The Surgical Valve Replacement

Published Date: 02 Nov 2017

1960s has markedly improved the outcome of patients

with valvular heart disease. Approximately 280 000 valve

substitutes are now implanted worldwide each year; out of which half are mechanical and remaining are bioprosthetic valves. Despite the

substantial improvements in prosthetic valve design and surgery

over the past decades, replacement of valves do not

provide a definitive cure. Prosthetic valve hemodynamics, durability, and thrombogenicity affects the outcome of patients undergoing valve replacement. Optimal prosthesis selection in the individual patient and its medical management and follow-up prevents many of the prosthesis-related complications

Types of Prosthetic Heart Valve

The ideal prosthetic valve should mimic the characteristics of

a native valve. It should have good hemodynamics, extensive durability, high resistance to thrombosis, and ideal implantability. Unfortunately, this substitute does not exist, and each of the available prosthetic valves has limitations.

Mechanical Valves

Three types of mechanical valve design exist: monoleaflet, bileaflet, and caged ball valves.

Caged Ball Valves

Caged ball valves consist of a silastic ball with a sewing ring and a cage formed by 3 metal arches, are no longer used. However, several patients still have caged ball valves and require follow-up.

Monoleaflet Valves

Monoleaflet valves consist of a single disk bounded by lateral or central metal struts. The valve opens at an angle of 60° to 80° producing 2 orifices

Bileaflet Valves

Bileaflet valves consists of 2 semilunar disks attached to a

valve ring by small hinges. The opening angle of the

leaflets ranges from 75° to 90° producing 3 orifices.

Bioprosthetic Valves

Stented Bioprostheses

The purpose of the design of bioprostheses is to mimic the anatomy of

the native valve. Porcine bioprosthetic

valves consist of 3 porcine valve leaflets coated with glutaraldehyde, which is mounted on a metallic or polymer supported stent. Pericardial valves are produced

from sheets of bovine pericardium mounted on a supporting stent.

Stentless Bioprostheses

Several stentless bioprosthetic valves have been

developed in order to improve valve hemodynamics and durability.

They are manufactured from whole porcine aortic valves or bovine pericardium.

Percutaneous Bioprostheses

For patients with symptomatic aortic stenosis with high operative risk, percutaneous aortic valve implantation is an alternative to standard aortic valve replacement

Bioprosthetic Versus Mechanical Valve

It is difficult to choose right valve for right patients. The first step

is to choose between a mechanical and a

bioprosthetic valve . The most important factors

to be considered here are the age & life expectancy of patient, preference, indication/contraindication

for warfarin therapy, and various comorbid condition. Of which much weightage is given to patient’s preference.

The criteria favoring mechanical valve include: (1) the informed

patient opts for a mechanical valve who has no contraindication

for anticoagulation long-term, (2) Who is already on

anticoagulation needing mechanical prosthesis in another position or those at high risk for thromboembolism), (3) who is at risk of

accelerated structural deterioration of bioprosthesis (young age,

hyperparathyroidism, Kidney disease), and (4) who is under 65 years of age with long life expectancy. Bioprosthesis preferred in the

following: (1) the informed patient opts for bioprosthesis;

(2) unavailability of anticoagulation (high risk or contraindicated, poor compliance, lifestyle);(3) who is under 65 years of age with limited

life expectancy; and (4) who is a woman of childbearing

age group. In pregnant patient and in young, bioprostheses degenerate more rapidly. Hence in middle aged woman who completed her family should be offered mechanical valve.

Prosthesis Model and Size

First the prosthesis type should be selected (mechanical versus biological), which has long-term durability and low thrombogenicity.

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).

Second is to select a prosthesis which provides superior hemodynamic performance that prevent prosthesis patient mismatch (PPM) by which minimizing postoperative transprosthetic gradients. Hence one should select the model which provides maximum effective orifice area (EOA) in relation to annulus size. The hemodynamic performance is essentially determined by the size and the total cross-sectional area of that prosthesis. The hemodynamic performance is not similar for all the prostheses. Newer generation prostheses are superior when compared to older ones.

Optimal surgical technique is very essential. For mitral valve replacement, the chordae should be preserved . Bileaflet valves are implanted in antianatomic position and monoleaflet valves should be oriented posteriorly.

