ULTRASTRUCTURAL ANALYSES OF BLOOD-INTERFACING LININGS FORMED WITHIN PARTIAL ARTIFICIAL HEARTS OR ABDOMINAL LEFT VENTRICULAR ASSIST DEVICES: A QUALITATIVE SCHEME FOR HUMAN PSEUDONEOINTIMAL ACCRETION KINETICS.

Following each of 21 clinical trials with the partial artificial heart or abdominal left ventricular assist device (ALVAD), we have examined the blood-interfacing human pseudoneointimal (PNI) linings formed on the fibril-flocked pumping surface by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The salient results of these ultrastructural analyses can be summarized: (1) early PNI accretion kinetics (< 24 hrs) involve plasma protein adsorption, entrapment of erythrocytes, platelets, lymphocytes, numerous neutrophils and macrophages, and the deposition of fibrin within fibril flock interstices (TEM); (2) the surface (< 24 hrs) consists of interconnected fibrin strands (SEM); (3) later PNI accretion kinetics (1-6 days) involve the formation of alternating cellular and fibrin layers (TEM); (4) the surface (1-6 days) consists of cellular aggregates (inter-membrane distances of 340 A) simulating an endothelial interface (SEM, TEM). Based on these analyses, a plausible sequence of events for human PNI accretion kinetics can be advanced, i.e., 0-24 hrs: (a) maximal foreign body response of blood in contact with Dacron fibrils, (b) cellular lysis and fibrin compaction; 1-6 days: (c) accretion and lysis of cellular aggregates (neutrophils, macrophages) 3-4micro thick, (d) accretion of linear fibrin aggregates, 8-10micro thick, and (e) cyclic replication (up to six) of phases c and d.