Mechanical Heart Valves are an indication for warfarin therapy

Mechanical Heart Valves

Permanent anticoagulation therapy is justified by an increased risk of thromboembolic complications after replacement of any valve with a mechanical prosthesis (1,2). Most heart valve defects are acquired later in life and are due to degenerative heart valve disease. Heart valve replacement becomes necessary when hereditary or acquired defects severely limit valve function.

Causes of heart valve defects (3):

  • Congenital heart valve defect in the infant.
  • Rheumatic fever - rarely seen now in western industrial nations
  • Changes to the valvular apparatus due to infection, immunological, ischaemic, traumatic or degenerative factors

Acquired valvular stenosis may be a consequence of organic changes to the tissue of the valve; insufficiency may be a secondary consequence of ventricle volume load or congestive heart failure.

Today, the indication for operation and/or interventional treatment of the heart valves is considered earlier (4). In Europe, corrective heart valve surgery is performed in approximately 25% of all heart operations: Mechanical heart valves are particularly long-lived, but require that the patient takes life-long oral anticoagulation medication (2). Biological heart valve prostheses have the benefit of not requiring prolonged anticoagulation, but calcify sooner and have to be replaced after 10 to 15 years (5), with an increased risk linked to the second valve replacement surgery.

Anticoagulation
All patients with mechanical valves require anticoagulation. For mechanical prostheses in the aortic position, an INR with warfarin therapy should be maintained between 2.0 and 3.0 for bileaflet valves and Medtronic Hall valves. An INR between 2.5 and 3.5 is the target for other disc valves and Starr-Edwards valves. For prostheses in the mitral position, the INR should be maintained between 2.5 and 3.5 for all mechanical valves.

Post-operative mortality and morbidity can be improved through individual adjustment of anticoagulation intensity, involvement of the patient, and the use of the international normalized ratio (INR) as control parameter. Studies such as ESCAT (Early Self Controlled Anticoagulation Trial) (6,7) have shown that in cases where patients practice self-management they remain within their optimum therapeutic target range for a higher percentage of time and so significantly reduce the rate of complications.

2006 ACC/AHA guidelines (8):

Risk factors:
Atrial fibrillation, previous thromboembolism, LV dysfunction, hypercoagulable conditions, older-generation thrombogenic valves, mechanical tricuspid valves, or more than 1 mechanical valve.

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References

1. Vongpatanasin W, Hillis LD, Lange RA. Prosthetic Heart Valves. N Engl J Med 1996; 335:407-416.
2. Gohlke-Barwolf C. [Current recommendations for prevention of thromboembolism in patients with heart valve prostheses] (german article). Z Kardiol 2001; 90 Suppl 6:112-117.
3. 
Braunwald E. Valvular heart disease. In: Braunwald E, Fauci AS, Kasper DL, Hauser SL, Longo DL, Jameson JL, eds. Harrison's principles of internal medicine. New York: McGraw-Hill, 2001; 1343-1355.
4. 
Carabello BA, Crawford FA. Valvular Heart Disease. N Engl J Med 1997; 337:32-41.
5. 
Ennker Jr, Lauruschkat A. Mechanische vs. biologische Herzklappen. Z Kardiol 2001; 90.
6. 
Koertke H, Korfer R. International normalized ratio self-management after mechanical heart valve replacement: is an early start advantageous? Ann Thorac Surg 2001; 72:44-48.
7. 
Koertke H, Zittermann A, Minami K, et al. Low-dose international normalized ratio self-management: a promising tool to achieve low complication rates after mechanical heart valve replacement. Ann Thorac Surg 2005; 79:1909-1914; discussion 1914.
8. 
From: ACC/AHA 2006 Guidelines for the Management of Patients With Valvular Heart Disease Journal of the American College of Cardiology Vol. 48, No. 3, 2006 Bonow RO, Carabello BA, Chatterjee K, de Leon AC Jr., Faxon DP, Freed MD, Gaasch WH, Lytle BW, Nishimura RA, O’Gara PT, O’Rourke RA, Otto CM, Shah PM, Shanewise JS. ACC/AHA 2006 guidelines for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Develop Guidelines for the Management of Patients With Valvular Heart Disease), American College of Cardiology Web Site: http://www.acc.org/clinical/guidelines/valvular/ index.pdf