Prosthesis-Patient Mismatch

Rahimtoola first proposed the term Patient-Prosthesis Mismatch in 1978.

When the EOA of a prosthesis is too small to the patient’s body size PPM occurs. Indexed EOA is the accepted parameter for identifying PPM.

Clinical Significance of PPM

In aortic PPM, there is less improvement in symptoms and functional class, exercise capacity, poor LV hypertrophy regression,

very less improvement in coronary flow reserve and high adverse cardiac events. PPM has both short-term and long-term mortality.

PPM has most significant impact in patients with depressed LV function and in young patients with regard to mortality and heart failure after AVR. Increased hemodynamic burden is poorly tolerated by a failing ventricle.

Mitral PPM is associated with increased

incidence of congestive heart failure, persisting pulmonary hypertension,

and decreased survival after MVR.

PPM Prevention

In patients undergoing AVR, the surgeon should make efforts to avoid severe PPM in all patients and also should avoid moderate PPM in patients with the following conditions: patients with LV dysfunction and/or severe LV hypertrophy, who are under 65 to 70

Years of age, and who do regular and/or intense physical activity.

Aortic PPM is avoided by calculating the

indexed EOA of the prosthesis before insertion

and if PPM is anticipated Aortic root is enlarged to accommodate prosthesis model

with better hemodynamic performance. Root enlargement should be done only in patients in whom severe PPM cannot be avoided.

Antithrombotic medical aid

Prosthetic valve patients area unit in danger of thromboembolic complications, together with general embolization, most ordinarily cerebral, and prosthetic occlusion inflicting valve obstruction and/or regurgitation. the danger of thromboembolic events is higher with mechanical than with bioprosthetic valves, higher with mitral than with aortal prosthetic valves, and better within the early (_3 months) versus late surgical section.6,7,43 the danger is also exaggerated within the presence of concomitant risk factors for occlusion, together with fibrillation, fifty-five dysfunction, left chamber dilation, previous occlusion, and hypercoagulable condition. Table four summarizes the overall recommendations for antithrombotic medical aid supported the corrective sort and position and therefore the

presence of risk factors.6,43,44 Patients with mechanical prostheses need long medical care with decoagulant. The choice of optimum international normalized quantitative relation (INR)target for oral medical care ought to additionally take under consideration the thrombogenicity of the individual corrective (Table 4).9 For patients with bioprostheses, decoagulant medical aid is mostly suggested throughout the primary three months once implantation on the explanation that endothelialization of the valve sewing cuff might take many weeks to complete (Table 4).6,7,9,43,45 However, many investigators46–48 have questioned the connection of this recommendation in patients with no thromboembolic risk factors, and per a recent survey, one hundred thirty of centers use solely Bayer throughout the primary 3months in these patients.49 once three months, decoagulant medical aid is indicated in patients with a bioprosthesis given that they need risk factors for occlusion. medical care management in physiological state needs a comprehensive evaluation of risks versus advantages.8 decoagulant is probably safe throughout the primary half-dozen weeks of gestation, but a risk of embryopathy exists if decoagulant is taken between half-dozen and twelve weeks of gestation.6,8 A attainable strategy so consists of using Lipo-Hepin throughout the primary trimester to avoid decoagulantembryopathy, followed by oral medical care up to the thirty sixth

week, with future replacement by Lipo-Hepin till

delivery.6,9

Noncardiac Surgery and aid

In the anticoagulated patient, the danger of exaggerated hemorrhage

during a noncardiac procedure should be weighed against the

increased risk of occlusion caused by stopping the

antithrombotic medical aid. several surgical procedures (including

dental procedures) within which hemorrhage are often controlled simply

do not need complete surcease of oral medical care.

When oral medical care surcease is important, the optimum

timing of ending depends on the amount of Bureau of Intelligence and Research

and the length of action of the oral medicament drug used.

