stainless steel coiled into a flexible spring enclosing the interior bore 64 a braided sheath 66 of plastic material encloses the coil alternatively as fig3 b shows the shaft 62 comprises a slotted stainless steel tube enclosing the interior bore 64 an array of slots 70 subtends the tube along its length the slots 70 subtend less than one circumference of the shaft 62 at an angle of between 270 to 300 degrees the slots 70 are also radially offset one from the other by about 30 to 120 degrees the slotted shaft 62 shown in fig3 b provides strength and flexibility along the length of the guide tube assembly 14 the slotted shaft 62 also transmits twisting motions torque from the handle assembly 12 to the electrode tip assembly 16 more directly than the coiled shaft 62 shown in fig3 further details of the slotted shaft 62 are disclosed in pending lundquist u s patent application ser no 07 657 106 filed feb 15 1991 and entitled 34 torquable catheter 10 and method 34 like the coiled shaft 62 in fig3 a a sheath 66 encloses the slotted shaft the sheath 66 is made from a plastic material such as polyolefin the handle assembly 12 includes a tubular stem 74 though which the proximal end of the guide tube assembly 14 extends for attachment to the tension screw assembly 60 adhesive attaches the proximal end of the coil to the tension screw assembly 60 the guide tube assembly 14 can be made in various lengths in the illustrated the guide tube assembly 14 is about 100 cm in length as fig1 and 2a b show a sleeve 76 couples the guide tube assembly 14 to the handle assembly 12 adhesive secures one end of the sleeve 76.