Relationship of cardiac morphologic alterations and electrical performance of various types of endocardial pacemaker leads implanted in dogs

Ann Sypniewski Radovsky, Purdue University

Abstract

Fifty-one specimens of reactive endomyocardium adherent to the distal portion of dexamethasone-eluting and nonsteroid endocardial pacing leads implanted in either the right atrium or the right ventricle of dogs for 6-182 weeks were evaluated. Connective tissue sheaths formed from proliferated endocardium and organized thrombus. Sheaths contained fibroblasts, macrophages, lymphocytes and mast cells and were 0.1-1.0 mm thick around the distal stimulating electrodes. The myocardium adjacent to peri-electrode connective tissue sheaths had multifocal myofibrillar lysis, atrophy and interstitial fibrosis. Leads with porus-surfaced electrodes containing dexamethasome tended to have thinner peri-electrode sheaths than leads with smooth surfaced electrodes without dexamethasone. There was a significant positive correlation (r = 0.6) between the voltage stimulation thresholds and the thickness of the connective tissue sheaths around the stimulating electrodes. In controlled experiments, a pair of pacemaker leads with similar electrodes, one of which contained dexamethasone, was implanted into the right ventricle of each of twelve dogs and maintained for either 3 weeks (n = 6 pairs) or 6 weeks (n = 6 pairs). Electrical stimulation thresholds were lower and peri-electrode connective tissue sheaths were (1) thinner (P $<$.005); (2) less cellular (P $<$.025): (3) less severely infiltrated with leukocytes; and had (4) fewer mast cells (P $<$.05) for leads with electrodes containing dexamethasone than for similar leads without dexamethasone. Correlations between peri-electrode connective tissue sheath thickness and electrical stimulation thresholds were similar for pacing leads in the 6 week duration experiment as for leads in the initial study, but both lead types in the three week duration study had higher electrical thresholds than could be explained on the basis of peri-electrode connective tissue thickness alone. In-vitro exposure to calcium ionophore of peri-electrode tissues from the 3 week-duration study resulted in higher concentrations of prostacyclin and lower concentrations of thromboxane B$\sb2$ in supernatants from tissues that had been adjacent to electrodes containing dexamethasone than from tissues from similar electrodes without dexamethasone.

Degree

Ph.D.

Advisors

Vleet, Purdue University.

Subject Area

Animal diseases

COinS