Figure 4: Positioning Basket Catheters.

(A) In right atrium, the sheath and catheter are advanced to the SVC where retracting the sheath causes the basket to self-expand. Slight torque may be required to maximize expansion and apposition. Optimally only 0-1 splines should traverse the tricuspid valve orifice. (B) In left atrium the sheath and catheter are advanced into the left superior pulmonary vein and the sheath is retracted. Slight manipulation may be needed to expand the basket outside of the vein. Again, only 0–1 spline should traverse the mitral valve orifice. (C) An undersized basket catheter will assume its natural spherical shape without any deformation suggesting limited endocardial contact. Intracardiac echocardiography (ICE) is often helpful in assessing endocardial contact. (D) An oversized basket catheter is most commonly recognized by an inability to expand the basket secondary to distal electrode restriction in a PV antrum. Further basket withdrawal is limited by the proximal electrodes encountering the trans-septal access site. (E) Withdrawal of basket out of the LUPV orifice results in slight spline prolapse into the left ventricle, although > 56 electrodes are in contact with the left atrial walls. (F) Regional Oversampling using the basket catheter. Here, the basket is manipulated to ensure higher sampling density at the LA roof, where a rotor was observed, at the cost of lower density sampling in the posterior and anterior walls where rotors were previously not seen. If no AF sources are identified, repositioning to systematically sample regions of the atria is suggested. (From Narayan SM, Krummen DE, Rappel W-J. Clinical mapping approach to diagnose electrical rotors and focal impulse sources for human atrial fibrillation. J Cardiovasc Electrophysiol [Internet]. 2012 May [cited 2012 Aug 6];23(5):447–54. Available from: http://www.ncbi.nlm.nih.gov/pubmed/22537106; with permission.)