1. 1. ' if / '*Li, ~L, Lri 9-) i ' ii-4, / ~>J. >.: i,~/ I i~ ii. i . , ,duly:_/L , /"I 'iL4LV, I/ , l. .i. L . W , .A; .. AiL/ ii i/ I rf . I I_ . l.i. .,~ II "II A H V. i. L , ,Vliil IELIEX.Fm.Ill.IV/ fiinlli 210131qjilcfliil / "!l,5lfll! I'iTl)iI q/ '"_L. iiIiI1/f. 4inIl4ic , :I0Lj, i)Tl! lIBl| I~! l:ill| IlESlI llllllilllll IIF l| BIl| lll0li'iYlllllllllllll BllllllllCHIEF PATRON Dr.A.M.ShamimCHAIRMAN,EDITORIAL COMMITTEEDr.M.Jalaluddin,FCPSEDITORIAL BOARDDr.Abduz Zaher,FRCPDr.A.K.Miah,PhDDr.A.R M.Sohrabuzzaman,FCPS Dr.Fakrul Islam,FACCDr.Reyan Anis,FRCPDr.Arun Kumar Sharma,FACC Dr.Md.Elias Ali,MDDr.Lutfor Rahman,MSDr.Md.Lokman Hossain,MSDr.Salauddin Ahmed Selim,DA Dr.A.H.M.Abul Monsur,D CardEDITOR Dr.Baren Chakraborty,FRCPASSISTANT EDITOR Dr.Mahbubor Rahman,FRCP Dr.Fahmida Zaman,FACCCHIEF EXECUTIVEDr.(Brig Gen) Manz0orA.Mollah (Retd. )SECRETARY,PUBLICATION COMMITTEEAIEmran ChowdhuryEDITORIAL STAFF Kuddus Hawladar Nipun Md.Mizanur RahmanThe world's rst successful heart valve surgery was performed 90 years ago by Elliot Cutler.Forty years later,Albert Starr and Lowell Edwards,an engineer,collaborated to pioneer the development of the rst successful,Food and Drug Administration (FDA) approved,mechanical caged-ball heart valve.Since then,more than 80 mechanical heart valve models have been developed.Patients undergoing mechanical mitral valve replacement require lifelong anticoagulation.Contributing to the long-standing success of these interventions,anticoagulation remains a key step in the prevention of valve thrombosis and thromboembolic stroke.The best approach in anticoagulant optimization is debatable.Still warfarin is the drug of choice.The search for alternative prophylaxis often pushes clinicians to off-label options.Novel anticoagulant, dabigatran has been approved in the United States for patients with nonvalvular atrial brillation.Due to its perceived convenience,some physicians have begun to prescribe it off label for mechanical valves. In this issue of journal Rahman et al published their experience of treating prosthetic valve thrombosis with prolonged streptokinase infusion in 15 cases of documented valve thrombosis and outcome of this modality of treatment appears to be execellent in this series of patients.Out of 15 patients treated only 1 patient died.Warfarin is also the drug of choice in pregnant women with prosthetic mechanical valve.In this issue of journal Ganguly et al presented their experience of treating 11 pregnant women with warfarin.There was no documented warfarin embryopathy in their series.The authors opined that warfarin appears to be the anticoagulant of choice for the pregnant women with mechanical prosthetic heart valves during pregnancy. Although coronary artery bypass graft (CABG) has been considered the "gold standard" for unprotected left main coronary artery disease (CAD) revascularization,more recently percutaneous coronary intervention (PCI) has emerged as a possible alternative mode of revascularization in carefully selected patients.In the present issue of the journal Momenuzzaman et al published their experience of unprotected Left main (LM) angioplasty on 79 consecutive patients in their hospital and the outcome appears encouraging.No death was noted during the procedure.Out of these 79 patients only 1 patient (1.3%) needed emergency CABG for LM dissection and another 4 patients (5.1%) died during limited followup.In this cohort of LM disease 34% patients presented with stable angina,32% with unstable angina,22% with post MI angina and 12% with post PCI angina.In stable patients with signicant LM disease still CABG is considered as the gold standard (Class 1 indication) from the survival point of view (ACC/ AHA Guideline Circulation.2012; 126: e354-e471) and PCI to