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Although high voltage direct current (DC) shock is a standard technique to terminate ventricular fibrillation
(VF), it can cause severe pain and tissue damage. The exact effect of the DC electric field, which can depolarize the
heart during VF is still unknown. We hypothesized that low-energy DC field in combination with pacing (pacing+DC)
could terminate VF by affecting the ventricular propagation pattern. In six Langendorff-perfused isolated rabbit hearts
with the ablated sinoatrial (SA) node, the DC field was delivered to the left ventricle (cathode) and right ventricle
(anode). We designed a timed protocol using LabVIEW programming that delivers pacing, DC and pacing+DC stimuli
for two seconds time intervals each. The pacing pulse (with varying pacing cycle length: 300ms-30ms) was delivered to
the apex. Transmembrane voltage was recorded with optical mapping technique for 16 seconds at a sampling rate of
2ms/frame. We crushed the sinoatrial node to reduce the heart rate. The baseline activation appeared to have endocardial
origins with a mean escape ventricular rate of 60 ± 5bpm at baseline. The DC field (30mA-60mA) alone increased the
mean heart rate to 120±5bpm. Although DC alone terminated VF in a few cases, the rate of termination was very low
(6.2%). However, when pacing+DC was applied, it was possible to terminate VF in 34 of 130 episodes in six rabbits.
The rate of successful defibrillation of VF with pacing+DC was significantly higher than that with DC alone (20% vs
6.2%, p<0.01). Pacing alone never terminated the VF. In conclusion, DC field may affect the conduction velocity in
normal condition. Pacing+DC intervention could lead to regularization of VF propagation and eventually to termination.
Further improvement of this approach may offer a higher success rate of defibrillation with lower energy requirements.
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