COMPARATIVE EVALUATION OF A STEROID ELUTING, TRANSVENOUS CARDIAC PACEMAKER LEAD IN CANINE AND OVINE MODELS
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An important factor in evaluating a transvenous cardiac pacemaker lead is selecting an appropriate animal model. We compared the implantation site characteristics of a transvenous cardiac pacing lead in canine and ovine models. A steroid eluting Medtronic CapSureFix Model 5068 active fixation, transvenous-pacing lead was implanted in the right ventricle of six dogs and five sheep. Pacing threshold values were collected for both groups of animals at 6 time points (1, 2, 3, 4, 8, and 12 weeks post-implant). On average, canine threshold values trended downward between weeks 3-12, but sheep values trended upward between weeks 4-12. The pacing thresholds were not significantly different for dogs and sheep (T-test with Hochberg correction for multiple comparisons). Twelve to fourteen weeks post-implant, four dogs and five sheep were euthanized and transmural cross-sections of the lead tip implant site (including perilead capsule and intramyocardial helix) were collected and examined histologically. Quantitative (nonparametric scoring) results showed better lead tip stability in dogs (stable) vs. sheep (moderately unstable to stable). The perilead, intraluminal capsule was longer in dogs than in sheep (9-24mm vs. 0.5-3.0mm, sheep) and active fibroproliferation was less. The lead tip capsule at the myocardial interface was thinner with lower fibroproliferative grade in dogs (0-1 vs. 0.5-3.0 sheep). In sheep, focal, mild to moderate dystrophic mineralization was observed which was absent in dogs. In summary, dogs had better pacing threshold trends, better lead stability, longer perilead sheaths, less active fibroproliferation, and much less dystrophic mineralization than sheep implanted with the same pacing lead for the same duration. The differences in the two animal models indicate that care must be taken when deciding the appropriate animal model for testing a transvenous cardiac pacemaker lead. Selection should be based on study goals in order to reduce animal model bias.
