Prosthetic heart valves
There are two main types of prosthetic heart valves, mechanical valves which are durable but require chronic anticoagulation
because of thrombogenicity and biological valves which are less durable, but also less thrombogenic. Biological valves do not require anticoagulation (unless there are other reasons for anticoagulation, such as atrial fibrillation).
Mechanical heart valves
Tilting disk valves: They are classified in single and double tilting disk (bileaflet) valves. Nowadays mainly double disk (bileaflet) valves are used.
Lillehei-Kaster) consist of a ring and a disk, that shifts between the opening position and the closing position, supported by metal struts. In the opening position the disc forms with the plane of the ring an angle of 60-80 degrees.
Bioprosthetic heart valves (Biological tissue valves or bioprostheses)
porcine, bovine, or equine tissue (valvular or pericardial), or homografts, which are preserved human aortic valves. In cardiac auscultation, normally functioning bioprosthetic (biological) valves do not differ from normal native valves. There are several types of bioprosthetic valves: .
Heterografts are: 1) Porcine valves properly suited to a suture ring made of synthetic material. Such valves are: Carpentier-Edwards, Hancock II and Mosaic (Medtronic). With echocardiography, for the Carpentier-Edwards valve at the mitral position, the expected peak velocity is about 1.5-2 m /sec and the expected mean pressure gradient of 5-9 mmHg. In the aortic position, the expected peak velocity is 2-3 m /sec and the expected mean pressure gradient 8-20 mmHg.
Pericardial valves are also two valve types used in transcatheter aortic valve implantation (TAVI): SAPIEN XT (Edwards LifeSciences) made of bovine pericardium and CoreValve (Medtronic) made of porcine pericardium. The valves used for TAVI are trileaflet bioprosthetic valves mounted in a wire mesh stent. Delivery of the valve is performed over a catheter and the stent is expanded in the position of the aortic valve. TAVI can be performed with a catheter advanced from the femoral artery in retrograde fashion across the aortic valve, or from a small thoracotomy with the catheter passed through the apex of the left ventricle and advanced across the aortic valve. This procedure is used for calcific aortic stenosis with the native valve being compressed but remaining in place. TAVI is indicated in patients with severe symptomatic aortic stenosis who have a high risk of adverse surgical outcomes due to comorbidities. Possible complications include stroke, vascular complications (at the entrance site at the femoral artery), and paravalvular regurgitation
Usually taken 24 hours after the donor's death, they are sterilized by antibiotics and maintained at a temperature of -196 ° C. The recorded Doppler velocities are approximately the same as those of native aortic valves.
Autograft (Ross operation)
Pulmonary autograft is the patient's own pulmonary valve implanted to replace a pathologic aortic valve, during a Ross operation. The pulmonary autograft consists of the pulmonary valve with its ring and a small part of the main pulmonary artery. The aortic valve and the aortic root are replaced with the autograft, to which the coronary arteries are then implanted. Subsequently, a pulmonary allograft (cadaveric graft) is implanted in place of the pulmonary valve. Advantages of this operation are that the autograft placed in the aortic position has a very good hemodynamic behavior and better durability than other biological valves. The disadvantage is that it is a technically difficult procedure that requires a long duration of extracorporeal circulation and is only performed in a few cardio-surgical centers with experience.
The patient should be informed about the advantages and disadvantages of each option. Mechanical valves have greater durability, but need lifelong anticoagulation, whereas bioprostheses are less durable, but have the advantage of a lower thrombogenic potential and do not need lifelong anticoagulation.
Selection of the type of prosthetic heart valve
In favor of a mechanical prosthetic valve are the following:
Age< 65 with a long life expectancy, no contraindications for anticoagulation, or a patient already receiving anticoagulation treatment.
In favor of a biological prosthetic valve are the following:
Age ≥ 65, or a limited life expectancy, a contraindication for anticoagulation, or a woman of child bearing age who desires pregnancy.