improve survival is reasonable as an alternative to CABG in selected stable patients with signicant (250%) diameter stenosis) unprotected left main CAD (Class Ila indication). lain: . ;i'l= Iiifl. '=Z I 1 , i'iI'iIig' 1.::Ti our I 1:-iiiuiaitilsi Igkjii -11-15 V - -I I -II/0' = + '-I!Iii:iii-iiiiII, !lii:1t18 years who underwent an elective,non- outpatient,open surgical procedure were enrolled.Subcutaneous enoxaparin 1 mg/ kg,twice daily,was used asbridging anticoagulation.The demographics,co- morbidities,and preoperative (medications,echocardiographic ndings,laboratory results) andpostoperative data were evaluated for their association with the occurrence of perioperative adverse events.The incidence of perioperative adverse cardiovascular (10.8% vs 10.7%,p= O.985) and noncardiovascular (11.9% vs 11.4%,p= O.989) events was similar in those patients with and without PHVs.Bleeding (18.6% vs 14.2%,p= O.989),thromboembolism (3.6% vs 2%,p=0.989),and mortality at 3 months (1.4% vs 1.3%,p=0.825) were also similar for the 2 groups.This study concluded that with close follow-up and strict adherence to the guidelines,patients with PHVs and patients with native heart valves undergoing noncardiac and nonvascular surgery have a similar risk of mortality and morbidity*. Unfractionated he arin (UFH) versus low molecular weight eparins (LMWH)The management of anticoagulation in patients with a PHVs can be especially difcult in two clinical situations:in patients who must withhold antithrombotic treatment before and after a surgery/ invasive procedure,and in those
2. 10. _pr9i_': *;i_i, v I ; .:i_uJiui_m;,'; m_1r; lsa1u526 ZaherA,Rahman M,KhayerA,Zaman R,et alwho have a bleeding complication while receiving warfarin/acenocumarol.Although low molecular weight heparins (LMWH) are an attractive alternative to other anticoagulant strategies because of their pharmacokinetic and pharmacodynamic properties,there is not enough clinical evidence to consider their effectiveness and safety to be denitive in both mentioned settings.One observational prospective study was carried out on a cohort of patients with PHVs and various thromboembolic risk factors.These patients were admitted in a hospital in several clinical situations that led to interruption of treatment with acenocumarol and were treated with enoxaparin as an alternative to other methods.All consecutive patients with mechanical heart valves were admitted in a hospital between May 1999 and January 2002 who had to interrupt treatment with acenocumarol and were treated with enoxaparin as an alternative to other methods were enrolled.All patients were followed up through clinical history during the hospitalization and by telephone after discharge to detect thromboembolic events.82 patients were identied and followed up for a mean of 2.8 months (range 1.5-3.5 months) after discharge.61 of them (74%) had one or more associated thromboembolic risk factors.Acenocumarol was interrupted to perform an invasive procedure in 74 patients and because of haemorrhagic complication in another 8 patients.Most patients received the standard enoxaparin dose (1 mg/ kg at 12 hour intervals).There were 8 minor and 1 major bleeding events during enoxaparin treatment.No thromboembolic complications were clinically detected during hospitalization or during follow up. The authors of the study opined that enoxaparin may be an effective and relatively safe substitute anticoagulant for patients with mechanical heart valves who must withhold acenocumarol.This study showed that enoxaparin in the high risk postoperative period is at least as safe and effective as UFH5.Clinical outcomes were not statistically different for patients receiving LMWH or UFH in another reported series.Nevertheless,there is a widely held