A percutaneous catheter system for use within the human body and an ablation catheter for ablating a selected tissue region within the body of a subject. The percutaneous catheter system can include two catheters thai are operatively coupled to one another by magnetic coupling through a tissue structure. The ablation catheter can include electrodes positioned within a central portion. The ablation catheter is positioned such that the central portion of a flexible shaft at least partially surrounds the selected tissue region. Each electrode of the ablation catheter can be activated independently to apply ablative energy to the selected tissue region. The ablation catheter can employ high impedance structures to change the current density at specific points. Methods of puncturing through a tissue structure using the percutaneous catheter system are disclosed. Also disclosed are methods for ablating a selected tissue region using the ablation catheter.