The invention relates to an alignment methodology based upon detection of asymmetric electric fields. An asymmetric electric field transducer 10 is located in a first vessel, and an electric field detector 100 is located in a second vessel. The detector uses the asymmetric field to align a connection means which traverses from one vessel to the other. The transducer and detector may be located on catheters. The transducer may be a pair of electrodes 22, 24, spatially separated around the catheter body 12 and aligned with the direction of needle deployment. The penetrating needle 20 may be located in the transducer catheter and ejected from an aperture 19 in the side wall. The needle may be curved. Transducer electrodes 39, 40, 41 (see figures 3a, 3b) may be located on the needle. The detector may comprise two ring electrodes 108, 110. A monitor system may be included to indicate alignment to a user. The invention finds particular application in vascular access via arteriovenous fistula in the haemodialysis population.
