Patient Prosthesis Mismatch

Patient prosthesis mismatch (PPM) is present when the effective orifice area of a normally functioning prosthetic valve is too small for the size of the patient, so that gradients are higher than expected and flow is obstructed.

It is quantified by the indexed effective orifice area (iEOA), which is the effective orifice area divided by body surface area. In the aortic position, with BMI under 30 kg/m2, moderate PPM is an iEOA of 0.85 to 0.66 cm2/m2 and severe PPM is 0.65 cm2/m2 or less.

With BMI of 30 kg/m2 or more, moderate PPM is 0.70 to 0.56 cm2/m2 and severe is 0.55 cm2/m2 or less. In the mitral position, moderate PPM is an iEOA of 1.2 to 0.9 cm2/m2 and severe is under 0.9 cm2/m2.

Moderate aortic PPM follows about 20 to 70% of surgical valve replacements (depending on the definition) and severe PPM about 2 to 20%. After transcatheter implantation severe PPM is less frequent in the aortic position, although it occurs.

Pathophysiology. A fixed small orifice raises the pressure gradient, which rises with the square of flow, so gradients climb with exercise and high output states. Pressure overload slows regression of left ventricular hypertrophy, limits exercise capacity and coronary flow reserve, and promotes ventricular remodelling.

In the mitral position it raises left atrial pressure and pulmonary pressure and favours atrial fibrillation. Severe PPM is linked to heart failure, earlier structural valve degeneration, and higher mortality, especially in patients under 70 years or with ejection fraction under 50%.

• Often asymptomatic.
• Exertional dyspnoea, reduced exercise capacity, angina, syncope or heart failure in severe cases, and failure of symptoms to improve after valve replacement.
• An ejection systolic murmur (aortic) or a diastolic rumble (mitral) with normal prosthetic sounds.
• Persisting left ventricular hypertrophy after aortic valve replacement.

• Calculation. iEOA = effective orifice area (measured by the continuity equation, or the reference value for the model and size) divided by body surface area. Report the BMI-adjusted category.
• Echocardiography at 6 weeks to 3 months after implantation.
  • Normal looking leaflets with normal motion.
  • Aortic: peak velocity usually 3 to 4 m/s, mean gradient 20 to 35 mm Hg, Doppler velocity index 0.25 or more (usually 0.30 or more in PPM), and acceleration time under 100 ms.
  • Mitral: mean gradient over 5 mm Hg, pressure half time under 130 ms.
• CT and transoesophageal echocardiography to exclude thrombosis, pannus and under expansion.
• Stress echocardiography when symptoms are out of proportion to resting gradients. Natriuretic peptide.

Differential diagnosis.

• Prosthetic valve thrombosis
• Pannus
• Structural degeneration of a bioprosthesis
• Dynamic left ventricular outflow obstruction
• High flow states (anaemia, thyrotoxicosis, sepsis, arteriovenous fistula)
• Pressure recovery effect
• Measurement error (outflow tract diameter, Doppler alignment)
• Prosthesis malposition or under expansion
• Infective endocarditis
• Left ventricular diastolic dysfunction or heart failure with preserved ejection fraction

• Prevention is the main strategy. Before surgery, calculate the projected iEOA using the reference effective orifice area of the intended valve and the body surface area. Aim for a projected iEOA of 0.85 cm2/m2 or more in the aortic position. Choose a valve with a larger effective orifice area (stentless, supra-annular, or a mechanical valve in suitable patients). Consider aortic root enlargement (Nicks, Manouguian or Konno) when severe PPM is projected and the surgical risk allows, consider the Ross procedure in selected young patients, and consider transcatheter implantation with a supra-annular device in a small annulus.
• Established mild to moderate PPM: control blood pressure, treat anaemia, use cardiac rehabilitation, and manage heart failure and atrial fibrillation as usual. Ramipril 2.5 mg orally once daily, increased every 2 to 4 weeks to 10 mg once daily (maximum 10 mg daily, and 5 mg daily at creatinine clearance under 30 mL/min), may help left ventricular hypertrophy regress and control blood pressure. Check potassium and creatinine 1 to 2 weeks after each change. Contraindicated in pregnancy and bilateral renal artery stenosis.
• Mitral PPM with atrial fibrillation: rate control to lengthen diastole, with bisoprolol 2.5 mg orally once daily, increased to 5 to 10 mg once daily, maximum 20 mg daily (do not exceed 10 mg daily at creatinine clearance under 20 mL/min or in severe liver impairment).
• Reintervention is considered only for severe symptomatic PPM with normal prosthetic function, falling ejection fraction, or severe pulmonary hypertension, and after a heart team assessment. Options are redo valve replacement with a larger prosthesis (with root enlargement if needed), or transcatheter valve-in-valve with fracture of the existing ring to enlarge the orifice.

Special groups.

• Obesity: use the BMI-adjusted thresholds, because indexing to body surface area overstates the mismatch.
• Women of childbearing age: choose the valve with the pregnancy plan and orifice area in mind.

Monitoring. Baseline echocardiography at 6 weeks to 3 months. Yearly echocardiography in severe PPM, assessing ventricular mass regression and ejection fraction. Blood pressure at each visit. Natriuretic peptide with symptoms.

Referral and escalation. Refer to the heart team before surgery in patients with a small body size or annulus. Refer after surgery for persisting symptoms or severe PPM. Urgent for heart failure or syncope.