Effects of dexamethasone elution on tissue reaction around stimulating electrodes of endocardial pacing leads in dogs.

A pair of endocardial pacemaker leads, identical except for the presence or absence of dexamethasone elution from the distal stimulating electrode, was implanted into the right ventricle of each of 12 dogs for either 3 weeks (n = six pairs) or 6 weeks (n = six pairs). Fibrous connective tissue sheaths (0.04 to 0.20 mm thick) formed around the distal porous-surfaced stimulating electrodes because of proliferation of endocardial connective tissue and adherence and organization of thrombus. Connective tissue sheaths were composed of fibroblasts within an abundant collagen matrix and contained scattered macrophages, lymphocytes, plasma cells, and mast cells. Connective tissue sheaths around dexamethasone-eluting leads were thinner (p less than 0.03), less cellular (p less than 0.10), and had fewer mast cells (p less than 0.10) than corresponding nonsteroid leads. There was mild multifocal interstitial fibrosis, myofiber atrophy, and myofibrillar lysis in the adjacent myocardium. Thresholds for electrical stimulation of the myocardium were consistently lower for pacing leads with dexamethasone-eluting stimulating electrodes than for leads without dexamethasone.