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Anticoagulation following cardiac surgical intervention

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These anticoagulation therapy guidelines refer to infants and children in the Paediatric and Congenital Cardiac Service who require anticoagulation following cardiac surgical intervention.

Refers to infants and children following:

  • placement of shunts and conduits e.g. Modified Blalock-Taussig shunt, Bi-directional cavopulmonary shunt, Extracardiac fontan etc
  • placement of artificial valves and following valve surgery
  • surgery on coronary arteries
  • placement of non-native tissue

See the Anticoagulation Guideline on the  Starship Clinical Guidelines for information on all other indications for Anticoagulation therapy for infants and children. Refer to this document for information on dose, administration, preparation, monitoring and adjusting

Modified Blalock-Taussig Shunts or Central Shunts, including Norwood Sano modification (i.e. any child with a gortex shunt from systemic to pulmonary artery)

Initial Treatment
Low dose heparin (10u/kg/hr) for all shunt sizes. Start the infusion 2-4 hours after arrival in PICU post op provided that bleeding is not an issue and following an APTT check as above. 
Check APTT 4 hours after starting infusion and adjust as per protocol.
Start aspirin (3-5mg/kg/day)4 once feeding recommended
Stop heparin infusion after the 2nd dose of aspirin unless CVL in situ
Long-Term Treatment
Continue aspirin (3-5mg/kg/day)4  long term until shunt takedown
If aspirin in stopped
Where an infant with a Gortex shunt is made NBM (i.e. NEC) - TPN is started and Aspirin therefore stopped. The infant should be given a low dose heparin infusion (10 units/kg/hr) OR subcutaneous low molecular weight heparin until the aspirin can be recommenced. 
Instructions for home
Continue low dose aspirin (3-5mg/kg/day) if develops a flu-like illness or chickenpox.

NB: It has previously been suggested that low dose aspirin be avoided in children following chicken pox or varicella immunisation due to theoretical risk of Reyes syndrome. However, this risk is small compared to the documented risk of shunt thrombosis without low dose aspirin treatment1,2. The combination of natural varicella infection (chicken pox) and aspirin use in anti-inflammatory (or "high") doses has been associated with Reye's syndrome, but association has not been demonstrated with antiplatelet ("low dose") aspirin treatment3. We therefore recommend that low dose Aspirin should be continued in all patients who are taking aspirin to maintain shunt patency

Bidirectional Cavopulmonary Shunt (BDG)

Initial Treatment
Low dose heparin (10u/kg/hr).Start the infusion 2-4 hours after arrival in PICU post op provided that bleeding is not an issue and following an APTT check. Check APTT 4 hours after starting infusion and adjust as per protocol.
Start aspirin (3-5mg/kg/day) 4 once eating
Stop heparin infusion after the 2nd dose of aspirin.
* However continue low dose heparin (10u/kg/hr) if:
    - central line insitu following a BDG (until CVL removal)
    - low cardiac output and prolonged intensive care course
    - patients with bilateral bidirectional Glenn shunts
Long-term Treatment 
Continue aspirin (3-5mg/kg/day)4 and continue long term until Fontan conversion.

Extra Cardiac Fontan

Initial Treatment 
Start low dose heparin infusion 2-4 hours post op in PICU at 2-4 hours post operation and continue until central line is removed (usually post op day 1-2)
Start Aspirin on day 1 post op (3-5 mg/kg/day)4 once eating and continue while commencing warfarin and continue Aspirin until the INR is over 1.8
Start Warfarin on the day pacing wires are removed (usually post op day 3-4) and aim for an INR of 2.0-2.5.
Initiate Warfarin using small doses (i.e 0.5 -1 mg total dose per day) as liver congestion in Fontan patients makes them prone to rapid rise in INR which is dangerous post operation
Long Term Treatment
After 3 week post operation aim for an INR of 2.0-3.0 when risk of effusion is lower
AVOID Aspirin and Warfarin combination at discharge
Avoid NSAID and Warfarin combination at discharge 

