Complications of a permanent transvenous pacing catheter in a horse

Gross and histopathological findings in a 9-year-old horse implanted with permanent transvenous pacing cardiac catheters, 18 and 34 months before its death, are described. Lesions consisting of extensive fibrino-haemorrhagic thrombi with large numbers of bacterial colonies were present along the electrode wires and on mural and valvular endocardial surfaces of the right heart. There was a locally extensive area of suppurative endocarditis around the attachment site of the atrial electrode, which was loosely attached by a thin band of membranous tissue to the endocardium. The ventricular electrode was firmly embedded in the myocardium and was surrounded by a dense area of fibrous connective tissue in which multifocal mineralized areas were seen. Histologically, there was evidence of terminal bacteraemia. The observed lesions are discussed with respect to findings in man and other animals with similar cardiac implants.