Pulmonary Thromboembolism and Myocarditis Resulting from a Large Pacing-Lead-Associated Right Ventricular Thrombus in a Dog with Chronic Cough as Presenting Sign.

Simple Summary: Dogs with an inappropriately slow heart rate can suffer from decreased endurance and fainting. In addition, they can experience sudden death, and in the long term, they can develop heart failure. Similarly to people, if the slow heart rate cannot be solved with drug therapy, an artificial pacemaker is implanted to increase the heart rate. In most cases, the pacemaker lead is introduced via a large vessel to the heart so that the chest does not have to be opened surgically. Though this procedure is less invasive than suturing the lead on the surface of the heart, it does introduce a foreign body into a great vessel and the heart. The present case report describes a dog, in which the pacemaker lead in the heart caused a large thrombus, which subsequently resulted in pulmonary thromboemboli. The dog presented with a progressively worsening cough and decreased exercise tolerance. Subsequently, lethargy, labored breathing and weakness developed. Because of a suspected bacterial lead-infection, antibiotics were administered, without clinical improvement. Due to worsening clinical signs, the owner elected for euthanasia. Necropsy showed a large thrombus in the right ventricle around the pacing lead and a massive pulmonary thromboembolism. No bacterial infection was apparent. In the present case report, we describe the clinical course and postmortem findings of a 12-year-old Labrador retriever dog with a third-degree atrio-ventricular block that developed a chronic cough, and later dyspnea and weakness as a result of massive pulmonary thromboembolism 3 years after implantation of a transvenous permanent pacemaker. A large soft tissue mass was seen in the right ventricular chamber around the pacing lead with echocardiography. Initially, this was thought to be caused by mural bacterial endocarditis based on hyperthermia, severe leukocytosis and the appearance of runs of ventricular tachycardia, the latter suggesting myocardial damage. While blood culture results were pending, antibiotics were administered without a positive effect. Due to clinical deterioration, the owner elected for euthanasia and a post-mortem examination confirmed a right ventricular thrombus and surrounding myocarditis, without signs of bacterial infection, and a massive pulmonary thromboembolism. We conclude that pulmonary thromboembolism should be considered in dogs with a cough that have an endocardial pacing lead implanted. Serial screening for proteinuria before and after implantation of an endocardial pacing lead would allow timely initiation of prophylactic antiplatelet therapy. Local myocarditis can develop secondary to an intracavitary thrombus, which can subsequently lead to runs of ventricular tachycardia. [ABSTRACT FROM AUTHOR]