An apparatus (20) includes an electrically-insulating tube (22), which includes a distal end (30) having a circumferential wall (38) that is shaped to define one or more perforations (34), configured for insertion into a body of a subject, an outer electrode (24), disposed over the distal end of the electrically-insulating tube, and configured to lie at least partly within a thrombus (66) while the electrically-insulating tube is inside the body, and an inner electrode (28), configured to lie, within the tube, opposite the perforations, while the outer electrode lies at least partly within the thrombus. The outer electrode is configured to attract the thrombus while the outer electrode lies at least partly within the thrombus and the inner electrode lies opposite the perforations, when a positive voltage is applied between the outer electrode and the inner electrode such that electric current flows through the perforations.
