Devices or methods such as for stimulating excitable tissue or sensing physiologic response or other signals that can use separate fixation mechanism is described. An implantable apparatus can include a modular electrostimulation electrode assembly that can include a first module and a second module that can be end user-attachable to each other and end user-detached from each other. The first module can include an electrostimulation electrode fixation support member that can be laid flat against or otherwise conform to a surface of a heart, and can define a centrally located open portal such as for permitting electrode access to the surface of the heart. The second module can include an electrostimulation electrode that can be inserted through the portal of the fixation support member such as to contact the surface of the heart such as to deliver chronic electrostimulation to the heart.