Acute Prosthetic Valve Obstruction

Acute prosthetic valve obstruction is sudden restriction of leaflet or disc motion in a mechanical or bioprosthetic valve, causing acute heart failure, shock or embolism. Main causes are thrombosis, pannus ingrowth and vegetations.

Epidemiology. Obstructive thrombosis occurs in about 0.3 to 1.3% of mechanical valves each year and is most frequent in mitral and tricuspid positions, with subtherapeutic anticoagulation as the main risk. Pannus is a slower process that causes late obstruction.

Causes and associations.

• Thrombosis: missed or subtherapeutic anticoagulation (INR under target), pregnancy, atrial fibrillation, low cardiac output and hypercoagulable state.
• Pannus ingrowth (months to years).
• Infective endocarditis with large vegetations.
• Entrapment by suture, chordae or a retained leaflet fragment.

Anticoagulation targets (usual practice). Mechanical mitral or tricuspid valve and mechanical aortic valve with risk factors: INR 3.0 (range 2.5 to 3.5). Bileaflet aortic valve without risk factors: INR 2.5 (range 2.0 to 3.0).

Pathophysiology. Reduced orifice area raises gradient across the valve, causing proximal congestion (pulmonary oedema with mitral prosthesis, systemic congestion with tricuspid prosthesis) or low forward flow (aortic prosthesis). Thrombus may embolise.

Presentation is dyspnoea, pulmonary oedema, shock, syncope, chest pain, embolic events (stroke, limb or mesenteric ischaemia), muffled prosthetic closing click, new murmur or absent clicks, and subtherapeutic INR. Obstruction of the aortic prosthesis can cause low output and syncope.

Red flags.

• Muffled or absent mechanical clicks.
• Shock, pulmonary oedema or embolic event with a prosthetic valve.
• INR under 2.0, recent interruption of anticoagulation, or pregnancy.

Transthoracic echocardiography (increased gradients, reduced effective orifice area, abnormal leaflet motion), then transoesophageal echocardiography to identify thrombus (large, soft, mobile thrombus) or pannus (small, dense, fixed) and vegetations. Cine fluoroscopy shows disc motion in mechanical valves, and gated CT shows thrombus and pannus. Check INR, anti-factor Xa if on heparin, full blood count, cultures (fever or vegetations), lactate and troponin.

Differential diagnosis. Prosthesis patient mismatch, regurgitation, endocarditis, left ventricular failure and other causes of pulmonary oedema.

Immediate. Admit to cardiac intensive care. Give oxygen, treat pulmonary oedema (furosemide 40 to 80 mg IV, non-invasive ventilation), and treat shock with inotrope or mechanical support if needed.

Anticoagulation. Unfractionated heparin 80 units/kg IV bolus then 18 units/kg/h, adjusted to anti-factor Xa 0.3 to 0.7 units/mL or activated partial thromboplastin time, unless contraindicated.

Left sided obstructive thrombosis in a critically ill patient.

• Emergency surgery (valve replacement or thrombectomy) is the first choice if a centre is available and the thrombus is large (area over 0.8 cm2) or the patient is critically ill.
• Fibrinolysis if surgery is not available or the risk is prohibitive: alteplase 10 mg IV bolus then 90 mg over 90 minutes with heparin held, or low dose slow infusion of alteplase 25 mg over 6 hours (without a bolus), repeated up to twice. Risks are major bleeding (about 5%), stroke or systemic embolism (about 5 to 10%), and recurrent thrombosis. Streptokinase is an alternative where alteplase is not available.

Right sided obstructive thrombosis. Fibrinolysis is first choice because of lower embolic risk.

Non-critical or small thrombus (under 0.8 cm2) with subtherapeutic anticoagulation. Intensified heparin, with repeated imaging at 1 to 3 days, and low dose fibrinolysis if no response.

Pannus. Surgery is the main treatment for significant obstruction.

Endocarditis. Cultures first, then antibiotics and early surgery.

Pregnancy. Seek specialist care. Low molecular weight heparin (enoxaparin 1 mg/kg every 12 hours, adjusted to anti-factor Xa 0.8 to 1.2 units/mL at 4 hours) or unfractionated heparin, with warfarin avoided in the first trimester when possible.

Long term. Re-establish therapeutic warfarin (INR 2.5 to 3.5 for a mechanical mitral valve, and 2.0 to 3.0 for a low risk bileaflet aortic valve). Educate on adherence.

Monitoring. Arterial pressure, echocardiographic gradients, INR or anti-factor Xa, neurological state and bleeding.

Referral and escalation. Cardiac surgery, cardiology and cardiac intensive care at once.

Special groups. In pregnancy, shared care with obstetrics and cardiac surgery. In renal impairment, use unfractionated heparin.