Mapping catheter with flex panel electrode assembly

An apparatus includes a catheter assembly and an end effector. The catheter assembly includes an outer sheath with a distal end. The end effector is associated with a distal end of the catheter assembly. The end effector includes a panel assembly with microelectrodes for electrophysiological (EP) mapping. The microelectrodes are configured in a matrix within the panel assembly and provide multiple points of contact with the target tissue for EP mapping. The panel assembly can transition between a first contracted state and a second expanded state. The panel assembly can fit within the outer sheath in the first state. The panel assembly can expand outwardly away from a longitudinal axis defined by the catheter assembly in the second state once exposed distally relative to the distal end of the outer sheath.