Tissue (Bioprosthetic) Heart Valves: How They Work and Why They Degenerate

Tetralogy of Fallot is one of the commonest surgical procedures, and the outcome depends on the exact anatomy delineated by a proper paediatric echo, but six years is not a very late stage — in India a lot of patients are operated on at this age or even older. The outcome of tetralogy repair even at 6 years is excellent, so this patient certainly needs surgical correction.

Myocardial bridging is not uncommon and is often seen on angiography. If it is asymptomatic, nothing needs to be done. If it is symptomatic, we normally do a stress thallium test — if positive, we recommend surgery; if negative, which is most of the time, only medical treatment is needed. If it is only myocardial bridging with no stenosis involved in other arteries (the circumflex or right coronary artery are normal), nothing needs to be done, but if the stress test is positive, surgery is recommended.

Tetralogy of Fallot is one of the commonest procedures in paediatric cardiac surgery, alongside ASD and VSD repair. It is a very commonly performed procedure with excellent outcomes — any paediatric cardiac centre does this routinely, and the clinical outcomes are excellent.

The patient should be referred for further evaluation at the appropriate time — not too early, but also not too late, because if it is too late the patient develops more comorbidities and the outcome may not be as good. For valve disease specifically, there are definite guidelines for mitral and aortic valve disease on when a patient should be referred for cardiac surgery; whether it can be done locally depends on whether it looks like a straightforward repair or replacement, or a more challenging one. The two important criteria are the patient's clinical symptoms — which functional class (1, 2, 3, or 4) — and the echo findings, which show the severity of stenosis or regurgitation, LV function, and pulmonary artery pressures. Together these decide whether the patient should be referred for surgical treatment, locally or elsewhere.

Cost primarily depends on two things: which valve is used — mechanical valves are significantly less expensive than tissue valves, and among tissue valves, third-generation valves cost more than second-generation ones — and the patient's clinical course, since a straightforward surgery without a long hospital stay or comorbidities costs less. The average cost generally starts from $9,000 and goes up to $15,000–$16,000.

Tissue heart valves, also called bioprosthetic valves, are made from animal tissue. Edwards worked with cardiac surgeon Alain Carpentier to develop porcine valves from pig tissue in the 1970s, and bovine pericardium was used to develop pericardial tissue valves in the 1980s.

The main reason tissue valves degenerate and eventually require reoperation is calcification of the valve tissue.

The glutaraldehyde solution historically used to preserve tissue valves was one of the factors contributing to calcification, which is why most manufacturers now focus on anti-calcification treatments designed to slow degeneration.

There is no perfect valve available today. A mechanical valve carries the lifelong risk of anticoagulation, while a tissue valve carries the risk of structural valve degeneration and eventual reoperation.