Effects of titanium can electrode size and shock history on defibrillation electrode impedance

As the size of the implantable defibrillator can used as a defibrillation electrode decreases, changes in circuit impedance may occur for a given single-lead to can electrode system. In addition, increased electrode anodization due to the higher current densities at the can may cause increased electrode impedance. The relationship between can shadow area and circuit impedance was quantified in a saline tank system using 100 monophasic anodal shocks. Decreasing the shadow area of the can by a factor of 2 increased circuit impedance by 18%. The impedance of a plate electrode was 1.6/spl plusmn/0.3 /spl Omega/ higher than a can electrode with the same shadow area. Anodization of the titanium electrode after 100 shocks resulted in a 6% increase in circuit impedance for the smallest electrodes. Decreased can size resulted in an increase in circuit impedance and anodization, but the effect of increased circuit impedance on defibrillation efficacy is unknown.