A catheter apparatus, comprising: an elongated tubular shaft extending along a longitudinal axis, wherein the elongated shaft includes a proximal portion and a distal portion; and a treatment assembly (116; 216; 416) at the distal portion of the shaft and configured to be located at a target location within a blood vessel of a human patient, wherein the treatment assembly (116; 216; 416) includes a pair of electrodes (154; 254a/b; 454a/b), wherein each electrode typically comprises at least one planar surface and/or each electrode typically comprises a crescent-shaped cross-sectional profile, wherein the treatment assembly includes a first strut or expansion member comprising a first electrode of the pair of electrodes and a second strut or expansion member, comprising the second electrode of the pair of electrodes wherein the first and second struts or expansion members (130, 140) are movably connected to the shaft, characterised in that the first strut or expansion member includes a first fixed end portion coupled to the shaft and a first free end portion slidably engaged with the shaft, and wherein the second strut or expansion member includes a second fixed end portion coupled to the shaft and a second free end portion slidably engaged with the shaft, wherein the first free end portion is slidably engaged with the shaft at a location distal of the first fixed end portion; and the second strut having a second free end portion slidably engaged with the shaft at a location proximal of the second fixed end, wherein the first fixed end portion and the second free end portion are generally adjacent along the shaft; wherein the first free end portion and the second fixed end portion are generally adjacent along the shaft, wherein the treatment assembly (116; 216; 416) is transformable between- a low-profile delivery configuration wherein the pair of electrodes (154; 254a/b; 454a/b) are in a staggered arrangement relative to each other along the longitudinal axis, and an expanded deployed configuration wherein the pair of electrodes (154; 254a/b; 454a/b) are aligned along an electrode axis that is orthogonal relative to the longitudinal axis wherein shaft and treatment assembly are configured to fit within a guide sheath or guide catheter having, for example, a 6F outer diameter. an elongated tubular shaft extending along a longitudinal axis, wherein the elongated shaft includes a proximal portion and a distal portion; and a treatment assembly (116; 216; 416) at the distal portion of the shaft and configured to be located at a target location within a blood vessel of a human patient, wherein the treatment assembly (116; 216; 416) includes a pair of electrodes (154; 254a/b; 454a/b), wherein each electrode typically comprises at least one planar surface and/or each electrode typically comprises a crescent-shaped cross-sectional profile, wherein the treatment assembly includes a first strut or expansion member comprising a first electrode of the pair of electrodes and a second strut or expansion member, comprising the second electrode of the pair of electrodes wherein the first and second struts or expansion members (130, 140) are movably connected to the shaft, characterised in that the first strut or expansion member includes a first fixed end portion coupled to the shaft and a first free end portion slidably engaged with the shaft, and wherein the second strut or expansion member includes a second fixed end portion coupled to the shaft and a second free end portion slidably engaged with the shaft, wherein the first free end portion is slidably engaged with the shaft at a location distal of the first fixed end portion; and the second strut having a second free end portion slidably engaged with the shaft at a location proximal of the second fixed end, wherein the first fixed end portion and the second free end portion are generally adjacent along the shaft; wherein the first free end portion and the second fixed end portion are generally adjacent along the shaft, wherein the treatment assembly (116; 216; 416) is transformable between- a low-profile delivery configuration wherein the pair of electrodes (154; 254a/b; 454a/b) are in a staggered arrangement relative to each other along the longitudinal axis, and an expanded deployed configuration wherein the pair of electrodes (154; 254a/b; 454a/b) are aligned along an electrode axis that is orthogonal relative to the longitudinal axis wherein shaft and treatment assembly are configured to fit within a guide sheath or guide catheter having, for example, a 6F outer diameter. a low-profile delivery configuration wherein the pair of electrodes (154; 254a/b; 454a/b) are in a staggered arrangement relative to each other along the longitudinal axis, and an expanded deployed configuration wherein the pair of electrodes (154; 254a/b; 454a/b) are aligned along an electrode axis that is orthogonal relative to the longitudinal axis wherein shaft and treatment assembly are configured to fit within a guide sheath or guide catheter having, for example, a 6F outer diameter.