In patients with a bileaflet mechanical valve or a Medtronic

Hall monoleaflet valve AVR and no risk factors, decoagulant will

be stopped forty eight to seventy two hours before the procedure (so that the

INR falls below one.5) and restarted at intervals twenty four hours once the

procedure once management of active hemorrhage.6,7,9,43,50 In alternative

patients with mechanical valves (MVR or AVR with ninety one risk

factors), decoagulant is mostly stopped seventy two hours before the

procedure, and Lipo-Hepin is started once the Bureau of Intelligence and Research falls below

2.0, then stopped four to six hours before the procedure, restarted

as presently as hemorrhage stability permits, and continued till the

INR is once more therapeutic. The valid approach is to use

intravenous unfractionated Lipo-Hepin, however potential advantages

exist to victimisation low–molecular-weight Lipo-Hepin, which may be

given on AN patient basis and, per recent studies,

51 seems to own acceptable risk. the security of this

approach, however, remains to be established in patients at

high risk of valve occlusion. Hence, for the present,

close watching with anti-Xa assays is suggested once

low–molecular-weight Lipo-Hepin is employed in patients with mechanical

valves.9

Future views

High variability of the Bureau of Intelligence and Research is that the strongest freelance

predictor of reduced survival once mechanical valve replacement.

52 In patients with mechanical prosthetic valves, the

Early Self-Controlled medical care Trial (ESCAT) has

revealed that self-management of medical care permits

patients to be maintained at intervals a lower and smaller Bureau of Intelligence and Research

range, which ends in fewer thromboembolic events rates

and during a twenty third improvement in semipermanent survival.53,54 though

these results area unit encouraging, it's vital to

emphasize that self-management isn't possible for all patients

and that it needs correct identification and education

of appropriate candidates.

In addition, alternatives to decoagulant medical aid area unit currently underneath

investigation, together with the employment of direct coagulase inhibitors

administered at fastened doses that don't need regular

monitoring, also because the use of antiplatelet medication or lower

doses of decoagulant in newer-generation bileaflet corrective

with an occasional thrombogenicity profile.

Self-management of medical care and/or the replacement

of decoagulant medical aid by newer approaches might facilitate to

improve the result of patients with mechanical valves and

thus expand their use.

Endocarditis bar

Patients with prosthetic valves area unit at high risk for carditis

because of the foreign valve surface and stitching ring.

Therefore, a long demand exists for antibiotic bar

for dental, endoscopic, and surgical procedures in

patients with a prosthetic valve.6,7,9 Patients and their treating

physicians/dentists ought to remember of the importance of

ensuring rigorous dental hygiene and getting blood cultures

for any symptom unhealthiness before beginning antibiotic medical aid.

Echocardiographic Follow-Up

Echocardiography is that the methodology of option to value prosthetic

valve operate. This analysis follows a similar

principles used for the analysis of native valves with some

important caveats represented below. an entire diagnostic technique

includes 2-dimensional imaging of the prosthetic valve,

evaluation of leaflet morphology and quality, mensuration

of the transprosthetic gradients and EOA, estimation of the

degree of regurgitation, analysis of fifty-five size and heartbeat

function, and calculation of heartbeat respiratory organ blood pressure.

After valve replacement, echocardiographic examination

should be performed at discharge or thirty days and half-dozen to twelve months

after operation and/or once a clinical suspicion of prosthetic

valve disfunction is gift.43 furthermore, regular follow-up is

recommended once five years in patients with a bioprosthesis.

Parameters of corrective operate

Leaflet Morphology and quality

Echocardiographic imaging of the valve occluder is restricted

by reverberations and shadowing caused by the valve parts.

Transesophageal diagnostic technique (TEE) will give

improved image quality and thereby improved detection

of cusp calcification and thickening, controller vegetations

caused by carditis, coagulum or pannus, and reduced

leaflet quality.55 within the case of mechanical corrective,

evaluation of leaflet quality are often tried with some

degree of success, however in our expertise, valve radiology is

definitely the simplest, most economical, and least invasive

technique which will be used for this purpose.

Quantitative Parameters

Transprosthetic speed and Gradient

The fluid dynamics of mechanical valves might take issue considerably

from those of native valves. The flow is eccentric in

monoleaflet valves and composed of three separate jets within the

bileaflet valves (Figure 3). as a result of the direction of the

transprosthetic jet could also be eccentric, apical, right parasternal,

and suprasternal windows ought to be examined fastidiously to

detect the highest-velocity signal in aortal prosthetic valves.

