HomeCirculationVol. 119, No. 7Prosthetic Heart Valves Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBProsthetic Heart ValvesSelection of the Optimal Prosthesis and Long-Term Management Philippe Pibarot and Jean G. Dumesnil Philippe PibarotPhilippe Pibarot From the Laval Hospital Research Center/Québec Heart Institute, Department of Medicine, Laval University, Québec, Canada. Search for more papers by this author and Jean G. DumesnilJean G. Dumesnil From the Laval Hospital Research Center/Québec Heart Institute, Department of Medicine, Laval University, Québec, Canada. Search for more papers by this author Originally published24 Feb 2009https://doi.org/10.1161/CIRCULATIONAHA.108.778886Circulation. 2009;119:1034–1048The introduction of valve replacement surgery in the early 1960s has dramatically improved the outcome of patients with valvular heart disease. Approximately 90 000 valve substitutes are now implanted in the United States and 280 000 worldwide each year; approximately half are mechanical valves and half are bioprosthetic valves. Despite the marked improvements in prosthetic valve design and surgical procedures over the past decades, valve replacement does not provide a definitive cure to the patient. Instead, native valve disease is traded for “prosthetic valve disease,” and the outcome of patients undergoing valve replacement is affected by prosthetic valve hemodynamics, durability, and thrombogenicity. Nonetheless, many of the prosthesis-related complications can be prevented or their impact minimized through optimal prosthesis selection in the individual patient and careful medical management and follow-up after implantation. The purpose of this article is to provide an overview of the current state of knowledge and future perspectives with regard to optimal prosthesis selection and clinical management after valve implantation.Types of Prosthetic Heart Valve DesignThe ideal valve substitute should mimic the characteristics of a normal native valve. In particular, it should have excellent hemodynamics, long durability, high thromboresistance, and excellent implantability. Unfortunately, this ideal valve substitute does not exist, and each of the currently available prosthetic valves has inherent limitations.Mechanical ValvesThree basic types of mechanical valve design exist: bileaflet, monoleaflet, and caged ball valves (Figure 1A, 1B, and 1C). Download figureDownload PowerPointFigure 1. Different types of prosthetic valves. A, Bileaflet mechanical valve (St Jude); B, monoleaflet mechanical valve (Medtronic Hall); C, caged ball valve (Starr-Edwards); D, stented porcine bioprosthesis (Medtronic Mosaic); E, stented pericardial bioprosthesis (Carpentier-Edwards Magna); F, stentless porcine bioprosthesis (Medtronic Freestyle); G, percutaneous bioprosthesis expanded over a balloon (Edwards Sapien); H, self-expandable percutaneous bioprosthesis (CoreValve).Caged Ball ValvesCaged ball valves, which consist of a silastic ball with a circular sewing ring and a cage formed by 3 metal arches, are no longer implanted. However, several thousands of patients still have caged ball valves, and these patients require follow-up.Monoleaflet ValvesMonoleaflet valves are composed of a single disk secured by lateral or central metal struts. The opening angle of the disk relative to valve annulus ranges from 60° to 80°, resulting in 2 distinct orifices of different sizes.Bileaflet ValvesBileaflet valves are made of 2 semilunar disks attached to a rigid valve ring by small hinges. The opening angle of the leaflets relative to the annulus plane ranges from 75° to 90°, and the open valve consists of 3 orifices: a small, slit-like central orifice between the 2 open leaflets and 2 larger semicircular orifices laterally.Bioprosthetic ValvesStented BioprosthesesThe design of bioprostheses purports to mimic the anatomy of the native aortic valve (Figure 1D and 1E). Porcine bioprosthetic valves consist of 3 porcine aortic valve leaflets cross-linked with glutaraldehyde and mounted on a metallic or polymer supporting stent. Pericardial valves are fabricated from sheets of bovine pericardium mounted inside or outside a supporting stent.Stentless BioprosthesesIn an effort