Antithrombotic treatment in patients with prosthetic heart valves
Bioprosthetic valves:Bioprosthetic (biological) valves are clearly less thrombogenic than mechanical ones, so they do not necessarily need anticoagulation. However, there is a risk of embolism during the initial postoperative period (mechanism: thrombus production on the prosthetic valve support ring). According to the guidelines in patients with a bioprosthetic valve in the mitral or tricuspid position, it is a good practice (with a category IIa-not absolute- indication) to administer anticoagulation with a vitamin K antagonist (acenocoumarol or warfarin) for the first 3 months after valve implantation. Postoperatively heparin (unfractionated or low molecular weight) is initially administered and treatment with a vitamin K antagonist (VKA) is also initiated. When the INR reaches therapeutic levels (2-3) heparin is discontinued and oral anticoagulant treatment is continued (with INR 2-3) for 3 months After 3 months, the risk of thromboembolism is much lower. (INR = international normalized ratio). Therefore, anticoagulation with VKA is discontinued, and permanent antithrombotic treatment with aspirin 80-100 mg (or clopidogrel 75 mg) per day is initiated.
Oral anticoagulation using a VKA should also be considered for the first 3 months after surgical mitral or tricuspid valve repair (a class IIa indication)
After surgical implantation of a bioprosthetic valve at the aortic position, because at this position there are higher blood flow velocities resulting in less risk of thrombosis, guidelines recommend administering only low dose aspirin (eg 80-100 mg daily) for the first 3 months after surgery. This has a Class IIa indication.
However, guidelines allow the option to give these patients (with an aortic bioprosthesis) in the first 3 months a VKA instead of aspirin but with a class IIb indication ( a "weak" indication).
Exception: In patients with a bioprosthetic valve that also have other risk factors for thromboembolism (such as: a previous embolic episode, atrial fibrillation, or severe left ventricular systolic dysfunction with an ejection fraction ≤ 35% or a hypercoagulable state), anticoagulation with INR 2-3 is administered lifelong (and not just for the first 3 months). This is an absolute (class I) indication for permanent anticoagulation.
After transcatheter aortic valve implantation (TAVI), dual antiplatelet therapy is administered for the first 3-6 months. This is followed by lifelong single antiplatelet therapy in patients who do not need oral anticoagulation for other reasons. In case of TAVI, where an additional thromboembolic risk factor (atrial fibrillation, left ventricular systolic dysfunction, hypercoagulability) is also present, a vitamin K antagonist (VKA) is permanently administered with target INR 2-3, while aspirin 80-100 mg, or clopidogrel 75 mg daily is given during the first year and then it is discontinued
Mechanical prosthetic heart valves
Thrombosis and thromboembolism risks are greater with a mechanical valve in the mitral than in the aortic position.
Mechanical valves of medium thrombogenicity are some other bileaflet valves with insufficient data.
Mechanical valves of high thrombogenicity are: the ball-cage valve (Starr-Edwards) and most single disk valves (with the exception of Medtronic Hall) such as Lillehei-Kaster, Omniscience, Bjork-Shiley and other single tilting-disc valves.
Good management of anticoagulation is important since a high variability of the INR is a strong independent predictor of
reduced survival after heart valve replacement with a mechanical prosthesis.
Patients with mechanical heart valves undergoing a percutaneous coronary intervention (PCI)
Initially triple antithrombotic treatment (VKA+aspirin+clopidogrel) is administered for 1 month (it may be given for up to a maximum duration of 6 months if the patient is considered to have a high thrombotic risk and a low bleeding risk). After the period of triple antithrombotic treatment, dual therapy (VKA+clopidogrel, or VKA+aspirin) follows until up to 12 months after coronary stent implantation. Then antiplatelet treatment is discontinued and the patient continues only VKA (anticoagulation). In patients with a high bleeding risk (when bleeding risk is considered as more important than ischemic risk), triple antithrombotic treatment is not given. Then treatment after PCI includes only a period of dual antithrombotic therapy (VKA+ clopidogrel) which can last up to 12 months. After that antithrombotic therapy continues only with the VKA. A high ischemic risk ( a high risk for a subsequent myocardial infarction) is considered to be present in patients presenting with an acute coronary syndrome or having certain characteristics of the coronary lesion (e.g. presence of thrombus, a complex lesion), whereas the bleeding risk is estimated by using the HAS-BLED score.
