• C D Deakin, R M McLaren, G W Petley, F Clewlow, and M J Dalrymple-Hay.
• Department of Anaesthesia, Southampton University Hospitals, NHS Trust, Southampton General Hospital, UK. cdeakin@compuserve.com
• Resuscitation. 1998 Oct 1; 39 (1-2): 43-6.

AbstractThe success of defibrillation is related to transmyocardial current. This current is inversely proportional to transthoracic impedance (TTI). A similar TTI between different pads and paddles is important to deliver a consistent therapeutic dose to all subjects. Failure to do so may result in either insufficient or excessive transmyocardial current leading to a risk of failed defibrillation or tissue damage respectively. Several different types of defibrillation paddles and self-adhesive defibrillation pads are currently available for clinical use but the TTI achieved with each type has not been established. We measured TTI using two types of commonly used paddles and self-adhesive pads to establish whether any significant differences exist between the products. TTI in 40 adult males was measured using defibrillation paddles and self-adhesive defibrillation pads placed in the antero-apical position. Measurements were made using a 30 kHz low amplitude AC current and taken at end-expiration. Mean TTI (omega)+/-S.D. was 68.2+/-16.1 (Hewlett Packard paddles; A), 62.8+/-13.2 (Hewlett Packard pads; B), 64.6+/-14.3 (PhysioControl paddles; C) and 95.6+/-22.3 (PhysioControl pads; D). Significant differences existed between all groups (P < 0.05) except between B and C. Differences in TTI between A, B and C were small and probably of no clinical significance. TTI in group D is significantly larger. Although transmyocardial current is related to TTI, the relationship is complex and differences in TTI alone cannot predict the outcome from defibrillation.

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