A medical probe, including a flexible insertion tube having a proximal segment and a deflectable distal segment, and containing first and second lumens running longitudinally through the insertion tube, wherein the first and second lumens are twisted around each other in the proximal segment, and run parallel to each other in the deflectable distal segment. The medical probe also includes first and second wires running respectively through the first and second lumens and having respective first and second distal ends, which are anchored within the deflectable distal segment of the insertion tube.