Interactions of blood with solid and porous endocardial electrodes for cardiac pacemakers

Two forms of implantable endocarial electrodes, solid and porous, used in conjunction with cardiac pacemakers have been compared in their interactions with human blood components. The platinum-iridium electrode tips were suspended in stirred, anticoagulated whole blood or blood products at 37 degrees C for period of 1 to 20 minutes, and then were examined by scanning electron microscopy. The various media employed were heparinized or citrated fresh whole blood, platelet-rich plasma, platelet-poor plasma, and washed platelets in a protein-free balanced salt solution. There were no significant qualitative differences between the reactions of the two forms of electrode. Plasma products, platelets, and erythrocytes adhered freely to the surfaces of both forms of electrode. Leukocytes were much less frequently encountered. Platelets were seen in two forms, those adherent directly to the metal surface with extensive spreading and formation of a monolayer, and platelets attached to the monolayer without spreading but with early shape-change. Quantitative differences between the two electrode forms were prominent. Solid electrodes had broad areas free of cellular accumulations or with only sparsely scattered platelets and erythrocytes. The wires of the porous electrodes were extensively coated on their outer surfaces with platelets and erythrocytes. It is postulated that the porous electrodes will carry appreciably more blood cells, particularly platelets, to the site of endocardial implantation, and these cells or their products may play a role in the tissue responses that result in implantation of the electrode.