notion that LMWH is not safe to use as bridge therapy for patients with mechanical PHVs.Recent prospective bridge studies do not support that view,demonstrating that LMWH used as bridge therapy is associated with low risks for thromboembolism and major bleeding even in patients with mechanical valves.Accordingly,the latest ACCP guidelines for perioperative management of patients on antithrombotic therapy recommend therapeutic-dose LMWH over IV UFH for bridge therapy,including in patients with mechanical heart valves7. Likewise latest guidelines from the American College of Cardiology and American Heart Association on management of patients with valvular heart disease endorse LMWH as an option for bridge therapys. Management is complicated by the absence of randomized trials examining peri-operative anticoagulation management.Thromboembolic risk increases substantially when oral anticoagulation is discontinued and valve thrombosis may be inapparent for 1-2 months.This delayed diagnosis makes it difficult to identify the incitingBangladesh j Cardiol,2013; 04-05(1):525-29event,either clinically or in experimental trials.Furthermore,the absence of early postoperative events may falsely suggest that peri-operative anticoagulation was safe and adequate.The approach to management therefore remains controversial.Seamless oral anticoagulation is preferred whenever possible and this is safe for a range of minor procedures,including cardiac catheterisation,dental and ophthalmic surgery"5'.Major surgical procedures require withdrawal of oral anticoagulation before surgery to lower the INR to 12 months n= l99 n=47 n=282 Streptococci 4 (2) 6 (13) 84 (30) Enterococci 16 (8) 5 (l l) 31 (11) Staphylococcus aureus 56 (28) 6 (13) 62 (22) Coagulase negative staphylococci 60 (30) I7 (36) T 34 (I2) HACE K Group 11 (4) Gram negative bacilli 23 (12) 2 (4) 13 (5) Fungi (Candida species) 17 (8) 4 (8) 3 (1) Polyrnicrobial/ miscellaneous 7 (3) 4 (8) l2 (4) Diphtheroids 9 (4) 5 (2) Culture negative 7 (3) 3 (6) 27 (I 0) PathologyInfection of mechanical prosthesis starts at the interface between sewing cuff and the native tissue which can lead to loosening of sutures,periprosthetic leaks,ring abscesses and fistulous tracks into surrounding tissues.Valvular incompetence with congestive heart failure,heart block,systemic embolization of vegetations and multiorgan infections with sepsis are important complications. With bioprosthetic valves,infection is often restricted to the cusps.The thrombotic vegetations in the biosynthetic material can lead to cusp rupture and perforation.If the sewing cuff is involved,the pathologic process is similar to that of mechanical prosthesis.
3. 15. /Iklilaruzzanran M,Nawaz TEarly Onset and Late Onset Prosthetic Valve EndocarditisProsthetic valve endocarditis (PVE) is categorized as early onset (EOPVE) and late onset (LO-PVE).However there is no general agreement on time and some authors consider 60 days,7 less than 6 month or 1 year2 after valve replacement as EO-PVE and thereafter as LO-PVE.V The risk of developing PVE is highest within the initial 12 months after replacement surgery with a peak during the rst 2 months.9Clinical presentationOne or more of the followingV Fever V Embolism with stroke and peripheral involvement' Heart failure ' Metastatic infection V New or changing murmurV SplenomegalyV New conduction abnormalities Most common causes of death are heart failure,arrhythmias,multi organ failure in the setting of severe sepsis and brain emboli.Infection with low virulence organisms manifest with a subacute or chronic course. DiagnosisRevised Duke criteria may be used as a diagnostic scheme when PVE is suspected. They are based on identication of causative organism and results of Transesophageal