Abstract: A catheter configured to guide and support a balloon catheter for use in and around a pulmonary vein and its ostium, has an elongated shaft and a distal assembly, the elongated shaft including a proximal portion with a first flexibility and a distal portion including a second flexibility greater than the first flexibility, the distal assembly including an elbow portion and a generally circular portion generally transverse to the longitudinal axis, the generally circular portion including a third flexibility greater than the second flexibility. Single axis location sensors and sensing ring electrodes are carried on the generally circular portion.

Abstract: Apparatus, consisting of a catheter having a distal end and a predefined outer diameter. The apparatus also has a plurality of elastic filaments, each filament having at least one electrode fixed thereto and having two ends fixed within the catheter distal end to hold the filament as a loop. The loop intertwines with one or more other loops of the other filaments so that the plurality of the filaments forms an open lattice, which expands when uncompressed to a lattice diameter at least 5 times greater than the outer diameter of the catheter.