Occasionally, AN abnormally high jet gradient corresponding

to a localized high speed could also be recorded by continuouswave

Doppler interrogation through the smaller central opening

of bileaflet mechanical prostheses within the aortal or mitral

position (Figures three and 4).56 This development might cause AN

overestimation of gradient and a false suspicion of corrective

dysfunction.

Effective opening space

EOA is calculated with the continuity equation, similar to

native semilunar valve space.25,26 once the EOA of a prosthetic

valve is measured, some specific caveats ought to be taken into

consideration. The substitution of the fifty-five outflow tract

(LVOT) diameter by the tagged corrective size within the

continuity equation isn't a legitimate methodology to work out the

EOA of aortal prostheses.57 For mitral prostheses, the EOA

is calculated by the continuity equation victimisation the stroke

volume measured within the LVOT. it's vital to stress

that the pressure half-time isn't valid to estimate the

valve EOA of mitral prostheses.25,58 Tables one and a pair of show

the normal reference values of EOA for the foremost normally

used prosthetic valves.

Doppler speed Index

The physicist speed index (DVI) could be a dimensionless quantitative relation of

the proximal speed within the LVOT thereto of flow speed

through the prosthesis: DVI_VLVOT/VPV. This parameter will

therefore be useful to screen for valve obstruction, notably

when the cross-sectional space of the LVOT can not be

obtained.59

Interpretation of High Gradients: identifying

Between High-Flow States, PPM, and Pathological

Valve Obstruction

The presence of exaggerated transprosthetic gradient (mean

gradient one hundred fifteen to twenty mm Hg for aortal prostheses and ninety five to

7 mm Hg for mitral prostheses) can not be equated with

intrinsic corrective disfunction.27,59 Hence, a high gradient

can be owing to AN associated subvalvular obstruction or a

high-flow state (eg, hyperadrenergism, controller regurgitation);

such occurrences are often suspected once the DVI is

normal (_0.35 for aortal or ninety.45 for mitral prostheses).

Conversely, the mix of a high gradient and an occasional

DVI suggests controller obstruction. In such cases, AN integrative

evaluation should be done; above all, the excellence

must be created between obstruction ensuing from PPM,

which is out and away the foremost frequent explanation for high surgical

gradients, and intrinsic corrective disfunction, which is a

pathological condition requiring additional investigation and treatment.

For this purpose, the subsequent formula are often used

(Figure 5).

Step 1

As a primary screening step, the chance of PPM as a

contributing issue are often assessed by scheming the projected

indexed EOA of the corrective established . This is

accomplished by dividing the EOA reference price for the

model and size of the corrective (Tables one and 2) by the

patient’s body expanse. If this projected indexed EOA is

_0.85 cm2/m2 within the aortal position or ninety one.2 cm2/m2 within the

mitral position (Table 3), then PPM isn't a conducive

factor. However, if the indexed EOA is below this price,

PPM could also be partly or all accountable for the high

gradient.

Step 2

The second step consists of scrutiny the EOA as measured

by physicist with the EOA reference price (Tables one and 2).

The measured EOA of a usually functioning corrective

should be near the reference price for a similar model and

size of corrective, whereas a considerably lower price is

compatible with intrinsic corrective disfunction.

Step 3

If the measured EOA is comparable to its reference price ninety one SD,

intrinsic disfunction is unlikely, and therefore the presence/severity of

PPM ought to be confirmed by scheming the indexed EOA. If

no PPM is gift, a technical pitfall or a high-flow state is

likely.

Step 4

If the EOA is below the reference price and if the corrective

is not a bileaflet mechanical valve, corrective valve disfunction

should be unreal, and confirmation ought to be sought-after

with alternative examinations like TEE, radiology, computed

tomography, or viscus catheterization. If, on the opposite hand,

the corrective could be a bileaflet mechanical valve and therefore the patient

is symptomless, localized high gradient is that the doubtless cause

(Figures three and 4). sadly, this development is usually

difficult to verify or exclude from the transthoracic diagnostic technique

(TTE). just in case of doubt, valve leaflet quality

can be evaluated with radiology (or TEE) and by trying

for indirect signs of corrective disfunction.