HAS-BLED stands for:
Hypertension (systolic >160 mmHg) or
Abnormal renal function (creatinine >2.2 or dialysis or renal transplant)
Abnormal liver function (Cirrhosis or Bilirubin >2x Normal or AST/ALT/ALP >3x Normal)
Stroke (history of previous stroke)
Bleeding (Prior major bleeding or predisposition to bleeding
Labile INR (unstable or high, remains in the therapeutic range for < 60% of the time)
Elderly (> 65 years)
Drugs (medication usage that predisposes to bleeding, such as NSAIDs or antiplatelet drugs) or
alcohol(≥ 8 drinks/week)
The presence of each of the above adds 1 point to the score.
A HAS-BLED score of ≥3 indicates high risk for major bleeding ( defined as intracranial hemorrhage, or bleeding requiring hospitalization, or hemoglobin decrease > 2 g/dL, and/or transfusion)
Clinical and echocardiographic follow-up of a patient with a prosthetic heart valveIn general, emphasis should be placed on informing the patient about proper adherence to anticoagulation and endocarditis prophylaxis.
According to the guidelines of the European Society of Cardiology (ESC) a patient who undergoes a valve replacement requires after 6-12 weeks a complete follow-up examination, including clinical examination (history of possible symptoms, cardiac auscultation to check for the expected auscultatory findings for the type of prosthetic valve and also to check for a possible new cardiac murmur), ECG, chest X-ray, transthoracic echocardiography (TTE) and blood tests.
Physical examination and cardiac auscultation of a patient with a prosthetic heart valveSignificant abnormal findings from the physical examination of a patient with a prosthetic heart valve may include a new or changed murmur, muffled valve sounds, or signs indicative of an embolic event (e.g. a neurological deficit in a case of an embolic stroke).
The expected auscultatory findings in patients with a prosthetic valve depend on the type of the valve prosthesis. Normally functioning biological prosthetic valves have the same auscultatory findings as normal native valves. Among the mechanical valves, the bileaflet mechanical valves, which are the type of mechanical valves currently implanted, do not produce an opening sound but only a metallic closing sound. Single-tilting disc mechanical valves produce an opening sound and a closing sound, while the cage-ball valves produce multiple opening sounds, due to the impact of the ball on the cage. On auscultation of the heart, the absence of the expected sounds produced by the prosthetic valves is a pathological finding indicative of limited valve mobility due to thrombosis or tissue hyperplasia.
All mechanical valves in the aortic position additionally produce a characteristic mild systolic ejection murmur. In contrast, the small normal regurgitation of blood (small physiological insufficiency) present in the mechanical valves does not produce a murmur. Therefore, in a patient with a mechanical aortic valve, the finding of a diastolic murmur is a pathological finding, indicating a paravalvular leak (paravalvular regurgitation).
Echocardiography of prosthetic heart valvesThe echocardiogram should include measurement of the transvalvular pressure gradient, color Doppler examination to search for a paravalvular regurgitation and assessment of ventricular function.
Echocardiographic findings and measurements within the first few weeks after surgery will serve as a reference for comparison with future findings. A basic parameter is the pressure gradient (pressure difference) across the valve when it is open. The measurement of the peak velocity and the calculation of the peak and mean transvalvular pressure gradient is performed with the continuous wave Doppler. All prosthetic valves have a peak transvalvular velocity which is higher than that of a normal, native valve. They also create a greater pressure gradient than a normal natural valve, given that the latter creates a negligible pressure gradient. As mentioned, depending on the type of prosthetic valve, there are some expected limits for the pressure gradient (some approximate limits have been given above).
Elevated transvalvular velocity and pressure gradient in a prosthetic valve, as compared to the expected values, is observed in cases of: 1) Valve malfunction causing stenosis (thrombus or pannus development, mechanical degeneration and stenosis due to degeneration and calcification of a bioprosthetic valve),
2) In cases of increased flow through of the valve with no narrowing of the valve (conditions with an increased cardiac output such as hyperthyroidism, anemia or a significant valvular or paravalvular regurgitation). In the case of significant regurgitation at the valve, there is a volume overload of the ventricular cavity located proximally to the valve, resulting in a larger volume of blood passing through the valve when it opens and thus in a higher velocity and pressure gradient.
