An adaptor for endovascular electrocardiography, comprising: a member having a first end, a second end, and an inner lumen, the first end connectable to a luer of a catheter and the second end connectable to a syringe, such that fluid from the syringe is flushed into the catheter through the inner lumen； and a metal insert, in particular a metal ring, disposed along the inner lumen of the member and located inside the member, the metal ring connecting through a sealed electrical connection to an outer side of the member. An assembly for endovascular electrocardiography, comprising: the adaptor； and a connector separate from the member of the adaptor coupled to the metal ring.
