This disclosure is directed to a catheter having a lasso electrode assemblywith amoveable spine. The lasso electrode assembly may have an array of sensingelectrodesand may be configured to engage the ostium of the vessel of a patient. Themoveablespine may have an ablation electrode and may travel along track around thecircumference of the lasso electrode assembly. By adjusting the position ofthemoveable spine, tissue may be ablated to form lesions around a circumferenceof thevessel.