3) In prosthesis-patient mismatch (PPM), where there is no valve dysfunction, but the valve is small for the patient's body size and circulatory needs.
Echocardiographic indications of prosthetic valve stenosisIn a prosthetic aortic valve (bioprosthetic or mechanical), indications of a significant stenosis are a peak flow velocity> 4 m / sec, a mean pressure gradient> 35 mmHg, an effective valve orifice <0.8 cm2, and an acceleration time > 100 msec. An indication for a possible stenosis or a moderate stenosis is a peak velocity between 3 and 4, a mean pressure gradient between 20 and 35, an effective orifice between 0.8 and 1.2 and an acceleration time between 80 and 100. The acceleration time is the time interval between the onset of blood flow through the valve and the peak flow velocity. Apart from the adequacy of valve opening, it is also affected by the heart rate and contractility of the left ventricle. When the shape of the flow signal obtained with the continuous Doppler is triangular with the peak velocity occurring early, this is a sign of normal flow, whereas when it is symmetrical and rounded, this is indicative of stenosis.
In a prosthetic mitral valve (biological or mechanical), a sign of significant stenosis is a peak flow velocity> 2.5 m / sec, a mean pressure gradient ≥ 10 mmHg,
an effective valve orifice<1 cm2 and a pressure half time (PHT) > 200 msec.
An indication of a possible stenosis, or moderate stenosis of a prosthetic mitral valve is a peak velocity is between 1.9 and 2.5 / a mean pressure gradient between 6 and 10 / an effective orifice area between 1 and 2 and a PHT between 130 and 200. Apart from valvular function, the PHT is also influenced by left ventricular diastolic function (compliance).
Calculation of the functional orifice area or effective orifice area (EOA) of prosthetic valvesThe functional orifice area or effective orifice area (EOA) of prosthetic valves is calculated with the continuity equation, which is based on the principle that flow in a heartbeat is the same through all areas of the circulation.
The EOA of a prosthetic valve in the mitral position is calculated as EOA = (CSA LVOT xVTI LVOT )/VTI PrMV,
CSA LVOT = 0.785 d2, where d is the diameter of the LVOT measured in the parasternal long axis echocardiographic view, just proximal to the aortic valve.
Useful videos !! (LINKS)
Assessment of Prostheses in Echocardiography 123sonography (Prof Thomas Binder)
Prosthetic Valve Assessment (William A. Zoghbi, MD) DeBakey Institute For Cardiovascular Education & Training
Prosthetic valve echocardiography
Prosthetic valve complications
Prosthetic valve thrombosisThere is an increased risk in case of inadequate anticoagulation in a patient with a mechanical prosthetic valve (INR significantly lower than target value) and mechanical prosthetic valves in the mitral position, or the older types of mechanical prosthetic valves (cage-ball, single leaflet). Clinical presentation can be with embolization, e.g. an embolic stroke, or acute limb ischemia, or acute valvular dysfunction causing acute pulmonary edema, or sudden death.
On physical examination diminished intensity of valve sounds may be present. On echocardiography or fluoroscopy, there is a reduced movement of the valve leaflets. There is also an increased transvalvular gradient on echocardiography.
Treatment: Anticoagulation with heparin. If the thrombus is <5 mm on echocardiography, then anticoagulation may suffice. If the thrombus is > 5 mm then apart from heparin, thrombolysis, thrombectomy or valve replacement will be required. Generally for thrombosis of left-sided prosthetic heart valves surgical treatment with valve replacement is indicated, unless there is a prohibitive surgical risk or a small thrombus. For thrombosis of a right-sided prosthetic valve, the treatment of choice is thrombolysis (fibrinolysis). Surgery is indicated if thrombolysis is unsuccessful 24 hours after discontinuation of the infusion.
In patients with prosthetic valves presenting with peripheral embolization, endocarditis should also be considered.
