Evaluation of a new defibrillation pathway: Tongue-epigastric/tongue-apex route. II. Impedance characteristics in human subjects

An automated device for defibrillation using a vertical shock pathway (tongue-epigastric or tongue-apex) has been developed. The energy requirements for defibrillation using vertical pathways are uncertain and will be determined largely by the impedance of the pathway. The purpose of this study was to determine the impedance characteristics of vertical defibrillation pathways in human subjects. Twenty patients undergoing elective cardioversion of atrial fibrillation or atrial flutter, or both, were studied. Patients received shocks from electrodes placed in tongue-epigastric or tongue-cardiac apex positions. The tongue electrode was a 12 cm2metal plate fixed to a standard plastic oropharyngeal airway. The epigastric or cardiac apex electrode was a 40 cm2self-adhesive pad. The electrodes were connected to a standard damped-sinusoidal waveform defibrillator.It was found that the two vertical shock pathways had substantially higher impedance than the standard transthoracic pathway: tongue-epigastric pathway 130 ± 11Ω (SD), tongue-apex pathway 115 ± 12Ω, transthoracic pathway 68 ± 11Ω (p < 0.05). The higher impedance is probably due to the longer interelectrode distances of vertical pathways: tongue-epigastric 33 ± 3 cm, tongue-apex 28 ± 3 cm, transthoracic 23 ± 3 cm (p < 0.05). Vertical pathway shocks were successful in the cardioversion of 15 of 20 patients. Four of the five patients in whom vertical shocks were unsuccessful subsequently underwent successful cardioversion by transthoracic shocks; the transthoracic shocks achieved a higher current because of lower impedance of the transthoracic route.It is concluded that vertical shock pathways in human subjects have higher impedance than do transthoracic pathways. Because of this higher impedance, higher energy may be required for vertical pathway defibrillation than for standard transthoracic defibrillation