Methods and systems of catheterization include a flexiblecatheter adapted for insertion into a heart of a living subject.The catheter has a lumen for passing an electricallyconductive fluid therethrough, which is propelled by a peristalticpump. A fluid reservoir connected to the lumen suppliesthe fluid to the catheter. Electrocardiogram circuitryis connectable to the subject for monitoring electrical activityin the heart. An electrically conductive cable divertsinduced charges in the fluid from the catheter electrodes,for example by shorting to a rotating element in the peristalticpump.