Risk factors include: atrial fibrillation, left ventricular systolic dysfunction, age > 70 years, mitral prostheses, cage-ball valves, the presence of more than 1 prosthetic heart valve. If there are clinical findings suggesting a stroke, a brain computed tomography (CT) should be performed immediately to exclude an intracranial hemorrhage ( in case of an intracranial hemorrhage anticoagulation is withheld and specialist help from a neurologist or neurosurgeon is also needed).
Patient-prosthesis mismatch (PPM)PPM is a situation where the problem is not prosthetic valve dysfunction, but a small prosthetic valve for patient needs. The effective orifice area (EOA) of the valve is indexed to body surface area (BSA), i.e. it is divided by the BSA. In a prosthetic valve in the aortic position when EOA / BSA> 0.85 cm2/m2, then there is only mild or no PPM. On the contrary, when EOA / BSA ≤ 0.65 cm2/m2 then there is considerable PPM and significant stenotic phenomena. Intermediate values below 0.85 but over 0.65 cm2/m2 suggest a moderate degree of patient prosthesis mismatch (PPM).
In a case of a prosthetic valve at the mitral position, when
EOA / BSA >1.2 cm2/m2, there is only mild or no mismatch between prosthetic valve and patient. Conversely, when EOA / BSA ≤ 0.9 cm2/m2, then there is considerable PPM and significant stenosis. Intermediate values, below 1.2 but over 0.9 cm2/m2 indicate a moderate degree of PPM.
Several studies link PPM with a decreased postoperative cardiac index, a worse New York Heart Association (NYHA) functional class, a higher likelihood of late adverse events and shorter mean patient survival.
Haemolysis in patients with prosthetic heart valvesA mild haemolysis is common in patients with mechanical prostheses (even with normal prosthetic valve function). Severe haemolysis is not common and is usually a result of prosthetic valve dysfunction (regurgitation, dehiscence, infection).
Blood tests in case of haemolysis show anemia (decreased hemoglobin and hematocrit), increased levels of lactate dehydrogenase (LDH) and reticulocytosis.
Treatment: Administration of folic acid and ferrous sulphate may be needed to increase production of erythrocytes. In severe cases, blood transfusions will be required and identification and treatment of the underlying problem (including valve replacement for cases requiring frequent blood transfusions).
Prosthetic valve endocarditis
The imaging modality of choice is transesophageal echocardiography (TEE) which can detect vegetations, or complications of prosthetic valve endocarditis, such as valve dehiscence or an abscess.
Prosthetic valve dehiscenceDehiscence (detachment) of the prosthetic valve suture ring from the valve annulus may occur in the early postoperative period due to surgical errors, the presence of extensive calcification of the valve annulus, infection (endocarditis), fragile valve annular tissue due to previous surgery, or chronic corticosteroid use. Late dehiscence of a prosthetic valve is due to infectious endocarditis. An indication of valve dehiscence is an abnormal rocking motion of the prosthetic valve in echocardiography or fluoroscopic examination. Dehiscence is an indication for emergency surgery.
Prosthetic heart valve structural degeneration
BIBLIOGRAPHY AND LINKS
Zoghbi, WA, et al. Recommendations for Evaluation of Prosthetic Valves With Echocardiography and Doppler Ultrasound. Journal of the American Society of Echocardiography 2009;22: 075-1014.
Baumgartner H, et al. 2017 ESC/EACTS Guidelines for the management of valvular heart disease: The Task Force for the Management of Valvular Heart Disease of the European Society of Cardiology (ESC) and the European Association for Cardio-Thoracic Surgery (EACTS), European Heart Journal, ehx391, https://doi.org/10.1093/eurheartj/ehx391
Bajaj R, Karthikeyan G, et al.CSI consensus statement on prosthetic valve follow up. Indian Heart Journal 2012; 64: S3 -S11 LINK https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4244813/pdf/main.pdf
Huang G1, Schaff HV, et al. Treatment of obstructive thrombosed prosthetic heart valve.J Am Coll Cardiol. 2013 ;62:1731-1736.