DOES REDUCING CAPACITANCE HAVE POTENTIAL FOR FURTHER MINIATURIZATION OF IMPLANTABLE DEFIBRILLATORS

Objective-To determine whether considerably smaller capacitors could r eplace 125 mu F capacitors as the standard for use in implantable defi brillators. Methods-Measured energy, impedance, voltage, and current d elivered were compared at defibrillation threshold in 10 mongrel dogs for defibrillation using 75 mu F and 125 mu F capacitors alternated ra ndomly. Defibrillation was attempted with biphasic shocks of comparabl e tilt between an endocardial lead in the right ventricular apex and a ''dummy'' active can of an experimental implantable device placed in the subpectoral position. Results-A reduction of capacitor size of 40% was associated with an increase in voltage of 21% and in current of 2 2%. With a 65% tilt, no significant differences were found between the two capacitances with respect to the impedance or energy required for defibrillation. Conclusions-Multiple advances in electrode material, electrode configuration, shock morphology, and shock polarity have red uced defibrillation energy requirements. Smaller capacitors could be u sed in implantable cardioverter/defibrillators without a major decreas e in effectiveness.