It is important to be aware of potential long-term problems with prosthetic valves. In particular, obstruction is a problem, and the sonographer needs to be aware of what to look for.
Firstly, remember the flow velocity across the mitral valve is lesser than the aortic valve. Given this, prosthetic mitral valves are more prone to obstruction by a thrombus, while aortic valves are more prone to obstruction by pannus (fibrous tissue overgrowth).(1) Pannus can occur within 6 months of implantation of a valve, but are more often seen after 5 to 6 years. It is commonly accompanied with thrombus. It is hard to detect pannus on TTE and is often diagnosed during surgery.
Doppler echocardiography is the best technique to assess prosthetic valves (2) as views may be limited on 2D. A number of views need to be taken in order to fully assess any obstruction. Velocities will be high, but this does not necessarily indicate valve obstruction, and could be due to transprosthetic regurgitation, or in high output states like hyperthyroidism or anemia.
Mitral valve obstruction is best assessed by measuring pressure half time, and a PHT > 200ms with a peak diastolic flow velocity of 2.5 m/s is indicative of obstruction.(3) Flow velocity is increased when the prosthetic aortic valve is narrowed or there is valvular regurgitation.
References
1. Barbetseas, John, Nagueh, Sherif F., Pitsavos, Christos, Toutouzas, Pavlos K., Quinones, Miguel A., Zoghbi, William A. Differentiating thrombus from pannus formation in obstructed mechanical prosthetic valves: an evaluation of clinical, transthoracic and transesophageal echocardiographic parameters J Am Coll Cardiol 1998 32: 1410-1417
2. Reisner SA, Meltzer RS. Normal values of prosthetic valve Doppler echocardiographic parameters: a review. J Am Soc Echocardiogr. 1988;1:201–210
3. John Chambers, Alan Fraser, Pat Lawford, Petros Nihoyannopoulos, Iain Simpson Echocardiographic assessment of artificial heart valves: British Society of Echocardiography position paper Br Heart J (Supplement) 1994;71:6-14
Firstly, remember the flow velocity across the mitral valve is lesser than the aortic valve. Given this, prosthetic mitral valves are more prone to obstruction by a thrombus, while aortic valves are more prone to obstruction by pannus (fibrous tissue overgrowth).(1) Pannus can occur within 6 months of implantation of a valve, but are more often seen after 5 to 6 years. It is commonly accompanied with thrombus. It is hard to detect pannus on TTE and is often diagnosed during surgery.
Doppler echocardiography is the best technique to assess prosthetic valves (2) as views may be limited on 2D. A number of views need to be taken in order to fully assess any obstruction. Velocities will be high, but this does not necessarily indicate valve obstruction, and could be due to transprosthetic regurgitation, or in high output states like hyperthyroidism or anemia.
Mitral valve obstruction is best assessed by measuring pressure half time, and a PHT > 200ms with a peak diastolic flow velocity of 2.5 m/s is indicative of obstruction.(3) Flow velocity is increased when the prosthetic aortic valve is narrowed or there is valvular regurgitation.
References
1. Barbetseas, John, Nagueh, Sherif F., Pitsavos, Christos, Toutouzas, Pavlos K., Quinones, Miguel A., Zoghbi, William A. Differentiating thrombus from pannus formation in obstructed mechanical prosthetic valves: an evaluation of clinical, transthoracic and transesophageal echocardiographic parameters J Am Coll Cardiol 1998 32: 1410-1417
2. Reisner SA, Meltzer RS. Normal values of prosthetic valve Doppler echocardiographic parameters: a review. J Am Soc Echocardiogr. 1988;1:201–210
3. John Chambers, Alan Fraser, Pat Lawford, Petros Nihoyannopoulos, Iain Simpson Echocardiographic assessment of artificial heart valves: British Society of Echocardiography position paper Br Heart J (Supplement) 1994;71:6-14
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