A tubular insert for a vessel comprises an inner stent and an outer stent. At least a portion of the inner stent is disposed within the outer stent. The outer stent has a longitudinal axis and is constructed to be free of any closed loops which are electrically conductive and which are disposed about the longitudinal axis such that the longitudinal axis passes through the closed loop. The inner stent has a longitudinal axis and is constructed so as to be free of any closed loops which are electrically conductive and which are disposed about the longitudinal axis such that the longitudinal axis passes through the closed loop. There is a substantially electrically non-conductive connection between the inner and outer stents. Desirably, a wall surface is defined by the outer and inner stents, and there are no closed, electrically conductive loops in the wall surface of the tubular insert.