Children with prosthetic heart valves

Z95.2

DESCRIPTION

Valve replacement may be required for severe valvular disease when valve repair is not feasible or advisable. The valves may be mechanical valves or bioprosthetic valves or preserved human tissue valves.

In children bioprosthetic valves tend to degenerate, calcify and have structural deterioration more frequently and more rapidly compared with adults.
Mechanical valves are more commonly used in children.

Complications include:

  • Valve failure. May be abrupt (tearing of components) or gradual (with calcification and stiffening of leaflets).
  • Prosthetic valve thrombosis.
  • Prosthetic valve endocarditis.
  • Haemolytic anaemia.

MEDICINE TREATMENT

After mechanical valve replacement warfarin therapy is indicated to achieve an INR of 2.5 (range 2.0–3.0):

  • Warfarin, oral, 0.1 mg/kg/daily.
    • Adjust the dose depending on INR.
    • Beware of haemorrhage.

PLUS

  • Aspirin oral, 1mg/kg/day. In patients at a low risk of bleeding.

LoEIII [15]

Warfarin dose adjustment based on INR

INR < 1.5 Verify adherence.
If non-adherent resume at previous dose.
If dosage adjustments needed increase dose by 20%
and review in 3 – 7 days.
INR 1.5–1.9 Verify adherence first.
Increase maintenance dose by 10%.
INR 2.0–3.0 No change needed.
In mitral valve prosthesis, INR should be closer to 3.0.
INR 3.1–4.0 Consider withholding one dose, and decrease by 10%.
INR 4.1–4.5 Decrease dose by 20%.
INR > 4.5 Withhold dose, evaluate INR daily until <4.5, then
restart at 20% below previous dose.

The half-life of warfarin is 40 hours; dose adjustments may thus be calculated over a 48-hour period. The 10% and 20% dose adjustments may not be precisely achieved; approximate doses are acceptable.
If warfarin of 1 mg per tablet is not available and dosage adjustments are problematic discuss with paediatric cardiologist.
Some medicines and foods interfere with the warfarin effect.

Medicines that enhance anticoagulant effect include:

  • allopurinol,
  • aspirin,
  • NSAIDS,
  • paracetamol (regular use),
  • valproate,
  • phenytoin,
  • imidazoles,
  • metronidazole,
  • macrolides, and
  • quinolones.

Medicines that diminish anticoagulant effect include:

  • carbamazepine,
  • phenobarbital,
  • phenytoin, (both diminished and enhanced effects have been reported)
  • nevirapine,
  • rifampicin.

Foods that contain high amounts of vitamin K and can decrease the effectiveness of warfarin, e.g.:

  • spinach,
  • parsley, and
  • brussel sprouts.

Certain drinks can increase the effect of warfarin e.g. cranberry juice.