An ablation system includes an electrical ablation element of elongate form with an electrically conductive element including a resistive part. A control unit includes a processing unit, a power unit and, optionally, a temperature sensor. The control unit in one embodiment carries out ablation in at least two phases, the first phase at a higher energy level and a second phase, after at least partial retraction of the resistive part, at a second lower phase in order to close any remaining lumen within a blood flow obstruction formed within the vessel during the first phase. Other embodiments provide for sensing retraction of the resistive part and effecting ablation during and/or after the retraction process in order to create a more effective occlusion barrier.
