[Maturation of the electrode-endocardium interface].

It's largely known that the implanted lead in the endocardium develops an inflammation and posterior fibrosis of the cardiac tissue, increasing the stimulation threshold. It's also demonstrated that the chronic threshold values keep relation with the electrode surface area. There are several factors in the fibrosis genesis according mechanical of physical properties of the lead, such as tension, tip design, surface area and the patient reaction to a foreign body. Electrical factor is not yet sufficiently studied. We developed an experimental study in 12 dogs, separated in two groups (four explanted at 8 days or subacute group, and eight explanted at 35 days or chronic group), looking for a correlation between current density crossing the interface endocardial-electrode and the posterior fibrosis. The mechanical factor was minimized by using small surface area electrodes, with little tension. Three leads were implanted in each dog, connected respectively to 0, 2.5 and 5 volts. The simultaneous working of two pacemakers in the same dog, was possible by programming one of them in VVI at 140 per minute, and the other in VOO at 75. The tirht lead was implanted as a reference. The threshold pacing values, in voltage and in current, the R wave and impedance were measured at implant and at explant of the leads. Differences statistically significative were observed between reference electrodes and electrical active ones, according their current density. The leads stimulating with great current density (more voltage) generated more fibrosis and therefore higher pacing threshold values and lower R waves and impedances. The convenience to stimulate at low voltages was seen.