We read with interest the recent article by Zhang et al. 1 in which the blood compatibility of titanium oxide was compared to LTI carbon. The authors state that ''LTI carbon was used as a reference material,'' yet the source of their reference material was not identified.
The LTI carbon used so widely in artificial heart valves is a material developed by General Atomic in San Diego. Until recently, the primary supplier of this material was Sulzer Carbomedics, which acquired the technology from General Atomic. The other supplier of pyrolytic carbon for medical applications was Sorin, who marketed products containing pyrolytic carbon components in those countries where CarboMedics did not have patent protection. St. Jude Medical developed their own processes to produce the material and only after 10 years of development achieved US Food and Drug Administration (FDA) concurrence (in 1992) that the material produced by them is safe and effective for use in heart valves. More recently, Medtronic received FDA approval (1996) for their own manufacturing processes for this material.
LTI carbon is not a generic material. By not identifying the source of their reference material, its composition, and surface finish (both of which affect blood compatibility), the results and conclusions reported by Zhang et al. are misleading and may have no bearing, as implied in their article, on the materials historically used so successfully in mechanical heart valves.