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Q1: What is the differential diagnosis to explain the presentation of these patients
The differential diagnosis involves either valvular pathology or ventricular failure. Valvular pathology can be due to either valve dehiscence,1 valvular obstruction,1 or prosthetic valve endocarditis.2 Prosthetic valve endocarditis can be early or late. Early occurs less than 60 days after the primary operation and is usually due to resistant Staphylococcus epidermidis, Gram negative baccili, and fungi.2 Late prosthetic valve endocarditis is usually due to Streptococcus species.2
Potential causes of ventricular dysfunction include the initial valvular lesions, coronary artery disease, systemic or pulmonary hypertension, and coincident cardiomyopathy.2 The presence of new murmurs makes the diagnosis of ventricular failure much less likely.
Valve obstruction was confirmed during x-ray screening and echocardiography in both patients.
Q2: What pathological mechanisms are possible causes of prosthetic valve obstruction and what has happened in case 2?
Pathological obstruction of prosthetic valves is due to either pannus or thrombosis of the valve. Pannus represents a fibrous overgrowth, which extends from the endocardium onto the prosthesis. While pannus is common on both biological and mechanical valves, acute prosthetic valve thrombosis is most commonly a complication of mechanical valves.1 In one large case series, the most frequent reoperative indications for prosthetic valve dysfunction were dehiscence, pannus, then thrombus.1
Case 1 is a presentation of valve thrombosis, confirmed at pathology.
Case 2 demonstrates pannus with fibrous overgrowth as shown in fig 2 (see p 476). The pannus can be seen extending from the inner ring of the tricuspid valve prosthesis onto the valve leaflets (both panels).
Q3: What is the most helpful investigation to differentiate these pathological mechanisms?
Before any investigation, the history and examination may aid the diagnosis. Pannus in-growth causing valve obstruction often has a more indolent onset, occurring primarily months to years after prosthesis implantation3,4 with an exponential rise occurring with time.1 Associated with this more insidious onset, pannus may present with less severe clinical manifestations, as demonstrated in case 2 compared with thrombotic valve obstruction.
Thrombosis on prosthetic valves can give rise to local mechanical problems including obstruction. This can occur acutely and be associated with rapid clinical deterioration. It may also lead to thromboembolism and peripheral ischaemic events—for example, stroke.2 Numerous factors may influence the rate of valve thrombosis. The most important of these being periods of suboptimal anticoagulation (especially if anticoagulation has been interrupted) which may not necessarily be obvious at presentation,2,4 low cardiac output and the presence of hypercoaguable states.2
Doppler echocardiography is currently the investigation of choice.4 Transthoracic echocardiography is limited in evaluating structural abnormalities of prosthetic valves by attenuation and acoustic shadowing.4 Transoesophageal echocardiography is superior and can assess the mechanism and aetiology of the obstruction.3,4 Thrombus typically appears larger than pannus and in the case of mitral valve thrombosis may extend into the left atrium. Thrombus may also be differentiated from pannus by a lower intensity signal on echocardiographic assessment.
Cardiac catheterisation for valve haemodynamics provides no discriminatory information to assess the underlying aetiology of valve obstruction.4,5 Radiographic screening of the valve will confirm the diagnosis of obstruction (as demonstrated in fig 1; see p 476).
Q4: What are the therapeutic options for patients with prosthetic valve obstruction?
Therapeutic options include pharmacological thrombolysis and surgery. Surgery is the traditional mode of treatment and has a reported mortality of 0%–69%.6 Thrombolytic therapy is an alternative to surgery and is considered the treatment of choice for tricuspid prosthetic valve thrombosis.6 Due to high risks of cerebral thromboembolism during thrombolysis for left sided prosthetic valve thrombosis (up to 12%), it should be reserved for high risk surgical candidates.6
Valve obstruction in both patients: in case 1 caused by valve thrombosis and in case 2 by pannus with fibrous overgrowth.
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