bivalirudin CPB — operational requirements: Non-heparin-coated circuit; ACT target >400 sec; no circuit stasis (bivalirudin is enzymatically degraded — stagnant blood will clot); continuous field irrigation; no protamine.
When other strategies apply: TPE + heparin is reasonable when time permits — at some centers (including Duke), TPE is performed in the OR for HIT patients requiring CPB as a case-by-case decision. Might not be feasible within a short donor organ ischemia window. Heparin after confirmed negative SRA is acceptable for true remote HIT (>3 months, functional assay negative). Epoprostenol + heparin: ~50 reported cases; limited to specialized centers.
Postoperative heparin avoidance: Eliminate all heparin — IV, flushes, heparin-bonded catheters, dialysis circuits, subcutaneous. Saline flushes only. Communicate explicitly to every team member and consulting service.
Post-transplant warfarin: LVAD explanted — device anticoagulation indication is gone. Anticoagulation decisions driven by HITT treatment course (DVT completion) and institutional post-transplant protocol.
SRA timing: No benefit repeating SRA immediately postoperatively — 3–5 day turnaround, will not change immediate management. Review the pre-transplant result when available.
✓ Case complete
All five scenarios complete — early recognition and 4Ts scoring, laboratory confirmation and anticoagulant selection in RV failure, managing HITT and warfarin transition, discharge documentation, and perioperative anticoagulation for urgent cardiac transplantation in subacute HIT.