Evaluation and Interpretation of Prosthetic

Valve Regurgitation

The approach to police work and grading corrective regurgitation

is similar thereto for native valves and involves analysis

of many physicist echocardiographic indexes.60 However,

care is required to separate physiological from

pathological corrective regurgitation. Mechanical prostheses

indeed have a traditional regurgitant volume called outflow

backflow. This "built-in" regurgitation on paper prevents

blood stasis and coagulum formation employing a laundry impact.

As hostile the pathological regurgitant jets, the normal

leakage backflowing jets area unit characterised by being short in

duration, narrow, and symmetrical. within the case of pathological

regurgitation, it's additionally vital to localize the origin of the

regurgitant jet(s) to differentiate paravalvular from transvalvular

regurgitation.

Prosthetic aortal Regurgitation

TTE typically provides an honest image of the LVOT

and prosthetic aortal regurgitation. Multiple views ought to be

used, also because the same principles and strategies used for

quantitation of native controller regurgitation.60 It should be

remembered, however, that terribly restricted information area unit offered on

the application and validation of quantitative parameters such

as the breadth of the regurgitant jet, effective opening space, and

regurgitant volume within the context of prosthetic valves.61 TEE

may give vital causative info like flail

bioprosthetic cusp, presence of pannus or coagulum interacting

with leaflet closure, corrective organic phenomenon, and placement

and size of paravalvular jets.55

Prosthetic Mitral Regurgitation

Assessment of prosthetic mitral regurgitation by TTE is

problematic as a result of the atrium sinistrum is basically occulted by the

acoustic shadowing caused by the golden parts of the

prosthesis. This downside is additional frequent in mechanical

valves than bioprosthetic valves. The presence of "occult"

mitral corrective regurgitation ought to be suspected once the

following signs area unit present: flow convergence downstream of

the corrective throughout pulsation, exaggerated mitral peak E-wave

velocity (_2 m/s) and/or mean gradient (_5 to seven metric linear unit Hg),

DVI _0.45, or unexplained or new worsening of respiratory organ

arterial high blood pressure. a choice tree analysis like that

proposed by Fernandes et al59 victimisation multiple parameters will

also be helpful. TEE ought to be performed consistently once

a clinical or TTE suspicion of pathological mitral regurgitation

is present.55

Identifying Indirect Signs of disfunction

The size and performance of the fifty-five and chamber chambers and therefore the

level of heartbeat respiratory organ blood pressure are often wont to

corroborate corrective disfunction severity. above all,

these measurements are often compared with previous measurements

and often area unit the primary sign to alert attention once the

regurgitation is troublesome to envision.

Additional Diagnostic Tests

Exercise testing and plasma symptom peptides area unit further

tests which will be wont to any document cut purposeful

capacity and/or early coronary failure ensuing from

prosthesis disfunction or PPM.

Long-Term Complications: Identification

and Management

Mechanical valves have a considerable risk of thromboemboli

and thrombotic obstruction and thus need semipermanent

anticoagulation medical aid, that successively is related to AN

increased risk of harm complications. yet,

contemporary mechanical valves have wonderful sturdiness. In

contrast, bioprosthetic valves have an occasional risk of occlusion

without medical care, however their sturdiness is restricted

by hardening or noncalcific tissue deterioration.62

Thromboembolic and hemorrhage Complications

Thromboembolic complications area unit a very important explanation for

morbidity and mortality in patients with a prosthetic heart

valve, with AN calculable incidence of clinical events travel

from 0.6% to 2.3% per patient-year.6,50 the danger of thromboembolic

complications is comparable for patients with mechanical

valves on decoagulant medical aid and bioprosthetic valves while not

warfarin medical aid. the danger of occlusion depends not

only on corrective sort however additionally on valve position and thrombogenicity,

patient risk factors, and antithrombotic treatment.

