Heparin-induced thrombocytopenia and cardiac surgery
Stem
A 66-year-old woman, 70 kg, admitted with a non-ST-elevation MI, has been on an unfractionated heparin infusion for 6 days. Her platelets fell from 240,000 to 85,000/µL, and today her left calf is swollen with a new deep vein thrombosis. Angiography showed critical left main disease. The anti-PF4/heparin immunoassay is strongly positive; a serotonin release assay is pending. Creatinine is normal. The surgeon wants to operate within 48 hours.
Question
How do you manage her anticoagulation, now and for bypass?
Ideal answer
HeadlineThis is acute HIT with thrombosis: all heparin stops now, including flushes, and she starts a direct thrombin inhibitor; if surgery cannot wait, bypass on bivalirudin.
- Stop every heparin source, low-molecular-weight heparin included, because even catheter flushes keep activating platelets.1
- Therapeutic argatroban or bivalirudin now, because thrombosis risk stays near 50% at 30 days after heparin stops.1
- Delay surgery if her coronaries allow, because elective operations wait for a negative functional assay.2,3
- If urgent, bivalirudin for bypass, 1 mg/kg load, 50 mg in the prime, 2.5 mg/kg/h, targeting 2.5 times baseline ACT.2
- No heparin after surgery; nonheparin prophylaxis, and daily platelets.3
Watch for: new arterial thrombosis, and bleeding after bypass, because bivalirudin has no reversal agent.
Breaking down the answer
- 4Ts — thrombocytopenia, timing, thrombosis, other causes; scores 0–3 low, 4–5 intermediate, 6–8 high.1 She scores high: a fall over 50%, onset at day 5–10 and new thrombosis. A low score effectively rules HIT out.
- Tests — the immunoassay is sensitive but its positive predictive value is only 2–15%; serotonin release or HIPA functional assays are the gold standard.2 Changes if: a negative immunoassay, which excludes HIT.
- Phases decide the pump — acute; subacute A, platelets recovered but both assays positive; subacute B, functional negative, immunoassay positive; remote, both negative.1 Heparin for bypass only is appropriate when the functional assay is negative, even if the immunoassay is still positive.3
- Bivalirudin on pump — half-life about 25 minutes, renally cleared, monitored by ACT or ecarin clotting time.2 Stagnant blood clots, so the perfusionist avoids stasis. Changes if: renal failure, where argatroban or plasmapheresis may be considered with more bleeding.2
- Rescue options when heparin is essential — plasma exchange, potent antiplatelet agents with heparin,1 or high-dose IVIG 1 g/kg daily for 2 days, graded IIb.3
- Warfarin — not in acute HIT; start only after platelets recover to at least 150,000, overlapping the parenteral agent for at least 5 days.1
Follow-up question
She goes on bypass with bivalirudin. After separation the chest tubes drain 400 mL in the first hour, the surgical field looks dry, and the ACT is still prolonged. The surgeon asks for protamine. What do you do?
Follow-up answer
HeadlineProtamine will not reverse bivalirudin; this is drug effect plus bypass coagulopathy, and I tell the surgeon and perfusionist.
Normothermia and good perfusion speed enzymatic clearance; I keep the pump blood moving and ask about modified ultrafiltration. I send platelets, fibrinogen and viscoelastic testing and give targeted plasma, cryoprecipitate and platelets. Hemodialysis and recombinant factor VIIa are last resorts in extreme bleeding.2 In EVOLUTION-ON, bivalirudin increased 2-hour blood loss but not 24-hour loss.2 I reassess drainage every 15–30 minutes.
Pitfalls that cost points
- Sending an immunoassay for every early post-bypass platelet fall; the expected nadir is at 48–72 hours, about half of baseline.1
- Calling the patient HIT-positive for life on an immunoassay alone, without functional confirmation.3
- Forgetting heparin-bonded pulmonary artery catheters and heparinized line flushes.
Rapid-fire
Q: What platelet pattern after bypass suggests HIT? A: A second fall after postoperative day 5–10, after early recovery.1
Q: HIT incidence after cardiac surgery? A: About 1.1–1.4%; one center suspected it in 3.6% and confirmed it in 1.4%.2,1
Q: How long before HIT antibodies usually disappear? A: Typically more than 100 days after diagnosis, which is why elective surgery waits.1
Q: Can delayed HIT follow heparin given only during bypass? A: Yes; it can start 5–10 days after a single intraoperative exposure, so platelets are watched afterward.3
Q: Usual CPB heparin dose and ACT? A: 300–400 units/kg,1 for an ACT above about 480 seconds, or 400 with some devices.2
Numbers to know
| Item | Value |
|---|---|
| 4Ts | Low 0–3, intermediate 4–5, high 6–81 |
| Thrombosis risk after stopping heparin | About 50% at 30 days1 |
| Bivalirudin for CPB | 1 mg/kg load, 50 mg prime, 2.5 mg/kg/h; ACT 2.5 × baseline2 |
| Bivalirudin half-life | About 25 min2 |
| Warfarin start | Platelets ≥ 150,000; overlap ≥ 5 days1 |
| Immunoassay positive predictive value | 2–15%2 |
Links
- Cardiopulmonary bypass: conduct and separation, Bleeding after cardiopulmonary bypass and protamine reactions, Anticoagulant reversal and inherited bleeding disorders, dic
- ASH guidelines on HIT (2018); STS/SCA/AmSECT anticoagulation for CPB (2018); AATS expert consensus on HIT
Sources
- 1.Postoperative thrombocytopenia in cardiac surgery: patterns, differential diagnosis and management of HIT · J Clin Med (PMC12733872), 2025 · pmc.ncbi.nlm.nih.govSummarizes ASH 2018 phases, 4Ts and practical recommendations; ASH full text was not reachable.
- 2.STS/SCA/AmSECT clinical practice guidelines: anticoagulation during cardiopulmonary bypass · STS / SCA / AmSECT (J Extra Corpor Technol, PMC5850589), 2018 · pmc.ncbi.nlm.nih.gov
- 3.From general guidance to surgical reality: adapting the heparin-induced thrombocytopenia algorithm for cardiac surgery · JTCVS Open (PMC13711180), 2026 · pmc.ncbi.nlm.nih.govCommentary on the AATS expert consensus document on HIT; quotes ASH 2018 recommendations and the AATS statements cited here.
Facts on this page were checked against these sources on Nov 2, 2026. Guidelines change; confirm doses against current institutional protocols.