Serial In Vitro Investigation of the Fracture Properties of Mechanical Heart Valves.

BACKGROUND

Mechanical valve prostheses may develop serious dysfunctions, leading to end-stage heart failure. In some cases, a high-risk redo operation is not an option. The first cases of interventional fracturing of mechanical valves have already been successfully performed, but systematic data on mechanical prostheses' fracture properties are lacking.

OBJECTIVES

The aim of this study was to assess the properties of mechanical heart valves crucial for interventional cardiologists: the pressure required to fracture valve leaflets; structural weak points of the prostheses; the behavior, velocity, and size of leaflet fragments; and the performance of commercially available angioplasty balloons.

METHODS

Seventeen mechanical bileaflet heart valve prostheses of various types, sizes, and manufacturers were examined under fluoroscopy, tested for catheter crossability using different angioplasty catheters, and subjected to balloon inflation in air and in a blood-mimicking fluid until leaflet fracture occurred. The movement and shape of the resulting fragments were recorded and measured.

RESULTS

Mechanical valves contain closed metal rings. Leaflets fracture at pressures between 1 and 6 bar. At pressures >8 bar, minor cracks develop in the carbon rings. Some of the leaflets may detach from the ring as a single piece. Leaflets are ejected from the ring at speeds of up to 0.02 m/s. The junction between the leaflets and the ring represents the structural weak point of prostheses.

CONCLUSIONS

It is feasible to fracture mechanical valve leaflets using commercially available angioplasty balloons. Cracking the carbon ring requires substantially higher pressure. For any clinical application, neuroprotection systems and postprocedural imaging appear essential.