Systemic Emboli

In patients with a prosthetic valve, thromboembolic events

are plausible to be associated with the valve unless well-tried

otherwise. The presence of a coagulum on the corrective might

not be confirmed by diagnostic technique as a result of the coagulum

is no longer gift, is simply too tiny to be detected, or is occulted

by the shadowing caused by the valve parts. The first

step within the management of a patient with a prosthetic valve

and a general clot event is to fastidiously assess the

adequacy of medical care management. If it's inadequate,

therapy is adjusted or reinstituted to realize and maintain a

therapeutic impact. If medical care has been adequate,

warfarin medical aid ought to be exaggerated to realize the next Bureau of Intelligence and Research

target, and yet hemorrhage risk assessment and therefore the

results of the investigation, Bayer may could also be another or

increased.6 Moreover, in patients with recent cerebral embolism

who area unit at high risk for harm transformation of

the cerebral infarction (infarct size a hundred thirty five of the cerebral

hemisphere and/or uncontrolled hypertension), it's preferred

to withhold oral medical care for a minimum of five days and use

intravenous Lipo-Hepin within the in the meantime.9

Prosthesis occlusion

Obstruction of prosthetic valves could also be caused by coagulum

formation (Figure 6A), pannus growth (Figure 6B), or their

combination. Pannus growth alone could also be encountered in

both bioprosthesis and mechanical valves. it's going to gift as a

slowly progressive obstruction caused by a subvalvular annulus,

in which case it's going to be troublesome to envision and so

distinguish from progressive structural valve deterioration

(SVD). Valve occlusion is most frequently encountered in

patients with mechanical valves and inadequate antithrombotic

therapy. occlusion additionally could also be seen in bioprosthetic

valves wherever it most frequently happens within the early surgical

period. Pannus and occlusion could also be gift alone or in

combination and cause acute or acute valve obstruction.

The incidence of impeding valve occlusion varies between

0.3% and 1.3% per patient-year in patients with mechanical

valves.50,63

Diagnosis

Valve occlusion ought to be suspected in any patient with any

type of prosthetic valve United Nations agency presents with a recent increase in

dyspnea or fatigue as a result of valve occlusion will develop

gradually and perniciously over many days or weeks.9 Suspicion

should be higher if there has been a amount of

interrupted or subtherapeutic medical care within the recent

past. In such cases, diagnostic technique ought to be done

promptly and may embody TEE, notably if the corrective

is within the mitral position.

Treatment

In nonobstructive left-sided prosthetic valve occlusion confirmed

by TTE or TEE, treatment consists of a brief course of

intravenous Lipo-Hepin with shut echocardiographic follow-up

plus adjustment of decoagulant medical aid and addition of Bayer

(100 mg) (Figure 7).63 However, if the medical treatment is

unsuccessful, surgery ought to be thought-about in patients with

large (_5 to ten metric linear unit as determined by TEE) or mobile

thrombi; lysis with plasminogen activator, enzyme, or recombinant

tissue protease is suggested in

other patients.6,7,63

Urgent or nascent surgery is that the treatment of selection in

critically unwell patients with impeding valve occlusion (Figure

7). during a recent series, operative mortality was 4WD to five

for patients with big apple Heart Association category III or

lower, whereas it reached V-day to twenty in patients with category

IV.63 The intervention might involve easy excision or

valve replacement. Rescue lysis ought to be thought-about

in patients unlikely to survive surgery or once surgical

treatment is inaccessible and therefore the patient can not be trans-

ferred.6,7,63 Effective medical care treatment is overriding

to the interference of perennial prosthetic valve occlusion

(Table 4).

Anticoagulant-Related Hemorrhage

In patients on semipermanent medical care, the annual risk of a

hemorrhagic event is ninety one per patient-year.50,64 irregular

comparative studies of bioprosthetic versus mechanical prostheses

reported that occlusion rates area unit similar with

the 2 styles of valves however hemorrhage is additional common with a

mechanical valve.64,65 In patients with mechanical valves, the

bleeding events area unit most frequently owing to excessive medical care,

which can be managed by withholding decoagulant and

monitoring the amount of medical care with serial Bureau of Intelligence and Research

determinations.6

Structural Valve Deterioration

Incidence of SVD

Mechanical prostheses have a superb sturdiness, and SVD

is very rare with modern valves, though mechanical

failure (eg, strut fracture, leaflet escape, occluder

dysfunction caused by lipide adsorption) has occurred with

some models within the past (Figure 6C).