to improve valve hemodynamics and durability, several types of stentless bioprosthetic valves have been developed (Figure 1F). Stentless bioprostheses are manufactured from whole porcine aortic valves or fabricated from bovine pericardium.Percutaneous BioprosthesesPercutaneous aortic valve implantation is emerging as an alternative to standard aortic valve replacement (AVR) in patients with symptomatic aortic stenosis considered to be at high or prohibitive operative risk (Figure 1G and 1H).1–5 The valves are usually implanted using a percutaneous transfemoral approach.4,5 To reduce the problems of vascular access and associated complications, a transapical approach through a small thoracotomy may also be used. At present, the procedure appears promising, but it remains experimental and is currently undergoing further investigation.Selecting the Optimal Prosthesis in the Individual PatientBioprosthetic Versus Mechanical ValveChoosing the right valve for the right patient is a difficult but essential process to optimize the outcome for patients undergoing valve replacement. The first step in this decision-making process is to choose between a mechanical and a bioprosthetic valve (Figure 2). The most important factors that should be considered in this first step are the patient’s age, life expectancy, preference, indication/contraindication for warfarin therapy, and comorbidities. In the recent American College of Cardiology/American Heart Association and European guidelines,6,7 the weight given to patient age has been reduced, whereas much greater importance is now given to the patient’s preference. The criteria in favor of using a mechanical valve include the following: (1) the informed patient wants a mechanical valve and has no contraindication for long-term anticoagulation; (2) the patient is already on anticoagulation (mechanical prosthesis in another position or at high risk for thromboembolism); (3) the patient is at risk of accelerated bioprosthesis structural deterioration (young age, hyperparathyroidism, renal insufficiency); and (4) the patients is <65 years of age and has a long life expectancy. On the other hand, a bioprosthesis may be preferred in the following situations: (1) the informed patient wants a bioprosthesis; (2) good-quality anticoagulation is unavailable (contraindication or high risk, compliance problems, lifestyle); (3) the patient is ≥65 years of age and/or has limited life expectancy; and (4) the patient is a woman of childbearing age. Bioprostheses degenerate more rapidly in young patients and during pregnancy. Hence, a woman in her late 30s or early 40s who has completed her family should probably be advised to have a mechanical valve.8Download figureDownload PowerPointFigure 2. Algorithm for the selection of the optimal prosthesis in the individual patient.Selection of the Prosthesis Model and SizeAfter the prosthesis type, ie, mechanical versus biological, is selected, one should logically contemplate the prosthesis models that have a well-established track record with regard to long-term durability (bioprostheses) and low thrombogenicity (mechanical prostheses) (Figure 2). Thromboembolic rates are a poor indicator of the valve thrombogenicity because they can be highly influenced by patient risk factors and antithrombotic management.9 Thrombogenicity of the individual prosthesis should thus be determined on the basis of reported valve thrombosis rates for that prosthesis in relation to anticoagulation intensity and valve position. In this regard, it should be noted that prostheses cannot be conveniently categorized according to basic design (eg, bileaflet, monoleaflet, etc) or date of introduction to determine the level thrombogenicity (see the Antithrombotic Therapy section).The next step is to choose a prosthesis model that provides superior hemodynamic performance to prevent prosthesis-patient mismatch (PPM) and thereby minimize postoperative transprosthetic gradients. Hence, among bioprostheses with similar durability or mechanical valves with similar thrombogenicity, one should preferably select the model that provides the largest valve effective orifice area (EOA) in relation to the patient’s annulus size (Tables 