Treatment of an aneurysm or other vascular defect can be facilitated or enhanced by a galvanic cell formed by an implantable medical device configured to be implanted at or within the aneurysm or other vascular defect. The implantable medical device can include a primary structure including an anodic metal and a cathodic metal. The anodic metal and the cathodic metal each form a fraction of a total surface area of the primary structure. A galvanic cell formed by the anodic metal and the cathodic metal is configured to induce a galvanic voltage within blood for a duration of time to promote thrombosis. The thickness of the anodic metal can be less than or equal to 5 μm, for example, to provide galvanic activity for between 5 and 30 minutes.