The rate of SVD in bioprosthetic valves (Figure 6D)

increases over time, notably once the initial seven to eight years

after implantation. With standard stented bioprostheses,

the freedom from structural valve failure is seventieth to ninetieth at ten

years and five hundredth to eightieth at fifteen years.6,43,50,62,66

Predictors of SVD

Risk factors antecedently found to be related to bioprosthetic

SVD embody younger age, bicuspid valve position, renal

insufficiency, and glandular disease.43,62,66 high blood pressure,

LV hypertrophy, poor fifty-five operate, and corrective size additionally

have been rumored as predictors of SVD in bioprostheses

implanted within the aortal position.66

Host-Related Factors

Bioprosthetic SVD is powerfully influenced by the age of the

patient at the time of implantation.43,62 the speed of failure of

bioprostheses is one hundred ten at ten years in old patients (_70

years of age) however is one hundred twenty to half-hour in patients a hundred and forty years of

age.43,62 many studies additionally counsel that bioprosthetic structural

failure is additional frequent within the mitral than within the aortal

position.43,66 This distinction is probably going associated with the upper

mechanical stress obligatory on the valve leaflets of mitral

bioprostheses throughout pulsation. Likewise, SVD of aortal bioprostheses

may be accelerated by general high blood pressure,

possibly as a results of a inveterately exaggerated pulse

closure stress.

Valve-Related Factors

Several studies tend to indicate that newer-generation bioprostheses

are additional sturdy than older ones.43,62,66 Some reports

also counsel that serous membrane valves may well be higher than

porcine valves during this regard,67 however alternative recent studies show

no considerable distinction between these two styles of

prosthesis.68

Pathogenesis of SVD

Degenerative method

Bioprosthetic valve tissues area unit cross-linked in glutaraldehyde

to reduce its antigenicity and to confirm chemical stabilization;

however, this chemical treatment might incline to bioprosthetic

tissue degeneration (Figure 8).62 Indeed, tissue fixation

with glutaraldehyde induces a metal flow as a results of

membrane injury, that provides, at the side of the residual

phospholipids of the membranes, AN atmosphere susceptible to

calcium crystal nucleation. Host factors and mechanical stress

then contribute to metal crystal growth. Such findings have

prompted makers to do completely different anticalcifying treatments

on bioprosthetic tissue within the hope of avoiding or

slowing SVD. Opposing previous beliefs, recent studies69–74

suggest that SVD might not be a strictly passive chronic

process however may involve active mechanisms like

immune rejection and arterial sclerosis (Figure 8).

Immune method

Recent studies counsel that bioprosthetic valves don't seem to be if truth be told

completely "immunologically inert" (Figure 8).73 Hence,

residual animal antigens may elicit body substance and cellular

immune responses, resulting in tissue mineralization and/or

disruption. A additional sturdy system may additionally justify

the additional speedy SVD sometimes ascertained in younger patients.

Atherosclerotic method

Recent studies additionally demonstrate AN association between

bioprosthetic SVD and several other coronary-artery disease risk factors,

including hypercholesteremia, diabetes, metabolic syndrome,

and smoking.66,70,72 furthermore, one retrospective study

reported that statin drug medical aid is related to slower progression

of SVD.71 These recent findings support the hypothesis

that the same as the native semilunar valve, the SVD of bioprostheses

may be connected, a minimum of partially, to AN coronary-artery disease

process (Figure 8). The infiltration of low-density lipoproteins

within the bioprosthetic tissue and their chemical reaction might

trigger AN inflammatory method and therefore the formation of froth

cells.74 In turn, the inflammatory cytokines and alter

low-density lipoproteins might induce AN osteoblastic differentiation

of stem/progenitor cells that have settled the

bioprosthetic tissue.75

Future views for the interference of SVD

This new information raises the chance that, beyond the

pretreatment of the cusp tissue by anticalcifying agents before

bioprosthesis implantation, treatment of the patient once

implantation may facilitate to avoid or delay SVD and thereby

enhance valve sturdiness. above all, the antiatherogenic

and antiinflammatory effects of statins may contribute to

slowing of the progression of SVD.71,75 additionally, lifestyle

changes to counter the consequences of the metabolic syndrome

could have helpful effects.72 patently, irregular trials

are required to verify these hypotheses.