1 and 2).10–15 The hemodynamic performance or “EOAbility” of the prosthesis is essentially determined by the size of prosthesis that can fit into the patient’s annulus and by the proportion of the total cross-sectional area of that prosthesis that is actually available for blood flow. To this effect, it should be underlined that the hemodynamic performance is not equivalent for all models of prostheses. Indeed, it is generally superior in newer compared with older generations of prostheses, in mechanical compared with stented bioprosthetic valves,16 in stentless compared with stented bioprosthetic valves,17,18 and in supraannular compared with intra-annular stented bioprostheses.19,20 A recent meta-analysis18 shows that, compared with stented bioprostheses, stentless valves provide larger EOAs, reduced transprosthetic gradients, and greater left ventricular (LV) mass regression, but at the expense of prolonged cardiopulmonary bypass time. Table 1. Normal Reference Values of EOAs for the Aortic ProsthesesProsthetic Valve Size, mmReference192123252729EOA is expressed as mean values available in the literature.*These results are based on a limited number of patients and thus should be interpreted with caution.Aortic stented bioprosthesis Mosaic1.1±0.21.2±0.31.4±0.31.7±0.41.8±0.42.0±0.410 Hancock II…1.2±0.11.3±0.21.5±0.21.6±0.21.6±0.210 Carpentier-Edwards Perimount1.1±0.31.3±0.41.50±0.41.80±0.42.1±0.42.2±0.410 Carpentier-Edwards Magna*1.3±0.31.7±0.32.1±0.42.3±0.5……11, 20 Biocor (Epic)*…1.3±0.31.6±0.31.8±0.4……12 Mitroflow*1.1±0.11.3±0.11.5±0.21.8±0.2……13Aortic stentless bioprosthesis Medtronic Freestyle1.2±0.21.4±0.21.5±0.32.0±0.42.3±0.5…10 St Jude Medical Toronto SPV…1.3±0.31.5±0.51.7±0.82.1±0.72.7±1.010Aortic mechanical prostheses10 Medtronic-Hall1.2±0.21.3±0.2…………10 Medtronic Advantage*…1.7±0.22.2±0.32.8±0.63.3±0.73.9±0.714 St Jude Medical Standard1.0±0.21.4±0.21.5±0.52.1±0.42.7±0.63.2±0.310 St Jude Medical Regent1.6±0.42.0±0.72.2±0.92.5±0.93.6±1.34.4±0.627 MCRI On-X1.5±0.21.7±0.42.0±0.62.4±0.83.2±0.63.2±0.627 Carbomedics Standard1.0±0.41.5±0.31.7±0.32.0±0.42.5±0.42.6±0.410Table 2. Normal Reference Values of EOAs for the Mitral ProsthesesProsthetic Valve Size, mmReference25 mm27 mm29 mm31 mm33 mmEOA is expressed as mean values available in the literature.*These results are based on a limited number of patients and thus should be interpreted with caution.†The strut and leaflets of the MCRI On-X valve are identical for all sizes (25 to 33 mm).Stented bioprosthesis Medtronic Mosaic1.5±0.41.7±0.51.9±0.51.9±0.5…15, 28 Hancock II1.5±0.41.8±0.51.9±0.52.6±0.52.6±0.729 Carpentier-Edwards Perimount*1.6±0.41.8±0.42.1±0.5……28Mechanical prostheses St Jude Medical Standard1.5±0.31.7±0.41.8±0.42.0±0.52.0±0.528 MCRI On-X†2.2±0.92.2±0.92.2±0.92.2±0.92.2±0.928It is also important to emphasize that major discrepancies exist among the different prosthesis models between the actual dimensions of the prosthesis and the labeled prosthesis size given by the sizers provided by the manufacturers. Consequently, it is inappropriate to compare the hemodynamic performance of different prosthesis models on the basis of their labeled sizes (Tables 1 and 2).21 Indeed, based on the sizers, the same annulus might, for instance, accommodate a size 23 of prosthesis X compared with only a size 21 of prosthesis Y.Once the prosthesis model and size have been selected, it is important to implant the prosthesis using an optimal surgical technique. In particular, for mitral valve replacement (MVR), it is recommended that the chordae be preserved to prevent postoperative deterioration in LV geometry and function.22 Moreover, in the mitral position, the surgeon should implant bileaflet valves in the antianatomic position and monoleaflet valves with their larger orifice oriented posteriorly to ensure more physiological flow patterns.23Prosthesis-Patient MismatchThe term valve PPM was first proposed in 1978 by Rahimtoola.24 PPM occurs when the EOA of a normally functioning prosthesis is too small in relation to the patient’s body size (and therefore cardiac output requirements), resulting in abnormally high postoperative gradients. The most widely accepted and validated parameter for identifying PPM