Potential MR hazard to patients with metallic heart valves: The Lenz effect

Abstract

The Lenz effect on the motion of metal containing moving parts of artificial heart valves has not been considered to date. In this paper the basic theory is outlined and a simple model applied to estimate worst-case forces on such valves. The results indicate a potential for forces over 100 times greater than for the more widely recognized ferromagnetic interaction. Resistive pressure effects comparable to cardiac pressure differences may occur for such valves in the mitral position even at fields as low as 1.5 T. The effect will increase linearly with field strength. Additional monitoring and perhaps even exclusion of such patients may be prudent, even at 1.5 T. (C) 2000 Wiley-Liss, Inc.