Studies of the Tissue Reaction Induced by Transvenous Pacemaker Electrodes. I. Microscopic Examination of the Extent of Connective Tissue Around the Electrode Tip in the Human Right Ventricle

The purpose of this study was to investigate the extent of connective tissue of the human right ventricle induced by cardiac pacing electrodes. Between January 1984 and July 1987, 34 consecutive patients with VVI‐pacing systems were autopsied in the Department of Pathology at the University of Frankfurt/M. The surrounding tissue of these 34 electrodes (17 Siemens Elema 412 S, five Medtronic 6957, one Medtronic 6959, one Medtronic 4011, three Biotronik D2K, three Biotronik K10, two Osypka FY 62, one Biotronik N, and one Siemens Elema 588) in the right ventricle were investigated histologically. The tissue was stained with Giemsa and the thickness of the connective tissue layer was measured. Stimulation threshold data at various times were known in four of eight screw‐in electrodes, in seven of 17 vitreous carbon electrodes and in two of seven smooth surface electrodes. Electrode surface area, implantation time, age of the patient and cause of death were comparable for all three electrode groups. However, a significant difference was found in the extent of connective tissue between the porous surface and screw‐in electrodes (128 ± 55 VS 397 ± 269 μm, P 0.01) and porous surface and smooth surface electrodes (128 ± 55 vs 307 ± 117 μm, P 0.01). No relation (r = 0.106) was found between the duration of implantation and the extent of connective tissue for the vitreous carbon electrodes (Siemens Elema 412 S). The lowest chronic stimulation thresholds were measured in the latter type of electrodes (0.5 ± 0.3 V) as compared to the screw‐in (0.75 ± 0.30 V) and smooth surface electrodes. We conclude from this study, that vitreous carbon electrodes induce only a small amount of connective tissue around the insertion site in the human right ventricle, as compared to other smooth surface or screw‐in electrodes. Chronic stimulation threshold data parallel those morphological results.