Thrombus formation around an endocardial pacemaker electrode: a scanning electron microscopic study and its relationship to abnormal threshold elevation

The author experienced an abnormal increase in stimulation threshold in one patient to whom a permanent endocardial electrode was implanted according to the temporary-permanent technique, but could safely exchange the electrode at the fifth postoperative day before exit block would have occurred. Around the extracted electrode there was a thrombus which was considered to be the main causative factor of abnormally increased stimulation threshold. The morphology of the surface of the thrombus and surface of the electrode was examined using a scanning electron microscope, and the author found that the membranous thrombus which surrounded the neck of the lead had a very fine network of configuration with multilayers and that, though macroscopically the electrode tip was clean and the metal was brilliant, there were scattered white masses strongly adhered to the surface of it. Thus in a case of rapid increase of stimulation threshold within a few days after implantation, it is advisable to withdraw the catheter and to implant another new one.