Echocardiography (TEE). ~ Culture and susceptibility testingGrowth of causative organism in culture is currently the only method to determine antibiotic sensitivity.Susceptibility testing is performed with isolates from blood,surgical specimens including embolic fragments,periprosthetic tissues,vegetations and tissue fragments obtained from bioprosthetic valves or abscess debribement.Positive blood cultures have been found between 78% to 91% of PVE.9~' Serologic methods and PCR are also available for the detection of some organisms. TEE is mandatory in all cases of suspected PVE.TEE is superior to Transthoracic Echocardiography for the detection of valvular vegetations,abscesses and perivalvular extension of infection. TreatmentThe appropriate therapy approach is medical treatment which may require combination with surgical treatment.Surgical treatment approachACC/ AHA guideline summary:Surgery forHm:2 1 prosthetic valve endocarditis (PVE)2Class I There is evidence and/ or general agreement that surgery is indicated in patients with PVE who develop one of the following: 1 Valve dysfunctionV Dehiscence seen by cine uoroscopy or echocardiographyV Evidence of increasing valve obstruction or worsening regurgitationI Complications such as abscess formation531 Bangladesh J Cardiol,2013; 04-05(1):530-33Class Ila - The weight of evidence or opinion is in favor of the usefulness of surgery in patients with PVE who develop one of the following: V Persistent bacteremia or recurrent emboli despite appropriate antibiotic therapyV Relapsing infectionClass III - There is evidence and/ or general agreement that surgery is NOT indicated in patients with PVE in the following setting: V Uncomplicated IE caused by a rst infection with a sensitive organismOther clinical situations in which surgical intervention should be considered are fungal PVE,S.aureus PVE,Pseudomonas and probably multi-resistant Enterococcus PVE. Surgery involves valve replacement with perivalvular tissue reconstruction. Medical treatment approachIn patients with no indication for surgery,antibiotics with close monitoring is necessary. In patients without indication for urgent surgery,antibiotics with monitoring is often adequate initial treatment. In patients with haemodynamic stability,surgery may be postponed until completion of antibiotic therapy.Early valve replacement without an urgent indication can increase the chance of mortality. Bactericidal agents with synergistic action should be given in combination.These regimens are displayed in Table 3. ~ ACCP guidelines 2012 suggest that in patients on vitamin K antagonist (VKA) with PVE,VKA may be discontinued at the time of initial presentation until it is clear that invasive procedures will not be required and patient has stabilized without signs of CNS involvement.When patient is stable without contraindications or neurologic complications,VKA therapy may be restarted.The risk of thromboembolism in PVE is higher than native valve endocarditis,with reports between 50% and 88% of patients.Antimicrobial therapy is the mainstay of prevention of embolisation and should be started without delay.'4Antimicrobial therapy of PVE in adults1kl"m :4.with normal renal functionPVE caused by Staphylococci Oxacillin/ Methicillin susceptible strains~ Nafcillin or Oxacillin or Flucloxacillin 12 g per 24 h IV in 4 to 6 equally divided doses for 26 wks or Vancomycin 30 mg/ kg per 24 h IV in 2 equally divided doses for 36 wks plus~ Rifampin 900 mg per 24 h IV or P0 in 3 equally divided doses for 26 wks plus~ Gentamicin 3 mg/ kg per 24 h IV or IM in 2 or 3 equally divided doses for the rst 2 wks