Treatment of SVD

SVD is that the most frequent explanation for reoperative valve replacement

in patients with a bioprosthesis. Whenever attainable, the

reoperative procedure ought to be performed early within the

disease method before fifty-five operate and symptomatic standing

deteriorate considerably.43

Future Perspective

Percutaneous implantation of a replacement bioprosthesis at intervals the

failed bioprosthesis implantation ("valve in valve") might

provide an honest various to surgical replacement of the

prosthesis, notably in speculative patients (Figure 6E).76

Infective carditis

The incidence of prosthetic valve carditis is ninety.5% per

patient-year, even with applicable antibiotic bar.

Prosthetic valve carditis is a very serious condition

with high mortality rates (30% to 50%).9,50 The identification

relies preponderantly on the mix of positive blood

cultures and echocardiographic proof of prosthetic infection,

including vegetations, paraprosthetic abscesses, or a new

paravalvular regurgitation.77 TEE is important thanks to its

greater sensitivity in police work these abnormalities.55 Despite

prompt and applicable antibiotic treatment, several patients

with prosthetic valve carditis can eventually need

surgery. Medical treatment alone is additional doubtless to reach

late prosthetic valve carditis (occurring ninety six months once

surgery) and in nonstaphylococcal infections. Surgery ought to

be thought-about within the following situations: failure of medical

treatment; hemodynamically vital corrective regurgitation,

especially if related to deterioration of fifty-five function;

large vegetations; and development of intracardiac

fistulas.6,9,77

Paravalvular Regurgitation

Paravalvular regurgitation generally is owing to infection, suture

dehiscence, or pathology and calcification of the native annulus,

leading to inadequate contact between the stitching ring and

annulus. tiny paravalvular regurgitant jets area unit ofttimes

(10% to twenty fifth of cases) seen on intraoperative TEE before

cardiopulmonary bypass weaning78,79 and will considerably

decrease or resolve once the injection of simple protein or within the

days, weeks, or months once operation because the healing method

evolves. Moderate or severe paravalvular regurgitation is rare

(1% to 2%) and needs returning to viscus bypass

for immediate correction. organic phenomenon of the corrective within the

late surgical amount could also be associated with operative technical

factors however is most frequently caused by carditis, in which

case emergency operation is mostly needed.

Long-term prognosis is mostly benign in patients with

mild paravalvular regurgitation known by perioperative

echocardiography, with progression of regurgitation requiring

reoperation in ninety one of patients at follow-up at ninety one to two

years.78 Hence, nearer follow-up seems even in these

patients, with surgical intervention bonded just for those

who develop symptoms, hemolysis, and/or progressive fifty-five

dysfunction.80 The paravalvular leaks are often repaired while not

valve replacement in a hundred and fifty of cases. In patients with severe

paravalvular mitral regurgitation refractory to aggressive

medical medical aid United Nations agency don't seem to be candidates for surgical intervention,

percutaneous implantation of AN Amplatzer body part occluder

device offers another therapeutic choice.81

Hemolysis

Blood tests for hematolysis (lactate dehydrogenase) ought to be

part of routine follow-up. an oversized proportion (50% to 95%) of

patients with mechanical valves have some extent of intravascular

hemolysis.50 However, anemia caused by hematolysis

is rare unless prosthetic regurgitation has occurred. Patients

with delicate to moderate anemia will typically be treated

conservatively with iron and B complex, _-blockers, and glycoprotein.

7 However, repeat valve surgery or surgical repair of

a paravalvular leak could also be required once prosthetic valve

hemolysis is related to severe anemia.

Conclusions

Many prosthesis-related complications are often prevented or

their impact reduced by individualised choice of the

optimal corrective at the time of valve replacement and by

careful medical management and periodic watching of

valve operate once operation. Prompt recognition of valve

dysfunction permits early treatment, typically with repeat surgical

intervention. many recent developments, together with the speedily

evolving field of transdermic valve implantation, lifestyle

and/or pharmacologic interventions for the interference

of bioprosthetic valve degeneration, and patient selfmanagement

of oral medical care, might amendment the face of

the current apply for the surgical management of valve

disease within the close to future.