1. A catheter comprising: an elongated catheter body; a distal tip section distal of the catheter body, including a tip electrode; a needle electrode coupled to an elongated flexible proximal tubing; an elongated guide tubing; and a needle control handle including a control and a piston slidably mounted in the needle control handle, the piston responsive to the control and coupled to the proximal tubing to move the needle electrode between a withdrawn position and an extended position relative to the tip electrode, the piston configured to be coupled with a luer connector configured for longitudinal movement with the piston relative to the needle control handle, the luer connector configured to pass first and second tubings into the needle control handle to pass first and second fluids, respectively, the first tubing configured to communicate with a lumen of the proximal tubing, wherein the lumen of the proximal tubing defines a first fluid path configured to pass the first fluid from the needle control handle to a distal end of the needle electrode, the proximal tubing extending through the guide tubing between the needle control handle and the distal tip section, the second tubing configured to pass the second fluid along a second fluid path isolated from the first fluid path, the second fluid path including entry into a gap between the guide tubing and the proximal tubing through an opening in a sidewall of the proximal tubing, the gap being sealed by a plunger member situated immediately proximal of the opening in the sidewall of the proximal tubing, the gap extending longitudinally along the guide tubing and terminating at a distal end of the guide tubing whereupon the second fluid is configured to pass into the tip electrode.