Endocardial lead systems for implantable cardioverter-defibrillators utilize large (12F) rigid catheters with spring defibrillation electrodes, and lead system failure has been observed during long-term implant. We evaluated a novel flexible 8F braided electrode catheter for pacing and defibrillation in canine experiments. Active fixation and pacing were accomplished using a screw-in distal electrode, and defibrillation pulses were delivered through a braided electrode. Two braided electrode catheters were positioned in the right ventricular apex (6 cm2) and in the superior vena cava-right atrial junction (5 cm2), respectively. An elliptical 13 cm2 surface area patch electrode was positioned along the left lateral cardiac border. Ventricular fibrillation (VF) was induced and monophasic and asymmetric biphasic shocks (leading voltages 260 to 1000 V) were delivered via dual and triple electrode configurations in each animal using a prospective randomized crossover study design. Mean right ventricular pacing threshold was 0.5 +/- 0.2 mA, with a mean electrogram amplitude of 11.1 +/- 2.8 mV during sinus rhythm prior to fibrillation and defibrillation. Two hundred seven VF inductions (mean 30 +/- 4 per animal) were analyzed. The mean defibrillation threshold could be reduced to 8.0 +/- 3.2 joules with biphasic shocks from 12.9 +/- 5.1 joules obtained for monophasic shocks using a dual electrode system (p less than 0.004). Mean shock leading voltage was correspondingly reduced to 488 +/- 100 V from 691 +/- 154 V (p less than 0.0006).(ABSTRACT TRUNCATED AT 250 WORDS)