Ventricular fibrillation: are swine a sensitive species?

Purpose: Legislation and sentiment have pushed large-animal electrophysiological research from the canine to the swine model. Anecdotal experience suggests that the swine is particularly sensitive to ventricular fibrillation (VF) induction, and radiofrequency ablation studies are consistent with this. Currently, no data exist directly comparing the VF threshold (VFT) in humans to swine. Because of the perceived difference in vulnerability to VF induction, we hypothesized that the VFT would be lower in swine compared to humans.

Methods: Six anesthetized open-chested swine, 31 ± 2 kg, were studied that were part of an ongoing study with up to 6 h of previous closed-chest percutaneous pacing with repeated VF cycles. Similar to the human study of Horowitz et al., 24 pulses of 4 ms each were applied at a rate of 100 Hz during the ST segment to the epicardium via a pair of 7-mm diameter platinum electrodes whose centers were 15 mm apart. Current was increased until VF was induced.

Results: The swine right ventricle (RV) VFT was 9.7 ± 2.1 mA [median = 9.0, interquartile range (IQR) = 7.8-12.0], and the left ventricle (LV) VFT was 10.7 ± 2.2 mA [median = 10.5, IQR = 8.8-12.5] (p = NS). Horowitz reported the RV VFT in six patients as 24.3 ± 5.2 mA [median = 24.5, IQR = 19.0-29.3] and the LV VFT in ten patients as 33.6 ± 9.5 mA [median = 36.5, IQR = 27.3-42.3] (p = .11). Both the RV and LV VFTs were lower for swine (p < 0.003), and each of the mean and median VFTs for the ventricles together was one third that of the humans.

Conclusions: Swine are about three times as sensitive to the electrical induction of VF as are humans.