is the indexed EOA, ie, the EOA of the prosthesis divided by the patient’s body surface area.10,25–27Table 3 shows the threshold values of indexed EOA generally used to identify PPM and to quantify its severity. Moderate PPM may be quite frequent in both the aortic (20% to 70%) and mitral (30% to 70%) positions, whereas the prevalence of severe PPM ranges from 2% to 10% in both positions.10,27–29Table 3. Threshold Values of Indexed Prosthetic Valve EOA for the Identification and Quantification of PPMMild or Not Clinically Significant, cm2/m2Moderate, cm2/m2Severe, cm2/m2Numbers in parentheses represent the range of threshold values that have been used in the literature.Aortic position>0.85 (0.8–0.9)≤0.85 (0.8–0.9)≤0.65 (0.6–0.7)Mitral position>1.2 (1.2–1.3)≤1.2 (1.2–1.3)≤0.9 (0.9)Clinical Impact of PPMSeveral studies have reported that aortic PPM is associated with less improvement in symptoms and functional class,30 impaired exercise capacity,31 less regression of LV hypertrophy,32 less improvement in coronary flow reserve,33 and more adverse cardiac events.30,34 Moreover, PPM has a significant impact on both short-term35,36 and long-term mortality.34,36,37 Recent studies also have reported that the impact of PPM is most significant in patients with depressed LV function with regard to heart failure and mortality after AVR.34,35 These findings reflect the fact that an increased hemodynamic burden is less well tolerated by a poorly functioning ventricle than by a normal ventricle. The impact of PPM also is more pronounced in young patients than in older patients,16 which might be related to the fact that younger patients have higher cardiac output requirements and are exposed to the risk of PPM for a longer period of time. Mitral PPM is independently associated with persisting pulmonary hypertension, increased incidence of congestive heart failure, and reduced survival after MVR.28,29Prevention of PPMIn light of data published in the literature, the surgeon should attempt to avoid severe PPM in every patient undergoing AVR or MVR. Likewise, every effort should be made to avoid moderate PPM in patients undergoing AVR and presenting with the following coexisting conditions: preexisting LV dysfunction and/or severe LV hypertrophy, age <65 to 70 years, and regular and/or intense physical activity.Previous studies10,38,39 have demonstrated that aortic PPM can largely be avoided by systematically calculating the projected indexed EOA of the prosthesis to be inserted (Tables 1 and 2) and, in the case of anticipated PPM, by using alternate procedures such as insertion of a prosthesis model with better hemodynamic performance and aortic root enlargement to accommodate a larger size of the same prosthesis model. Recent studies have reported that this procedure can be performed safely for this purpose,39–41 whereas earlier studies showed evidence to the contrary.42 Hence, root enlargement should probably be considered only in patients in whom the risk of severe PPM cannot be avoided with the use of a better-performing prosthesis and in whom the risk-to-benefit ratio of doing such a procedure is considered advantageous (eg, young patients with no or mild aortic calcification). The prevention of PPM in the mitral position represents a much greater challenge than in the aortic position because valve annulus enlargement or stentless valve implantation is not an option in this situation.27,28Long-Term ManagementAntithrombotic TherapyPatients with prosthetic valves are at risk of thromboembolic complications, including systemic embolization, most commonly cerebral, and prosthetic thrombosis causing valve obstruction and/or regurgitation. The risk of thromboembolic events is higher with mechanical than with bioprosthetic valves, higher with mitral than with aortic prosthetic valves, and higher in the early (<3 months) versus late postoperative phase.6,7,43 The risk also is increased in the presence of concomitant risk factors for thromboembolism, including atrial fibrillation, LV dysfunction, left atrial dilation, previous thromboembolism, and hypercoagulable condition. Table 4 summarizes the general recommendations for antithrombotic therapy based on the prosthesis type