Prosthetic Heart Valves
Bioprosthetic Valves
Types
- Auto-graft (self-to-self) e. g., pulmonic valve placed in the aortic position in the same patient
- Homograft (allograft) transfer from one human to another, e. g., aortic homograft
- Heterograft (xenograft) transfer from animal to human
- Porcine—a pig's aortic valve placed on stents, attached to a sewing ring and glutaraldehyde stabilized; the most common brands are Hancock, Carpentier-Edwards, and Intact (aortic)
- Bovine pericardium—a cow's pericardium fashioned into a tri-leaflet valve mounted on stents and a sewing ring; the most common brands are Carpentier-Edwards, Ionescu-Shiley(withdrawn from US market), and Mitroflow
Complications
- Calcification/degeneration
- Infective endocarditis
- Perivalvular leak
- Dehiscence
- Thrombus
- Stenosis
- Regurgitation (valvular, perivalvular)
- Valve bed abnormalities (pseudoaneurysm, ring abscess)
M-Mode
- Limited
- Leaflet thickness > 3 mm is abnormal
- Coarse flutter of the tissue leaflets is abnormal
- Normal septal motion soon after cardiac surgery ( < 6 months) may indicate significant mitral or aortic regurgitation
- Evaluate left ventricular function
2-D
- May identify leaflet thickness, calcification, leaflet motion, thrombus, dehiscence, vegetation
- Evaluate left ventricular function
Doppler
- All prosthetic valves are inherently stenotic. The degree of obstruction is dependent on the type, size, and site of the prosthetic valve.
- Evaluate patients soon after surgery (within 30-days) to obtain baseline Doppler values.
- Heart rate, blood pressure, and left ventricular function should be noted as the examination begins.
- An average of 5 to 10 beats should be utilized to obtain the hemodynamic measurements.
- Bioprosthetic Mitral Valve
- Note the transducer position where the optimal Doppler signal was obtained so it may be used for follow-up studies (most often the apical or para-apical position)
- Determine the peak velocity; a peak velocity > 2. 5 m/sec may indicate stenosis or significant regurgitation.
- Determine the pressure half-time; a PHT > 180 msec may be abnormal.
- Determine mitral valve area by the pressure half-time method; a mitral valve area < 1. 8 cm2 may be abnormal.
- Determine the mitral valve area by the continuity equation
- Determine the mean pressure gradient; a mean pressure gradient > 10 mm Hg may be abnormal.
- Determine the presence and severity of mitral regurgitation
- A perivalvular leak is abnormal
Bioprosthetic Aortic Valve
- Note the transducer position where the optimal Doppler signal was obtained so it may be used for follow-up studies (most often the apical or right parasternal position)
- Determine the peak velocity
- Determine the maximum instantaneous pressure gradient; a peak pressure gradient > 45 mm Hg may be abnormal.
- Determine the mean pressure gradient; a mean pressure gradient > 25 mm Hg may be abnormal.
- Determine the aortic valve area using the continuity equation
- Determine the velocity ratio
- Determine the presence and severity of aortic insufficiency
- A perivalvular leak is abnormal
Bioprosthetic Tricuspid Valve
- Tissue valves are most often placed in the tricuspid position to lower the incidence of thrombosis.
- Determine the peak velocity
- Determine the pressure half-time, using the formula for mitral valve replacement
- Determine the tricuspid valve area by the pressure half-time method, using the formula for mitral valve replacement
- Determine the mean pressure gradient
- Determine the presence and severity of tricuspid regurgitation
- A perivalvular leak is abnormal
Bioprosthetic Pulmonic Valve
- A peak velocity of > 2.5 msec may be abnormal
- Determine the presence and severity of pulmonary insufficiency
- A perivalvular leak is abnormal
Mechanical Valves
Types
- Ball and cage (Starr-Edwards is the most common)
- Caged disc (Beall is the most common; no longer available)
- Tilting disc (Bjork-Shiley, Medtronic-Hall are the most common; the Bjork-Shiley is no longer available: problem of strut fracture)
- Bileaflet (St. Jude valve is probably the most frequently used mechanical valve; it has three orifices, which promote central flow, and is the least stenotic prosthetic valve)
Complications
- Thrombus
- Pannus (fibrous ingrowth of tissue, which may lead to regurgitation or stenosis)
- Perivalvular leak
- Dehiscence
- Infective endocarditis
- Hemolysis
- Ball/disc variance
M-Mode
- Limited in value
2-D
- Somewhat helpful in evaluating for the complications of mechanical
valves although reverberations make the diagnosis difficult
Doppler
- All prosthetic valves are inherently stenotic. The degree of obstruction is a function of prosthesis type, size, and site
- Evaluate patients soon after surgery (within 30 days) to obtain baseline Doppler values.
- Heart rate, blood pressure, and left ventricular function should be noted as the examination begins
- An average of 5 to 10 beats should be utilized to obtain the hemodynamic measurements
Caution: When attempting to rule out significant mitral regurgitation in a prosthetic mitral valve, you must remember that the prosthetic valve will "mask" the mitral regurgitation from the Doppler ultrasound due to the high acoustic impedance difference between the valve and blood. Multiple views and transesophageal echocardiography will overcome the problem of masking.
Mechanical Mitral Valve
- Note the transducer position where the optimal Doppler signal was obtained so it may be used for follow-up studies (most often the apical or para-apical position).
- Determine the peak velocity; a peak velocity > 2. 5 msec may indicate stenosis or significant regurgitation.
- Determine the pressure half-time; PHT>180 msec may be abnormal
- Determine mitral valve area by the pressure half-time method; a mitral valve area < 1. 8 cm2 may be abnormal.
- Determine the mean pressure gradient; a mean pressure gradient > 10 mm Hg may be abnormal.
- Determine the mitral valve area by the continuity equation
- Determine the presence and severity of mitral regurgitation
- A perivalvular leak is abnormal.
Mechanical Aortic Valve
- Note the transducer position where the optimal Doppler signal obtained so it may be used for follow-up studies (most often the at apical or right parasternal position)
- Determine the peak velocity
- Determine the maximum instantaneous pressure gradient; peak pressure gradient > 45 mm Hg may be abnormal
- Determine the mean pressure gradient; mean gradient > 25 mm Hg may be abnormal
- Determine the velocity ratio
- Determine the aortic valve area using the continuity equation
- Determine the presence and severity of AR
- A perivalvular leak is abnormal
Mechanical Tricuspid Valve
- Determine the peak velocity.
- Determine the pressure half-time, using the formula for MVR
- Determine the tricuspid valve area, using the formula for MVR
- Determine the mean pressure gradient
- Determine the presence and severity of tricuspid regurgitation.
- A perivalvular leak is abnormal.
Evaluation of Prosthetic Valve by TEE
- Evaluation of mitral regurgitation (extremely important due to masking)
- Evaluation for anatomic detail :
- Vegetations
- Thrombi
- Valve ring abscess or pseudoaneurysm
- Valve bed fistula (e.g., aortic root—right atrium)
- Inspection of left atrium or appendage
- Surface study is inadequate for diagnosis
- Intraoperative monitoring for perivalvular leak, valve regurgitation and/or dysfunction