Anticoagulation for Valve Surgery - Aspirin / Warfarin

Mitral Valve Repairs
Short term low dose aspirin 3-5mg/kg/day (maximum 75mg/day)
Start day one post op, take for 6 months then stop 
Homograft Valves (in either aortic or pulmonary position)
Do not use aspirin unless requested by surgeon 
Porcine/Bovine Tissue Valves in any position (Contegra, Mosaic, Freestyle, Hancock)
Low dose aspirin 3-5mg/kg/day (maximum 75mg/day)
Start day one post operation, take for 6 months then stop.
Mechanical Valves (St Judes, On-X Carbon) 
Initial management
Start aspirin on day 1 post op  (3-5 mg/kg/day)4 once eating, and continue aspirin while commencing warfarin until the INR is over 1.8. Then can stop aspirin
Warfarin started on the evening of day one or two after operation (longer if redo procedure) 
If unstable, selective use of low dose heparin may be required 
Cautious dosing if liver impairment, on amiodarone or other competitive drugs, or if post operative bleeding was an issue (i.e. For 50 -70 kg adolescent give maximum of 5mg day 1, 3 mg day 2 and 3 mg day 3)
Aim for INR 2.0 to 3.0 initial two weeks postoperatively (later may be higher) 
Have a low threshold for echo to check for post operation pericardial effusion in warfarinised patients.
Long term management for INR
Aortic valve INR range = 2.0 to 3.0
Mitral valve INR range = 2.5 to 3.5
NB: Low dose aspirin may be added at the cardiologist's discretion/preference, particularly in patients with mechanical mitral valves.

Anticoagulation following surgery on coronary arteries

e.g unroofing of intramural origins during arterial switch

  • Low dose aspirin 3-5mg/kg/day (maximum 75mg/day)
  • Start day one post operation
  • Duration: 6 months

Anticoagulation following other surgical procedures

Anticoagulation is occasionally used following other surgical procedures - confirm with the surgeon. Aspirin 3-5 mg /kg daily for 6 months in the following scenarios:

  • If there has been patch plasty of pulmonary arteries 
  • Artificial material in systemic circulation; for example patch repair of coarctation of aorta repair or large ASD patch 
  • Work done in low flow areas, for example pulmonary veins


  1. Li JS, et al. Clinical outcomes of palliative surgery including a systemic-to-pulmonary artery shunt in infants with cyanotic congenital heart disease: Does aspirin make a difference? Circulation. 2007; 116: 293-7
  2. Heidari-Bateni G, et al. Defining the best practice patterns for the neonatal systemic-to-pulmonary artery shunt procedure. J Thorac Cariovasc Surg 2014; 147: 869-73
  3. Schror K. Aspirin and Reye syndrome: a review of the evidence. Pediatr Drugs 2007; 9(3): 195-204
  4. Monagle, P. et al Antithrombotic therapy in Neonates and Children. Antithrombotic therapy and prevention of thrombosis 9th Ed: American college of chest Physicians Evidence-Based Practice guidelines. Chest 2012; 141: 2, suppl e737S ,
  5. Woods, DJ (editor), New Zealand Formulary for Children [Internet]. 2016 [updated 2016 March 1; 2015 Sept 1; cited 2016, March 18]. Available from:
  6. Marevan (Warfarin) [New Zealand data sheet]. GlaxoSmithKline NZ Auckland [updated 27/01/2015]. Available from URL:
  7. Coumadin(Warfarin) [New Zealand data sheet]. Pharmacy Retailing (NZ) Limited Trading as Healthcare Logistics NZ, Auckland [updated 15/11/2015]. Available from URL:
  8. Heparin sodium [New Zealand data sheet]. Hospira NZ Auckland [updated 26/05/2015]. Available from URL:

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Document Control

  • Date last published: 08 August 2016
  • Document type: Clinical Guideline
  • Services responsible: Paediatric Cardiology
  • Author(s): Kirsten Finucane, Marion Hamer, E Rumball, John Artrip
  • Owner: Marion Hamer
  • Review frequency: 2 years