4. 16. .2 .9 -o E u >.in {'5 5-:o 9' =U 4-5 :o L) 532/ Il 0.12ug/ mL0 Aqueous penicillin G 24 million units per 24 h IV either continuously or in 4 or 6 equally divided doses for 6 wks or0 Ceftriaxone 2 g/24 h IV or IM in 1 dose for 6 wksplus0 Gentamicin 3 mg/ kg per 24 h IV or IM in 1 dose or 3 equally divided doses for 6 wksCulture negative PVE Early onset (31 year)0 Vancomycin 30 mg/ kg per 24 h IV in 2 equally divided doses 6 wks plus0 Gentamicin sulfate 3 mg/ kg per 24 h IV/ IM in 3 equally divided doses 2 wks plus0 Rifampin 900 mg/24 h PO/ IV in 3 equally divided doses 6 wks plus0 Cefepime 6 g/24 h IV in 3 equally divided doses 6 wksLate (>1 year) 0 Vancomycin 30 mg/ kg per 24 h IV in 2 equally divided doses 6 wks plus0 Gentamicin sulfate 3 mg/ kg per 24 h IV/ IM in 3 equally divided doses 2 wks plus0 Rifampin 900 mg/24 h PO/ IV in 3 equally divided doses 6 wks plus0 Ciprooxacin 1000 mg/24 11 P0 or 800 mg/24 h IV in 2 equally divided doses 6 wksPVE caused by Enterococci Strains susceptible to penicillin and Vancomycin;high- level resistance to gentamicin and streptomycin must be determined: 0 Aqueous penicillin G 18-30 million units per 24 h IV either continuously or in 6 equally divided doses for 6 wks or Ampicillin 12 g per 24 h IV in 6 equally divided doses for 6 wks or0 Vancomycin 30 mg/ kg per 24 h IV in 2 equally divided doses for 6 wks;not to exceed 2 g per 24 h unless concentrations in serum are inappropriately lowplus0 Gentamicin 3 mg/ kg per 24 h IV or IM in 3 equally divided doses for 6 wksIntrinsic penicillin resistance (penicillin/ ampicillin MIC 232 uglmL)0 Vancomycin 30 mg/ kg per 24 h IV in 2 equally divided doses for 6 wks plus0 Gentamicin 3 mg/ kg per 24 11 IV or IM in 3 equally divided doses for 6 wksPVE caused by Fungi0 Initial phase surgery plus amphotericin B (0.7 to 1mg/ kg per day) along with 5-ucytosine (1501ng/ kg per day in 4 divided doses) for 2 6 weeks.Liposomal amphotericin is an alternative drug. 0 For Candida PVE,this should be followed with suppressive second phase of oral therapy with uconazole (200 to 400 mg daily or another triazole) forPVE caused by HACEK 0 Ceftriaxone 2 g per 24 11 IV or IM in 1 dose for 6 wks or0 Ciprooxacin 1000 mg per 24 h P0 or 800 mg per 24 h IV in 2 equally divided doses for 6 wksprolonged periods. Prevention0 Patients with prosthetic valves are at relatively high risk of PVE. 0 Antibiotic prophylaxis is reasonable for all dental procedures that involve manipulation of gingival tissues or periapical region of teeth or perforation of oral mucosa. 0 Antibiotic prophylaxis is reasonable for procedures on respiratory tract or infected skin,skin structures,or musculoskeletal tissue. 0 In patients scheduled for elective cystoscopy and/ or other urinary tract manipulation who have enterococcal urinary tract infection or colonization,antibiotic therapy to eradicate enterococci from the urine before procedure may be reasonable.If procedure is not elective,it may be reasonable to give antimicrobial regimen active against enterococci. 0 Prophylaxis during dental procedures may be given with single dose oral amoxicillin 2 gms 30-60 minutes before the procedure.Alternatives are oral clarithomycin,azithromycin or ceftriaxone 1gm IV/ IM. 0 Common diagnostic procedures such as bronchoscopy,gastrointestinal endoscopy,imaging studies with contrast and TEE carry minimal risk and are not recommended for prophylaxis. -15