and position and the presence of risk factors.6,43,44 Patients with mechanical prostheses require lifelong anticoagulation with warfarin. The choice of optimum international normalized ratio (INR) target for oral anticoagulation should also take into account the thrombogenicity of the individual prosthesis (Table 4).9Table 4. Antithrombotic Therapy in Patients With Prosthetic Heart ValvesWarfarin (INR 2–3)Warfarin (INR 2.5–3.5)Aspirin (75–100 mg)(+) Indicates that although the guidelines generally recommend the therapy, recent studies do not support this recommendation and/or evidence in favor of the recommendation is lacking.*Prosthesis thrombogenicity: low: St Jude Medical, On-X, Carbomedics, Medtronic Hall; medium: bileaflet valves with insufficient data, Bjork-Shiley; high: Lillehei-Kaster, Omniscience, Starr-Edwards. Note that the European guidelines recommend higher INR target for prostheses with medium and high thrombogenicity (AVR and no risk factors, 3.0 for medium and 3.5 for high; MVR and/or risk factors, 3.5 for medium and 4.0 for high).†Risk factors: atrial fibrillation, LV dysfunction (LV ejection fraction ≤35%), left atrial dilation (left atrial diameter ≥50 mm), previous thromboembolism, spontaneous echocardiographic contrast, and hypercoagulable condition.Modified from McAnulty JH, Rahimtoola SH. Antithrombotic therapy for valvular heart disease. In: Fuster V, O'Rourke RA, Walsh RA, Poole-Wilson P, eds. Hurst’s The Heart. New York, NY: McGraw-Hill; 2008:1800–1807.44 Reprinted with permission from the publisher, copyright © 2008, the McGraw-Hill Companies.Mechanical prostheses First 3 mo after replacement++ After first 3 mo Aortic valve Low thrombogenicity*+(+) Medium thrombogenicity*+(+) High thrombogenicity*++ Aortic valve plus risk factor†++ Mitral valve with/without risk factor†++Bioprostheses First 3 mo after replacement Aortic valve(+)+ Aortic valve plus risk factor†++ Mitral valve++ Mitral valve plus risk factor++ After first 3 mo Aortic valve+ Aortic valve plus risk factor†++ Mitral valve+ Mitral valve plus risk factor†++For patients with bioprostheses, warfarin therapy is generally recommended during the first 3 months after implantation on the rationale that endothelialization of the valve sewing cuff may take several weeks to complete (Table 4).6,7,9,43,45 However, several investigators46–48 have questioned the relevance of this recommendation in patients with no thromboembolic risk factors, and according to a recent survey, ≈30% of centers use only aspirin during the first 3 months in these patients.49 After 3 months, warfarin therapy is indicated in patients with a bioprosthesis only if they have ≥1 risk factors for thromboembolism.Anticoagulation management in pregnancy requires a comprehensive evaluation of risks versus benefits.8 Warfarin is probably safe during the first 6 weeks of gestation, but a risk of embryopathy exists if warfarin is taken between 6 and 12 weeks of gestation.6,8 A possible strategy therefore consists of using heparin during the first trimester to avoid warfarin embryopathy, followed by oral anticoagulation up to the 36th week, with subsequent replacement by heparin until delivery.6,9Noncardiac Surgery and Dental CareIn the anticoagulated patient, the risk of increased bleeding during a noncardiac procedure must be weighed against the increased risk of thromboembolism caused by stopping the antithrombotic therapy. Many surgical procedures (including dental procedures) in which bleeding can be controlled easily do not require complete cessation of oral anticoagulation. When oral anticoagulation cessation is necessary, the optimum timing of drug withdrawal depends on the level of INR and the duration of action of the oral anticoagulant drug used. In patients with a bileaflet mechanical valve or a Medtronic Hall monoleaflet valve AVR and no risk factors, warfarin can be stopped 48 to 72 hours before the procedure (so that the INR falls below 1.5) and restarted within 24 hours after the procedure after control of active bleeding.6,7,9,43,50 In other patients with mechanical valves (MVR or AVR with ≥1 risk factors), warfarin is generally stopped 72 hours before the procedure, and heparin is started when