Medical apparatus includes a sheath having a lumen with a distal opening. A flexible probe, which is adapted for insertion through the sheath, includes an insertion shaft, an end section, which is connected to the distal end of the insertion shaft, a tip electrode extending over the tip of the end section, and proximal electrodes distributed along the end section. The probe is manipulable, within the sheath, between a retracted configuration in which the end section is contained within the lumen so that only the tip electrode protrudes through the distal opening, and an extended configuration in which the entire end section protrudes from the distal opening and assumes an arcuate shape. An energy generator applies electrical energy only to the tip electrode while the probe is in the retracted configuration and to at least the proximal electrodes while the probe is in the extended configuration.