Prosthetic Heart Valve

Prosthetic Heart Valve 2018-01-30T16:37:48+00:00

Relevant physical signs

  • Inspection
    • Midline sternotomy scar
    • No saphenous vein / radial artery harvesting scar
    • Audible click by the bedside
  • Peripheries
    • Stigmata of infective endocarditis
    • Pulse
      • Rate
      • Rhythm (mitral lesions)
      • Character – slow rising or collapsing in aortic valve prosthesis stenosis / regurgitation
    • Anaemia, scleral icterus
    • Raised jugular venous pressure and v waves – complication of severe native valve disease
  • Precordium
    • Apex beat
      • Displaced – native MR / AR lesion
      • Not displaced – native AS / MS lesion
    • Right ventricular heave – pulmonary hypertension may not reverse following corrective surgery
    • Palpable heart sounds – clicks
    • Auscultation
      • S1 and S2 – both native, one prosthetic or both prosthetic?
        • Mitral valve prostheses are in time with carotid pulse
        • Aortic valve prostheses are not in sync with carotid pulse
        • Starr-Edwards ball and cage valves have an opening and closing click
          • Closing click always louder than opening click
          • Listen carefully for the native valve heart sound before deciding that two clicks are due to a double valve replacement
      • Crisp valvular click – sign of well-functioning valve
      • Ejection systolic flow murmur in aortic prostheses
        • Differentiate from stenotic prosthesis by looking out for other signs of severe aortic stenosis – slow-rising, low-volume pulse, narrow pulse pressure, soft S2, S4 etc.
      • Listen for para-prosthetic regurgitant murmur – sign of prosthesis malfunction
  • Complications of prosthetic valves
    • Anticoagulation
      • Pronator drift – previous intracranial haemorrhage
      • Bruising
    • Valve haemolysis
      • Conjunctival pallor
      • Scleral icterus
    • Valve failure
      • Regurgitant murmurs
      • Stenotic murmurs
      • Pulmonary oedema
      • Raised jugular venous pulsation
      • Peripheral oedema
    • Valve thrombosis and thromboembolic disease
    • Infective endocarditis

Types of prosthetic heart valve

  • Mechanical: Starr-Edwards (ball and cage), single-tilting disc (Bjork-Shiley) or double-tilting disc (St Jude)
    • Bjork-Shiley valves provide laminar flow, reducing the incidence of haemolysis
  • Bioprosthetic: homograft or heterograft

Choice of prosthesis

  • Anticoagulation
    • Mechanical valves require lifelong anticoagulation
    • Bioprosthetic valves do not require lifelong anticoagulation
  • Durability
    • Mechanical valves last 20 – 30 years
    • Bioprosthetic valves often last 10 – 15 years

Investigation

  • Full blood count to look for anaemia (valve haemolysis, blood loss from anticoagulation)
  • Coagulation screen to look at international normalized ratio (under or over-anticoagulation)
  • Renal and liver function (will affect anticoagulation)
  • If having fever – blood culture to look for organisms which can cause infective endocarditis
  • If icteric
    • Drop in haemoglobin level
    • Bilirubin – increase in unconjugated bilirubin
    • Lactate dehydrogenase – high
    • Serum haptoglobin – low (<30)
    • Peripheral blood film – red cell fragments
  • Electrocardiogram to look for any rhythm disturbance, LVH
  • Chest radiograph
    • Can see prosthetic valve on X-ray
    • On lateral chest radiograph, can determine whether the prosthesis is aortic or mitral
      • Draw a line from the carina to the cardiac apex
      • Pulmonary and aortic valves will be above this line
      • Mitral and tricuspid valves are below the line
      • Second line may be drawn perpendicular to the patient’s upright position
        • Aortic valve in upper left quadrant
        • Mitral valve in the lower right quadrant
        • Pulmonary valve in the upper right quadrant
        • Tricuspid valve in the lower left quadrant
      • Confounded if aortic root is displaced inferiorly – e.g. aortic root abscess
    • Cardiomegaly
    • Signs of pulmonary hypertension – dilated pulmonary arteries
    • Pulmonary oedema
  • Trans-thoracic echocardiogram
    • Assess prosthetic function
    • Look for stenosis or regurgitation across the prosthesis
  • Fluoroscopy to rapidly assess valve function (closure)
  • MRI is safe with most prosthetic heart valves, save old Starr-Edwards valves

Management

  • Anticoagulation for metallic valves (lifelong)
    • No role yet for novel anticoagulants
    • Bridging with intravenous heparin is recommended when initiating anticoagulation
    • For long term anticoagulation, choice is warfarin; target INR:
      • 2.0 – 3.0: in patients with St Jude AVR and no risk factors (see below)
      • 2.5 – 3.5
        • Patients with Starr-Edwards AVR
        • St Jude AVR with risk factors (AF, previous VTE, hypercoagulable state, ↓LVEF)
        • Mitral valve prostheses
    • Sub-therapeutic INR
      • Admit for bridging with intravenous heparin
    • Over-anticoagulation
      • Avoid reversal of anticoagulation unless there is major bleeding
        • Withhold warfarin and allow INR to fall to therapeutic range
      • For major bleeding
        • Prothrombin complex concentrate
        • Intravenous vitamin K 1mg for partial reversal, 2.5 – 5mg for more complete reversal
        • Novoseven is not recommended due to the risk of valve thrombosis
  • Infective endocarditis
    • Prophylaxis against infective endocarditis is required for prosthetic heart valves
      • Amoxicillin 2g IV or PO 30 – 60 minutes before procedure
      • Penicillin allergy: azithromycin 500mg / clindamycin 600mg IV 30 – 60 minutes before
    • Blood culture to identify IE organism (Staphylococcus, Streptococcus viridans, Enterococcus faecium)
    • Trans-thoracic / trans-oesophageal echocardiogram to look for vegetations
    • Microbiology
      • Within two months of surgery: usually nosocomial
      • After 12 months of surgery: same pathogens causing native valve endocarditis
    • Antibiotic therapy
      • Empiric, within 12 months of surgery: vancomycin + gentamicin
      • Empiric, after 12 months: cloxacillin + gentamicin
      • Add rifampicin to the above regimens if proven staphylococcal infection
  • Valve haemolysis
    • Supportive transfusions
    • Iron supplementation
    • Pentoxifylline 400mg TDS may reduce valve haemolysis by improving erythrocyte deformability

Summary

Sir, this patient has a prosthetic aortic / mitral valve, which is currently functioning well. On examination of the peripheries, there are no stigmata of infective endocarditis. The pulse is regular, and of normal volume. There are no signs of anaemia or jaundice. The jugular venous pulsation is not elevated. On examination of the precordium, there is a midline sternotomy scar, with no corresponding saphenous vein or radial artery harvesting scar. There is a click which coincides with the second / first heart sound, which is audible to the naked ear. The click is crisp, and there is a flow murmur across the aortic valve. There are no other added sounds, and there is no evidence of para-valvular regurgitation. I would expect this patient to be on anticoagulation, although I did not see any bruises which may complicate this. There is no evidence of valve haemolysis.

In summary, this patient has a prosthetic aortic / mitral valve which is currently functioning well.

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