5. 17. Aklitaruzzainan M,Nawaz TReferences1. Mylonakis E,Calderwood SB.lnfective endocarditis in adults.N EnglJ Med 2001;345:1318-30.2. Rivas P,Alonso J,Moya J,et al.The impact of hospital acquired infections on the microbial etiology and prognosis of late-onset prosthetic valve endocarditis.Chest 2005;128:764-71.3. Pibarot P,Dumesnil JG.Prosthetic heart valves.Selection of the optimal prosthesis and long term management.Circulation 2009;119:1034-484. Karchmer AW.Antimicrobial therapy of prosthetic valve endocarditis.Uptodate 20135. Jegatheeswaran A,Butany J.Pathology of infectious and inammatory diseases in prosthetic heart valves.Cardiovasc Pathol 2006;15:252-55.6. Anguera I,Miro JM,San Roman JA,et al.Periannular complications in infective endocarditis involving prosthetic aortic valves.AmJ Cardiol 2006;98: 1261-68.7. Sandre RM,Shafran SD.lnfective endocarditis:review of 135 cases over 9 years.Clin Infect Dis 1996;22:276-86.8. Tornos B,lung B,Permanyer-Miralda G,et al.lnfective endocarditis in Europe:lessons from Euro heart survey.Heart 2005;91:571-75.9. Wang A,Athan E,Pappas PA,et al.International Colloboration on Endocarditis- Prospective Cohort Study Investigators.Contemporary clinical prole and outcome533 Bangladesh J Cardiol,2013; 04-05(1):530-33of prosthetic valve endorcarditis.JAMA 2007;297:1354-61. 10. LiJS,Sexton DJ,Mick N,Nettles R,Fowler VG Jr,Ryan T,Bashore T,Corey GR.Proposed modications to the Duke criteria for the diagnosis of infective endocarditis.Clin Infect Dis 2000;30:633-38.11. Lopez J,Revilla A,Vilacosta I,et al.Denition,clinical prole,microbiologic spectrum and prognostic factors of early onset prosthetic valve endocarditis.Eur HeartJ 2007;28:760-5.12. Bonow R0, Carabello BA,Chatterjee K,et al.ACC/ AHA 2006 guidelines for the management of patients with valvular heart disease.A report of the American College of Cardiology/ American Heart Association Task Force on Practice Guidelines (Writing committee to revise the 1998 guidelines for the management of patients with valvular heart disease). J Am Coll Cardiol 2006; 48:e1.13. Baddur LM,Wilson WR,Bayer AS,et al.AHA/ IDSA.lnfective endocarditis.Circulation 2005;111;e394-e434.14. Whitlock RP,Sun JC,Fremes SE.Antithrombotic and thrombolytic therapy for valvular disease.Chest 2012 Feb;141(2 Suppl): e576S-600S. 15. Wilson W,Taubert KA,Gewitz M,et al.Prevention of infective endocarditis.Guidelines from the American Heart Association.Circulation 2007;116:1736-54.16. National Institute of Clinical Excellence.Prophylaxis against infective endocarditis.2008. NICE Clinical Guideline 64CH-, l!1i|1!, lE! l!1t31,. /93,123 1111-Jkall/ I
6. 18. 534 Hossain L,Ahmed / I, Ahsan 5Bangladesh J Cardiol,2013; 04-05(1):534-38IChoice of Prosthetic Valves:iviechonicolValves Versus Tissue ValvesL Hossain,A Ahmed,S Ahsan Labaid Cardiac Hospital,Dhaka,Bangladesh. The ideal prosthetic heart valve (PHV) that combines excellent hemodynamic performance and long-term durability without increased thromboembolic risk or the need for long-term anticoagulation does not exist.Hence,patients and their physicians need to choose between a mechanical and a tissue (bioprosthetic) valve.In general,the advantageous durability of mechanical valves is offset by the risk of thromboembolism and the need for long- term anticoagulation and its associated risk of bleeding.In contrast,bioprosthetic valves do not require long-term anticoagulation yet carry the risk of structural failure and reoperation. There is an extensive variety of prosthetic valves.The two most commonly used are the mechanical valve and the stented tissue valve.The two common types of mechanical valves,tilting-disc and bileaet valves have comparable durability and both require life-long anticoagulation therapy due to their associated thrombotic risk.Mechanical valves have advantages and disadvantages,the most important of which is their greater durability (20-30 years) than tissue bioprosthetic valves (10-15 years).Their greater durability translates into lower reoperation rates among these patients,compared with patients with bioprosthetic valves.Although mechanical valves are more durable than bioprosthetic valves,mechanical valves also have several disadvantages that a provider and patient must consider.Blood ow