For all the electrophysiologists out there, the best trick for crossing the interatrial septum that is resistant to transseptal puncture came from the group in Pessac Bordeaux, France.
Although rare, these authors found that 6 of 280 (2%) of transseptal crossings were difficult. They proposed a simple solution: After they ensured accurate positioning of the transseptal sheath and needle on the interactrial septum, they applied unipolar radiofrequency electrocautery energy at 20W (using it's "cut" setting) to the needle within the sheath and advanced the needle slightly against the septum to cross. The contact was achieved outside the patient at the proximal end of the needle with the energy transmitted to its tip. RF energy was effective at perforating the septum in all 6 patient's in 4 +/- 4 seconds and no complications occurred.
Reference: A Straightforward Solution for Interatrial Septae Resistant to Transseptal Punctures. Knecht S, Matsuo S, Wright M, et al. Hopital cardiologique du Haut L'Eveque, Pessac Bordeaux, France. Poster PO5-41, Heart Rhythm VolL 5, Issue 5S, May 2008.