Cardiac damage in dogs with chronically implanted automatic defibrillator electrode catheters and given four episodes of multiple shocks.

In 14 dogs, a newly designed automatic defibrillator electrode catheter with paired ventricular and superior vena caval electrodes was implanted transvenously into the right ventricular (RV) apex for 26 weeks. Twelve dogs were given multiple (mean total = 21.3) near-threshold (mean delivered energy = 17.6 joules) shocks via the lead at 0, 5, 12, and 26 weeks after implantation. Two days after the last shocks, the dogs were killed and the cardiac alterations were evaluated at necropsy and by histopathology. The lead induced mild to moderate cardiac alterations of (1) endocardial fibrosis, either as flat or papillary lesions, and of (2) segments of smooth thin fibrous sheath formation over the lead with adhesions to the adjacent endocardium. Mild cardiac alterations were induced by the shocks including myocardial necrosis and calcification, concentrated in the ventricular septum and RV free wall adjacent to the ventricular electrodes, and foci of postnecrotic fibrosis. The chronically implanted lead was determined to be safe and effective in dogs.