resistance to the flow of electricity through the heart muscle during *defibrillation due to the thoracic structures lying between the defibrillation paddles and the heart. These structures include the skin and soft subcutaneous tissues, the ribs and sternum, the lungs, and the pericardium. The best way to reduce the impedance, and thus to deliver the maximum available current to the heart, is to use defibrillation gel pads (see coupling agents), to deliver the shock when the lungs are empty of air, or to press firmly down if using hand-held paddles. Transthoracic impedance is usually between 70 and 80 ohms.
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