of apparatus 230 when utilizing a balloon catheter such as catheter 232 the inflated balloon may act as an insulator of increased impedance for directing a pulsed electric field along a desired electric flow path as will be apparent alternative insulators may be utilized as seen in fig6 when the helical electrode 236 physically contacts the wall of renal artery ra the generator 100 may generate a pef such that current passes between the helical electrode 236 and the shaft electrode 238 in a bipolar fashion the pef travels between the electrodes along lines li that generally extend along the longitudinal dimension of the artery the balloon 234 locally insulates and or increases the impedance within the patient 39 s vessel such that the pef travels through the wall of the vessel between the helical and shaft electrodes this focuses the energy to enhance denervation and or other neuromodulation of the patient 39 s renal nerves e g via irreversible electroporation fig7 illustrates an apparatus 240 similar to those shown in fig4 6 in accordance with another embodiment of the invention the apparatus 240 comprises a balloon catheter 242 having an expandable balloon 244 and a shaft electrode 246 located proximal of the expandable balloon 244 the apparatus 240 further comprises an expandable.