the INR falls below 2.0, then stopped 4 to 6 hours before the procedure, restarted as soon as bleeding stability allows, and continued until the INR is again therapeutic. The validated approach is to use intravenous unfractionated heparin, but potential benefits exist to using low–molecular-weight heparin, which can be given on an outpatient basis and, according to recent studies,51 appears to have acceptable risk. The safety of this approach, however, remains to be established in patients at high risk of valve thrombosis. Hence, for the time being, close monitoring with anti-Xa assays is recommended when low–molecular-weight heparin is used in patients with mechanical valves.9Future PerspectivesHigh variability of the INR is the strongest independent predictor of reduced survival after mechanical valve replacement.52 In patients with mechanical prosthetic valves, the Early Self-Controlled Anticoagulation Trial (ESCAT) has revealed that self-management of anticoagulation allows patients to be maintained within a lower and smaller INR range, which results in fewer thromboembolic events rates and in a 23% improvement in long-term survival.53,54 Although these results are encouraging, it is important to emphasize that self-management is not feasible for all patients and that it requires proper identification and education of suitable candidates.In addition, alternatives to warfarin therapy are now under investigation, including the use of direct thrombin inhibitors administered at fixed doses that do not require regular monitoring, as well as the use of antiplatelet drugs or lower doses of warfarin in newer-generation bileaflet prosthesis with a low thrombogenicity profile.Self-management of anticoagulation and/or the replacement of warfarin therapy by newer approaches may help to improve the outcome of patients with mechanical valves and thus expand their use.Endocarditis ProphylaxisPatients with prosthetic valves are at high risk for endocarditis because of the foreign valve surface and sewing ring. Therefore, a lifelong requirement exists for antibiotic prophylaxis for dental, endoscopic, and surgical procedures in patients with a prosthetic valve.6,7,9 Patients and their treating physicians/dentists should be aware of the importance of ensuring rigorous dental hygiene and obtaining blood cultures for any febrile illness before starting antibiotic therapy.Echocardiographic Follow-UpEchocardiography is the method of choice to evaluate prosthetic valve function. This evaluation follows the same principles used for the evaluation of native valves with some important caveats described below. A complete echocardiography includes 2-dimensional imaging of the prosthetic valve, evaluation of leaflet morphology and mobility, measurement of the transprosthetic gradients and EOA, estimation of the degree of regurgitation, evaluation of LV size and systolic function, and calculation of systolic pulmonary arterial pressure. After valve replacement, echocardiographic examination should be performed at discharge or 30 days and 6 to 12 months after operation and/or when a clinical suspicion of prosthetic valve dysfunction is present.43 Moreover, regular follow-up is recommended after 5 years in patients with a bioprosthesis.Parameters of Prosthesis FunctionLeaflet Morphology and MobilityEchocardiographic imaging of the valve occluder is limited by reverberations and shadowing caused by the valve components. Transesophageal echocardiography (TEE) can provide improved image quality and thereby improved detection of cusp calcification and thickening, valvular vegetations caused by endocarditis, thrombus or pannus, and reduced leaflet mobility.55 In the case of mechanical prosthesis, evaluation of leaflet mobility can be attempted with some degree of success, but in our experience, valve fluoroscopy is definitely the best, most economical, and least invasive technique that can be used for this purpose.Quantitative ParametersTransprosthetic Velocity and GradientThe fluid dynamics of mechanical valves may differ substantially from those of native valves. The flow is eccentric in monoleaflet valves and composed of 3 separate jets in the bileaflet valves (Figure 3). Because the