Methods and systems of catheterization include a flexiblecatheter adapted for insertion into a heart of a livingsubject. The catheter has a lumen for passing an electricallyconductive fluid therethrough with the fluid exitingthe catheter at the distal portion. The lumen is connectableto an irrigation pump to form a fluid communicationtherewith. A fluid reservoir connected to the lumen suppliesthe fluid to the catheter. Electrocardiogram circuitryis connectable to the subject for monitoring electricalactivity in the heart. An electrically conductive cable divertsinduced charges in the fluid from the catheter electrodes,for example by connection to an isolated ground ofthe electrocardiogram.