around the mechanical valve results in high sheer stresses,which can result in platelet activation and a higher risk for thrombosis on the valve surface and a subsequent risk for embolism.Given this risk,all patients with mechanical heart valves require lifelong anticoagulation,most commonly with a vitamin K antagonist (VKA) such as warfarin.Although warfarin use is efcacious in reducing thrombosis risk,it heightens hemorrhagic risk2 For example,a 60-year-old male with a mechanical valve replacement has a lifetime risk of bleeding of 41% compared with a 12% risk in a similarDr.Md.Lokman Hossain,M5 (CTS),Senior Consultant,Cardiac Surgery.Dr.Amran Ahmed,MD,Consultant Cardiac Surgeon Dr.Md.Shameem Ahsan,MBBS,Registrar,Cardiac SurgeryCorrespondence:Dr.Md.Lokman Hossain MS (CTS), Senior Consultant,Cardiac Surgery. Labaid Cardiac Hospital,House-I,Road-4, Dhanmondi,Dhaka-I205, Bangladesh.Tel- 880-2-8610793-8. e-mail- Iokman54@hotmail. compatient with a bioprosthetic valve replacement3.Two historic randomized clinical trials compared outcomes after valve replacement with a rst-generation porcine heterograft and the original Bjork-Shiley tilting-disc mechanical valve:the Edinburgh Heart Valve Trial,conducted between 1975 and 1979 with an average follow- up of 12 years and the Veteran Affairs (VA) Cooperative Study on Valvular Heart Disease,conducted between 1979 and 1982 with an average follow-up of 15 years"'5.The Edinburgh trial alone showed a small survival advantage associated with a mechanical valve in the aortic but not in the mitral position;both trials showed increased bleeding associated with mechanical valves and increased reoperation with tissue valves;and both showed that structural failure of tissue valves and overall thromboembolic complications were greater after mitral than after aortic valve replacement.Although these trials are notable for their prospective,randomized design,their major limitation is that comparisons were made between rst-generation porcine heterografts and the Bjork-Shiley mechanical valve,all of which are now obsolete.Thus,the ability to extrapolate these data to decisions made in modern practice is limited. The 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.Three basic types of mechanical valve design exist:bileaet,monoleaet,and caged ball valves. Caged ball valves,which consist ofa silastic ball with a circular sewing ring and a cage formed by 3 metal arches,are no rarely implanted.Monoleaet valves are composed of a single disk secured by lateral or central metal struts.Bileaet valves are made of2 semilunar disks attached to a rigid valve ring by small hinges.The opening angle of the leaets relative to the annulus plane ranges from 75 to 90,and the open valve consists of 3 orices:a small,slit- like central orice between the 2 open leaets and 2 larger semicircular orices laterally7. The original mechanical prosthesis was the ball-and-cage (StarrEdwards) valve,in which a silastic ball was housed in a metal cage.This was followed by second-generation tilting disc valves (eg Bjork- Shiley) where a single disc opens and closes on a hinged strut.The current generation comprises bileaet valves
7. 19. Hossain L,/Iluned / I, / ll1S(1l1 S Choice of the aortic/ mitral prosthesis.In favour of a mechanicalprosthesis535 Bangladesh] Cardiol,2013; 04-05(1):534-38A mechanical prosthesis is recommended according to the desire ofthe informed patient and ifthere are no contraindications for long-term anticoagulationClassadeterioration! A mechanical prosthesis is recommended in patients at risk ofaccelerated structural valveA mechanical prosthesis is recommended in patients already on anticoagulation as a result ofhaving a mechanical prosthesis in another va Ive position. inthe aortic position and