direction of the transprosthetic jet may be eccentric, apical, right parasternal, and suprasternal windows should be examined carefully to detect the highest-velocity signal in aortic prosthetic valves. Occasionally, an abnormally high jet gradient corresponding to a localized high velocity may be recorded by continuous-wave Doppler interrogation through the smaller central orifice of bileaflet mechanical prostheses in the aortic or mitral position (Figures 3 and 4).56 This phenomenon may lead to an overestimation of gradient and a false suspicion of prosthesis dysfunction. Download figureDownload PowerPointFigure 3. Numerical simulation showing the flow velocity distribution in bileaflet mechanical valves at a cardiac output of 5 L/min. A, Normally functioning bileaflet prosthesis. The flow velocity within the central orifice is higher than that in the lateral orifices. Accordingly, the peak gradient across the central orifice is 19 mm Hg, which is higher than the actual peak transprosthetic gradient (10 mm Hg). B, Mild prosthesis dysfunction with 25% restriction in the opening of 1 leaflet. The peak gradient is 20 mm Hg. C, Severe prosthesis dysfunction with 1 leaflet blocked in the closed position. The peak gradient is 50 mm Hg. Courtesy of Drs Othman Smadi and Lyes Kadem, Concordia University, Montreal, Québec, Canada.Download figureDownload PowerPointFigure 4. Localized high gradient in a mitral bileaflet valve. A, Visualization of lateral (narrow arrow) and central (large arrow) jets on color Doppler image. B, C, Two Doppler envelopes are superimposed. The highest one, which presumably reflects the velocity within the central orifice, yields a value of peak gradient of 21 mm Hg, whereas the smallest one (lateral orifices) provides a gradient of 12 mm Hg.Effective Orifice AreaEOA is calculated with the continuity equation, similar to native aortic valve area.25,26 When the EOA of a prosthetic valve is measured, a few specific caveats should be taken into consideration. The substitution of the LV outflow tract (LVOT) diameter by the labeled prosthesis size in the continuity equation is not a valid method to determine the EOA of aortic prostheses.57 For mitral prostheses, the EOA is calculated by the continuity equation using the stroke volume measured in the LVOT. It is important to emphasize that the pressure half-time is not valid to estimate the valve EOA of mitral prostheses.25,58Tables 1 and 2 show the normal reference values of EOA for the most commonly used prosthetic valves.Doppler Velocity IndexThe Doppler velocity index (DVI) is a dimensionless ratio of the proximal velocity in the LVOT to that of flow velocity through the prosthesis: DVI=VLVOT/VPV. This parameter can therefore be helpful to screen for valve obstruction, particularly when the cross-sectional area of the LVOT cannot be obtained.59Interpretation of High Gradients: Distinguishing Between High-Flow States, PPM, and Pathological Valve ObstructionThe presence of increased transprosthetic gradient (mean gradient >15 to 20 mm Hg for aortic prostheses and >5 to 7 mm Hg for mitral prostheses) cannot be equated with intrinsic prosthesis dysfunction.27,59 Hence, a high gradient can be due to an associated subvalvular obstruction or a high-flow state (eg, hyperadrenergism, valvular regurgitation); such occurrences can be suspected when the DVI is normal (>0.35 for aortic or >0.45 for mitral prostheses). Conversely, the combination of a high gradient and a low DVI suggests valvular obstruction. In such cases, an integrative evaluation must be done; in particular, the distinction must be made between obstruction resulting from PPM, which is by far the most frequent cause of high postoperative gradients, and intrinsic prosthesis dysfunction, which is a pathological condition requiring more investigation and treatment. For this purpose, the following algorithm can be used (Figure 5). Download figureDownload PowerPointFigure 5. Algorithm for the interpretation of high transprosthetic gradient. IEOA indicates indexed EOA.Step 1As a first screening step, the possibility of PPM as a contributing factor can be assessed by calculating the projected indexed EOA of the prosthesis implanted. This
