Lasso catheter with tip electrode

1. Medical apparatus, comprising:

a sheath, adapted for insertion into a body of a patient and having a lumen with a distal opening;

a flexible probe, which is adapted for insertion through the sheath and comprises:

an insertion shaft, having a distal end;

an end section, which is connected to the distal end of the insertion shaft and comprises a distal tip;

a tip electrode extending over the tip; and

a plurality of proximal electrodes distributed along the end section,

wherein 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; and

an energy generator, which is configured to apply electrical energy only to the tip electrode while the probe is in the retracted configuration and to apply the electrical energy to at least the proximal electrodes while the probe is in the extended configuration, wherein the probe comprises a transducer, which is configured to provide a signal indicating that the probe is in the retracted configuration.

2. The apparatus according to claim 1 , wherein the transducer is one of multiple position transducers, which are disposed along the end section and are configured to provide signals indication of a position of the end section within the body.

3. The apparatus according to claim 1 , wherein the sheath comprises a positioning element in proximity to the distal opening, and wherein the energy generator is configured to apply the electrical energy only to the tip electrode when the signal provided by the transducer indicates that the transducer is within a predetermined minimum distance of the positioning element.

4. A method for treatment, comprising:

inserting a sheath, having a lumen with a distal opening, into body of a patient;

inserting a flexible probe through the sheath so that an end section, at a distal end of the probe, protrudes from the distal opening and assumes an arcuate shape;

while the end section protrudes from the distal opening, bringing the arcuate shape into contact with tissue in the body and actuating a plurality of electrodes, distributed along the end section, to apply electrical energy to the tissue;

withdrawing the flexible probe into the sheath so that the end section is contained within the lumen and only a tip electrode, at a distal tip of the end section, protrudes through the distal opening; and

while the end section is contained within the lumen, bringing the tip electrode into contact with the tissue, and actuating only the tip electrode with the electrical energy, wherein withdrawing the flexible probe comprises receiving a signal from a transducer in the probe indicating that the probe is in the refracted configuration.

5. The method according to claim 4 , wherein receiving the signal comprises receiving signals from multiple position transducers, which are disposed along the end section and are configured to provide an indication of a position of the end section within the body.

6. The method according to claim 4 , wherein the sheath comprises a positioning element in proximity to the distal opening, and wherein actuating only the tip electrode comprises applying the electrical energy only to the tip electrode when the signal provided by the transducer indicates that the transducer is within a predetermined minimum distance of the positioning element.